INVESTIGATION OF MECHANISMS OF RADIOLYTIC H2 PRODUCTION IN C-S-H: INFLUENCE OF WATER CONTENT AND RADIATION INDUCED DEFECTS

Keywords: Radiolysis, C-S-H, concrete, adsorbed water, relative humidity

Water radiolysis is a major concern for the conditioning of radioactive waste in cement materials. Synthetic calcium silicate hydrates (C-S-H), the main hydrates of concrete, were synthesized with different calcium to silicate ratios and relative humidity. The samples were irradiated under γ-and electron beam irradiation. The radiolytic hydrogen production was quantified and the radiation induced defect produced at low temperature was characterized by electron paramagnetic resonance. The results show that the radiolytic H2 production and defect production are 20% sensitive to the relative humidity .

INTRODUCTION

Radioactive waste can be classified according to various criteria: origin, physical and chemical nature, level and type of radioactivity, lifetime, etc. In France, radioactive waste is managed according to classification in six categories, which are based on the radioactivity content and the half-life of the waste (figure 1): According to ANDRA's National Inventory of Radioactive Materials and Wastes published at the end of 2020 [START_REF]National Inventory of Radioactive Materials and Waste[END_REF], Low-and intermediate-Level short-lived wastes (LILW-SL) accounted for 60 % of the total volume of radioactive wastes produced in France, or 945,000 m 3 and 0.03 % of the total radioactivity of radioactive wastes in France. In contrast, the estimated volume of Intermediate-level long lived waste (ILW-LL) is around 43,000 m 3 . These low and intermediate level wastes, resulting from the decommissioning of nuclear facilities, are usually conditioned in calcium silicate cement to ensure the stability and the confinement of the radioactivity for disposal and future geological storage.

The use of a cement matrix sis prioritized because it offers many advantages: (i) the process and raw materials are inexpensive; (ii) the matrix can be tailored to reach various properties such as stability and strength and (iii) the alkalinity of calcium silicate cements allows the precipitation of a large number of radionuclides to limit their diffusion [START_REF] Atkins | Application of Portland cement-based materials to radioactive waste immobilization[END_REF]). However, the ionizing radiations emitted by the waste lead to dihydrogen release, which has to be quantified and minimized for the safety of nuclear disposal. [START_REF] Bonin | Pressure building during the early stages of gas production in a radioactive waste repository[END_REF][START_REF] Chartier | Influence of formulation parameters of cement based materials towards gas production under gamma irradiation[END_REF] The cement paste is mainly composed of calcium silicate hydrates (abbreviated C-S-H1 ) (about 60 % -70 %) and calcium hydroxide (portlandite mineralogic phase). In such hydrates, the H2 source is either structural hydroxyls, adsorbed water or pore water [START_REF] Kaddissy | Radiolytic Events in Nanostructured Aluminum Hydroxides[END_REF][START_REF] Kaddissy | Efficient hydrogen production from irradiated aluminum hydroxides[END_REF]. Since it is a material with various possible compositions and a complex nano-and microstructure [START_REF] Allen | Composition and density of nanoscale calcium-silicatehydrate in cement[END_REF][START_REF] Pellenq | A realistic molecular model of cement hydrates[END_REF], the radiolytic process leading to hydrogen release in such a material is challenging and not well understood. Although the behaviour of cement paste under irradiation has been studied in the literature [START_REF] Bibler | Radiolytic Gas Generation in Concrete Made with Incinerator Ash Containing Transuranium Nuclides[END_REF]) [START_REF] Bouniol | A comprehensive model to describe radiolytic processes in cement medium[END_REF]) [START_REF] Ewing | Radiation effects in nuclear waste forms for high-level radioactive waste[END_REF][START_REF] Allen | Composition and density of nanoscale calcium-silicatehydrate in cement[END_REF][START_REF] Bouniol | A comprehensive model to describe radiolytic processes in cement medium[END_REF][START_REF] Bouniol | Experimental evidence of the influence of iron on pore water radiolysis in cement-based materials[END_REF][START_REF] Dezerald | Cement As a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters[END_REF], Le Caër et al. 2017) [START_REF] Chartier | Influence of formulation parameters of cement based materials towards gas production under gamma irradiation[END_REF]) (Acher 2017), only few data related to the H2 gas production of C-S-H are available [START_REF] Yin | Influence of calcium to silica ratio on H2 gas production in calcium silicate hydrate[END_REF][START_REF] References | Investigation of the behaviour of cement matrices and their hydrates under γ and electron irradiation[END_REF]). An enhancement of H2 production in C-S-H compared to bulk water and an increase of the yield with the specific surface has been established. The impact of relative humidity (RH) does not seem to have been studied, even though the morphology of C-S-H and distribution of water in the solid are strongly affected by RH and even though RH will increase with time, due to the exchange of water with the wet host geological medium. Structural investigations of these hydrates by SAXS and Neutron scattering have shown [START_REF] Allen | A small-angle neutron scattering study of cement porosities[END_REF] [START_REF] Thomas | The surface area of cement paste as measured by neutron scattering: evidence for two CSH morphologies[END_REF] [START_REF] Allen | Development of the fine porosity and gel structure of hydrating cement systems[END_REF]) that the average number of stacking layers increases with the water content, from 4.5 (with 10 % water content) to 11 (with 30 % water content) [START_REF] Chiang | Microstructure determination of calciumsilicate-hydrate globules by small-angle neutron scattering[END_REF]) and the total thickness of one nanoparticle ranges from 4 to 10 nm (Figure 2). These observations are corroborated by atomic force microscopy that gives for those C-S-H nanoparticles 30-60 nm2 surface and 5 nm thickness [START_REF] Nonat | The structure and stoichiometry of C-S-H[END_REF].

Figure 2. Schematic of a C-S-H nanoparticle.

Based on the structural model presented in figure 2, four types of water can be described in C-S-H gels [START_REF] Roosz | Distribution of Water in Synthetic Calcium Silicate Hydrates[END_REF]): the structural hydroxyl groups contained in the layers (0.08-0.1 g/g of dried C-S-H, depending on the calcium to silica ratio), the water confined in the interlayer space (0.12 g/g that decreases upon heating under vacuum), the water adsorbed on the external surface of the nanoparticle (0.04 to 0.4 g/g of dried C-S-H, depending on the RH) and the water condensed in the pores between the nanoparticles (for RH> 90%). However, in the practical range of hygrometry and temperature used in storage, only adsorbed water and pore water contents are expected to vary.

We tried here to go further than a mere quantification of H2 production by linking it to the various primary species produced under irradiation using a low temperature analysis. Our main purpose was to identify the H2 precursor and the oxidative counterpart to H2 production that remains trapped in the material, as no O2 is usually produced under irradiation of hydrates.

MATERIALS AND METHODS

Synthesis of C-S-H

C-S-H samples were synthesized from reaction of amorphous silica (SiO2, AEROSIL 380, Degussa) and calcium oxide (CaO) in excess of water. Reagent grade calcium carbonate (CaCO3, VWR Company) was calcined at 960 °C for 24 hours to obtain calcium oxide. Stoichiometric amounts of CaO and SiO2 were mixed in order to produce C-S-H samples having an initial C/S ratio of 1.6.

The materials were mixed with ultrapure water (Milli-Q 18 MΩ) with a water to solid mass ratio of 50 in 1 L sealed bottles. Then, they were shaken on a rotating rack for 1 month at room temperature (i.e. 25°C) to obtain equilibrium. Then, samples were filtered using a Büchner funnel and a filter paper (0.22 µm, Millipore) and rinsed. Usually, solid sample is rinsed with an organic solvent to obtain pure samples. In our study, this step was prohibited in order to avoid the presence of organic compounds, which would give a supplementary contribution to radiolytic H2 production.

The concentrations of remaining calcium and silicon ions in the filtered solutions were determined by ICP-AES.

The samples were freeze-dried during 4 days and then they were cured in a desiccator chamber at 30%, 60%, 75%, and 85% relative humidity (RH) under a nitrogen atmosphere at room temperature until their weight stabilized (approximatively 4 weeks). The relative humidity was controlled by saturated salts: 30% RH with Magnesium Chloride, 60% RH with Sodium Bromide, 75% RH with Sodium Chloride and 85% RH with Potassium Chloride.

Sample Characterization

The characterization methods (X ray diffraction, thermogravimetric analysis and electron paramagnetic resonance) are described in the supporting information.

Sample chemical composition

The experimental C/S ratios were indirectly checked by the chemical analysis of the solution at the end of the synthesis as previously described [START_REF] Yin | Influence of calcium to silica ratio on H2 gas production in calcium silicate hydrate[END_REF]. The pH values and [CaO], [SiO2] in solution according to C/S ratio indicate that samples were at equilibrium according to the solubility curve [START_REF] Flint | Study of the system CaO-SiO_2-H_2O at 30℃ and of the reaction of water on the anhydrous calcium calcium silicates[END_REF] [START_REF] Roller | The system calcium oxide-silica-water at 30. the association of silicate* ion in dilute alkaline solution[END_REF] [START_REF] Taylor | 726. Hydrated calcium silicates. Part I. Compound formation at ordinary temperatures[END_REF] [START_REF] Greenberg | Investigation of the Colloidal Hydrated Calcium Silicates. II. Solubility Relationships in the Calcium Oxide-Silica-Water System at 25°C[END_REF] [START_REF] Grutzeck | Silicon-29 magic angle spinning nuclear magnetic resonance study of calcium silicate hydrates[END_REF] [START_REF] Lecoq | Etude de l'hydratationa concentration controlee du silicate tricalcique et des caracteristiques de ses produits de reaction[END_REF]) [START_REF] Cong | 29Si MAS NMR study of the structure of calcium silicate hydrate[END_REF]

Irradiation experiments and gas analysis

C-S-H samples were γ-irradiated using a 60 Co source experimental irradiator at Marcoule (Gammatec, Steris, France). Approximately 120 mg were introduced in 12 mL Pyrex glass ampules, which were then flame-sealed under argon at about 900 mbar to avoid oxygen presence. Attention has been paid to avoid modifying the water content of the samples during the sealing, which has been confirmed by TGA measurements. Glass ampules were placed on a rotating plate to ensure the spatial homogeneity of the dose delivery. Dosimetry was performed with red Perspex dosimeters and the absorbed dose is known with a 5.6 % standard deviation.

Samples were irradiated by using an average dose rate of 600 Gy/h at 25 ± 1°C up to 100 and 200 kGy of absorbed doses. For each absorbed dose, two independent samples were irradiated.

The amount of dihydrogen produced during γ-irradiation was evaluated by using a micro-gas chromatography (490 Micro-GC, Agilent) equipped with a compression system (SRA Instruments) to provide 1 bar of pressure at the input of the µ-GC injector. The channel used for hydrogen analysis contains a Molecular Sieve 5A PLOT column under argon at 28 psi pressure and a micro thermal conductivity detector (µ-TCD). The oven and detector temperatures were respectively 90 and 120 °C, with an acquisition time of 2 minutes.

The hydrogen production yield, denoted as the G-value and expressed in mol/J, corresponds to the amount of dihydrogen produced per amount of absorbed energy. For each C-S-H sample, apparent hydrogen radiolytic yield G(H2) was assessed by calculating the slope of the hydrogen production as a function of the absorbed dose. Normalized apparent hydrogen radiolytic yields Gnorm(H2), expressed in mol/J, were calculated by normalizing apparent hydrogen radiolytic yields by the initial water mass fraction, which was measured. The standard deviation of the yields was estimated to be less than 15 %.(see table S1) Electron beam irradiations were used for EPR experiments. The C-S-H samples were irradiated at 77K using a linear accelerator located in NIMBE, Saclay, France. The pulse-width was 10 ns and the electron energy was 10 MeV and the repetition rate was 5 Hz. No sample heating was detected. The typical dose delivered per pulse determined using the Fricke dosimeter was 6 Gy/pulse.

RESULTS

X-Ray powder Diffraction

The purity of C-S-H samples was controlled by X-Ray powder Diffraction (XRD). An example of a characteristic XRD pattern is presented in supporting figure S2. The X ray diffraction pattern is completely compatible with our previous results. [START_REF] Yin | Influence of calcium to silica ratio on H2 gas production in calcium silicate hydrate[END_REF] In short, the experimental patterns show that the samples present the diffraction peaks corresponding to the tobermorite structure [START_REF] Grangeon | On the nature of structural disorder in calcium silicate hydrates with a calcium/silicon ratio similar to tobermorite[END_REF]), a natural mineral analogue of C-S-H, and additional peaks are attributed to a small amount of calcium hydroxide (portlandite phase) and calcium carbonate (calcite phase). The appearance of portlandite is probably due to the further hydration process during the storage, because of possible residual water after lyophilisation. Calcite is commonly found in C-S-H since it is known to react with CO2 from the atmosphere. In our case, carbonation of the samples most likely occurred in the desiccators. The interlayer distance in the tobermorite phase is determined by the position of the ( 001) peak (between 6 and 10° in the 2theta scale) using the structural model described by [START_REF] Grangeon | On the nature of structural disorder in calcium silicate hydrates with a calcium/silicon ratio similar to tobermorite[END_REF]) (see figure 3). According to [START_REF] Gaboreau | Hydration Properties and Interlayer Organization in Synthetic C-S-H[END_REF], the values of d001 in the 10-13 Å range correspond to a simple water layer separating the C-S-H foils, the decrease in distance with the increase in C/S arising from the omission of Si tetrahedral combined with the insertion of Ca 2+ in the interlayers space. Whatever the C/S ratio, the layer-to-layer distance decreases slightly (0.5 Å) with the relative humidity, as already observed by Cong [START_REF] Cong | Effects of the temperature and relative humidity on the structure of C-S-H gel[END_REF] and Gaboreau [START_REF] Gaboreau | Hydration Properties and Interlayer Organization in Synthetic C-S-H[END_REF]. This decrease corresponds most probably to a change of the water content in the interlayer, leading to a local shrinkage. However, the decrease is too limited, even at low RH, to consider that the interlayer space is empty of water molecules [START_REF] Gaboreau | Hydration Properties and Interlayer Organization in Synthetic C-S-H[END_REF].

Thermogravimetry analysis

An example of a characteristic thermogram is presented in Fig. S1B. Three steps of decomposition are observed. The first one, from 30 to 300°C, corresponds to the loss of the sum of pore water, crystallization water and hydroxides [START_REF] Taylor | Bound water in cement pastes and its significance for pore solution compositions[END_REF]). The second step, from 410 to 500°C, corresponds to the decomposition of few amounts of portlandite (Ca(OH)2) [START_REF] Krakowiak | Nano-chemomechanical signature of conventional oil-well cement systems: Effects of elevated temperature and curing time[END_REF]. In the third step, the weight loss from 550 to 750°C, results from the decomposition of carbonates. Note that temperature boundaries are approximate and depend on the heating rate and on how the water interacts with solid surfaces.

A typical result of the TGA analysis is given in Table 1. The amount of water sensitive to the RH is of about 5% of the total water.

Hydrogen production under gamma irradiation

An example of the evolution of H2 as a function of dose is given in Figure 5. The quantity of H2 produced increases linearly with the dose. The radiolytic yields for each sample, at each RH, was deduced from the slopes of the lines. The yields were calculated either with respect to the total mass of C-S-H and water, considering the total energy deposited in the whole system, or with respect to the energy received solely by water. Table 2, Table 3 and Figure 6 present hydrogen production under gamma irradiation from various C-S-H as a function of water content. When calculated with respect to the total amount of material (Table 2), the G values vary from 0.35×10 -7 mol J -1 to 0.7×10 -7 mol J -1 . In agreement with our previous measurements, G values tend to decrease when the C/S ratio increases [START_REF] Yin | Influence of calcium to silica ratio on H2 gas production in calcium silicate hydrate[END_REF]. The yields are comparable to the one measured in bulk water (0.45×10 -7 mol J -1 )

showing that C-S-H produce the same quantity as an equivalent mass of bulk water. Figure 6 and table 2 show that G values vary by less than 20% with various water content, to be compared to a relative error of 15% (see table S1). Therefore it is difficult to affirm that the water content have a significant effect on H2 production. The same trend was reported in Ca 2+ exchanged-Montmorillonites [START_REF] Fourdrin | Water radiolysis in exchanged-montmorillonites: the H2 production mechanisms[END_REF], where the raw G(H2) is almost constant for all RH.

This result highlights a great efficiency of the radiolysis of -OH groups (both for FW and CBW)

and of the recombination of hydrogen atoms. The G(H2) of C-S-H is very close to the G(H2) of cement paste S3 (S3 is mainly composed of C-S-H, about 93%) reported by Le Caër [START_REF] Le Caër | Production of H2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study[END_REF]). On the contrary, distinctive tendencies were noticed for Na exchanged Montmorillonites (Na -MX80, Na-Mt) and geopolymers (Geo-Na, Geo-K, Geo-Cs), where the raw G(H2) increases with water content [START_REF] Fourdrin | Water radiolysis in exchanged-montmorillonites: the H2 production mechanisms[END_REF]) [START_REF] Chupin | Water content and porosity effect on hydrogen radiolytic yields of geopolymers[END_REF] or for synthetic montmorillonite, where G(H2) decreases with water content [START_REF] Lainé | Reaction mechanisms in swelling clays under ionizing radiation: influence of the water amount and of the nature of the clay mineral[END_REF]. The marginal role of the amount of water on G values is traditionally interpreted through ultraefficient energy transfer phenomena from the solid to the liquid [START_REF] Le Caër | Radiolysis of Confined Water: Hydrogen Production at a High Dose Rate[END_REF], Rotureau et al. 2005).

Indeed, in our case, energy transfer processes can appear as an increase of the yield calculated with respect to the amount of energy received by water, when the water content decreases (see Table 3). However, the value presented in Table 3 must be used carefully, as they can also hide the radiolytic events that can occur within the material. Therefore, for practical applications, we can simply consider that the solid produces hydrogen with the same efficiency as the liquid. It means also that, simple drying strategies that do not remove structural water may not be efficient to decrease significantly H2 production in C-S-H. Unfortunately, treatments that remove structural water (i.e. heating under vacuum) are prohibited, as the material integrity may be affected. We point out that the primary G value of bulk water (in Figure 6) is measured with the addition of potassium bromide to prevent the back reaction of oxidative radicals with dihydrogen [START_REF] Schwarz | Hydrogen Yields in the Radiolysis of Aqueous Solutions1[END_REF]) [START_REF] Schwarz | The Effect of Solutes on the Molecular Yields in the Radiolysis of Aqueous Solutions1[END_REF], allowing the measurement of the primary G value of bulk water at room temperature. The C-S-H themselves can produce efficient dihydrogen whatever the calcium content, that is to say, there are some species, which can behave like storage site of oxidative radicals in these hydrates.

Radiation induced defects

Considering that in materials containing hydroxyl groups, the transient oxidative species can be stored in paramagnetic radiation induced defects (RIDs), [START_REF] Kaddissy | Efficient hydrogen production from irradiated aluminum hydroxides[END_REF] we conducted a quantification of the paramagnetic species induced by irradiation by electron paramagnetic resonance (EPR).This study was first conducted at low temperature (77K) in order to identify the primary radicals produced by irradiation

We checked that gamma irradiation did not lead to modification of the crystallographic properties, i.e. that only radiation induced defects (RID) were created, even at 200 kGy (figure S4). Figure 7 presents the EPR spectra of electron irradiated at 77 K of C-S-H with C/S=0.80 with different relative humidity. The results evidence that there is minimal differences when the relative humidity varies from 3% (freeze-dried) to 60%. These results are in accordance with the measurements of hydrogen gas production and show that adsorbed water has a minimal effect on irradiation primary processes. Owing to these similarities , we will describe together RIDs for the different relative humidities.

A doublet separated by 50 mT assigned to H radicals observed in all C-S-H samples [START_REF] Kaddissy | Efficient hydrogen production from irradiated aluminum hydroxides[END_REF]. The hyperfine constant is very close to that for free H atom (50.8 mT).

The signal presents also the signature of a superhyperfine coupling, with two shoulders separated by 1.3 mT, indicating weak interactions of the H atom with its surrounding. [START_REF] Päch | Scavenger Assisted Trapping of Atomic Hydrogen in Si8O12-Cages[END_REF] The rest of the ESR spectrum is composed of a complex, central line centered around g=2.010. This line presents a broad shoulder, hereafter designed as RID I, around g=2.065

for C-S-H 0.80, 0.97 and 1.30 and g=2.044 for C-S-H 1.14 and 1.40 (fig. S5). According to similar distributions that have been reported for hole centers trapped in alkali aluminosilicate or silicate glasses (Table S3), we assign this defect to a O • center.

A narrow singlet line with g=2.0029 is attributed either to carbon contamination [START_REF] Griscom | Electron spin resonance studies of defect centers induced in a high-level nuclear waste glass simulant by gamma-irradiation and ion-implantation[END_REF] or to different type of oxygen hole center [START_REF] Dutt | Compositional dependence of trapped hole centers in gamma-irradiated calcium aluminosilicate glasses[END_REF].

The high field signal corresponding to g=1.994 reveals an anisotropic signal (called RID II in the following). From the comparison with various published results in table S3, this signal is attributed to an O2 -species. It can come from the following reactions:

• + • → (Eq. 1)

+ • → + (Eq. 2)
Similar reactions can be found in the general scheme of basic water radiolysis [START_REF] El Omar | Revisited water radiolysis at elevated pH by accounting O3˙-kinetics at low and high LET[END_REF], and are indeed the deprotonated counterpart to the ones proposed in hyperquenched glassy water to explain the efficient production of superoxide [START_REF] Bednarek | Hydroperoxyl Radical Generation by γ-Irradiation of Glassy Water at 77 K[END_REF]. The formation of both H radicals and centers (RID I) points towards the existence of homolytic dissociation process that are only marginally affected by water.

⋯ → ⋯ • + • (Eq. 3)
The ratio G(RID I+II)/G(H2) between 1 and 2 suggest also that H° recombination (Eq. 4) is the natural source of hydrogen (H2 )

• + • → (Eq. 4)

As a minor competing reaction, the formed H atoms can also be trapped :

• → • (Eq. 5)

The competition between H atom recombination (Eq. 4) and trapping (Eq. 5) explain why the concentration of Htrapped is lower than the concentration in RIDs(table 4), whose recombination is less efficient at this temperature

The amount of H trapped increases slightly (Table 4) with the water content whereas RID I and II remain the same considering the experimental errors. This indicates that adsorbed water at low temperature provides additional H trapping sites.

In a second time, we studied also the stability of the different radiation damage with temperature. RID I decreases with the temperature and converts into RID II. This confirms that RID II comes from RID I recombination through equations 1 and 2. After annealing at 280 K (Figure S6), the shape of the signal is very close to those observed in pure irradiated portlandite in the same condition, but with the intensity is 10 times smaller. EPR spectrum is the superposition of different lines tentatively attributed to O2 -, O3 -and CO2 -. Therefore, we attribute these signals to residual radicals trapped in the portlandite phase of our samples. The radiation induced defects formed in the C-S-H themselves disappear completely at room temperature. This is a strong difference with the observations in hydroxides and oxohydroxides [START_REF] Kaddissy | Radiolytic Events in Nanostructured Aluminum Hydroxides[END_REF], where the H and RID were stable at room temperature, RID providing in this case the oxidative counterpart to H2 production. A correlation of this behaviour is that the oxidative counterpart to H2 remains also unknown in C-S-H, but peroxide and oxygen are the most probable oxidized products (Eq. 6).

+ → + (Eq. 6)

Indeed, calcium peroxide has been proposed as a major product in irradiated concrete [START_REF] Bouniol | The solubility constant of calcium peroxide octahydrate in relation to temperature; its influence on radiolysis in cement-based materials[END_REF]). However, no oxygen production as ever been observed in irradiated concrete or C-S-H. This raises the interesting question of the actual solubility of O2 in the interlayer space.

We point out that no evidence in our results allows proposing that the radiation events leading to defect formation occur more within the material or within the water (adsorbed or interlayer).

The only indication we have is the low temperature recombination of H and RIDs, suggesting that these radiation induced defects are formed in mobile environment, i.e. near water. As observed in photocatalysis on amorphous materials, the water would therefore play a critical role in stabilizing radiogenerated charge carriers [START_REF] Litke | Role of Adsorbed Water on Charge Carrier Dynamics in Photoexcited TiO2[END_REF][START_REF] Shirai | Water-Assisted Hole Trapping at the Highly Curved Surface of Nano-TiO2 Photocatalyst[END_REF].

CONCLUSIONS

The production of radiolytic dihydrogen of different C-S-H samples has been quantified and shows a limited effect of the relative humidity on the radioytic yields. The arising radiation induced defects have been identified as H° atoms, O -° and O2 -centers at 77K, but disappear at room temperature. Their formation points toward a direct radiolysis of material OH bonds.

Figure 1 .

 1 Figure 1. Simplified classification of radioactive waste according to its radioactivity and its halflife. Reproduced from (Lainé 2017).

Figure 3 .

 3 Figure 3. Interlayer space of C-S-H samples deduced from XRD patterns as a function of the C/S ratio at different RH. The error on the d001 value is estimated at 0.5 Å (Holmboe et al. 2012).

Figure 4 (FreezeFigure 4 .

 44 Figure4(and the complementary figureS3and tableS2) shows the distribution of CBW and FW of C-S-H samples with 1.3 C/S ratio cured at different RH. As expected, our results show that the chemically bonded water content is almost constant, within the error bars, whereas free water increases with relative humidity. This validates a posteriori our treatment. Free water (FW) is also observed for freeze-dried samples, as it is already observed in clays[START_REF] Lainé | Reaction mechanisms in swelling clays under ionizing radiation: influence of the water amount and of the nature of the clay mineral[END_REF]). This result confirms that freeze-dried samples are very sensitive to the surrounding environment (CO2, RH)[START_REF] Li | Advanced concrete technology[END_REF]. According to the molecular formula of the corresponding tobermorite phases (11 Å phase, (Ca5Si6O16(OH)2•5H2O)[START_REF] Galvánková | Tobermorite Synthesis Under Hydrothermal Conditions[END_REF] [START_REF] Richardson | Model structures for C-(A)-S-H(I)[END_REF]) and the analysis of Roosz et al.[START_REF] Roosz | Distribution of Water in Synthetic Calcium Silicate Hydrates[END_REF], the CBW content corresponds to a single layer of water adsorbed in the interlayer. This result is coherent with the interlayer space measurements presented in §3.1. In this latter interpretation, the FW content (5-15%) corresponds to water adsorbed on the external surface of the nanoparticle presented in Figure2.

Figure 5 .

 5 Figure 5. Dose dependence of H2 production for hydrated 1.30 C-S-H equilibrated at different relative humidity at room temperature (freeze-dried, 30, 60, 75 and 85 % RH).

Figure 6 .

 6 Figure 6. Correlation between the water content obtained from TGA and G(H2) for different nanotructured materials. This work ( 0.80 C-S-H, 0.97 C-S-H, 1.14 C-S-H, 1.30 C-S-H, 1.40 C-S-H), Na exchanged montmorillonite (Na + -MX80) (Fourdrin et al. 2013), calcium exchanged montmorillonite (Ca 2+ -Mt) (Fourdrin et al. 2013), geopolymer (Geo Na) (Chupin et al. 2017), Boehmite ( ALOOH S and ALOOH L) (Kaddissy et al. 2019) Synthetic Montmorillonite (Lainé et al. 2017), Portland Ultimat CEM I (Chartier et al. 2018), cement paste S3 (Le Caër et al. 2017), bulk water).

Figure 7 .

 7 Figure 7. EPR spectra of electron irradiated at 77 K of 0.80 C-S-H with different relative humidity, irradiated at 30 kGy.

Figure 8 .

 8 Figure 8. Temperature evolution of the total intensity of EPR spectra related to RID I (blue points) and RID II (red points).

Table 1 . Typical water, portlandite and calcite contents calculated from thermogravimetry analysis of 1.40 C-S-H samples cured at different relative humidity. The relative uncertainty is estimated to be 10%.

 1

		Water content (%)	Portlandite (%)	Calcite (%)
	Freeze-dried	14.2	5.8	3.5
	30%	17.3	7.7	3.3
	60%	16.9	4.7	4.2
	75%	18.5	3.3	4.7
	85%	20.8	3.0	2.6
	Chemically Bonded Water (CBW, i.e. crystallization water and structural water) and Free Water
	(FW) which corresponds to water molecules more weakly bonded, were calculated according to
	(Taylor 1986) (Lainé et al. 2017) (Le Caër et al. 2017): free water weight loss occurs between
	ambient and 105°C while chemically bonded water weight loss occurs between 105°C and

Table 2 . Hydrogen radiolytic yields (10-7 mol/J) (calculated with respect to the total energy received by the system) released from Gamma irradiated C-S-H samples with different C/S ratio hydrated at different RH at room temperature. The standard deviation of the yields are estimated to be 15% for all samples. G(H2) (mol/J×10 -7 ) (calculated with respect to the total energy received by the system)

 2

					Real C/S ratio
			0.80	0.97	1.14	1.30	1.40
		f.d.	0.52±0.08 0.56±0.08 0.46±0.07 0.50±0.08 0.32±0.05
	RH (%)	30%	0.69±0.10 0.39±0.06 0.44±0.07 0.37±0.06 0.35±0.06
		60%	0.61±0.10 0.58±0.09 0.49±0.07 0.42±0.07 0.36±0.06

Table 3 . Hydrogen radiolytic yields (10 -7 mol/J) (calculated with respect to the energy received solely by water) released from Gamma irradiated C-S-H samples with different C/S ratio hydrated at different RH at room temperature. The standard deviations of the yields are estimated to be 15% for all samples. Gnorm. (H2) (mol/J×10 -7 ) (calculated with respect to the energy received solely by water) Real C/S ratio

 3

			0.80	0.97	1.14	1.30	1.40
		3%	3.2±0.5	4.0±0.6	2.9±0.4	3.7±0.6	2.3±0.3
		30%	4.2±0.6	2.4±0.3	2.8±0.3	2.3±0.2	2.0±0.3
	RH (%)	60%	3.2±0.5	3.1±0.5	2.8±0.4	2.4±0.4	2.1±0.3
		75%	2.9±0.4	2.8±0.4	2.1±0.3	2.1±0.3	1.9±0.3
		85%	2.6±0.4	2.5±0.5	2.1±0.3	1.5±0.2	1.7±0.3

Table 4 . Concentration and yield in radiation induced defects for different RH and C/S ratios. The experimental accuracy is estimated to be ±35%. Hydrogen radiolytic yields released from Gamma irradiated C-S-H samples at room temperature are recalled. f.d. stands for freeze dried

 4

	C-S-H.
	C/S ratio	0.80	0.80	0.80	0.97	1.14	1.30	1.40
	RH	f.d.	30%	60%	f.d.	f.d.	f.d.	f.d.
	H atoms (/g)	1.3 10 16 2.4 10 16 2.4 10 16 2.0 10 16 5.4 10 15 8.5 10 15 4.4 10 15
	RID (/g)	1.4 10 18	1 10 18	1.5 10 18 1.6 10 18 1.5 10 18 5.4 10 17 1.4 10 18
	G(RID I+II) (mol/J×10 -7 )	0.81	0.6	0.85	0.89	0.82	0.60	0.81
	G(H2) (mol/J×10 -7 )	0.52	0.69	0.61	0.56	0.46	0.50	0.32

calculated with respect to the total energy received by the system)

The general formula is (CaO)x (SiO2)y (H2O)z with CaO/SiO2 (abbreviated C/S) varying from 0.66 to


S Deshayes

D Leite Ferreira

J Madelaine

Y Oulkhouir

K Campbell

H Fouquet

S Teulier

R Magnier

M Heyndrickx

D Lerouge

D Leite Ferreira

E Bergot

Aurelien Justet
email: justet-a@chu-caen.fr

Étude D-CBP : Évaluation des délais de prise en charge du cancer broncho-pulmonaire au sein du service de Pneumologie et d'Oncologie Thoracique du CHU de Caen

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Le cancer broncho-pulmonaire est l'un des cancers les plus mortels. Les de ĺais de prise en charge peuvent influencer la survie des patients. L'objectif de cette e tude e tait d'évaluer les de ĺais de prise en charge diagnostique et the ŕapeutique des patients admis dans le service de

INTRODUCTION

Le Cancer Broncho-Pulmonaire (CBP) est l'un des cancers les plus fréquents en France. Chez l'homme, il s'agit du deuxième type de cancer le plus fréquent et de la première cause de décès par cancer. Chez la femme, il s'agit du troisième type de cancer en terme d'incidence et de la deuxième cause de décès [START_REF]Projection de l'incidence et de la mortalité en France métropolitaine en 2017 -Rapport technique -Ref : RAINCMETRO17 n.d[END_REF].

Malgré des données discordantes concernant la relation entre le délai de prise en charge du CBP et la survie des patients, le raccourcissement des délais diagnostique et thérapeutique pourrait avoir un impact sur leur pronostic, notamment en cas de mise en place du dépistage de cette pathologie, qui entrainerait une augmentation du nombre de patient à explorer [START_REF] Gould | Timeliness of care in veterans with non-small cell lung cancer[END_REF][START_REF] Redaniel | Diagnostic Intervals and Its Association with Breast, Prostate, Lung and Colorectal Cancer Survival in England: Historical Cohort Study Using the Clinical Practice Research Datalink[END_REF][START_REF] Gonzalez-Barcala | Timeliness of care and prognosis in patients with lung cancer[END_REF][START_REF] Shin | Delay to curative surgery greater than 12 weeks is associated with increased mortality in patients with colorectal and breast cancer but not lung or thyroid cancer[END_REF]. Les données collectées comportaient : les caractéristiques sociodémographiques, les données cliniques, la présentation radio-clinique, les caractéristiques tumorales ainsi que des éléments concernant le parcours du patient tels que les dates de la première consultation, de la première imagerie réalisée, du contact avec le service de pneumologie et d'oncologie thoracique, de l'examen diagnostique, du bilan d'extension, du bilan fonctionnel et du traitement. Lorsque le patient était exclu après une première présentation en RCP, la cause de l'exclusion était recueillie.

En

L'objectif principal de l'étude était d'évaluer les délais de prise en charge diagnostique et thérapeutique du cancer broncho-pulmonaire au sein du service de pneumologie et d'oncologie thoracique du CHU de Caen Normandie en prenant comme critère principal le délai entre la date de réalisation de la première imagerie anormale et la date de mise en place du traitement quel qu'il soit, défini comme le Délai Global (DG).

Les objectifs et critères d'évaluations secondaires étaient :

-D'évaluer le Délai d'accès au Diagnostic (DD) défini comme le délai entre la date de la première imagerie anormale et la date du diagnostic.

-D'évaluer le Délai d'accès au Traitement (DT) défini comme le délai entre la date du diagnostic et la date de mise en traitement quel qu'il soit.

-D'identifier les facteurs qui pourraient être associés significativement à un allongement de ces trois délais. Enfin la localisation tumorale est également un facteur identifié dans des études antérieures [START_REF] Devbhandari | Implications of a negative bronchoscopy on waiting times to treatment for lung cancer patients: results of a prospective tracking study[END_REF]. Les lesions periphériques sans atteintes mediastinales ne sont généralement pas accessibles par voie endoscopiques. Le recours à une ponction transthoracique voire à une exploration chirurgicale allongent considérablement ce délai. Ces dernières années ont vu le développement de nouvelles techniques endoscopiques permettant une rentabilité diagnostique intéressante dans l'exploration des tumeurs périphériques [START_REF] Oki | Ultrathin Bronchoscopy with Multimodal Devices for Peripheral Pulmonary Lesions. A Randomized Trial[END_REF]. La généralisation de l'utilisation de ces techniques pourrait considérablement réduire le délai diagnostique chez ces patients.

Dans notre étude, le délai diagnostique était de 22 jours contre 21,5 jours dans l'étude de l'INCA [START_REF] Pourcel | Waiting times for cancer care in four most frequent cancers in several French regions in 2011 and 2012[END_REF] et de 33 jours dans l'étude américaine [START_REF] Schultz | Hospital characteristics associated with timeliness of care in veterans with lung cancer[END_REF]. Dans notre étude, l'âge semblerait être associé à un DD plus long : les comorbidités des patients (cardiovasculaires, traitements par anticoagulants/anticoagulants) ainsi que la nécessité d'une consultation onco-gériatrique pourraient expliquer cette différence. Néanmoins, une étude menée dans un CHU francilien chez des patients de moins et de plus de 70 ans, ne retrouvait pas de différence de délai de prise en charge entre ces deux groupes [START_REF] Giroux Leprieur | Delay between the initial symptoms, the diagnosis and the onset of specific treatment in elderly patients with lung cancer[END_REF].

Enfin, notre délai avant traitement était de 24,5 jours. Ce délai était équivalent avec celui retrouve dans l'étude nord-américaine (27 jours) [START_REF] Schultz | Hospital characteristics associated with timeliness of care in veterans with lung cancer[END_REF]. Il était en revanche raccourci par rapport à celui publié par l'équipe toulousaine au début des années 2000 (35 jours) [START_REF] Leveque | Analyse des délais de prise en charge des cancers thoraciques : étude prospective[END_REF]. Une des raisons pouvant expliquer la différence entre ces deux chiffres est l'essor des thérapies ciblées par voie orale au cours de ces dix dernières années. Notamment avec la mise en place de recommandations au niveau européen pour l'optimisation des procédures opératoires standard en biologie moléculaire pour le traitement des patients par thérapie ciblée [START_REF] Dietel | Diagnostic procedures for non-small-cell lung cancer (NSCLC): recommendations of the European Expert Group[END_REF].

Cependant, de façon surprenante, il n'existait pas de différence de délai d'accès au traitement entre les carcinomes bronchiques non à petites cellules de stade IIIC-IV épidermoïdes et nonépidermoïdes. Cela est vraisemblablement due au statut tabagique des patients nonépidermoïdes : 58 % d'entre eux étaient tabagiques actifs, ne justifiant probablement pas l'attente d'une éventuelle addiction oncogénique avant de débuter le traitement systémique [START_REF]Cancer bronchique non à petites cellules -Référentiel national de RCP -Ref : RECOKBRNONPETCEL15 n.d[END_REF].

Plusieurs limites existent dans ce travail dont la principale tient en la taille de l'effectif qui a rendu impossible la réalisation d'une analyse multivariée. En conséquence, il nous a été impossible d'identifier des facteurs indépendants d'allongement des différents délais étudies.

Il aurait également été intéressant d'étudier ou de modéliser l'impact de l'allongement de ces délais sur le pronostic de ces patients.

Les données concernant la valeur pronostique des délais de prise en charge des patients de cancer pulmonaires est parfois discordante dans la littérature et est probablement dépendante du temps de croissance tumorale Les données récentes issues d'une cohorte historique de patients atteints de cancer pulmonaire illustrent ce paradoxe. Dans ce travail, un délai diagnostique plus long était associé à une mortalité plus faible (comparaison d'un délai diagnostic de trois à six mois contre moins d'un mois avec un hazard ratio à 0,87 avec IC à 95 % [0,80 -0,95]) [START_REF] Redaniel | Diagnostic Intervals and Its Association with Breast, Prostate, Lung and Colorectal Cancer Survival in England: Historical Cohort Study Using the Clinical Practice Research Datalink[END_REF]. Une étude rétrospective réalisée en Espagne, retrouvait également qu'un délai plus long était associé à une survie allongée [START_REF] Gonzalez-Barcala | Timeliness of care and prognosis in patients with lung cancer[END_REF]

  Pneumologie et d'Oncologie Thoracique du CHU de Caen Normandie. Matériel et méthode Il s'agit d'une e tude rétrospective, monocentrique et observationnelle, portant sur l'ensemble des patients pris en charge pour un Cancer Broncho-Pulmonaire (CBP) de Juin 2017 a ̀ Janvier 2018 du CHU de Caen. Les de ĺais étudiés sont : le De ĺai Global (imagerie anormaletraitement), le De ĺai d'acce s au Diagnostic (imagerie anormale-diagnostic) et le De ĺai d'acce s au Traitement (diagnostic-traitement). Résultats 127 patients sont inclus dans cette e tude. Le De ĺai Global me dian e tait de 55.5 jours [31,25 ; 393], le De ĺai d'acce s au Diagnostic me dian e tait de 22 jours [13 ; 49] et le De ĺai d'acce s au Traitement me dian e tait 24.5 jours [12,25 ; 45]. Discussion Les de ĺais de prise en charge de notre e tude concordent avec ceux de la littérature. Des axes d'amélioration sont en cours d'élaboration en accord avec le plan cancer 2014-2019 afin de créer un parcours de soins spécifique pour ces patients au sein de notre institution. Mots clés : Cancer broncho-pulmonaire, De ĺai, Diagnostic, Traitement, Parcours. D-CBP study : Evaluation of lung cancer management times. Introduction Lung cancer is the leading cause of cancer-related death. Delays may have an impact on patient survival. The objective of this study was to evaluate the diagnostic and therapeutic management times for patients admitted for lung cancer treatment in the Respiratory Department of CHU de Caen Normandie. MATERIALS AND METHODS This is a retrospective, single-center and observational study, conducted on all patients treated for lung cancer from June 2017 to January 2018 in our department of pneumology in the Caen Normandie CHU. The main median times were investigated were: Global Time (abnormal imaging-treatment), Diagnosis time (abnormal imaging-diagnosis) and Treatment Time (diagnosis-treatment). RESULTS One hundred and twenty-seven (127) patients were included. Median global time was 55.5 days [31,25; 393], median diagnosis time was 22 days [13; 49], and median treatment time was 24.5 days [12,25; 45]. DISCUSSION Our treatment times are consistent with those previously published. Areas for improvement are being developed in accordance with the 2014-2019 cancer plan, in particularly the creation in our institution of a specific care pathway for patients with lung cancer. Keywords: Lung Cancer, Delay, Diagnostic, Treatment, medical pathway.

  France, dans le cadre du plan cancer 2009-2013, une étude portant sur les différentes étapes de la prise en charge du CBP a été effectuée dans huit régions françaises. Il a été retrouvé un délai médian de 45 jours entre la première imagerie anormale et le traitement ; Le délai médian entre la première imagerie anormale et le diagnostic anatomopathologique était de 16 jours. Et enfin, le délai médian entre la Réunion de Concertation Pluridisciplinaire (RCP) et le traitement était de 15 jours [6]. Ce constat a conduit au développement d'une « politique active de maitrise des délais de prise en charge » établie par le plan cancer 2014-2019 [7]. Dans ce contexte, l'étude D-CBP a été effectuée afin d'évaluer les délais de prise en charge diagnostique et thérapeutique du Cancer Broncho-pulmonaire au sein du service de Pneumologie et d'Oncologie Thoracique du Centre Hospitalier-Universitaire (CHU) de Caen Normandie. MATERIELS ET METHODES Ce travail est une étude rétrospective, observationnelle, monocentrique menée au sein du service de Pneumologie et d'Oncologie Thoracique du CHU de Caen Normandie de juin 2017 à janvier 2018. Cette étude a reçu l'approbation du comité d'éthique du CHU de Caen (N° 2294) L'ensemble des patients dont le dossier a été présenté en RCP d'oncologie thoracique pour suspicion de CBP ont été inclus de façon consécutive, et les données ont été recueillies a posteriori. Les patients présentant une localisation thoracique d'un autre cancer, un mésothéliome pleural malin, une pathologie bénigne thoracique ou la surveillance de nodule pulmonaire étaient exclus de cette étude. L'ensemble des procédures à visée diagnostiques et thérapeutiques étaient réalisées au sein des services de Pneumologie et d'Oncologie thoracique et du service de Chirurgie Thoracique du CHU de Caen Normandie. Le traitement par radiothérapie était réalisé dans le service de Radiothérapie du Centre de Lutte Contre le Cancer François Baclesse a ̀ Caen.

L

  'ensemble des délais étudiés dans ce travail sont représentés dans la Figure 2 et détaillés dans le Tableau 3. La principale variable d'intérêt était le Délai Global médian, qui correspondait au délai entre la première imagerie et la mise en place d'un traitement, qui était de 55.5 jours [31,25 ; 393] (Figure. 2). Plusieurs paramètres étaient susceptibles d'allonger significativement ce délai comme la présentation clinique ou la localisation tumorale, l'extension tumorale, le bilan diagnostique ou la prise en charge thérapeutique. En effet, le DG était allongé chez les patients pour lesquels le diagnostic était fortuit (p = 0,02), ou pour ceux qui présentaient une tumeur localisée au thorax (p = 0,03). En outre, la réalisation d'une ponction transthoracique (p = 0,02), d'un TEP-TDM (p = 0,001) ou une prise en charge chirurgicale (p = 0,005) allongeaient significativement le DG (Tableau 3). Enfin, nous avons séparé les 8 mois durant lesquels notre étude a eu lieu en période de deux mois et il n'a pas été retrouvé de différence statistiquement significative entre chaque période en termes de DG médian : Juin-Juillet = 53.2 jours ; Aout-Septembre = 52.4 jours ; Octobre-Novembre = 56.4 jours ; Décembre-Janvier = 55.2 jours (p = 0,789). Afin d'analyser plus finement et d'identifier les facteurs limitants de notre parcours de soins, nous avons également étudié le Délai d'accès au Diagnostic (DD) et le délai d'accès au Traitement (DT). Le DD médian était de 22 jours [13 ; 49]. Ce délai était allongé significativement chez les patients plus âgés et en fonction du type d'examen nécessaire au diagnostic. En effet, le DD médian était de 11 jours chez les moins de 60 ans et de 31 jours chez les patients de plus de 60 ans (p = 0,015). D'autre part, il existait une variation du DD en fonction de l'examen ayant permis d'effectuer le diagnostic (p = 0,028), avec un DD allongé en cas de ponction transthoracique sous scanner (26,5 jours) et de thoracoscopie (96 jours) ou de pleuroscopie médicale (43 jours) comparativement à une fibroscopie bronchique (17 jours) ou une échoendoscopie bronchique (32 jours). Le délai médian entre l'examen diagnostic et l'obtention du statut mutationnel par séquençage de nouvelle génération était de 23 jours (53 patients). Le DT médian était de 24,5 jours [12,25 ; 45] au sein de notre étude. Ce délai semblait varier en fonction du type histologique (p = 0,001), du stade de la maladie (p = 0,007) et du traitement institué (p = 0,007). Effectivement, il paraissait notamment plus court en cas de carcinome bronchique à petites cellules (6,5 jours) en comparaison aux non-épidermoïdes notamment (26,5 jours). Cependant, il n'y avait pas de différence significative (p = 0,75) du DT des carcinomes épidermoïdes (23 jours) en comparaison aux non-épidermoïdes (25 jours) en cas de stade IIIC-IV. Le DT était de 22 jours en cas de stade IV (toutes histologies confondues) contre 64 jours en cas de stade I et de 71 jours lors de la nécessité d'un traitement chirurgical contre 19,5 jours en cas de traitement systémique. DISCUSSION L'objectif de l'étude D-CBP était d'évaluer les délais de prise en charge diagnostique et thérapeutique du cancer broncho-pulmonaire au sein du service de Pneumologie et d'Oncologie thoracique du CHU de Caen Normandie. Les caractéristiques de notre population, son parcours de soins et sa distribution concernant le type de traitement réalisé est similaire à l'étude observationnelle KBP-2010 réalisée dans les hôpitaux français généraux sur l'année 2010 avec comme objectif principal d'estimer la mortalité à cinq ans des patients atteints d'un CBP et comme objectifs secondaires de décrire les caractéristiques de ces patients [8]. Le DG médian retrouvé dans notre étude était de 55.5 jours [31,25 ; 393]. Il est difficile de situer ce délai avec ceux dans la littérature. La plupart des études publiées au début des années 2000 en France et à l'étranger retrouvaient un DG plus long. Dans une étude similaire réalisée au CHU de Toulouse, le DG médian était de 9,2 semaines soit 67,2 jours [9]. Aux États-Unis, une étude rétrospective multicentrique portant sur 2 372 patients a retrouvé un DG médian de 63 jours [10]. Cependant dans un travail plus récent publié par l'Institut National du Cancer en France, le DG moyen national était de 49,1 jours [6]. Il est important de noter l'existence de variations significatives du DG en fonction des différentes régions françaises dans cette étude. Nous avons identifié la présentation clinique, la localisation et l'extension tumorale, l'exhaustivité du bilan diagnostique et le type de prise en charge thérapeutique comme facteurs pouvant influencer le DG. Des résultats similaires avaient été retrouvés par nos collègues toulousains, en particulier concernant le mode de révélation. Par ailleurs, les patients symptomatiques bénéficiaient aussi d'un bilan diagnostique plus rapide, souvent dans la cadre d'une maladie métastatique et donc d'un traitement médical [6]. De façon attendue, les patients présentant un stade localisé ont un DG allongé, en raison de la nécessité d'un bilan d'extension plus important, dont le TEP TDM et du temps nécessaire à l'organisation d'une prise en charge chirurgicale.

Figure 1 :

 1 Figure 1 : Flow-Chart de l'étude D-CBP.

Figure 2 :

 2 Figure 2 : Délai de parcours de soins de l'étude D-CBP (médiane avec 1 er

  58% des cas, les patients étaient adressés par un autre service du CHU de Caen Normandie et dans 51% des cas le premier contact avec le service de Pneumologie était directement une hospitalisation (de jour ou conventionnelle). Le délai entre la consultation chez le médecin traitant et le pneumologue était de 16.5 jours.

	Dans Le premier examen diagnostic réalisé était une fibroscopie bronchique dans 66 % des cas et
	elle permettait d'obtenir le diagnostic chez 52 % des patients. Les examens permettant
	d'obtenir le diagnostic était ensuite l'écho-endoscopie bronchique (21 %), la ponction sous
	scanner (12 %) et enfin la neurochirurgie (5 %). Le délai médian pour réaliser une
	fibroscopie, une écho-endoscopie et une ponction sous scanner était respectivement de 2,5
	jours, de 3,5 jours et de 11,5 jours.

Concernant la méthodologie statistique, les logiciels EXCEL® et SPSS IBM V25® ont été utilisés pour l'ensemble des analyses. Les variables quantitatives ont e te ́ présentées avec des médianes ainsi que les premiers et troisièmes quartiles associés, des effectifs et pourcentages.

Les variables qualitatives ont e te ́ comparées a ̀ l'aide d'un test de Khi-2 ou exact de Fischer.

Les variables quantitatives continues (médianes) ont été́ comparées deux a deux en utilisant le test non paramétrique de Mann-Whitney. Pour les comparaisons de médianes intéressant plus de deux groupes, un test de Kruskall-Wallis était utilisé. Le degré de signification statistique a e te ́ fixe ́ a ̀ 5 %.

RESULTATS

De juin 2017 à Janvier 2018, sur les 200 dossiers de patients qui ont été présentés en RCP d'oncologie thoracique au CHU de Caen Normandie, 127 patients ont été inclus dans l'étude D-CBP (Figure 1). L'ensemble des caractéristiques des patients est résumé dans le Tableau 1. Parmi les 127 patients, 67 % étaient de sexe masculin et l'âge médian était de 66 ans. Ils présentaient un Performans Status entre 0 et 1 dans 83 % des cas. Il existait un tabagisme actif chez 51 % des patients et une exposition à l'amiante chez 26 %. Chez 75 % des patients, le mode de révélation était une symptomatologie (isolée ou multiple) dont les plus fréquentes était une altération de l'état général (29 %), une toux ou une dyspnée (21 %), des douleurs thoraciques (16 %), des troubles neurologiques (13 %) ou une hémoptysie (7 %). Le diagnostic était fortuit chez 29 patients soit 23 %. Le type histologique le plus fréquent était un adénocarcinome chez 65 patients (51 %) et la majorité des patients était de stade IV au diagnostic (62 %). Une mutation KRAS était retrouvée chez 38 %, de l'EGFR chez 9 % et un réarrangement ALK chez 5 % des patients. Les sites métastatiques les plus fréquents étaient le cerveau (23 %), l'os (18 %), le poumon (14 %), le foie (11 %), les surrénales (11%), puis la plèvre (8 %). Les détails concernant le parcours de soins des patients tels que le mode d'adressage, le mode de découverte ou diagnostique sont résumés dans le Tableau 2. Dans environ la moitié des cas (48 %), le premier praticien consulté était le médecin traitant. La première imagerie réalisée était un scanner thoracique dans 44 % des cas et une radiographie pulmonaire dans 32 % des cas. Cette première imagerie était réalisée dans 68 % des cas à l'extérieur du CHU de Caen Normandie. Le délai médian pour l'obtention d'un scanner thoraco-abdomino-pelvien injecté était de 5 jours et de 19 jours pour un TEP-scanner avec injection de 18 Fluorodésoxyglucose (TEP-TDM). Par ordre décroissant, le traitement réalisé était un traitement systémique dans 71 % des cas, puis une chirurgie d'exérèse (16 %), des soins palliatifs exclusifs (7 %) et enfin une radiochimiothérapie (4 %). Six jours était nécessaire pour obtenir le compte rendu anatomopathologique, et six nouveaux jours s'écoulait en médiane pour que le dossier soit présenté en RCP, puis la consultation d'annonce était effectuée 5 jours plus tard. Le traitement systémique était débuté 14 jours en médiane après la décision en RCP, et la chirurgie 57 jours après.

  . Cette apparente contradiction s'explique par le fait que les délais étaient plus courts en cas de stade tumoral avancé, d'âge plus élevé ou de mauvais état général, ce qui correspond également à des facteurs de mauvais pronostics et constituent donc des facteurs de confusion, justifiant ainsi la nécessité d'une approche analytique multivariée dans ce type d'étude. D'autre part, le contexte pandémique actuel lié à la COVID-19, conforte l'idée qu'une optimisation des délais de prise en charge est nécessaire chez tous les patients présentant une maladie chronique et notamment en cancérologie. Ainsi, une méta-analyse parue en 2020 sur les délais de prise en charge, tout type de traitement confondus, des sept cancers les plus fréquents (incluant le cancer bronchique), a retrouvé qu'un retard de prise en charge de seulement 4 semaines entraine une augmentation significative de la mortalité[START_REF] Hanna | Mortality due to cancer treatment delay: systematic review and meta-analysis[END_REF]. 'élaboration de parcours de soins est d'autant plus nécessaire à l'heure où la question du dépistage du CBP en France est de plus en plus prégnante et va probablement entraîner une augmentation du nombre de patient à explorer voire à prendre en charge.Cette étude, réalisée au sein du CHU de Caen Normandie a ainsi permis d'effectuer un état des lieux du parcours de soins et des délais de prise en charge du patient atteint de CBP. Un parcours spécifique et unique, en lien avec les différents intervenants incluant les médecins généralistes, est par conséquent en cours d'élaboration au sein de notre institution afin d'optimiser la prise en charge de ces patients.

	Afin d'améliorer les délais de prise en charge, différents procédés sont décrits dans la
	littérature. Tout d'abord, l'information et la communication autour des patients à risque de
	CBP est primordiale, afin que la première consultation médicale soit la plus précoce possible.
	Ensuite, la sensibilisation des médecins traitants aux points d'appel clinique et à la
	prescription d'examen complémentaire adapté est importante. Enfin, la correction des délais
	peut aussi passer par la mise en place de parcours de soins spécifiques pour ces patients au
	sein des institutions hospitalières afin de faciliter l'accès à une consultation médicale
	spécialisée (pneumologue, oncologue, chirurgien thoracique, cardiologue) mais également
	aux examens complémentaires nécessaires (radiologues, médecin nucléaire).

Aux Pays-Bas, il a été proposé la mise en place d'un « RODP » (Rapid Outpatient Diagnostic Program) : sur une hospitalisation de deux jours, les patients chez qui sont suspectés un CBP bénéficient d'une évaluation clinique, d'un scanner thoraco-abdominopelvien, d'un TEP-TDM, d'une Exploration Fonctionnelle Respiratoire et d'un examen endoscopique bronchique, ce qui a permis d'obtenir un DG de 25 jours [17]. Au Canada, le « Time to Treat Program » a été institué. Une liste de symptômes et de critères précis a été transmis aux médecins traitants. Lorsqu'un patient est adressé au centre pour suspicion de CBP, un « navigateur » va organiser les différents rendez-vous (imagerie, examen diagnostic) avant toute consultation médicale. Des créneaux spécifiques d'imagerie et de diagnostic sont ainsi dédiés aux soins au sein de ce programme. Ces différents éléments ont permis d'obtenir un DG de 20 jours [18]. L

PARCOURS DE SOINS DES PATIENTS n (%) MEDECIN PREMIERE CONSULTATION PREMIER EXAMEN DIAGNOSTIC REALISE


Cahuc

D Ambrosio
email: dambrosi@enit.fr

A Tongne

V Wagner

G Dessein

O Cahuc

A new damage evolution criterion for the coupled Eulerian-Lagrangian approach: Application to three-dimensional numerical simulation

Keywords: damage evolution, coupled eulerian-lagrangian (CEL), orthogonal cutting, segmented chip formation, frictional behavior

Introduction 10

The coupled Eulerian-Lagrangian (CEL) method based on the combination of Lagrangian and Eulerian formalisms has been recently applied to various manufacturing processes. Qiu et al. [START_REF] Qiu | Application of a Coupled Eulerian-Lagrangian approach on geomechanical problems involving large deformations[END_REF] highlighted the great advantage offered by the CEL approach in combining the benefits of both traditional formulations (i.e., Lagrangian and Eulerian) by defining an Eulerian workpiece and a Lagrangian tool that avoid contact and mesh distortion problems. Consequently, there is increasing interest in simulating severe plastic deformation 15 (SPD) processes using the CEL formulation. Abdelhafeez et al. [START_REF] Abdelhafeez | A Coupled Eulerian Lagrangian Finite Element Model of Drilling Titanium and Aluminium Alloys[END_REF] successfully simulated drilling of aluminum and titanium alloys, demonstrating the CEL model's higher computational efficiency and accuracy. With a CEL model, Wu et al. [START_REF] Wu | FEM prediction of dislocation density and grain size evolution in high-speed machining of Al6061-T6 alloy using microgrooved cutting tools[END_REF] investigated the evolution of dislocation density and grain size in orthogonal cutting of Al6061-T6 alloy using micro-grooved cemented carbide cutting tools. The complex friction stir welding process was also simulated using the CEL approach proposed by Tongne et al. [START_REF] Tongne | On material flow in Friction Stir Welded Al alloys[END_REF]. These authors were able to describe the formation mechanisms of regular banded structures in a friction stir weld bead. However, in the CEL approach, friction within the workpiece resulting from damage to the newly born interfaces is neglected.

Recently, interest has also been directed toward the potential application of the CEL method to simulate orthogonal cutting. However, in machining processes, material separation can occur within the manufactured parts owing to damage [START_REF] Vaziri | Evaluation of chip formation simulation models for material separation in the presence of damage models[END_REF]. The resulting new interfaces are not explicitly described in the Eulerian formulation as they are in the Lagrangian formulation, where the mesh can describe newly born interfaces [START_REF] Rodriguez | Numerical Methods for the Modelling of Chip Formation[END_REF]. Therefore, the interfacial friction that maintains the material resistance after full damage is not considered in the Eulerian formulation. In this study, we propose a new damage evolution law that considers the friction at the interface after full damage. By considering that frictional behavior is at the origin of segmented chip formation, this approach is applied to orthogonal cutting. Its advantage over other processes is the possibility of extensively comparing simulation and experiment with forces, temperatures, chip morphology, etc., which, in other processes, is more complicated to access and to follow the tool-workpiece contact zone to make comparisons [START_REF] Boldyrev | EFG-simulation of the free orthogonal cutting and cutting forces prediction[END_REF]. It follows that, if it is possible to correctly simulate orthogonal cutting with this approach, predicting chip formation mechanisms and chip morphology, the approach and the material behavior laws can then be extended to other processes. Ducobu et al. [START_REF] Ducobu | Application of the Coupled Eulerian-Lagrangian (CEL) method to the modeling of orthogonal cutting[END_REF] were the first to apply the CEL approach to orthogonal cutting successfully. The major outcome to assess the validity of their two-dimensional (2D) CEL model, based on the Johnson-Cook (JC) constitutive law, was the closeness between the results of the new and the traditional Arbitrary Lagrangian-Eulerian (ALE) and Lagrangian models. Subsequently, they extended the previous 2D model to achieve a three-dimensional (3D) simulation of orthogonal cutting, succeeding in predicting the lateral material flow during plastic deformation [START_REF] Ducobu | Finite element modelling of 3D orthogonal cutting 295 experimental tests with the Coupled Eulerian-Lagrangian (CEL) formulation[END_REF]. The first simulation using this approach reporting segmented chip prediction was presented by Shuang et al. [START_REF] Shuang | Numerical analysis of chip formation mechanisms in orthogonal cutting of Ti6Al4V alloy based on a CEL model[END_REF]. Their 2D model was based on a modified JC law, but no damage law was included. The authors also did not compare the Ti6Al4V chip morphology obtained by simulation with experiments, except qualitatively. The first application of aluminum alloys was reported by Ducobu et al. [START_REF] Ducobu | Coupled Eulerian-Lagrangian (CEL) simulation for modelling of chip formation in 300 AA2024-T3[END_REF]. Based on a JC law describing the material plastic behavior, the authors correctly simulated continuous chip formation employing Bao-Wierzbicki (B-W) [START_REF] Bao | On fracture locus in the equivalent strain and stress triaxiality space[END_REF] model for damage initiation. However, an average error of approximately 20% between the simulated and measured shear forces should be noted. Agmell et al. [START_REF] Agmell | Development of a simulation model tostudy tool loads in pcBN when machining AISI 316[END_REF] first developed a 3D CEL model to simulate the chip mechanism formation in AISI 316L. Based on the JC constitutive law, the simulation predicted the segmented chip, but an accurate comparison of chip morphology was not performed. The simulated and measured average forces are close to each other, although the oscillation resulting from chip formation is almost nonexistent in the measurements, but it is evident in the simulation. Therefore, it is understood that the model does not accurately simulate the experimental chip formation mechanism. Recently, Xu et al. [START_REF] Xu | Machining simulation of Ti6Al4V using coupled Eulerian-Lagrangian approach and a constitutive model considering the state of stress[END_REF] developed a 3D model based on a newly developed plastic behavior law capable of predicting both segmented chip formation and the existence of a material-side flow. The damage laws in all models introduced have been based on the JC law for the initiation and energy criteria for evolution. Determining the parameters for these criteria requires many tests to characterize the material behavior as a function of strain, strain rate, and temperature to build a constitutive model [START_REF] Cheng | A constitutive model for Ti6Al4V considering the state of stress and strain rate effects[END_REF]. Moreover, although in mechanical testing one attempts to reproduce conditions developed during manufacturing processes, the thermo-mechanical conditions in some processes, such as machining and friction stir welding, are different from those encountered in conventional mechanical testing [START_REF] Iturbe | Mechanical characterization and modelling of Inconel 718 material behavior for machining process assessment[END_REF].

Reviewing the various works in the literature on orthogonal cutting simulation with the CEL approach, summarized in Table 1, to highlight the differences makes it clear that several elements need to be improved to increase the predictive ability of the models. Independent of the approach, none of the reviewed CEL Most of the models are based on the JC plastic law or its modified versions. Some contradictions can be seen.

For example, Shuang et al. [START_REF] Shuang | Numerical analysis of chip formation mechanisms in orthogonal cutting of Ti6Al4V alloy based on a CEL model[END_REF] can predict different forms of segmented chips with modified JC, whereas Xu et al. [START_REF] Xu | Machining simulation of Ti6Al4V using coupled Eulerian-Lagrangian approach and a constitutive model considering the state of stress[END_REF] states that the JC constitutive law cannot successfully predict segmented chip mechanisms. At the same time, the only work demonstrating remarkable differences in the simulated chips is that of Shuang et al. [START_REF] Shuang | Numerical analysis of chip formation mechanisms in orthogonal cutting of Ti6Al4V alloy based on a CEL model[END_REF], in which the damage law was not reported. Therefore, it is clear that several incongruities can be found in previous studies, confirming the need to improve existing models to predict chip formation mechanisms using the CEL approach.

Therefore, in this work, a new damage evolution criterion is proposed to integrate the friction between the newly born surfaces in the workpiece when simulating 3D orthogonal cutting through the CEL method.

2 Modeling and simulation of orthogonal cutting

Description of the orthogonal cutting model

The 3D model is developed in the ABAQUS/Explicit framework. It is created using the CEL approach, which allows the modeling of a Lagrangian tool and an Eulerian workpiece. In this way, the workpiece material moves through fixed mesh elements according to the Eulerian formulation, overcoming the mesh distortion problem. The fixed Eulerian mesh domain is sufficiently large to cover the evolving workpiece geometry, especially chip formation. This ABAQUS/Explicit method is based on the volume of fluid method [START_REF]Abaqus 6.10 user's manual, eulerian analysis[END_REF]. The Eulerian volume fraction for each Eulerian element is introduced. An element wholly filled with the material has a fraction equal to 1, whereas if no material is present, it is equal to 0. Therefore, the surrounding Eulerian volume at the beginning is empty, whereas the workpiece Eulerian volume is filled. Chip formation causes the empty elements to become either partially or completely filled with material during cutting. The Eulerian framework, workpiece and void, and Lagrangian tool in the initial condition are displayed in Fig. 1.

The extent of this extra volume must contain the desired material flow. In this case, the height along the y direction is set to include at least three consecutive segmented chips in the various tests performed, and the depth in the z direction is defined to contain the observed lateral material flow.

The element type for the Eulerian medium, workpiece, and void is an eight-node thermo-mechanical coupled linear Eulerian brick element (EC3D8RT). A size of 5 microns in the cutting zone and an orientation of 90 • with respect to the cutting direction of the Eulerian parts are established based on [START_REF] Xu | Machining simulation of Ti6Al4V using coupled Eulerian-Lagrangian approach and a constitutive model considering the state of stress[END_REF] outcomes. The tool elements are eight-node linear thermo-mechanical coupled brick elements (C3D8RT).

The sketch of the boundary conditions is presented in Fig. 2 and facilitates the explanation. On the bottom surface, the displacements along y are blocked. A velocity along x equal to the cutting speed on the left surface is assigned, blocking the z direction to avoid material flow. The tool is fixed and modeled as a rigid body. The only initial condition set is the temperature, which is selected according to the type of test. The tool-workpiece contact condition is modeled with Coulomb's law by setting a friction coefficient of 0.3 [START_REF] Melkote | Advances in material and friction data for modelling of metal machining[END_REF].

It is assumed that the heat generated by friction can be divided equally between the tool and workpiece [START_REF] Rech | Characterisation of friction and 325 heat partition coefficients at the tool-work material interface in cutting[END_REF] and that all the energy dissipated by the friction is converted into heat.

Constitutive law

Plastic behavior

The plasticity of the model is based on the widely used JC law (1), which describes the material behavior during plastic deformation, with temperature, strain, and strain rate all taken into account. The decision to use this law is made because of its wide use in the literature, allowing comparison of this model with other models.

σ = [A + Bε n ] 1 + C ln ε εo 1 - T -T o T m -T o m (1)
The model parameters for the two materials AA6082-T6 [START_REF] Chen | Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities[END_REF] and AA7075-T6 [START_REF] Zhang | A modified Johnson-Cook model of dynamic tensile behaviors for 7075-T6 aluminum alloy[END_REF] are taken from the literature and are listed in Table 2. Base Material E (GPa)

ν ρ (kg/m 3 ) k (W/m • C) c (J/kg • C) AA6082-T6 73

Damage initiation and evolution

The damage initiation is described using the traditional ductile criterion governed by state variable w:

w = ∆ε pl εpl o (2)
where ∆ε pl is the plastic strain increment and εpl o is the plastic strain at the onset of damage. During deformation, the state variable w increases monotonically from 0 to 1 at the onset of damage. Even though εpl o generally depends on the stress triaxiality and strain rate, it is assumed to be dependent only on the strain rate. Its calibration is made through experimental tests reproducing the experimental shear angles and chip 110 segmentation frequencies. A piecewise linear function is proposed, as shown in Fig. 3 for the two materials. For damage evolution, instead of using the linear damage variable D = ∆ε pl εpl f , the following multiplicative function f (η, T ), which depends on the stress triaxiality η and temperature T , is proposed:

D = ∆ε pl εpl f f (η, T ) (3)
where εpl f is the plastic strain at failure, which depends on the characteristic length L c of the element. Therefore, the material damage evolution properties are expressed in terms of the displacement at failure,

u f = εpl f L c
. Before expressing f (η, T ), it is important to describe the proposed approach. First, it is noteworthy that the stress triaxiality η is equal to -0.33 for uniaxial compression, 0.33 for uniaxial tension, 0 for pure shear and -∞ for hydrostatic pressure. The stress triaxiality can be expressed as

η = σ m σ        σ m = (σ 1 + σ 2 + σ 3 ) /3 σ = 1 2 (σ 1 -σ 2 ) 2 + (σ 2 -σ 3 ) 2 + (σ 3 -σ 1 ) 2 (4)
where σ m is the hydrostatic pressure and σ is the von Mises equivalent stress. The expression for f (η, T ) is given by

f (η, T ) = (c 1 -c 2 ) η max (T ) -η c η + c 2 (5)
c η = η max (T ) -η min (T ) (6)
and c 1 and c 2 are the extreme values of D for the full and zero frictional effects, and they are fixed at 0.4 and 0.95, respectively. The goal of the proposed damage evolution law is to add additional resistance to the damaged material to the frictional interface. This is needed because, during damage, the material better resists compression than tension. By defining a temperature-dependent parameter, η max (T ), the frictional interface is considered. Stress triaxiality equal to or lower than η min leads to full frictional behavior, whereas if it is greater than or equal to η max , there is no friction, as displayed in Fig. 4a. By assuming that the stress triaxiality is constrained within uniaxial compression (η = -0.33) and uniaxial tension (η = +0.33), a transition zone c η = 0.66 is imposed for the material behavior description. Then, by integrating the η max dependency on the element temperature, as schematically represented in Fig. 4b, thermal softening is taken into account and differences in the frictional behavior are considered. The η max (T ) parameter dependency on temperature is as follows:

η max (T ) =                η 0 if T < T 0 (η f -η 0 ) T -To T f -To mc + η 0 if T 0 ≤ T ≤ T f η f if T ≥ T f (7)
where T 0 is room temperature, while T f is the critical temperature when the aluminum alloys lose their strength due to microstructural modifications. The parameter tuning of the chip formation mechanism is η max . Therefore, its limits for both materials, η 0 and η f , as well as the temperature dependency, are inversely calibrated to reproduce the chip formation mechanism obtained experimentally. The function f (η, T ) is programmed in the ABAQUS subroutine VUSDFLD and is called the field variable in the tabular damage evolution law environment.

Therefore all the elements introduced in the model are following. At damage initiation, the equivalent plastic strain depends linearly on the strain rate and acts directly on the shear angle. Once the damage has started, the interaction at the interface is described by equation (3), which influences the chip separation mechanism.

The novel separation criterion integrating the friction between the newly formed surfaces allows the simulation of chip formation mechanisms using the CEL approach. In the first subsection of the Results and discussion section, the calibration process is explained by illustrating how the temperature dependence of η max (equation 7) is derived, and the results of the simulations performed once all dependencies are defined then discussed in the rest of the section.

Experimental setup

Tests are performed on a SOMAB Genymab 900 multitasking lathe (max cutting speed 30 m/min and max cutting force 10 kN), and four different configurations are tested on 3-mm-thick AA6082-T6 and AA7075-T6

sheets. The depth of cut is kept constant at 1 mm and the rake angle is set at 0 • , while the other parameters 130 are summarized in Table 3. Two tests for each configuration are performed, one with a high-speed camera A sketch of the experimental setup and HSC and IR images (post-processed with MATLAB) are presented 135 in Fig. 6. The HSC images are used to measure the primary shear angle, while the mean temperature in the primary shear plane and the maximum temperature in the secondary shear plane are determined using IR camera images. Local heating of the plates is performed using a blowtorch. The machined parts are blackpainted to control the emissivity of the aluminum alloys, and the emissivity is calibrated using preliminary tests. In addition, in all high-temperature tests, to check that the information provided by the IR camera is 140 correct, a thermocouple is inserted into the back of the plates, as shown in Fig. 6b. Additional information about the sensors (HSC and IR) is presented in the Appendix.

For chip preparation, the samples are polished down to 1/4 µm, and AA7075-T6 chips are chemically etched by exposure to Keller's reagent to reveal the grains. The etched samples are inspected using an optical microscope (Olympus PMG3), while the other observations were are using a Keyence VHX6000 microscope.

145

Changes caused by different test conditions, at room temperature or preheating, were investigated with Vickers hardness measurements. They are made on polished samples using a Zwick ZHU 2,5 durometer with a load of 4.9 N and a duration time of 10 s. Three indentations are performed in each different zone that makes up the chip.

Results and discussion

Influence of the damage variable on chip formation mechanism

The novelty introduced in this study is related to the damage evolution criterion. It depends on the stress triaxiality and coefficient η max , the latter of which directly affects the stiffness degradation in the shear band. In the calibration phase of the model, this parameter is changed manually to act on the formed chip geometry in the various tests performed on the different materials. Fig. 7 shows the results three types of chips obtained under the same conditions (cutting speed, depth of cut, and initial temperature) and material properties by changing the value of η max . Decreasing η max results in D approaching 0.95, resulting in a In the experiments, a continuous chip is obtained only in the hot configurations of alloy AA7075-T6. By analyzing the chip transversal microstructure and the hardness in the various areas that make up the chip, the difference between the two tests at room temperature and with pre-heating is evident, as displayed in Fig. 9. The microstructure obtained at room temperature (Fig. 9b) is similar to those of the base material (Fig. 9a) but deformed by shear. However, in the test with pre-heated plates, the microstructure begins to have characteristics different from those of the base materials, such as various grains with different shapes, sizes, and orientations (Fig. 9c). The different microstructures are due to dynamic recovery, which is the governing softening mechanism during hot deformation of AA7075-T6 at high temperatures up to 350 • C [START_REF] Wang | Constitutive modeling of flow behavior and microstructure evolution of AA7075 in hot tensile deformation[END_REF].

Furthermore, the measured hardness decreases dramatically in the hot configuration owing to the gradual transformation of the strengthening precipitates (Fig. 9d). As a result, a continuous chip is obtained instead of a segmented chip (Fig. 10).

Hence, based on the experiments and literature, η max coefficient is made temperature-dependent. The high mechanical strength of aluminum alloys in the T6 state is due to the high density of strengthening precipitates induced by heat treatments [START_REF] Gladman | Precipitation hardening in metals[END_REF]. However, once certain temperatures are reached, these precipitates begin to progressively grow, losing their strengthening effect and causing a drastic decrease in the material's mechanical strength [START_REF] Maisonnette | Effects of heat treatments on the microstructure and mechanical properties of a 6061 aluminium alloy[END_REF] because of dynamic recovery and dynamic recrystallization. The critical temperatures in the two materials are different, and, based on previous studies, are fixed between 250 -350 • C for AA6082-T6 [START_REF] Xu | Investigation on compressive formability and microstructure evolution of 6082-T6 aluminum alloy[END_REF] and between 200 -300 • C for AA7075-T6 [START_REF] Dalai | Mechanical Behavior and Microstructure Evolution During Deformation of AA7075-T651[END_REF]. Consequently, the η max parameter changes within the ranges until the critical temperature T f is reached, as shown in Fig. 11. The values attributed to the model parameters are listed in Table 4.

Table 4: Damage constitutive model parameters for the two materials. approximation by the model. The model consistently reproduces the observed experimental oscillation that coincides with chip formation. It is noteworthy that the model can capture the differences in the periodicity of the forces depending on the test. However, some differences are observed, and these are related to experimental inaccuracies. In Fig. 12a, the experimental first peak is lower than the simulated one, but this difference is associated with the slight inaccuracy of the depth of cut during the AA6082-T6 tests owing to the deformation caused by the previous pass. In contrast, in the hot test (Fig. 12d), in the simulation, a homogeneous temperature is predefined throughout the piece, but during experiments the heating is local at the first contact points with the tool. Therefore, at these points, the temperature may have exceeded the preset temperature of 180 • C or in any case the exposure to these high temperatures induced an excessive decrease in the resistance of the material. However, once the first few millimeters are advanced, the forces begin to approach each other. Fig. 13a shows the mean values of all forces with their standard deviations.

BM c 1 c 2 c η η f η 0 m c T f AA6082-T6 0.
Overall, the prediction of the model is reliable, with an error that is always below 10%. Similarly, the ability of the model to predict the chip segmentation frequency is accurate, as shown in Fig. 13b, where the simulated average time to chip creation in the 21 m/min configurations agrees with the experimental results.

With respect to the temperature, as observed from the thermal field obtained through the numerical simulation displayed in Fig. 14, the temperature rise resulting from plastic deformation is always higher in AA7075-T6 than in AA6082-T6. The temperature measurements with the IR camera allow estimating the average temperature in the primary shear zone by averaging the temperature in the pixels along with AB, as displayed in Fig. 6d. Similarly, the maximum temperature at the interface with the tool is estimated by averaging the maximum values among the pixels in the white dashed rectangle recorded in each image (Fig. 6d). The same is done in the simulations, and the comparison for all configurations is shown in Fig. and its ability to describe heat generation resulting from tool-workpiece interaction. Therefore, the model 210 reliability in predicting the thermo-mechanical quantities developed during the process, such as forces and temperatures, is demonstrated.

Chip morphology

The goal of introducing the new damage evolution criterion is to predict the type of chip formation mechanism, depending on the cutting conditions. We also aim to get as close as possible to the experiments in Regardless of what occurs in the cutting plane, a remarkable material side flow for both aluminum alloys occurred during the experiments. Similarly, an out-of-plane deformation is observed in the simulation. Therefore, the chip thicknesses obtained experimentally and by simulation are compared for the configuration at room temperature and 21 m/min for both materials, as shown in Fig. 18. The simulation proved capable of predicting the material side flow well with an error of 2% and 8% for AA7075-T6 and AA6082-T6, respectively. From a qualitative point of view, by observing both the front and back of the chip in the two configurations, the results obtained with the simulation can be considered successful. This result is important, especially regarding the frequent assumption made in many simulations of the orthogonal cutting process in which it is considered a 2D process [START_REF] Calamaz | A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti-6Al-4V[END_REF]. It is evident that, in the case of aluminum alloys, the deformation out of the plane is significant and could probably be detrimental to the application of digital image correlation technique measure the strain and strain rate gradient in shear zones. For AA7075-T6 [START_REF] Zhang | Characterization of material strain thermal softening effects 330 in the cutting process[END_REF] and Ti6Al4V [START_REF] Harzallah | Numerical and 305 experimental investigations of Ti-6Al-4V chip generation and thermo-mechanical couplings in orthogonal cutting[END_REF],

the digital image correlation technique is successfully applied for 0.25-mm-depth of cuts. However, if higher depths of cuts are used, the out-of-plane strain can be problematic for strain measurements through digital image correlation, leading to poor image sharpness and unsuccessful measurement owing to the material side flow [START_REF] Zouabi | Kinematic Fields Measurement during Orthog-335 onal Cutting Using Digital Images Correlation: A Review[END_REF].

Conclusion

A 3D numerical simulation of orthogonal cutting with a CEL approach based on a new inversely calibrated damage evolution criterion is proposed. The damage evolution function is developed and calibrated on tests with AA6082-T6 and AA7075-T6 under different experimental conditions, replacing the laborious

Figure 1 :

 1 Figure 1: 3D orthogonal cutting model including Eulerian workpiece, Eulerian void, Lagrangian tool and dimensions.

Figure 2 :

 2 Figure 2: Boundary conditions.

Figure 3 :

 3 Figure 3: Equivalent plastic strain at damage initiation εpl o as function of strain rate.

Figure 4 :

 4 Figure 4: Conceptual dependencies representation of a) f (η, T ) on stress triaxiality and b) ηmax on temperature.

  and another with an infrared (IR) camera, while forces are always recorded with a Kistler 9129AA loadcell at 1500 Hz. The experimental setup is shown in Fig.5, with details on the tool and the force and video acquisition system.

Figure 5 :

 5 Figure 5: Experimental setup a) Lathe machine, b) tool detail, c) acquisition systems (forces and high speed cameras).

Figure 6 :

 6 Figure 6: Sketch experimental setup a) front and b) top view. Frame from c) HSC and d) IR (after post-treatment).

Figure 7 :

 7 Figure 7: Stress-strain curve in the chip formation. a) Begin elastic deformation, b) yield point, c) damage initiation w = 1 and D = 0, d) material stiffness degradation limit (ε pl f ). Influence of ηmax on the chip formation mechanism

  Von mises stress and damage variable evolution in the tracked elements.

Figure 8 :

 8 Figure 8: Influence of ηmax on the simulation. Continuous ηmax= 0.7, segmented ηmax= -0.7.

Figure 9 :

 9 Figure 9: Microstructure of the base material and the chip obtained in configuration at room temperature and pre-heated and hardness in the chip different zones.

Figure 10 :

 10 Figure 10: Segmented and continuous chips obtained in the tests at 21 m/min on AA7075-T6.

4. 2 Figure 11 :

 211 Figure 11: Evolution of ηmax as function of the temperature.

Figure 12 :

 12 Figure 12: Forces evolution during the formation of at least three consecutive chips in all tests performed at 21 m/min.

  Chips segmentation frequency at 21 m/min.

Figure 13 :

 13 Figure 13: Comparison between experiment and simulation of cutting forces and chip segmentation frequency.

Figure 14 :Figure 15 :

 1415 Figure 14: Thermal field in different configurations: a), b) AA6082-T6 and c), d) AA7075-T6.

215

  terms of chip morphology. The results obtained shown in Fig. 16 demonstrate the achievement of both set (a) AA6082-T6 -Room temperature. (b) AA6082-T6 -Pre-heated. (c) AA7075-T6 -Room temperature. (d) AA7075-T6 -Pre-heated.

Figure 16 :

 16 Figure 16: Comparison between chip obtained experimentally and numerically.

  . The geometric values are presented in Table5, with a focus on configura-(a) Simulated chip showing peak, valley, width and shear angle. (b) Chip obtained from experiment showing peak, valley and width.

Figure 17 :

 17 Figure 17: Identification of chip geometry characteristics.

  (a) Back and frontal view of AA6082-T6 chip obtained experimentally and numerically. (b) Back and frontal view of AA7075-T6 chip obtained experimentally and numerically.

Figure 18 :

 18 Figure 18: Comparison between chip thickness after cutting at 21 m/min at room temperature due to material side flow.

  and complex material testing required to develop constitutive equations. With the new approach, integrating the friction between newly formed surfaces during cutting, the changes induced by experimental conditions 245 resulting in different interactions between consecutive chips (and different mechanisms, from severely segmented to continuous chips) are correctly reproduced. At the same time, the simulation does not suffer a loss in quality in predicting the physical quantities generated during the process and can also capture the outof-plane deformations that occur during orthogonal cutting. Moreover, the simulation can correctly capture

Table 1 :

 1 Summary of the reviewed models, showing the main information, including material behavior laws and type of model (2D or 3D) schematically. Base material (BM), continuous (Cont.) and segmented (Seg.).

	Author	BM	Plastic	Damage	Damage	Model Chip
	-	-	behaviour initiation evolution	-	type
	Ducobu et al [8]	Ti6Al4V	J-C	N/A	N/A	2D	Cont.
	Ducobu et al. [9]	Ti6Al4V	J-C	N/A	N/A	3D	Cont.
	Shuang et al. [10]	Ti6Al4V	J-C TANH	N/A	N/A	2D	Seg.
	Ducobu et al. [11]	AA2024-T3	J-C	B-W	Energy	2D	Cont.
	Agmell et al. [13]	AISI 316L	J-C	J-C	Energy	3D	Seg.
	Xu et al. [14]	Ti6Al4V	Proposed	J-C	Energy	2D/3D	Seg.
	This work	AA6082-T6 / AA7075-T6	J-C	Proposed Proposed	3D	Both
	models exhibited the ability to predict different chip formation mechanisms (continuous and segmented).

Table 2 :

 2 Workpiece and tool material properties.

	AA6082-T6	305	307	0.0044	0.68	1.31	1	582
	AA7075-T6	473	210	0.033	0.38	1.5	1	635

Base Material

A (MPa) B (MPa) C n m εo (s -1) T m ( • C)

Table 3 :

 3 Orthogonal cutting parameters.

Table 5 :

 5 Chips geometry.

	BM	Config.	Peak	Valley	Witdh	Shear angle
		Exp.	2.55 ± 0.19 0.78 ± 0.27 1.59 ± 0.42	26
	AA6082-T6 -RT	Sim.	2.34 ± 7.2 1.05 ± 0.06 1.50 ± 0.07	30
		absolute err.	9%	25%	6%	13%
		Exp.	2.73 ± 0.10 1.13 ± 0.21 1.65 ± 7.2	20
	AA6082-T6 -PH	Sim.	2.4 ± 0.01 1.31 ± 0.02 2.02 ± 0.18	24
		absolute err.	13%	13%	18%	16%
		Exp.	1.64 ± 0.07 0.76 ± 0.17 0.98 ± 0.07	33
	AA7075-T6 -RT	Sim.	1.35 ± 0.05 0.65 ± 0.05 1.03 ± 0.07	30
		absolute err.	21%	15%	5%	10%
	10% (except for a few cases in which it exceeded 20%), confirming the overall good predictive quality of the
	simulation in capturing complex phenomena such as the cyclic formation of shear bands and the formation
	of chips during orthogonal cutting.

Acknowledgements

The authors want to thank Leo Bellon for the execution of orthogonal cutting tests.

Funding

This work was supported by the European Union's Marie Skodowska-Curie Actions (MSCA) Innovative Training Networks (ITN) H2020-MSCA-ITN-2017 under the grant agreement N • 764979.

Data Availability

The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.

the material behavior of the processed part from its elastic response to the degradation induced by damage initiation and propagation. This result is auspicious for extending the new damage evolution criterion by considering the friction within the Eulerian workpiece in severe deformation processes simulated through the CEL approach.

CRediT authorship contribution statement

Appendix A

Infrared camera

Calibration and data recording were managed by Altair software. The specifications for the measurements performed in room temperature and pre-heated tests are listed in Tab. [START_REF] Rodriguez | Numerical Methods for the Modelling of Chip Formation[END_REF]