Fidelia Ibekwe-Sanjuan
email: fidelia.ibekwe-sanjuan@univ-amu.fr

Combining an arts-informed and textual approach to teaching information and communication theories

This paper report on an experiment of using a hybrid pedagogical approach to tackle the challenge of teaching « Information and Communication theories » to students enrolled in Master of Communication and Digital Content at the School of Communication and Journalism of Aix Marseille University in France. The hybrid pedagogical approach combines the classical textual/verbal approach with an arts informed pedagogy, augmented by creative writing and storytelling activities. The fact that the arts-informed approach was not used in isolation but in combination with the traditional textual/verbal approach and creative writing and storytelling activities offered students a wide choice of learning modalities through which they could express themselves. Our preliminary findings suggest that using a hybrid pedagogical approach rather than one single pedagogical approach improved students' understanding of the abstract concepts implied by the communication theories discussed during the lectures. Students illustrated their understanding of these theories by recasting them in various real life or plausible situations during the creative writing activity which we call "Communication Stories" or cStories.

Introduction

Teaching a theoretical course can be challenging on many levels. The concepts involved are often far removed from the daily lives of students and their immediate impacts are not always perceptible. The ideas and concepts involved could also have a historical dimension, or be subject to debate and to multiple interpretations which make it difficult for students to understand their implications in everyday life. This is particularly true of information and communication theories. Information and communication are fundamental concepts present across all disciplines. As such, they have received hundreds of abstract definitions that are often contradictory and have given rise to a huge body of publications [1, 2]. There is no one accepted definition of these two universal concepts that is true for all people and for all times. The need to resort to other modalities of expression aside from the textual or verbal arose from my accumulated experience that magisterial lectures have a low student engagement rate, a high boredom factor which subsequently leads to low student attendance of classes. Engaging the students using alternative modes of expression other than textual or verbal has the capacity to engage and to improve class attendance while enabling students to better appropriate the course content. I have therefore been exploring a hybrid pedagogical approach integrating an arts-informed pedagogy (draw and write technique), a creative writing activity and an embodied pedagogy (storytelling, staging and acting) into the more classical textual/verbal approach in order to improve students' participation, appropriation of the course content and hence their learning outcomes.

The draw-and-write technique is an instance of an arts-informed visual research method. Hartel [3] explored this approach in her teaching and research at the School of Information Science of the University of Toronto. The technique appears to have originated in the United Kingdom in the 1980s in the field of education before being tried in other fields such as healthcare, engineering, environmental science, geography, industrial design and psychology. It has been used to study a wide range of phenomena ranging from menopause, the concept of librarian, celebrities, autism, and information-seeking. Therefore, as an investigation technique, it is not limited to any one field. It offers participants an alternative mode of expression to articulate ideas and perceptions that words alone may not capture adequately. Hartel [3] developed the iSquare protocol [START_REF]Theories of Information, Communication and Knowledge[END_REF] which is an instance of the draw and write technique, and used it to explore her students' conceptions of information. Have reported in Ibekwe-SanJuan [4], some preliminary findings of how the iSquare protocol was used to explore students conceptions of information at the School of Communication and Journalism of Aix Marseille University in France. I have also published on a website my experience of introducing an arts-informed approach in this course [START_REF] Buckland | Information as thing[END_REF] . However, the overall hybrid pedagogical approach has not been published before. This paper reports how we adapted the iSquare technique to the teaching « Information and Communication theories » (thus to cSquares) to students enrolled in a Master of Communication and Digital Contents at the same school in France and how we augmented the iSquare protocol by adding creative writing and storytelling activities. I also present for the first time the results of a thematic analysis of the storytelling activity (cStories). The rest of this paper is organised as follows: section §2 gives an overview of the different stages of the pedagogical approach deployed in this course; section §3 is devoted to my findings and section §4 outlines future perspectives research.

Methodology

The hybrid pedagogical approach adopted combined the classical textual/verbal approach with an arts informed pedagogy augmented with creative writing and storytelling activities. The course "Information and Communication Theories" in which this hybrid pedagogical approach was deployed is a compulsory course for students enrolled in different tracks of the Master of Communication and Digital Content at the School of Journalism and Communication of Aix-Marseille University in France. The course runs for eight weeks, at a rhythm of three-hour class per week. In the following subsections, we detail the four stages of this hybrid approach, namely (2.1) Draw and write activity; (2.2) textual/verbal lectures; (2.3) drawings exhibition and creative writing (cStories construction); (2.4) staging and storytelling (from cSquares to cStories).

Draw and write activity: making cSquares

In the first class, the whole course structure is explained to students. It is impressed upon them that while the draw and write activity may appear childish, it is a tested pedagogical and research approach used in various context including health therapy (autism, victims of trauma). The draw and write activity is an adaptation of the iSquare protocol (a 4" X 4" piece of white paper on which students are required to respond to the question "What is information?" in the form of a drawing and also to complete the phrase, "Information is…" on the backside of the same paper as well as fill in demographic information (age, gender, specialty enrolled in). We adapted it to the study students pre-conceptions of communication and have called this the "cSquare" by analogy. We simply changed the instruction to «Complete the sentence below "Communication is.." for the verbal definition. The verso of the paper is left blank for the drawing part (see Figure 1 below). Students are also asked to provide brief demographic information such as age, gender and the master's track they are enrolled in. Our students were aged between 21-23 years old with an average of 22 years. They were given ten minutes to perform the exercise.

The rationale in performing the draw and write activity at the very beginning of the course is to gather the preconceptions students have of the main concepts before they receive the instructor's lectures. Once students complete their drawings, these are collected and kept by the instructor for further use. The students are informed that they will have to reuse the drawings towards the end of the course in creative writing and storytelling activities (see §2.3 and §2.4 hereafter). Since I began implementing this hybrid pedagogical approach, I have collected 332 drawings, broken down as follows: 24 cSquares in 2014; 52 iSquares in 2015 [START_REF] Hartel | An Arts-informed study of information using the draw-and-write technique[END_REF] , 74 cSquares in 2015, 65 cSquares in 2016, 57 cSquares in 2017 and 60 cSquares in 2018). The numbers of drawings collected per year varied according to student intake for that year.

On the verso, make a drawing in answer to the question "What is communication?" and then complete the following sentence:

Communication is:

Age: ------Sex: -------Specialty: ------Initials -------(Draw side of the cSquare) Fig. 1. Example of blank cSquare for the draw and write activity.

Lectures via the classical textual/verbal approach

The draw and write activity is immediately followed by six weeks of "traditional" lectures during which the instructor uses both verbal and textual modalities to explain the tenets of the major information and communication theories and their implications for analysing and understanding events involving human interactions. The theories presented stem from three research traditions:

Drawings exhibition and creative writing (cStories construction)

The exhibition of the students' drawings is done in the week following the traditional textual/verbal lecture. Students are required to form groups of three or four to view all the drawings during a two hour exhibition period. The instructions given are to choose a story which can be a real life event (past or present) or an imaginary but plausible one involving communication situations which can be explained by one or several of the theories they had learnt about during the course. They are to use some of the drawings on the cSquares to illustrate their story although they can also cull other images from the Internet. During the exhibition, students take pictures of their chosen cSquares and then work on their story during the week outside of class. The number of drawings used in each story is only limited by the students' capacity to reuse them in their storytelling activity within the allocated time (see §2.4 below) and by the internal coherence they can find between the drawings and their story. Also, the number of theories they can invoke to explain the communication phenomena at work in their story is left to their discretion. Students then have one week out of class during which they work on writing their stories with their group members and on designing their visual aids, usually in the form of slides on which they feature the chosen cSquares with texts and other images eventually. The stories constructed by the students after the exhibition of cSquares are called cStories.

Storytelling and staging activity: from cSquares to cStories

In this final and fourth stage of the hybrid pedagogical approach, students present the result of their creative writing activity in front of their peers during the last week of the course. Each group is given ten minutes for their presentation and all the students in a group are expected to participate. Our pedagogical objectives in this stage are three-fold: i) assess students' understanding of the communication theories presented during the lectures;

ii) evaluate their understanding of real life or plausible situations through the lenses of communication theories;

iii)

evaluate their ability to reuse the drawings done before receiving the textual/verbal lecture to illustrate real life or plausible situations. Hence, this stage calls upon other modalities for learning such as creative writing, storytelling, staging and acting and information and communication design.

Students are required to prepare slides featuring the drawings (cSquares) they chose alongside other textual and visual artefacts. Some students also staged a related short play involving role-playing. The scripts used in their presentations were collected as well as the slides, thus enabling us to build up a corpus of "cStories" which can be used for future studies (see §3.2). Figure 2 hereafter is an overview of our hybrid pedagogical approach.

Findings

In §3.1, the results of the thematic analysis of a selection of drawings are presented and in §3.2, examples of the cStories illustrate students grasp of communication theories at work in real-life situations.

Thematic analysis of the cSquares

I performed a thematic analysis of the first batch of 74 cSquares collected during the 2015 classes in order to understand what prior conceptions students had of communication before receiving the lecture content. Thematic analysis is a qualitative analysis method involving human interpretation of knowledge artefacts. In other words, "Thematic analysis goes beyond simply counting phrases or words in a text and moves on to identifying implicit and explicit ideas within the data [START_REF] Ibekwe-Sanjuan | The journey of information. How students perceive information in France using the draw and write technique[END_REF] ». I examined the drawing side of the cSquares attentively in order to determine what they portrayed. Then, relying on my background knowledge, I sought to correlate the themes depicted on the drawings with the information and communication theories evoked during our lectures. This process is unavoidably hermeneutical in that much depends on the interpreter's knowledge of the subject matter and what s/he is looking for. However, to reduce the subjective element of the interpretation process, I triangulated it by consulting the textual definitions on the other side of the cSquares to see if they lent credence to my interpretation or diverged from them. A detailed comparative thematic analysis of the first set of iSquares and cSquares is available on the cSquares website5 . I will simply summarise the salient points of the thematic analysis of the cSquares below. My first observation was that although the drawings were done before the students received the course content, their drawings and texts echoed well-known mass media and of interpersonal communication theories propounded by 20th century communication pioneers. I classified the drawings into one of the following four categories: (i) Interpersonal communication: the drawings in this category evoked the theories propounded by Palo Alto school (Gregory Bateson, Paul Watlawick) and their research at the Mental Research Institute on the schizophrenic communication problems between psychiatric patients, their caregivers and family members in hospital settings which often resulted in a double bind. (ii) Machine mediated communication: this second group of drawings depicted the beginnings of mass media in the first half of the 20th century with telephones, newspapers, radio and television and their move towards information and communication technology (pictures of the internet, personal computers, emails, mobile phones) which have become pervasive towards the end of the 20th century. (iii) Mass media manipulation effect: a third group of cSquares captured the popular and tenacious belief that the mass media influence people's opinion and their perception of reality and not always in a disinterested fashion. These drawings are reminiscent of the functionalist theories of mass communication propounded by Harold Lasswell and Paul Lazarsfeld in the first half of the 20 th century when they sought to quantify the short term effects of mass media campaigns (radio, cinema and television) on public opinion in the United States, via quantitative and empirical methods (surveys). This gave rise to Lasswell's 5W communication model and Lazarsfeld's two-step flow model of communication. (iv) Internet and global village. This fourth group of drawings mostly evoked Marshall McLuhan's theories on the evolution of information and communication technologies (ICTs) and their impact on society, in particular his famous "medium is the message" aphorism as well as his prediction in "The Gutenberg Galaxy" (1962) that the next set of technological inventions will make the world a global village 6 . The drawings depicted the earth as continents interconnected by ICTs.

Secondly, I also observed that in the students' perception, Shannon-Weaver's linear mathematical theory of information is not opposed to Wiener's circular cybernetic model but that both formed a continuum. This perceived proximity is all the more pertinent if one bears in mind the fact that the most influential theories of information and communication were propounded quasi-simultaneously by researchers who knew each other and mixed in the same circles: Claude Shannon (The Mathematical Theory of Communication 1948), Norbert Wiener (Cybernetics and control in the animal and the machine, 1948) and Gregory Bateson (Steps to an ecology of Mind 1972) all attended the Macy conferences7 in New York between 1941 and 1960. Harold Lasswell's theory on mass media (5W communication model) was also made public in 1948! Finally, thematic analysis also showed the importance of the disciplinary background (domain bias) over linguistic, cultural and geographic biases, i.e., students' conceptions of information and communication were more likely to be influenced by the courses they had done before enrolling in to this Masters' course than by any other factor (geographic origins, linguistic or cultural factors). See [4] for more details. It is quite remarkable that students were able to capture the main features of complex and abstract theoretical discourse propounded several decades ago (as early as 1927 for some) by the erudite scholars on the concept of communication using drawings on a small piece of paper, without having to resort to a lengthy verbal discourse or to elaborate graphic representations.

cStories: communication theories in action

Around 86 cStories have been collected over four years (2015-2018). The fewer number of cStories compared to the cSquares is because it is a group activity, and I only began a systematic collection of the cStories since 2016. A presentation of a few stories from the 2015 series can be found on the cSquares website8 . The next section is devoted to a thematic analysis of the whole collection of cStories.

A thematic analysis of the cStories

First the texts of the 86 cStories collected between 2015 and 2018 were read to determine the theme of each story, the communications theories evoked and how they shed light on the relevance of these theories in modern times. This led me to identify seven thematic classes. As in the analysis of cSquares, the process of assigning a story to a thematic class is unavoidably subjective and the outcome depends on the pragmatic and hermeneutic goals of the analyst/interpreter. Table 1 hereafter summarises the salient features of each thematic class. As shown in this table, 32% of the stories came under the "chosen theories" category. These are real or imaginary situations interpreted through the lens of one or more chosen communication theories. Stories recounting the "history of communication came in the second position (21%). In the third place, "communication modalities" (18,6%) referred to stories on how people communicate use different communication modalities (verbal, non-verbal and machine mediated communication such as the Internet, web, mail, radio, TV, telephone, social media). In the fourth position were stories illustrating the use of communication theories in political campaigns. Here we found stories recounting how the Obama's, Trump's, Clinton's electoral campaign strategies brought into play some of the communication theories discussed in the textual/verbal lectures. In the fifth position were a few stories illustrating how specific mass media theories were deployed in advertisements and communication campaigns of global brands such as Ikea, Benetton, McDonalds, Apple, Coca-Cola, etc. Lastly, the two thematic classes "communication satire" (4,7%) and "misuse of communication" (4,7%) were ex-aequo in the sixth position.

Themes of the cStories

Nb

Communication theories evoked and literary devices used

History of communication 18

The cStories take us on a "journey" of communication across history. These stories evoke the first forms of human communication (non verbal and oral) and the formalisation of rhetoric and argumentation techniques by Aristotle used as a communication tool for persuasion in ancient Greece. Fast forward several centuries and we encounter the major communication theories in the 20 th century: Shannon's mathematical theory of communication for its "information transmission, information as a statistical measure" aspect; Norbert Wiener comes simultaneously to introduce the importance of "feedback and retroaction" in communication; Harold Lasswell is evoked for his "pavlovian hypodermic syringe" model of communication that explains the functioning of the mass media; Stuart Hall is also cited for having highlighted the importance of cultural codes on how a message is received; the Palo Alto school features for its theories on interpersonal communication, its "communication as behaviour" and "importance of the context over the content" axioms as well as for its insistence that communication is a social process that cannot be studied in isolation. Marshall McLuhan's "global village" and "medium is the message" axioms serve to explain the apparition of ICTs (Internet, web, social media, ...). Each communication theory is placed in a setting that sheds light on how it accounts for certain aspects of the complex communication phenomena. Communication satire 4

These cStories use allegory, satire and metaphors to cast contemporary communication modalities, artefacts and devices (ICTs) as historical, religious or mythological deities. A good example of such a story can be found on the cSquare website here9 .

Communication in politics 7

Stories here focus on the use of the mass media and social media in political communication campaigns, especially in elections. We encounter once again McLuhan's prediction that ICTs will make the world a global village; Paul Lazarsfeld's 2 step-flow of communication to reach certain segments of the population using leverage of social media. Obama's use of the media and social media in his campaigns and Trump's 2016 election were amongst some of the popular stories in this series.

Communication campaign strategy 5

These stories use a plausible campaign strategy as background to illustrate the relevance of several communication theories in persuading a target audience to act in a certain way (sway its opinion, buy a product, etc).

Understanding real life social phenomena through the cStories

Two examples of cStories serve to illustrate the creativity of the students and their ability to interpret real life events or imaginary social phenomena through the lenses of abstract communication theories.

In general, stories classified under "communication campaign strategy" illustrate how the marketing and advertisement industries still call on mass media theories propounded in the first half of the 20 th century to achieve their goals. A cStory in the 2015 series showcased the planning stages of an international marketing campaign aimed to launch a fictitious product by a team of communication consultants. This cStory artfully illustrated the fact that to attain a marketing goal, it is often necessary to draw from more than one communication theory. The different stages of the campaign were illustrated by seven drawings. The first stage of the design of the advertisement campaign labelled « Know your target » drew on Harold Lasswell's hypodermic syringe model of communication to design one-way messages to a target audience. However, since Lasswell's model alone cannot account for how public opinion can be changed, the students equally drew on Lazarsfeld's two-step flow communication model to reach those segments of the audience that are refractory to the mass media and are likely to be influenced by opinion leaders, or by their circle of friends or colleagues. In the text of their story, the students explained how certain brands or messages become successful because they have been adopted by celebrities who serve as opinion leaders. By analogy, the shepherd in the drawing in cSquare 67 (Fig 4 . hereafter) is the celebrity or the opinion leader influencing his flock of followers. The next stage relied on Roman Jakobson's six functions of language to define the three objectives of the campaign which were cognitive, affective and conative. Marshall McLuhan's prediction that ICTs will make the world a global village was evoked next to show how certain commercial brands such as Apple's iPhone or McDonalds have become global household names. In a fourth stage, the students raised the teleological question (intention) via a drawing that portrayed the fact that the same message can be interpreted in different ways depending on the cultural context in which it is received and therefore the cultural element needs to be integrated in the design of a marketing campaign. As an example of how a message can be misunderstood by the target audience, the students cited the case of Benetton a company that specialises in provocative publicity campaigns that often ended up having a negative effect than the positive one intended by the company. The question of feedback was tackled in the fifth stage where the students correctly analysed the strategic importance of the empowering capabilities that web 2.0 technologies have given to customers allowing them to have a powerful voice and therefore the capacity to trigger a negative buzz that can destroy the reputation of companies, brands and celebrities in a few days. The students correctly analysed that feedback can be a positive thing in that it can enable an organisation to adjust its message but it can also be negative in the case of bad buzz. The theoretical justification for the importance of feedback is of course Wiener's cybernetics theory of communication. Wiener defined two types of feedback: positive feedback which accentuates the phenomenon and negative feedback which diminishes the effect expected. Once again, students illustrated the consequences of a negative feedback by citing the case of IKEA who had removed all feminine presence in one of its catalogues destined to Saudi Arabia in order to conform to that kingdom's very conservative outlook on women's role in society. This however generated a negative feedback from viewers in the western world. The story then concluded by recalling the three ingredients deemed fundamental for a successful communication campaign: choosing one's target, defining one's objectives and choosing the adequate means to get the message across as effectively as possible. A second story from the "chosen theories" category was used to illustrate the relevance of Shannon's linear information transmission model and particularly of noise and interference in the case of a real life event. The background was the fatal collision of two planes caused by communication problems that resulted in heavy casualties. The accident took place on 27 th march 1977 at the airport of Los Rodeos at the north of Tenerife island where a KLM plane attempting to take off and running at more than 260km per hour collided with a Pan American plane on the runway. 583 people died, "making it the deadliest accident in aviation history10 ."

1)

In part 1 entitled "The scenario", the students set the scene by describing the events that led to the two planes being on that particular airport. In the first stage entitled "Two planes were diverted", we learn that flight Pan Am 1736 flying from Los Angeles was informed that a bomb attack by a local separatist movement had caused the Las Palmas airport on Canary islands where it was scheduled to land to be closed. The crew asked to wait for the airport to be reopened but was ordered to fly to Los Rodeos, a neighbouring regional airport. Flight KLM 4805 also received the same order. In the second stage entitled "Traffic jam at Tenerife", we learn that the airport of Tenerife where the two planes had been diverted to was experiencing a traffic jam. Five big jumbo jets were already stationed on it whereas this airport was not equipped to receive such traffic. Furthermore, the runway was covered in fog. After an announcement that the Las Palmas airport had reopened, two planes were authorised to prepare for take off. At 16:51 hours, one of the planes obtained authorisation to start its engine. At 16:52 hours, the second plane also requested and obtained permission to start its engine. The two planes began to taxi on the runway for take off. The third stage entitled "The drama looms close", the sequence of communication failures leading to the accident is staged. At 17:00 hours, the control tower ordered the American Boeing (PanAm 1736) to begin taxiing up the runway and to take exit 3. The crew was in doubt about the number of the exit: was it the « third » or the « first ». The plane also began to lose its way in the fog. At the same time, the KLM flight began taxiing on the runway where the lighting was out of order. In the absence of this lighting, the PanAm flight crossed exit 3 without being aware of it. In a fourth stage 4 entitled "The collision", the control tower gave "clearance" to the KLM flight but this does not mean that the latter had the authorisation to take off. The pilot began the manoeuvre and accelerated on the runway without seeing all the messages. At 17:06:41 hours, the two planes collided into each other.

In part two of the story entitled « Links with information-communication theories », the students explained the communication failures through the prism of chosen theories. First, Shannon's linear communication model illustrated the negative effect of noise in a channel in the transmission and reception of messages between the control tower and the planes' crews. The noise and interference during message transmission caused the PanAm crew to confuse « third » and « first » and to remain on the track without knowing which exit to take. The students' interpretation here is quite astute because in Shannon's mathematical theory of communication noise and uncertainty are usually seen as positive things because they increases the level of entropy which in turn creates uncertainty and surprise and subsequently imply a high information content. In this reallife scenario, we see that entropy had a very negative human consequence because noise and uncertainty in message received proved fatal and caused hundreds of death. This illustrates if need be that the purely mathematical and statistical nature of Shannon's theory of communication is not adapted to human communication. The fact that the noise on the channel raised the degree of entropy and that the information content was high did not result in a positive social and human outcome. Indeed, a high degree of noise means that the information failed to be received correctly leading to negative real-life consequences. Thus while Shannon's mathematical theory of communication has proved crucial for telecommunications and for data compression, it is not at all preoccupied by the social outcome of what it encodes and transmits and should therefore not be applicable to human communication. The effects of entropy in this story is indeed more wienerian than shannonian. Shannon and Wiener gave conflicting definitions of information ad entropy. For the former, information is positively associated with noise, entropy, surprise and uncertainty. For Norbert Wiener in the "The Human Use of Human Beings", entropy was the absolute evil to be combated because it caused disorder in a system, leading eventually to its disintegration. In contrast with Shannon, information was synonymous with order and regulation for Wiener.

Next, the students evoked Marshall McLuhan's questionable distinction between "hot" and "cool" media to explain the PanAm crew's inability to compensate for the failure of one of the five senses 11 in decoding the message received. According to McLuhan, hot media have a "high definition" because the information received by the senses is rich but paradoxically, they encourage less participation from the brain. Hot media develop or enhance one sense to the detriment of the other senses. McLuhan classified in this category radio, cinema (film), printed books and photography. "Cool media" on the other hand had a "low definition", they affect many senses simultaneously and profoundly while giving only a low degree of information. They therefore a strong participation from the receiver in order to determine its signification. McLuhan put in this category television (whose definition was very low in the 1960s), seminars, comic books, voice and the telephone. The students argued that when the functioning of a hot media is impaired, perception becomes blurred because one cannot turn to another sense. In this instance, the radio was the hot media which solicited the hearing sense (audition) of the crew but when the radio reception was impaired, the crew was thrown into doubt more so as the other sense they could have solicited (sight) was also impaired due to the presence of fog on the runway. Finally, theories stressing the importance of context and of non verbal communication in any human interaction were evoked to explain the catastrophic failure in communication between the crews of the two planes and the control tower: Palo Alto school's axioms on interpersonal communication, in particular, Gregory Bateson and Paul Watlawick's focus on the context and meta-communication over the verbal content of messages; Ray Birdwhistell's analysis of the importance of kinesics and Edward T Hall's work on proxemics in The Silent language were all invoked in the closing paragraph of the story.

Perspectives for Future Research

The use of an arts-informed approach in a classroom setting is a bottom-up pedagogical approach that empowers students to express their conceptions of complex and abstract phenomena and to reutilise them by showcasing real life events or plausible situations involving human interactions. What is remarkable in this experience is that the students' pre-conceptions of communication expressed in their drawing (cSquares) prior to receiving the instructor's lectures reflected some of the shared conceptions of information and communication debated in the scientific literature. The fact that the arts-informed approach was not used in isolation, but in combination with the traditional textual/verbal lecture and augmented with creative writing and storytelling activities, offered students a wide choice of learning modalities which increased their engagement in the course and the learning outcomes. The cStories showed that the students not only understood the abstract concepts implied by the communication theories discussed during the lectures, but were also able to recast them in real life situations (political campaigns, advertisements, use of social and the mass media). The cStories enhanced students' appropriation of course content and added more depth to the thematic analysis performed on individual drawings. Since I began implementing this hybrid methodology in the teaching of this theoretically-oriented course, I have observed a higher degree of student engagement during the arts-informed pedagogical approach than during the verbal lectures. Also the arts-based activities help students to prepare for their final written examination of the course.

I have yet to fully exploit the contents of the cSquares and cStories. For instance, I would like to carry out a comprehensive analysis of the textual definitions of communication given on the recto side of the cSquares and compare them with the drawings. The cStories are still largely an untapped material. Several possibilities for analysing this material are possible. Their texts can be subjected to a text mining process in order to map the recurrent themes, the theories often associated together and the contexts in which they are evoked. A discourse analysis of the corpus of cStories can also be done in order to identify argumentative cues and rhetorical markers used by the students in constructing their stories. This will be a matter for future investigation.

Fig. 3 .

 3 Fig. 3. Pie chart showing the distribution of the stories in the seven thematic classes.

Fig 4 .

 4 Fig 4. cSquare 67 depicting "sheperd-flock" or opinion leader phenomenon

Table 1 .

 1 The distribution of the 86 cStories over four years(2015-2018) in the seven thematic classes we identified.

	Thus we encounter Lasswell's

The protocol was designed by Jenna Hartel and presented here: http://www.isquares.info/isquare-protocol.html.

See the cSquares website for more details https://csquares.weebly.com/.

The course in which the iSquare were gathered was given for one year only, hence the fact that the rest of the drawings concerned communication theories, hence cSquares.

http://en.wikipedia.org/wiki/Thematic_analysis

https://csquares.weebly.com/ and https://csquares.weebly.com/analysis-of-isquares-and-csquares.html.

The reader can find a more detailed analysis of these four categories of cSquares here: https://csquares.weebly.com/analysis-of-the-csquares.html.

See https://en.wikipedia.org/wiki/Macy_conferences for more details on these historic and interdisciplinalry meetings.

More details are available here https://csquares.weebly.com/from-csquares-to-c-stories.html.

See the paragraph on the communication religion satire here https://csquares.weebly.com/from-csquares-to-cstories.html.

According to the dedicated Wikipedia page: https://en.wikipedia.org/wiki/Tenerife_airport_disaster.

Humans are usually endowed with five basic senses: sight (vision), hearing (audition), taste (gustation), smell (olfaction), and touch (sensation)


Thomas Cadu
email: thomas.cadu@u-bourgogne.fr

Michael Berges

Olivier Sicot
email: olivier.sicot@u-bourgogne.fr

Véronique Person

Benoit Piezel

Laetitia Van Schoors

Vincent Placet

Stéphane Corn

Romain Léger

Loïc Divet

Patrick Ienny

Stéphane Fontaine

Ifsttar / Cpdm

Keywords: A, Laminates B, Mechanical properties E, Cure E, Thermosetting resin Flax

published or not. The documents may come

What are the key parameters to produce a high-grade bio-based composite? Application to flax/epoxy UD laminates produced by thermocompression.

These days, structural laminated composite materials are mainly composed of non-renewable fossil resources, such as synthetic fibers and petro-sourced resins. However, the environmental footprints of these composite materials are important. As with for example the European directive 2000/53/EC, regulation encourages the industry to reduce environmental impacts of materials [START_REF] Shah | Developing plant fibre composites for structural applications by optimising composite parameters: a critical review[END_REF][START_REF] John | Biofibres and biocomposites[END_REF].

Moreover, the public opinion is more and more sensitive to these issues. Since the production of vegetal fibers adapted for this kind of applications needs 5 to 7 times less energy than glass fibers production [START_REF] Duigou | Environmental Impact Analysis of the Production of Flax Fibres to be Used as Composite Material Reinforcement[END_REF][START_REF] Brosius | Natural Fiber Composites Slowly Take Root[END_REF], these fibers can be a viable solution to replace synthetic ones. This is why the use of vegetal fibers to replace glass fibers as composite reinforcements in some industrial sectors, such as automotive industries or civil engineering, has emerged during the last decade. Consequently, the flax industry currently develops new production techniques to offer reinforcements with adapted structures to composite materials manufacturing. Indeed, the low density of flax fiber (around 1.5 [START_REF] Baley | Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase[END_REF][START_REF] Amiri | Standard density measurement method development for flax fiber[END_REF]) and their good mechanical properties can lead to composite materials with specific stiffnesses and strengths comparable to the glass fiber-reinforced ones [START_REF] Verpoest | A general introduction to composites, highlighting the advantages of flax and hemp composites[END_REF][START_REF] Charlet | Contribution à l'étude de composites unidirectionnels renforcés par des fibres de lin : relation entre la microstructure de la fibre et ses propriétés mécaniques[END_REF][START_REF] Coroller | Effect of flax fibres individualisation on tensile failure of flax/epoxy unidirectional composite[END_REF]. However, the structure of flax fiber wall is complex and results from the association of multiple constituents (cellulose, hemicellulose, pectin, lignin, waxes, water…) [START_REF] Baley | Fibres naturelles de renfort pour matériaux composites[END_REF][START_REF] Morvan | Building flax fibres: more than one brick in the walls[END_REF]. This structure can already be perceived as a micro-composite material, in which the pectin plays the role of matrix, reinforced by highly-crystalline cellulose fibrils linked together by hemicellulose, leading to a complex and non-linear tensile behavior of the fiber [START_REF] Charlet | Contribution à l'étude de composites unidirectionnels renforcés par des fibres de lin : relation entre la microstructure de la fibre et ses propriétés mécaniques[END_REF]. In addition, it is challenging to use flax fiber as reinforcements for structural composite materials, because of their low thermal stability and their hydrophilic behavior [START_REF] John | Biofibres and biocomposites[END_REF][START_REF] Charlet | Contribution à l'étude de composites unidirectionnels renforcés par des fibres de lin : relation entre la microstructure de la fibre et ses propriétés mécaniques[END_REF][START_REF] Alix | Effect of chemical treatments on water sorption and mechanical properties of flax fibres[END_REF][START_REF] Van De Velde | Thermal and Mechanical Properties of Flax Fibres as Potential Composite Reinforcement[END_REF]. This affects their in-service and durability properties [START_REF] Hearle | The fine structure of fibers and crystalline polymers. III. Interpretation of the mechanical properties of fibers[END_REF][START_REF] Berges | Influence of moisture uptake on the static , cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates[END_REF].

The performances of a structural bio-based composite material are intimately related to the quality and robustness of its manufacturing process. The parameters of processing influence the microstructure, e.g. the volumetric content of fiber, matrix and void, but also the arrangement of the fibers within the matrix. For a flax fiber reinforced laminated composite, the fibers bring the mechanical resistance and play a decisive role in the hydrophilic properties of the composite. The porosities lead to stress concentrations and lower the mechanical properties [START_REF] Liu | Effects of the cure cycles on void content and mechanical properties of composite laminates[END_REF]. They also increase the moisture uptake of the composite by creating free spaces. As a result, in order to optimize the mechanical properties and the durability of a composite, it is necessary to control its fabrication process to ensure an adapted microstructure. Depending on the various process techniques and parameters found in the literature, unidirectional flax fiber reinforced laminated composites seem to have a range of volumetric fiber content between 26 and 65 %, and a volumetric void content between 1.5 and 10 % [START_REF] Berges | Influence of moisture uptake on the static , cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates[END_REF][START_REF] Van De Weyenberg | Influence of processing and chemical treatment of flax fibres on their composites[END_REF][START_REF] Masseteau | An evaluation of the effects of moisture content on the modulus of elasticity of a unidirectional flax fiber composite[END_REF][START_REF] Scida | Influence of hygrothermal ageing on the damage mechanisms of flax-fibre reinforced epoxy composite[END_REF][START_REF] Li | Hydrothermal ageing mechanisms of unidirectional flax fabric reinforced epoxy composites[END_REF][START_REF] Li | The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites[END_REF][START_REF] Martin | Comparison of the properties of scutched flax and flax tow for composite material reinforcement[END_REF], leading to tensile properties with a range of Young's modulus between 9 and 33.6 GPa and tensile strength between 133 and 350 MPa [START_REF] Berges | Influence of moisture uptake on the static , cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates[END_REF][START_REF] Van De Weyenberg | Influence of processing and chemical treatment of flax fibres on their composites[END_REF][START_REF] Masseteau | An evaluation of the effects of moisture content on the modulus of elasticity of a unidirectional flax fiber composite[END_REF][START_REF] Scida | Influence of hygrothermal ageing on the damage mechanisms of flax-fibre reinforced epoxy composite[END_REF][START_REF] Li | Hydrothermal ageing mechanisms of unidirectional flax fabric reinforced epoxy composites[END_REF][START_REF] Li | The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites[END_REF][START_REF] Martin | Comparison of the properties of scutched flax and flax tow for composite material reinforcement[END_REF].

For the use of thermocompression-like manufacturing processes, the fabrication steps are often the same: (i) preparing and conditioning of the bio-based reinforcements; (ii) curing the composites and reaching specific temperature and pressure conditions to crosslink the resin without degrading the reinforcements; (iii) cooling and (iv) post-curing to complete the cross-linking of the resin.

A particular attention must therefore be paid to each of the previous manufacturing step in order to optimize and control both final microstructural and mechanical properties of the produced composites [START_REF] Van De Velde | Thermoplastic pultrusion of natural fibre reinforced composites[END_REF].

Insofar as the bio-based reinforcements are hydrophilic, their preparation or their conditioning before curing is very important. Vegetal fiber moisture content depends on the history of storage. Some authors highlighted a detrimental effect of moisture content on the fiber/matrix adhesion [START_REF] Masseteau | An evaluation of the effects of moisture content on the modulus of elasticity of a unidirectional flax fiber composite[END_REF][START_REF] Bledzki | The effects of acetylation on properties of flax fibre and its polypropylene composites[END_REF]. In parallel, severe drying of vegetal fiber before manufacturing is assumed to lower the mechanical properties of the fiber [START_REF] Masseteau | An evaluation of the effects of moisture content on the modulus of elasticity of a unidirectional flax fiber composite[END_REF][START_REF] Le Duigou | Improving the interfacial properties between flax fibres and PLLA by a water fibre treatment and drying cycle[END_REF]. Thus, fluctuations in water content of the reinforcements can induce variability in the final properties of bio-based composites. Since the initial water content of the fiber is a process parameter difficult to control, many authors choose nevertheless to dry fibers before manufacturing their bio-based composite materials [START_REF] Li | The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites[END_REF][START_REF] Masania | Effect of Fibre Volume Content on the Mechanical Performance of Natural Fibre Reinforced Thermoplastic[END_REF][START_REF] Monti | Mechanical behaviour and damage mechanisms analysis of a flax-fibre reinforced composite by acoustic emission[END_REF][START_REF] Wolfahrt | Effect of moisture absorption on selected mechanical properties of natural fiber composites based on woven flax fibers and polypropylene[END_REF][START_REF] Duigou | Long term immersion in natural seawater of Flax/PLA biocomposite[END_REF][START_REF] Memon | Fabrication and Mechanical Properties of Jute Spun Yarn/PLA Unidirection Composite by Compression Molding[END_REF][START_REF] Madsen | Fractographic observations of the microstructural characteristics of flax fibre composites[END_REF][START_REF] Kim | Effect of water absorption fatigue on mechanical properties of sisal textilereinforced composites[END_REF][START_REF] Gassan | Effect of cyclic moisture absorption desorption on the mechanical properties of silanized jute-epoxy composites[END_REF][START_REF] Newman | Auto-accelerative water damage in an epoxy composite reinforced with plainweave flax fabric[END_REF]. This choice aims to ensure repeatable mechanical properties of their final composites.

The curing step is assumed to be the most significant one to ensure the fabrication of the best possible bio-based composite. In this step, four interrelated processing parameters are managed: (i) the curing temperature; (ii) the temperature ramp up, (iii) the curing duration and (iv), if required, the applied pressure. The choice of a resin is generally determined according to several criteria. During the process, it is necessary to guarantee the best possible impregnation and a crosslinking temperature which does not damage the reinforcements. It is also necessary to guarantee good synergy between reinforcements and matrix (fiber/matrix adhesion and ability to deform together without interface breakage). Finally, temperatures during future in-service conditions determine the minimum glass transition temperature the resin must reach.

Before crosslinking the resin, a first step consists in optimizing and terminating the impregnation of the reinforcements. In facts, when optimal manufacturing conditions are investigated, it is necessary to fluidize the unpolymerized matrix to ensure a good impregnation. This depends on thermal and rheological properties of the matrix [START_REF] Ho | Critical factors on manufacturing processes of natural fibre composites[END_REF]. For thermoset resins, the first part of the curing cycle is generally processed under pressure and at a temperature below the crosslinking temperature of the resin [START_REF] Liang | Thermo-compression forming of flax fibre-reinforced polyamide 6 composites: influence of the fibre thermal degradation on mechanical properties[END_REF][START_REF] Guen | Tailoring the vibration damping behaviour of flax fibre-reinforced epoxy composite laminates via polyol additions[END_REF][START_REF] Poilâne | Propriétés mécaniques de préimprégnés lin/époxyde[END_REF]. Before polymerization, it is noticeable that thermoplastic resins exhibit higher viscosity, compared to thermosets ones. Generally, fluidizing thermoplastic resins requires higher temperatures and higher pressures are used [START_REF] Liang | Thermo-compression forming of flax fibre-reinforced polyamide 6 composites: influence of the fibre thermal degradation on mechanical properties[END_REF]. This is why thermoset resins appear to suit better the manufacturing of long vegetal fibers thanks to two effects. On one hand, the low viscosity of the uncured resins (about 1 Pa.s at 25°C for epoxy [START_REF] Penn | Epoxy Resins[END_REF]) allows a good reinforcement impregnation. On the other hand, the lower the curing temperatures are, the lower the risk of thermal degradation of fiber is.

Thermoplastic resins often require temperatures above 200°C up to more than 400°C [START_REF] Whitten | [END_REF] while some epoxy can crosslink at room temperature and curing temperature are lower than 200°C [START_REF] Penn | Epoxy Resins[END_REF].

After impregnation, the temperatures, pressures and durations are set to values allowing the best possible crosslinking of the resin and the best rate of reinforcement as possible. Crosslinking temperatures and durations are specified by resin supplier. Generally, resin data sheets indicate, for several combinations of temperatures and durations, the expected glass transition temperature (Tg) of the polymerized resin. Moreover, the in-service temperatures lead to the choice of resins whose glass transition temperatures are sufficient. In fact, structural bio-based composites dedicated to automotive industry or civil engineering shall undergone in-service temperatures below 90°C. Resins with Tg above 100°C are thus often the standard. Manufacturers can then choose specific cycles compatible with the nature of the reinforcement and then adapt their fabrication conditions to their facilities and imperatives of time.

There are many examples of polymers used to obtain bio-based composites. For instance, Liang et al. [START_REF] Liang | Thermo-compression forming of flax fibre-reinforced polyamide 6 composites: influence of the fibre thermal degradation on mechanical properties[END_REF] have investigated the influence of processing parameters on the manufacturing of flax/polyamide-6 by thermo-compression. Their results objectively show that this type of matrix seems to be rather incompatible with flax reinforcements because of the poor mechanical performance of the manufactured composites. This is assumed to be caused by high curing temperature requirements (between 230 and 250°C), that induce severe damages of reinforcements, especially of hemicellulose and lignin [START_REF] Baley | Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase[END_REF]. Other authors [START_REF] Van De Velde | Effect of material and process parameters on the mechanical properties of unidirectional and multidirectional flax/polypropylene composites[END_REF] produced flax/polypropylene composites by thermo-compression at different temperatures (190°C and 210°C). Studied curing durations lasted between 3 and 5 minutes.

200°C for 3.5 minutes was considered as the best possible combination to improve mechanical properties (modulus and tensile strength) of their material.

In the case of thermosets, the influence of the curing temperature on the final composite properties has not been studied as much as in case of thermoplastics. This is probably because using thermosets involves lower temperatures and thus less thermal degradation of fiber reinforcements.

However, a compromise must be reached between durations and temperatures of the curing cycle.

Epoxies or unsaturated polyesters are generally used [START_REF] Poilâne | Propriétés mécaniques de préimprégnés lin/époxyde[END_REF][START_REF] George | Mechanical properties of flax fibre reinforced epoxy composites[END_REF][START_REF] Hughes | Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites[END_REF][START_REF] Saidane | Assessment of 3D moisture diffusion parameters on flax/epoxy composites[END_REF][START_REF] Duc | Damping of thermoset and thermoplastic flax fibre composites[END_REF][START_REF] Duigou | Exploring durability of interfaces in flax fibre/epoxy microcomposites[END_REF]. Some authors apply high temperatures (≈ 130°C) to cure flax/epoxy composite materials by thermo-compression [START_REF] Poilâne | Propriétés mécaniques de préimprégnés lin/époxyde[END_REF][START_REF] George | Mechanical properties of flax fibre reinforced epoxy composites[END_REF][START_REF] Duc | Damping of thermoset and thermoplastic flax fibre composites[END_REF] for a minimal duration (≈ 2 h). Others propose to cure flax/epoxy [START_REF] Saidane | Assessment of 3D moisture diffusion parameters on flax/epoxy composites[END_REF][START_REF] Duigou | Exploring durability of interfaces in flax fibre/epoxy microcomposites[END_REF] or polyester/epoxy [START_REF] Hughes | Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites[END_REF] at room temperature. This induces very long cycle times (>12 h) that could not be adapted to industrial objectives.

The curing pressure also has significant effects on the quality of the fabricated bio-based composites. In particular, volumetric fiber content and void content can be drastically modified with the pressure. In the case of bio-based composites, the higher the applied pressure is, the higher the reinforcement volumetric ratio and mechanical properties are [START_REF] Gning | Influence of process and test parameters on the mechanical properties of flax/epoxy composites using response surface methodology[END_REF]. It is known that an increase in the volumetric void content leads to a decrease in the mechanical properties [START_REF] Li | The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites[END_REF]. However, by thermocompression, the maximum fiber content for epoxy resin reinforced with unidirectional long vegetal fibers encountered in the literature seems to be 65 % [START_REF] Berges | Influence of moisture uptake on the static , cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates[END_REF][START_REF] Van De Weyenberg | Influence of processing and chemical treatment of flax fibres on their composites[END_REF][START_REF] Masseteau | An evaluation of the effects of moisture content on the modulus of elasticity of a unidirectional flax fiber composite[END_REF][START_REF] Scida | Influence of hygrothermal ageing on the damage mechanisms of flax-fibre reinforced epoxy composite[END_REF][START_REF] Li | Hydrothermal ageing mechanisms of unidirectional flax fabric reinforced epoxy composites[END_REF][START_REF] Li | The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites[END_REF][START_REF] Martin | Comparison of the properties of scutched flax and flax tow for composite material reinforcement[END_REF][START_REF] Newman | Auto-accelerative water damage in an epoxy composite reinforced with plainweave flax fabric[END_REF]. Polypropylene resin reinforced with unbalanced flax fabric reached 57.2 to 59.6 % under 20 bars in the work of Wolfahrt et al. [START_REF] Wolfahrt | Effect of moisture absorption on selected mechanical properties of natural fiber composites based on woven flax fibers and polypropylene[END_REF]. Shah et al. [START_REF] Shah | Determining the minimum, critical and maximum fibre content for twisted yarn reinforced plant fibre composites[END_REF] found a theoretical maximum volumetric fiber content of 60 % for unidirectional composite laminates of jute fibers. Also, increasing pressure induces a decrease in volumetric void content [START_REF] Li | The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites[END_REF] until a certain level of pressure which will be called optimal pressure [START_REF] Liholt | Volumetric composition in composites and historical data[END_REF]. Above this optimal pressure, the impregnation if affected, the resin cannot fill the voids of the fully compacted fiber assembly and the void content increases [START_REF] Liholt | Volumetric composition in composites and historical data[END_REF] and the fibers are so close together that the stress transfer between fibers and matrix become inefficient [START_REF] Shah | Determining the minimum, critical and maximum fibre content for twisted yarn reinforced plant fibre composites[END_REF].

The purpose of the post-curing step is to complete the crosslinking of the resin in order to obtain a composite as stable as possible. The resin suppliers generally indicate that the temperatures and post-curing durations should be identical to those used in crosslinking the resin. Two cases can be found in the literature. Authors who do not take into account the effect of the temperature on fibers, in this case the post-curing can be performed at high temperature (>150°C) [START_REF] Guen | Tailoring the vibration damping behaviour of flax fibre-reinforced epoxy composite laminates via polyol additions[END_REF], and those who perform post-curing at lower temperature (<70°C) to minimize fiber degradation caused by water removal [START_REF] Hughes | Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites[END_REF][START_REF] Duigou | Exploring durability of interfaces in flax fibre/epoxy microcomposites[END_REF]. Different durations are also implemented (from 45 min to 14h) [START_REF] Hughes | Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites[END_REF][START_REF] Duigou | Exploring durability of interfaces in flax fibre/epoxy microcomposites[END_REF].

This state of the art shows that many authors adapt their manufacturing processes to their specific needs. The numerous previous contributions help to illustrate the relations between the final mechanical and microstructural properties of composites and their manufacturing conditions. However, each case is often unique. Depending on the type of reinforcement, resin or manufacturing tools, the published results do not clearly provide direction to help the scientific or industrial community to design a robust fabrication process of bio-based structural composite materials.

It is then important to consider that the particular nature of the reinforcements must be taken into account to set the manufacturing conditions of bio-based composites. The control and the understanding of the influence of each manufacturing step on the expected properties of the composites must be achieved. This will help to define clear scientific and technological approaches for the manufacture of robust and repeatable bio-based composite laminated structures.

The purpose of this study is to show how the conditioning, curing conditions and post-curing steps impact (i) the quality of the crosslinking of the matrix, (ii) the microstructure of the composites (volumetric void and fiber contents) and (iii) the properties of stiffness and ultimate tensile strength of the composites manufactured.

To achieve this objective, studies were carried out using pure unidirectional flax reinforcements impregnated with a petro-sourced (DGEBA -DiGlycidyl Ether of Bisphenol A) epoxy resin. The chosen process is thermo-compression. Based on the results, the consequences of the choices for each required fabrication step on the final mechanical properties of the composites will be discussed.

Materials and methods

Fibers and matrix

In this study, pure unidirectional reinforcements FlaxTape™ 110, supplied by the company LINEO©, were used. We measured a density of 1.45 for flax fibers, using Archimedes' principle.

This reinforcement has been selected for its good and reproducible mechanical properties, induced by its industrial production. Moreover, the structure of this reinforcement is purely unidirectional, without sewing yarns. This makes the distribution of the resin easier and reduces induced shear interferences during tensile tests.

The matrix used is a DGEBA epoxy resin (SR 8500 -density 1.17) amine hardener (SZ 8525density 0.94) system produced by Sicomin© (weight ratio 4:1). We measured a density of 1.19 for cured matrix, using Archimedes' principle. Epoxy is a widely used thermoset resin, even for bio-based composite laminates. With a hot press process, the supplier recommends to cure composites at 80°C for 1 hour. Under these conditions, the supplier indicates that the resin has a gel time of 8 minutes and reaches the glass transition temperature (Tg) between 104 °C and 106 °C. To confirm this value, modulated differential scanning calorimetry analyses were carried out on two samples of pure resin thermo-pressed at 80°C in the optimal conditions of curing and post-curing determined in the study. A Tg of 109°C was measured, which is compatible with the aimed in-service conditions of this kind of composite materials.

Manufacturing process

The purpose of the manufacturing process is to produce plates in order to study the influence of multiple parameters on the quality and mechanical performance of these composite materials: (i) the conditioning of the reinforcements, (ii) the curing temperature, (iii) the curing pressure, (iv) the cooling speed, (v) the exit temperature, (vi) the post-curing temperature and (vii) the post-curing duration.

Conditioning

Two batches of fibers were used to produce composite materials: the first batch of reinforcement was not conditioned and stored under ambient conditions. During the storage, a

Voltcraft® DL-141TH, humidity and temperature data logger was placed in a flax fibers storage box.

Records have been automatically done every 10 minutes. The temperature has been measured at 22 ± 2 °C and the humidity at 30 ± 5 % RH. The second batch of reinforcement was conditioned in a climatic chamber (Vötsch® VC 7100) at 23 ± 1 °C and 50 ± 1 % HR for 7 days before manufacturing.

Impregnation and hand layup

The plies have been manually layed up and impregnated in a specific mold protected by Teflon sheets (figure 1). The draping cycle was as follows: a resin layer is spread on the lower part of the mold.

A first ply is positioned in the mold, a resin layer is applied in the center of the flax layer, as it can be seen on figure 1 a). (The resin will be spread under the curing pressure effect as schematized on figure 1 b) and c)). This sequence continues until the stacked number of plies is reached. Finally, the mold is closed and ready to be positioned in the thermo-compression press. This step was performed in 1h ± 5

mins. This duration is compatible with the pot-life of around 85 minutes at 23°C given by the manufacturer Sicomin©.

Curing and Post-curing

A Fontijne Grotnes TPC 321 hot press has been used for curing pure unidirectional laminated composites plates. A reference curing cycle is presented in figure 2. First, the temperature increases from 20°C to 40°C in 10 minutes (2 °C/min). This step allows to lower the viscosity of the resin and to optimize the impregnation of the reinforcement by the matrix. Pressure (CP) is applied as soon as temperature reaches 40°C and maintained throughout the next steps, until the end of the cooling step.

Second, the temperature is raised in 15 minutes to the desired curing temperature (CT) (60°C or 80°C)

and is maintained for one hour. Third, the mold is cooled from CT to a specified exit temperature ET Since different parameters have been studied to evaluate their influence on the mechanical properties of the composites, the reference curing cycle has been modified to obtain different materials.

This is summarized in Table 1, which is completed by a nomenclature, to designate the plates according to their manufacturing conditions. In the rest of this paper, a plate will be identified with this nomenclature. For instance, a curing cycle with the reference parameters, shown in bold in table 1, will be labelled by the following sequence: C/12P/3B/80/nat/20/x/x.

Specimen preparation

Unidirectional tensile specimens were cut with a water lubricated circular saw. The specimens were immediately dried with an absorbent paper after the cutting to avoid water sorption. According to geometry 4 from ISO 527 standard, their dimensions are 250 mm long, 25 mm wide. The 12 plies specimens have a thickness between 1.7 and 1.8 mm under 3 bars. The 20 plies specimens have a thickness between 2.6 and 3.5 mm depending on the applied pressure (the higher the pressure is, the lower the thickness is). Before testing, the specimens have been conditioned at 23 ± 1 °C and 50 ± 1 % HR for 7 days minimum in a climatic chamber (Vötsch® VC 7100). The specimens have not been equipped with tabs.

Determination of volumetric composition

Volumetric composition of the composite was determined by weighing method inspired from ASTM D 3171 -99. For each produced plate, one specimen, described above, was weighed with a Kern PRS balance (0.1 g precision), its width and thickness were measured with a numeric caliper (0.01 mm precision) and its length was measured with a ruler (0.5 mm precision). The determination of the resin and the fibers densities is explained in the physicochemical characterization section. Then, the volumetric fiber, resin and void contents were calculated with the following equations:

(Eq. 1)

(Eq. 2)

(Eq. 3)

(Eq. 4)

with Wf: fibers weight (g); Aw: areal weight of the fabric (g.m ); Vp: volumetric void content (%). This determination of volumetric composition is sensitive to small deviations of specimen's dimensions' measurements and to the reinforcement density dispersion.

Then, samples have been measured precisely and the uncertainty of measurements has been taken into account in calculations. Moreover the stack of 20 plies averaged the variation of the reinforcement density along the roller width.

Microscopic observations

Untested 20 x 20 mm specimens were cut with a water lubricated circular saw then dried in absorbent paper. They were coated with EpoFix© resin from Struers and conditioned at 23 ± 1 °C and 50 ± 1 % HR for 7 days before their observation under a Nikon Eclipse LV150 optic microscope. These observations were conducted to inspect the composite microstructure, especially the presence of porosities, for different manufacturing pressures.

Mechanical testing

Tensile tests were conducted on unidirectional 0° samples according to the ISO 527-4 standard on a MTS Criterion C45, equipped with a 100 kN load cell and a 50 mm gauge length extensometer. Test speed was set at 1 mm.min -1

. For each plate, 4 specimens were tested. According to the ISO 527-4 standard, the Young's modulus for unidirectional fiber-reinforced composite is measured in a strain range of 0.05 % to 0.25 %. This strain range is well-suited to synthetic fiber-reinforced composites but not to flax fiber-reinforced composites. Indeed, the tensile curve for a flax fiber-reinforced composite is not linear [START_REF] Berges | Influence of moisture uptake on the static , cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates[END_REF][START_REF] Poilâne | Polymer reinforced by flax fibres as a viscoelastoplastic material[END_REF]. As presented on figure 3, this nonlinearity results in the appearance of an inflection on the stress-strain curve, often in the strain range of 0.05 % to 0.25 %. If the standard is used to calculate the tensile modulus of our unidirectional composites, it will be thus under-estimated. For this reason, two modules E1 and E2 are defined in the dotted areas on the figure 3, respectively the squares and the circles ones. The strain range of these areas depends on the position of the inflexion point on the curve, which differs with the processing parameters variations.

Physicochemical characterization

Modulated Differential Scanning Calorimetry (MDSC) analyses

MDSC analyses have been performed with a TA Instrument DSC 250 differential scanning calorimeter. MDSC has been preferred to classic DSC because it allows separating reversible and nonreversible phenomena. This enables to measure the glass transition temperature (Tg) of the material despite the thermal phenomena due to fibers which can disrupt the signal. For each analysis thermal cycle has been carried out from 25°C to 130°C and the Tg has been determined using the reversible signal. For each plate, analyses have been performed on 2 samples.

Thermo-gravimetric analyses

In order to estimate water content of the fibers, depending on their storage conditions before manufacturing process, thermo-gravimetric analyses have been carried on flax fibers samples using a NETZSCH STA 449 F1. Based on this study [START_REF] Baley | Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites[END_REF], isothermal analyses have been performed on conditioned and non-conditioned fibers. Each were carried out at 105°C for 14h then 150°C for 5h in one run.

Density measurements

Densities of fibers, resin and composites, have been measured using Archimedes' principle.

Each sample has been successively weighed in air and in dodecane solution. Dodecane has been chosen to avoid solvent sorption by the fibers. Density of the sample (d) has been calculated using the equation 5. For each plate, 5 samples have been weighed.

(Eq. 5)

with m air : mass of the sample measured in the air (g) ; m dod : mass of the sample measured in dodecane (g) ; d air : density of the air (6.10 -4 g.m 3 at 21°C) ; d dod : density of dodecane (0.7487 g.m 3 at 21 °C).

Results

In this section, results are presented in order to classify the influence of processing steps on micro-structural properties (volumetric fiber content, volumetric void content, glass transition temperature) and mechanical ones (both E1, E2 moduli and ultimate tensile strength σ max ) of fabricated laminates. Before discussing these results, a statistic variance test (ANOVA) has been implemented to ensure that the variation observed between two groups of specimen is statistically significant. The significance of the variation between the average values will be noted S and is calculated with S = .

F is calculated with the intergroup variance (variance considering all specimens) divided by the intragroup variance (mean value of the variances of the two groups of specimens) and is determined on a 95% safety Snedecor F- The most influential manufacturing parameter on the microstructure of laminates is the pressure. On a 20 ply-laminate, the volumetric fiber content is around 38 % for 1 bar, 45 % for 3 bars and 51 % for 5 bars. The volumetric void content is also impacted by the pressure; contents of around 2.4%, 2.5% and 3.1 % were measured respectively for 1, 3 and 5 bars. By TGA analysis water content has been measured between 5 and 7% in mass for non-conditioning fibers and to 7% for conditioned fibers which is in accordance with the literature [START_REF] Baley | Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites[END_REF]. The glass transition temperature of each composite has been measured and compared with the one given by the manufacturer for pure matrix cured 2 hours at 80°C (106°C). In all cases it was slightly upper. The matrix is thus assumed to be well crosslinked.

Mechanical properties (E1, E2 and σ max )

In the following observations, the process parameters were classified in terms of rank of influence on the studied properties of the composites (moduli and ultimate tensile strength). Ranks 1 and 2 correspond respectively to major and minor influences on the properties of the composites. An influence is considered to be major when the observed variation on the average values of the studied properties of the composites is greater than 15% with S > 1. A minor influence corresponds to observed property variations between 10% and 15% with S > 1. The 3 rd rank corresponds to a trend of mean value evolution (average variation > 10% and with 0.5 < S < 1) with a low significance. The letter X denotes a negligible evolution. The following table (Tab 2) sums up the criteria used to classify the parameters.

Influence of the processing parameters on E1:

The figure 4 shows that the different processing parameters have different effects on E1. Some processing parameters have a negligible influence: the curing temperature, the cooling speed and the post-curing temperature induce less than 10% change in the E1 value and S lower than 0.2. However, even if the post-curing duration has no significant effect on the mean value of E1, a clear reduction of the standard deviation was observed for durations of 2h and 4h (64% reduction of the standard deviation from no post-curing to 2h post-curing duration). The specimens tested to determine the influence of post-curing duration have been randomly selected on the plates. Moreover, the specimens with post-curing of 1h have not been all tested then the ones with 2h, etc. i.e. The order in which we tested these samples was also random. This tends to indicate that the reduction of the dispersion of the results is linked to the duration of the post-curing more than it was in the selection or in test conditions of the samples. To produce reproducible laminates, this parameter is thus important and it will be classified as a 2 nd rank parameter.

On the other hand, the fiber conditioning, the pressure and the exit temperature have significant consequences. For 12 ply-laminates, using conditioned reinforcements leads to a 12% increase of E1 mean value (S = 1.20). Conditioning of fiber is then a 2 nd rank parameter.

Moreover, as a consequence of the increase in the reinforcement rate, increasing curing pressure induces 16% and 23% increase in E1 mean value when the pressure is increased from respectively 1 bar to 3 bar and from 1 bar to 5 bars (S = 1.37 between 1 and 3 bar and S = 4.55 for 1 to 5). Finally, a 21% increase of E1 mean value is observed when the composite is unmolded at room temperature, in comparison with an outlet at 60°C (S = 2.04). Thus, pressure and exit temperature will be classified as 1 st rank parameters.

Influence of the processing parameters on the E2 modulus:

As with E1, the curing temperature and the cooling speed have no significant influence of the E2 modulus, with less than 10% variation of the mean value and S lower than 0.2, as shown in Figure 5.

As observed for the E1 modulus, the post-curing duration has no significant influence (less than 6%) on E2 modulus. However, a clear reduction of the standard deviation is observed for 2h and 4h of postcuring (32% reduction of the standard deviation from no post-curing to 2h post-curing duration). As indicated for E1, specimens were randomly selected and tested, so to ensure reproducible laminate fabrication, the post-curing duration has to be considered as a 2 nd rank parameter on E2.

Contrary to the observations made on the module E1, a rank 3 influence can be observed concerning the post-curing temperature, with a 13% increase in E2 between 60°C and 80°C (S = 0.54).

As seen in the case of E1, the fiber conditioning, the pressure (1 to 3 bars) and the exit temperature respectively increase E2 of +20-25% (S = 5.64-2.68), +20% (S = 1.59) and +28% (S = 3.72).

These process parameters are then classified as 1 st rank ones.

Influence of processing parameters on the ultimate tensile strength σ max :

The fibers conditioning, the curing temperature and the post-curing temperature have negligible impacts (in the range of studied parameters) on the ultimate tensile strength, with less than 10% variations and S lower than 0.6, as shown in Figure 6. The post-curing duration still has the same effect as for the E1 and E2 moduli: there is no significant change in the mean value but a clear decrease of the standard deviation for durations of 2h and 4h is observed (52% reduction of the standard deviation from no post-curing to 2h post-curing duration). As indicated for E1 and E2, specimens were randomly selected and tested. To ensure reproducible laminate fabrication, the post-curing duration effect on σ max can also be considered important and will also be classed as a 2 nd rank parameter.

The exit temperature has lower influence on σ max than on moduli but a trend can still be observed with a 16% increase of the mean value when the composite is unmolded at room temperature, in comparison with an outlet at 60°C (S = 0.68). The increase of the curing temperature from 60°C to 80°C induces a 12% increase of σ max mean value but regarding the ANOVA test this variation is considered as non-significant (S = 0.15).

Cooling speed has a 2 nd rank influence on σ max . Hence, reducing cooling speed from 2°C/min to natural cooling (0.083 °C/min) induces a 14% increase in σ max (S = 2.50).

The pressure still has a major influence on σ max , in relation with the evolution of the volumetric fiber content, with an increase of 18% between 1 bar and 3 bars (S = 1.86) and 22% between 1 bar and 5

bars. The pressure will be classified as 1 st rank parameter.

The following table (Tab 3) sums up the previously illustrated results in terms of process parameters influence rank on fabricated laminates final properties.

The most important parameters to achieve good mechanical properties have been identified.

The pressure applied during the process determines the microstructure and has a paramount effect on the mechanical properties. The exit temperature has an important effect on both E1 and E2 moduli.

Also, both moduli are impacted by the conditioning, but even though E1 modification is non negligible, E2 modification is more significant. To ensure a repeatable fabrication, the post-curing duration is the most important parameter. Although these parameters influence has been identified, the phenomenon leading to the modification of the properties are numerous and complex. The goal of the following section is to discuss the link between process parameters and induced mechanical properties.

Discussion

The figure 7 sums up the tested parameters, their influence on the composites mechanical properties and the optimal process cycle, in the range of studied parameters. Our goals were to optimize mechanical properties and reduce process duration. This study underlined that, at least, four manufacturing parameters have a major impact on composites mechanical properties. Nevertheless, we did not study some parameters such as the impregnation method, the temperature ramp up and the curing duration.

The pressure is a rank 1 parameter for both moduli and the ultimate tensile strength.

Microscopic observations of our composites specimens (Figure 8) confirm that the volumetric fiber content increases when the pressure increases from 1 to 3 bars and from 3 bars to 5 bars, even though mechanical properties only improve from 1 to 3 bars. Moreover, the volumetric void content, stable from 1 to 3 bars, slightly increases from 3 to 5 bars, which indicates that the optimal pressure was exceeded at 5 bars. This optimal pressure is most likely to be between 3 and 5 bars.

The exit temperature is a rank 1 parameter for both moduli. It could be related to the freeze of the epoxy network organization. This would lead to residual stresses that could affect the mechanical properties.

The conditioning of the fibers is a rank 1 parameter for E2 modulus and a rank 2 parameter for E1 modulus. The significant effect on both moduli we observed is in agreement with literature, in which it was found that moisture content strongly affects mechanical properties of flax fiber [START_REF] Baley | Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites[END_REF]. However we did not determined the optimal conditioning parameters in this study.

The post-curing duration is a rank 2 parameter for both moduli and the ultimate tensile strength. Our results show that a sufficient post-curing duration homogenizes the mechanical properties. Post-curing has generally two effects: completing the reticulation of the resin and releasing the internal stresses. The glass transition temperature (110 ± 1.4°C) is stable and post-curing temperature does not have a significant effect on it, which means that we can exclude the effect on the reticulation. Although, internal residual stresses can modify the damage and failure mechanisms leading to a dispersion of the results. Thus, this would be consistent with the observed evolution of the properties.

Based on the results of this study, some recommendations can be made to obtain flax-epoxy composites with good properties. A picture and a macroscopic observation of the composite fabricated with our recommended manufacturing process is presented on figure 9.

First, matrix has to be chosen to crosslink at compatible temperatures. Temperatures around 80°C seem to be well adapted. Indeed, they reduce the risk of potential degradation of fiber and enable the use of matrix that can achieve a good cross-linking in a relatively short manufacturing time. Then, it is important to control the moisture content of fiber to ensure a reproducible manufacturing process.

Conditioning fibers before the production of composites looks the most suitable for vegetal fibers since it improves composites moduli. The optimal conditioning parameters have to be determined, depending on fiber and matrix natures. Also, among the parameters we studied, the pressure was the one with the greatest influence on composites properties. Thus, it is important to be careful about the pressure used.

It was shown that an optimal pressure exists. In our case, the pressure was set to 3 bars but the optimal value is between 3 and 5 bars. The optimal value has to be determined for each reinforcement, because it depends on its structure and weight. Moreover, the end of the curing cycle should not be neglected since the exit temperature has a major impact on both moduli. It is recommended to use a controlled cooling speed (-1 or -2 °C/min) down to 20°C. Even though the "natural" cooling in the thermocompression press down to 20°C gave the best results in terms of ultimate tensile strength, it is much longer and may not be the most suitable choice for industrial production. Finally, in order to homogenize and reduce standard variation of composite mechanical properties, it is useful to carry out a post-curing step. Indeed the dispersion of the properties in bio-based composites is one obstacle to the use at a larger scale of this kind of materials in the industry. Its duration has to be determined to suit the acceptable standard deviation for the considered usage. However, we observed that the dispersion is reduced down to a minimum (after 2h in our case) and constant afterward. To confirm and validate the relevance of this step it should be interesting to quantify its impact on global environmental footprint through complete life cycle assessment.

Conclusion

This study aimed at developing and optimizing a reliable manufacturing process for laminated composites using flax fibers. The influence of many process parameters has been studied. These parameters have been classified according to their impacts on mechanical properties, allowing the determination of the most critical ones. Indeed, the fiber conditioning, the pressure, the cooling speed, the exit temperature and the post-curing duration proved to be the most decisive parameters in terms of mechanical properties. Thus, this paper gives some keys to obtain a good quality vegetal fibers composite and the method used can be adapted for different fibers or matrix.

To complete this study, the influence of some other parameters could be investigated, such as the temperature ramp up and the curing duration that were not studied here. Moreover, on the basis of this study, models should be developed to link processes steps and properties in order to generalize this approach to composites made with different vegetal fibers.

  What are the key parameters to produce a high-grade bio-based composite? Application to flax/epoxy UD laminates produced by thermocompression Thomas Cadu, Michael Berges, Olivier Sicot, Véronique Person, Benoît Piezel, Laetitia van Schoors, Vincent Placet, Stéphane Corn, Romain Léger, Loïc Divet, et al. To cite this version: Thomas Cadu, Michael Berges, Olivier Sicot, Véronique Person, Benoît Piezel, et al.. What are the key parameters to produce a high-grade bio-based composite? Application to flax/epoxy UD laminates produced by thermocompression. Composites Part B: Engineering, 2018, 150, pp.36 -46. 10.1016/j.compositesb.2018.04.059. hal-01889210 Introduction

(

  20 °C, 40 °C or 60 °C) at a defined cooling speed (CS): approximatively -0.083°C/min for natural cooling (nat), -1°C/min or -2 °C/min. The controlled accelerated cooling speeds (-1 or -2 °C/min) are imposed and controlled thanks to a cold unit (Frigosystem© RACA) connected to the thermo-compression press.Finally, a post-curing is conducted within 2 days. Between curing and post-curing the plates were stored in a climatic chamber (Vötsch® VC 7100) at 23 ± 1 °C and 50 ± 1 % HR. The post-curing is carried out in an oven (Memmert UN 450+) for a fixed temperature (PCT) and duration (Δt PC) (60°C or 80°C for 1h, 2h and 4h).

- 2 ) 3 )

 23 ; N: number of plies; L: length of the specimen (m); l: width of the specimen (m); Vf: volumetric fiber content (%) ; ρf: fiber density (g/m 3 ); Vc: composite volume (m ; Vr: volumetric resin content (%) ; Wc: composite weight (g); ρr: resin density (g/m 3

Figure 1 :

 1 Figure 1: Impregnation of a ply a), spread of the resin under curing pressure effect b), resin distributed over all the plate c).

Figure 2 :Figure 3 :Figure 4 :

 234 Figure 2: curing cycle of composites

Figure 5 :

 5 Figure 5: Influence of the fabrication parameters on the E2 modulus (GPa) with: 1 st rank influence in black, 2 nd rank influence in dark grey, 3 rd rank influence in light grey and negligible influence in white. Influence of: NC -C) fibers conditioning, P) pressure, CT) curing temperature, CS) cooling speed, ET) exit temperature, PCT) post-curing temperature and Δt PC) post-curing duration.

Figure 6 :

 6 Figure 6: Influence of the fabrication parameters on the ultimate tensile strength (MPa) with: 1 st rank influence in black, 2 nd rank influence in dark grey, 3 rd rank influence in light grey and negligible influence in white. Influence of: NC -C) fibers conditioning, P) pressure, CT) curing temperature, CS) cooling speed, ET) exit temperature, PCT) post-curing temperature and Δt PC) post-curing duration.

Figure 7 :

 7 Figure 7: Flow chart of the manufacturing process and impacts of the different parameters on mechanical properties

Acknowledgements

This project is supported by the Bourgogne Franche-Comté region.

Declaration of interest: none

Post-Curing temp.

Post-Curing duration

Rank of influence on mictrostr.

Tg