Esma Ismailova, Electronic textiles, textiles électroniques, matériaux avancés

Special issue: Electronic textiles

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[dropcap]E[/dropcap]lectronic textiles is a multidisciplinary field which is not limited to the characterization and development of novel materials and devices. The field also targets technologies related to the interconnection of electronic functionalities leading to smart networks and to the development of hybrid approaches integrating flexible devices with traditional solid‐state electronics.

Furthermore, unlike other emerging technologies, electronic textiles are, in part, based on one of humankind’s oldest technologies. Well‐established sectors, such as the textile and fashion industries, thus play a central role in material and process development, and not just in “end‐game” commercialization. This unique connection to industry makes electronic textiles an exciting and dynamic research field where academia and the private sector work hand in hand to advance all aspects of the technology.

[Extract from the Editorial]

 

This special issue on electronic textiles was edited by Esma Ismailova (researcher at the Centre Microélectronique de Provence of Mines Saint-Étienne), Tobias Cramer, and Daniel T. Simon, the organizers of the Symposium “Electronic textiles” (E‐MRS Spring 2017 meeting).
It was planned together with Wiley and the European Materials Research Society (E‐MRS).

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Esma Ismailova, textiles électroniques, matériaux avancésADVANCED MATERIALS TECHNOLOGIES
Volume3, Issue 10
Special issue: Electronic textiles
Esma Ismailova, Tobias Cramer, Daniel T. Simon (ed.)
Wiley, October 2018

 

 

 

 

 

 

FDM

Could additive manufacturing be the future of the plastics industry?

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There has been a significant revolution in the world of materials as 3D printing has proved its potential for innovation. Now it must be put into practice. While 3D printers are increasingly present in prototyping workshops, they have been slow to replace the processes traditionally used in the plastics industry. This is because these technologies are too restrictive, in terms of both available materials and performance, which is still low for parts having specific uses.

Article written by Jérémie Soulestin, researcher at IMT Lille Douai.

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[dropcap]P[/dropcap]olymers now represent the vast majority of materials used in 3D printing for all purposes. But the use of additive manufacturing for industrial needs has remained primarily confined to metals. For industry professionals, the use of polymers is limited to prototyping. This reluctance to combine 3D printing and plastic materials on an industrial scale can be explained by the low diversity of polymer materials compatible with this process. The most widely-used technologies, such as stereolithography, rely on thermosetting resins which polymerize during the process. Yet these resins represent only a small share of the polymer materials used by the plastics industry. Fused deposition modeling (FDM) is slightly better-suited to industrial needs. It is based on thermoplastic polymers, which soften when heated during the process, then harden when they return to room temperature. This technical difference makes it possible to make use of materials which are more commonly used in the plastic industry and are therefore better aligned with market demand.

FDM technology was invented in 1989 by Scott Crump, founder of Stratasys, which is now one of the leading manufacturers of 3D printers. It is a very straightforward process. A filament made from thermoplastic polymer is fed into the machine. It is pushed through a heated nozzle to produce a malleable string measuring a few micrometers in diameter. The 3D part is obtained by continuously depositing this string, layer by layer, by moving the nozzle or the printer table, or both in all directions. The simplicity of the FDM process, coupled with the expiry of Stratasys’s patent for the technology, has led to exponential growth in 3D desktop printers. These small-scale machines are mainly intended for the general public and the maker community but have also made their way into design offices and corporate fablabs. Prices range from €220 for 3D printers for beginners who want to discover additive manufacturing to more than €2,000 for 3D desktop printers designed to create prototypes.

FDM technology: turning hope into reality

Although the FDM process is probably the best-suited solution for producing short-run plastic parts, it is not able to miraculously meet the needs of the plastics industry. Even if professional machines that are much more expensive than 3D desktop printers were to be used, there are drawbacks with the thermoplastic polymers available which limit the potential for FDM applications. The philosophy of FDM machine manufacturers – especially manufacturers of professional machines – is still based on the use of proprietary materials. In other words: for a certain brand of printer, only the polymers sold by that brand or its partners are compatible. The process is configured to ensure the quality of parts made using proprietary materials. Users have little control in terms of changing the settings or using other materials.  Even though some brands offer a wide range of materials with different characteristics (hard, soft, translucent, chemically-resistant, biocompatible etc.), they are still limited to a few thermoplastic polymers. The proliferation of suppliers of filaments for 3D printers has not made up for gaps in the catalogue of usable materials. For specific industrial applications – especially high-performance parts like automobile or aircraft components – but even for less technical applications, manufacturers have not yet been won over by this technology. The reason that thousands of different kinds of plastics exist is undoubtedly linked to the fact that each application requires specific properties.

On top of that, there are inherent problems with the FDM process. In general, parts made using FDM are more porous and rougher on the surface than those made with conventional processes like extrusion or injection. This is due to the fact that strings are deposited layer by layer. Because they have a cylindrical shape, a space is created between two strings placed next to one another. As a result, the surface of the part is not smooth and some cavities are located inside. This porosity can be controlled by applying high pressure on the material as the string is being deposited so that the cylinders are compressed and less space is left. But that still may not be enough to meet specifications for high-performance parts. Moreover, it does not solve the problem of surface roughness, since no layer can be compressed on the top layer. The only way to reduce this roughness would be to decrease the diameter of the cylinders and therefore the outlet of the filament nozzle, which would reduce the flow rate of material – and consequently increase production time.

Other promising technologies

These drawbacks of FDM could certainly be overcome by using machines based on polymer pellets instead of filaments. Manufacturers are taking steps in this direction in order to theoretically make it possible to use pellets of any thermoplastic polymer. The Freeformer technology marketed by Arburg, a German injection-moulding specialist, does just that. It is based on two injection units that can melt the polymer pellets, which makes it possible to create parts which require both hard and soft materials or use soluble materials. The molten polymer is deposited in the form of droplets to build the part, rather than in cylindrical threads. In this way, the process is somewhat different from FDM, but it is essentially based on the same principle, and is better-suited to meet the needs of the plastics industry. But research and development work must still be carried out to better understand the possibilities offered by this new process and tap into its full potential.

Future advances in 3D printing technology will depend on the use of additive manufacturing for mass production. For now, this technology is not suited to most applications that require high mechanical performances, but that could change. The aeronautics industry is a good example of the challenges that lie ahead for additive manufacturing. Although aircraft parts are still produced with conventional materials and processes, manufacturers are increasingly using composite materials. These composites are produced with techniques that resemble 3D printing. Combining them with technologies similar to FDM on robotic arms would be one way to greatly improve the performance of parts obtained through additive manufacturing. If such hybrid processes proved to be effective, the performance of 3D printed parts could improve significantly. It would then be possible to use additive manufacturing to produce structural aircraft components, instead of just their prototypes.

silicon

Silicon and laser: a brilliant pairing!

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Researchers at Télécom ParisTech, in partnership with the University of California, Santa Barbara (UCSB), have developed new optical sources. These thermally-stable, energy-saving lasers offer promising potential for silicon photonics. These new developments offer numerous opportunities for improving very high-speed transmission systems, like datacomms and supercomputers. Their results were published in Applied Physics Letters last summer, a journal edited by AIP Publishing.

 

Silicon photonics is a field that is aiming to revolutionize the microelectronics industry and communication technologies. It combines two of the most significant inventions: the silicon integrated circuit and the semiconductor laser. Integrating laser functions into silicon circuits opens up a great many perspectives, allowing data to be transferred quickly over long distances compared to conventional electronic solutions, while benefiting from silicon’s large-scale production efficiency. But there’s a problem: silicon is not a good at emitting light. The laser emissions are therefore achieved using materials from column III of the famous periodic table and one element from column V, specifically, boron or gallium with arsenic or antimony.

Researchers from Télécom ParisTech and the University of California, Santa Barbara (UCSB) have recently presented a new technology for preparing these III-V components by growing them directly on silicon. This technological breakthrough enables researchers to obtain components with remarkable properties in terms of power output, power supply and thermal robustness. The results show that these sources have more stability in the presence of interfering reflections—a critical aspect in producing low-cost communication systems without an optical isolator. Industrial giants such as Nokia Bell Labs, Cisco, Apple and major digital stakeholders like Google and Facebook have high hopes for this technology. It would allow them to develop the next generation of extremely high-speed optical systems.

The approach currently used in the industry is based on thermally adhering a semiconductor laser (developed with a III-V material) to a structured silicon substrate to direct the light. Thermal adhesion does not optimize costs and is not easily replaced, since silicon and III-V elements are not naturally compatible. However, this new technology will pave the way for developing laser sources directly on silicon, a feat that is much more difficult to achieve than for other components (modulator, guides, etc.) For several years now, silicon has become an essential component in microelectronics. And these new optical sources on silicon will help the industry adapt its manufacturing processes without changing them and still respond to the current challenges: produce higher-speed systems that are cost-effective, compact and offer energy savings.

This technological breakthrough is the result of collaboration between Frédéric Grillot, a researcher at Télécom ParisTech, and John Bowers, a researcher at the UCSB. The work of Professor Bowers’ team contributed to developing technology that produced the first “hybrid III-V on silicon” laser with Intel in 2006. In 2007, it won the “ACE Award” (Annual Creativity in Electronics) for the most promising technology. The collaboration between John Bowers and Frédéric Grillot and his team is one of the few that exist outside the United States.

 

 

quèsaco mécatronique, mechatronics

What is mechatronics?

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Intelligent products can perceive their environment, communicate, process information and act accordingly… Is this science fiction?  No, it’s mechatronics! Every day, we come in contact with mechatronic systems, from reflex cameras to our cars’ braking systems. Beyond the technical characteristics of these devices, the term mechatronics also refers to the systemic and comprehensive nature of their design. Pierre Couturier, a researcher at IMT Mines Alès, answers our questions about the development of these complex multi-technology systems.

 

What is mechatronics?

Mechatronics is an interdisciplinary and collaborative approach for designing and producing multi-technology products. To design a mechatronic product, several different professions must work together to simultaneously solve electronic, IT and mechanical problems.

In addition, designing a mechatronic product means adopting a systemic approach and taking into account stakeholders’ needs for the product over its entire lifecycle, from design, creation, production, use, to dismantling.  The issues of recycling and disposing of the materials are also considered during the earliest stages of the design phase. Mechatronics brings very different professions together and this systemic vision creates a consensus among all the specialists involved.

 

What are the characteristics of a mechatronic product?

A mechatronic product can perceive its environment using sensors, process the information received and then communicate and react accordingly in or on this environment. Developing such capacities requires the integration of several technologies in synergy: mechanics, electronics, IT and automation. Ideally, a product is designed to self-run and self-correct based on how it is used. With this goal in mind, we use artificial intelligence technologies and different types of learning: supervised, non-supervised or reinforced learning.

 

What types of applications are mechatronic products used for?

Mechatronic products are used in many different fields: transport, mobility, robotics, industrial equipment, machine-tools, as well as in applications for the general public… Reflex cameras, which integrate mechanical aspects with mobile parts are one example of mechatronic products.

In the area of transport, we also encounter mechatronics on a daily basis, for example with the ABS braking assistance system that is integrated into most cars. This system detects when the wheels are slipping and releases the driver’s braking request to restore the wheel’s grip on the road.

At IMT Mines Alès, we are also conducting several mechatronic projects on health and disability, including a motorized wheel for an all-terrain wheelchair. The principle is to provide the wheelchair with electrical assistance proportional to how the individual pushes on the handrail.

 

What other types of health projects are you leading at IMT Mines Alès?

In the health sector, we have developed a device for measuring the pressure a shoe exerts on the foot for an orthopedic company from Lozère. This product is intended for individuals with diabetes who have a loss of sensation in their feet: they can sometimes injure themselves by wearing inappropriate shoes without feeling any pain. Using socks equipped with sensors placed at specific places, areas with excessive pressure can be identified. The data is then sent to a remote station which transfers the different pressure points to a 3D model. We can therefore infer what corrections need to be made to the shoe to ensure the individual’s comfort.

We have also developed a scooter for people with disabilities, featuring a retractable kickstand that is activated when the vehicle runs at a low speed, to prevent the rider from falling. Also, in the area of disability, we have worked on a system of controls for electric wheelchairs that involve both a touchpad with two pressure areas to move forward and backward and touch sensors activated by the head to move left or right.

 

What difficulties are sometimes encountered when developing complex mechatronic products?

The first difficulty is to get all the different professions to work together to design a product.  There are real human aspects to manage! The second technical difficulty is caused by the physical interactions between the product’s different components, which are not always predictable. At IMT Mines Alès, for example, we designed a machine for testing the resistance of a foam mattress. A roller moved across the entire length of the mattress to wear it out. However, the interaction between the foam and roller produced electrostatic phenomena that led to electric shocks. We had underestimated their significance… We therefore had to change the roller material to resolve this problem. Due to the complexity of these systems, we discovered physical interactions we had not expected during the design phase!

To avoid this type of problem, we conduct research in systems engineering to assess, verify and validate the principles behind the solution as soon as possible in the design phase, even before physically making any of the product’s components. The ideal solution would be to design a product using digital modeling and simulation, and then produce it without the prototype phase… But that’s not yet possible! In reality, due to the increasing complexity of mechatronic products, it is still necessary to develop a prototype to detect properties or behaviors that are difficult to assess through simulation.

 

supercritical fluid

What is a supercritical fluid?

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Water, like any chemical substance, can exist in a gaseous, liquid or solid state… but that’s not all! When sufficiently heated and pressurized, it becomes a supercritical fluid, halfway between a liquid and a gas. Jacques Fages, a researcher in process engineering, biochemistry and biotechnology at IMT Mines Albi, answers our questions on these fluids which, among other things, can be used to replace polluting industrial solvents or dispose of toxic waste. 

 

What is a supercritical fluid?

Jacques Fages: A supercritical fluid is a chemical compound maintained above its critical point, which is defined by a specific temperature and pressure. The critical pressure of water, for example, is the pressure beyond which it can be heated to over 100°C without becoming a gas. Similarly, the critical temperature of CO2 is the temperature beyond which it can be pressurized without liquefying. When the critical temperature and pressure of a substance are exceeded at the same time, it enters the supercritical state. Unable to liquefy completely under the effect of temperature, but also unable to gasify completely under the effect of pressure, the substance is maintained in a physical state between a liquid and a solid: its density will be equivalent to that of a liquid, but its fluidity will be that of a gas.

For CO2, which is the most commonly used fluid in supercritical state, the critical temperature and pressure are relatively low: 31°C and 74 bars, or 73 times atmospheric pressure. Because CO2 is also an inert molecule, inexpensive, natural and non-toxic, it is used in 90% of applications. The critical point of water is much higher: 374°C and 221 bars respectively. Other molecules such as hydrocarbons can also be used, but their applications remain much more marginal due to risks of explosion and pollution.

What are the properties of supercritical CO2 and the resulting applications?

JF: Supercritical CO2 is a very good solvent because its density is similar to that of a liquid, but it has much greater fluidity – similar to that of a gas – which allows it to penetrate the micropores of a material. The supercritical fluid can selectively extract molecules, it can also be used for particle design.

A device designed for implementing extraction and micronization processes of powders.

 

Supercritical CO2 can be used to clean medical devices, such as prostheses, in addition to the sterilization methods used. It removes all the impurities to obtain a product that is clean enough to be implanted in the human body. It is a very useful complement to current methods of sterilization. In pharmacy, it allows us to improve the bioavailability of certain active principles by improving their solubility or speed of dissolution. At IMT Mines Albi, we worked on this type of process for Pierre Fabre laboratories, allowing the company to develop its own research center on supercritical fluids.

Supercritical CO2 has applications in many sectors such as materials, construction, biomedical healthcare, pharmacy and agri-food as well as the industry of flavorings, fragrances and essential oils. It can extract chemical compounds without the use of solvents, guaranteeing a high level of purity.

Can supercritical CO2 be used to replace the use of polluting solvents?

JF: Yes, supercritical CO2 can replace existing and often polluting organic solvents in many fields of application and prevents the release of harmful products into the environment. For example, manufacturers currently use large quantities of water for dyeing textiles, which must be retreated after use because it has been polluted by pigments. Dyeing processes using supercritical CO2 allow textiles to be dyed without the release of chemicals. Rolls of fabric are placed in an autoclave, a sort of large pressure cooker designed to withstand high pressures, which pressurizes and heats the CO2 to its critical state. Once dissolved in the supercritical fluid, the pigment permeates to the core of the rolls of fabric, even those measuring two meters in diameter! The CO2 is then restored to normal atmospheric pressure and the dye is deposited on the fabric while the pure gas returns into the atmosphere or, better still, is recycled for another process.

But, watch out! We are often criticized for releasing CO2 into the atmosphere and thus contributing to global warming. This is not true: we use CO2 that has already been generated by an industry. We therefore don’t actually produce any and don’t increase the amount of CO2 in the atmosphere.

Does supercritical water also have specific characteristics?

JF: Supercritical water can be used for destroying hazardous, toxic or corrosive waste in several industries. Supercritical H2O is a very powerful oxidizing environment in which organic molecules are rapidly degraded. This fluid is also used in biorefinery: it gasifies or liquefies plant residues, sawdust or cereal straw to transform them into liquid biofuel, or methane and hydrogen gases which can be used to generate power. These solutions are still in the research stage, but have potential large-scale applications in the power industry.

Are supercritical fluids used on an industrial scale?

JF: Supercritical CO2 is not an oddity found only in laboratories! It has become an industrial process used in many fields. A French company called Diam Bouchage, for example, uses supercritical CO2 to extract trichloroanisole, the molecule responsible for cork taint in wine. It is a real commercial success!

Nevertheless, this remains a relatively young field of research that only developed in the 1990s. The scope for progress in the area remains vast! The editorial committee of the Journal of Supercritical Fluids, of which I am a member, sees the development of new applications every year.

 

aneurysm

A digital twin of the aorta to prevent aneurysm rupture

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15,000 Europeans die each year from rupture of an aneurysm in the aorta. Stéphane Avril and his team at Mines Saint-Étienne are working to better prevent this. To do so, they develop a digital twin of the artery of a patient with an aneurysm. This 3D model makes it possible to simulate the evolution of an aneurysm over time, and better predict the effect of a surgically-implanted prosthesis. Stéphane Avril talks to us about this biomechanics research project and reviews the causes for this pathology along with the current state of knowledge on aneurysms.

 

Your research focuses on the pathologies of the aorta and aneurysm rupture in particular. Could you explain how this occurs?   

Stéphane Avril

Stéphane Avril: The aorta is the largest artery in our body. It leaves the heart and distributes blood to the arms and brain, goes back down to supply blood to the intestines and then divides in two to supply blood to the legs. The wall of the aorta is a little bit like our skin. It is composed of practically the same proteins and the tissues are very similar. It therefore becomes looser as we age. This phenomenon may be accelerated by other factors such as tobacco or alcohol. It is an irreversible process that results in an enlarged diameter of the artery. When there is significant dilation, it is called an aneurysm. This is the most common pathology of the aorta. The aneurysm can rupture, which is often lethal for the individual. In Europe, some 15,000 people die each year from a ruptured aneurysm.

Can the appearance of an aneurysm be predicted?

SA: No, it’s very difficult to predict where and when an aneurysm will appear. Certain factors are morphological. For example, some aneurysms result from the malformation of an aortic valve: 1 % of the population has only two of the three leaflets that make up this part of the heart. As a result, the blood is pumped irregularly, which leads to a microinjury on the wall of the aorta, making it more prone to damage. One out of two individuals with this malformation develops an aneurysm, usually between the ages of 40 and 60. There are also genetic factors that lead to aneurysms earlier in life, between the ages 20 and 40. Then there are the effects of ageing, which make populations over 60 more likely to develop this pathology. It is complicated to determine which factors predominate in relation to one another. Especially since if at 30 or 40 an individual is declared healthy and then starts smoking, which will affect the evolution of the aorta.

If aneurysms cannot be predicted, can they be treated?

SA: In biology, extensive basic research has been conducted on the aortic system. This has allowed us to understand a lot about what causes aneurysms and how they evolve. Although specialists cannot predict an aneurysm’s appearance, they can say why the pathology appeared in a certain location instead of another, for example. For patients who already have an aneurysm, this also means that we know how to identify the risks related to the evolution of the pathology. However, no medication exists yet. Current solutions rely rather on surgery to implant a prosthesis or an endoprosthesis — a stent covered with fabric — to limit pressure on the damaged wall of the artery. Our work carried out with the Sainbiose joint research unit [run by INSERM, Mines Saint-Étienne and Université Jean Monnet], focused on gathering everything that is known so far about the aorta and aneurysms in order to propose digital models.

What is the purpose of these digital models?

SA: The model should be seen as a 3D digital twin of the patient’s aorta. We can perform calculations on it. For example, we study how the artery evolves naturally, whether or not there is a high risk of aneurysm rupture, and if so, where exactly in the aorta. The model can also be used to analyze the effect of a prosthesis on the aneurysm. We can determine whether or not surgery will really be effective and help the surgeon choose the best type of prosthesis. This use of the model to assist with surgery led to the creation of a startup, Predisurge, in May 2017. Practitioners are already using it to predict the effect of an operation and calculate the risks.

Read on IMTech: Biomechanics serving healthcare

How do you go about building this twin of the aorta?  

SA: The first data we use comes from imaging. Patients undergo CAT scans and MRIs. The MRIs give us information about blood flow because we can have 10 to 20 photos of the same area over the duration of a cardiac cycle. This provides us with information about how the aorta compresses and expands with each heart beat. Based on this dynamic, our algorithms can trace the geometry of the aorta. By combining this data with pressure measurements, we can deduce the parameters that control the mechanical behavior of the wall, especially elasticity. We then relate this to the composition of elastin, collagen and the smooth muscle cell ratio of the wall. This gives us a very precise idea about all the parts of the patient’s aorta and its behavior.

Are the digital twins intended for all patients?

SA: That’s one of the biggest challenges. We would like to have a digital twin for each patient as this would allow us to provide personalized medicine on a large scale. This is not yet the case today. For now, we are working with groups of volunteer patients who are monitored every year as part of a clinical study run by the Saint-Étienne University hospital. Our digital models are combined with analyses by doctors, allowing us to validate these models and talk to professionals about what they would like to be able to find using the digital twin of the aorta. We know that as of today, not all patients can benefit from this tool. Analyzing the data collected, building the 3D model, setting the right biological properties for each patient… all this is too time-consuming for wide-scale implementation. At the same time, what we are trying to do is identify the groups of patients who would most benefit from this twin. Is it patients who have aneurysms caused by genetic factors? For which age groups can we have the greatest impact? We also want to move towards automation to make the tool available to more patients.

How can the digital twin tool be used on a large scale?  

SA: The idea would be to include many more patients in our validation phase to collect more data. With a large volume of data, it is easier to move towards artificial intelligence to automate processing. To do so, we have to monitor large cohorts of patients in our studies. This means we would have to shift to a platform incorporating doctors, surgeons and researchers, along with imaging device manufacturers, since this is where the data comes from. This would help create a dialogue between all the various stakeholders and show professionals how modeling the aorta can have a real impact. We already have partnerships with other IMT network schools: Télécom SudParis and Télécom Physique Strasbourg. We are working together to improve the state of the art in image processing techniques. We are now trying to include imaging professionals. In order to scale up the tool, we must also expand the scope of the project. We are striving to do just that.

Around this topic on I’MTech

How biomechanics can impact medicine – Interview with Jay Humphrey

Sampe, composite

Laure Bouquerel wins the SAMPE France competition for her thesis on composite materials for aeronautics

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Simulating deformations during the molding stage in a new composite material for the aeronautics industry: this is the subject of Laure Bouquerel’s research at Mines Saint-Étienne as part of her CIFRE PhD thesis with INSA Lyon. The young researcher, winner of the SAMPE France competition, will present her work at the SAMPE France technical days in Bordeaux on 29 and 30 November 2018 and will compete for the World Selection in Southampton during the European meetings in September.

 

An aircraft must be lightweight… But durable! The aircraft’s primary parts, such as the wings and the fuselage, form its structure and bear the greatest stress. These pieces, which were initially manufactured using aluminum, were progressively replaced by composite materials containing carbon fibers and polymer resin for enhanced mechanical performance and resistance to corrosion, while also reducing the mass. The mass issue is at the heart of the aeronautical transport industry: savings on mass leads to a higher payload proportion for aircrafts, while also decreasing fuel consumption.

Traditionally, composite materials for primary parts are molded using indirect processes. This involves using a set of carbon fibers that are pre-impregnated with resin. The part is manufactured by an automated process that superimposes the layers, which are then cured in an autoclave, a pressurized oven. This is currently the most widely used process in the aeronautics industry. It is also the most expensive, due to the processes involved, the material used and its storage.

“Hexcel offers a direct process using a new-generation material it has developed: HiTape®. It is a dry, unidirectional reinforcement composed of carbon fibers sandwiched between two thermoplastic webs. It is intended to be deposited using an automated process, then molded before the resin is injected,” Laure Bouquerel explains. The researcher is conducting a thesis at Mines Saint-Étienne on this material that Hexcel is working to develop. The goal is to simulate the molding process involving the stacking of carbon fiber reinforcements in order to better understand and anticipate the deformations and defects that could occur. This work is what earned the young materials specialist an award at the SAMPE France* competition.

Anticipating defects to limit costs

“The carbon fibers in the HiTape® material are all aligned in the same direction. The rigidity is at its maximum level in the direction of the fibers. Several layers are deposited in different directions to manufacture a part. This offers very good rigidity in the desired directions, which were identified during the design phase for the structure,” Laure Bouquerel explains. Yet due to the HiTape® material’s specific structure and the presence of the thermoplastic web, specific deformations occur during the molding phase. The tension in the reinforcement is predominant and wrinkling can occur when the material is bent. Finally, friction can occur between the various reinforcement layers.

“The appearance of wrinkling is a classic. As they become wrinkled, the fibers are no longer straight, and the load placed on the material will not be transferred as well,” the researcher observes. “These wrinkles also cause the development of areas that are less dense in fiber, where the resin will accumulate after the molding stage, creating zones of weakness in the material.” As these deformations appear, the final part’s overall structure is weakened.

The aim of Laure Bouquerel’s thesis work is to digitally simulate the molding process for the HiTape® material in order to identify and predict the appearance of deformations and then improve the molding process through reverse engineering. Why the use of digital simulation? This method eliminates all the trial and error involving real materials in the laboratory, thus reducing the time and cost involved in developing the product.

A great opportunity for the young researcher

A graduate of Centrale Nantes engineering school, the young researcher became specialized in this field while working toward her Master’s in advanced materials from Cranfield University in England. After earning these two degrees, she further defined her vocation during her work placement year. Laure Bouquerel began her career with Plastic Omnium, an automobile parts supplier in Lyon, and with Airbus in Germany, which explains her specialization in composite materials for the aeronautics industry.

As a winner of the SAMPE France competition, the PhD student will present her work at the SAMPE France technical days in Bordeaux on 29 and 30 November and will participate in the SAMPE Europe competition in Southampton from 11 to 13 September. This will provide a unique opportunity to give visibility to her work. “It will be an opportunity to meet with other industry stakeholders and other PhD students working on similar topics. Talking with peers can inspire new ideas for advancing our own research!”

[box type=”info” align=”” class=”” width=””]

*An international competition dedicated to materials engineering

SAMPE (Society for the Advancement of Material Process Engineering) rewards the best theses on the study of structural materials through an international competition. The French edition, SAMPE France, which Laure Bouquerel won, was held at Mines Saint-Étienne on March 22 and 23. The global competition will be held in Southampton from September 11 to 13 during the SAMPE Europe days. The aim of these international meetings is to bring together manufacturers and researchers from the field of advanced materials to develop professional networks and present the latest technical innovations.[/box]

 

 

astatine, L'astate montre enfin sa liaison halogène !

Astatine halogen bond finally revealed!

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Astatine is the last member of the halogen family, which also includes fluorine and chlorine. These chemical elements have a distinct feature: they are able to form an unusual kind of bond with molecules. Yet for astatine, the existence of this specific halogen bond had never before been proven. This is because in its natural state, astatine is the rarest element. Now all that has changed. The bond was revealed thanks to work by Subatech (a research unit including IMT Atlantique, CNRS and the University of Nantes) and the CEISAM. Their results have been published in the prestigious journal Nature Chemistry on March 19th.

 

Fluorine, chlorine, bromine, iodine? Toothpaste, swimming pool, photographic film, fish! Four chemical elements, and four objects that even those of us who are unscientific can associate with them. At first glance, brushing your teeth and swimming have little in common. And yet the four chemical elements mentioned above are all part of the same family: the halogen family. In fact, incandescent “halogen” lamps owe their name to the iodine and bromine contained in their bulbs. This just proves that in our lives we are often in contact with halogens, sometimes daily, for example with the chlorine that makes up half of our table salt (the other half is sodium). These elements are also well known to chemists, who in the early 20th century brought to light their ability to create an unusual type of bond: the halogen bond. These bonds are weaker than typical chemical bonds yet are significant enough to play a role in the development of liquid crystals, conductive polymers, and nanoporous materials.

However, this chemical family includes an element that is more discreet. Astatine, the fifth and last member of the group, is not very sociable: you’re unlikely to have come across this one during your lifetime. This is because scientists estimate the entire amount of astatine in the earth’s crust at less than 30 grams. It is the least abundant of all the elements naturally present on Earth. Its scarcity makes it difficult to study, and researchers even questioned its ability to form halogen bonds. The mystery was even more intriguing since experience so far had shown a link between the atom’s property and the strength of the halogen bond—astatine was suspected to be the source of the strongest halogen bonds. However, this still needed to be proven experimentally.

Now this has been accomplished, thanks to the Subatech and CEISAM teams, research laboratories which include participants from IMT Atlantique, CNRS and the University of Nantes. The work published on March 19 in the prestigious Nature Chemistry journal not only revealed astatine’s ability to create a halogen bond but confirmed that it is the strongest of its kind.  These results greatly contribute to understanding this element which is so difficult to study due to its extreme rarity. “The halogen bond shows that it is possible to form stable molecular structures with astatine,” explains Julie Champion, a chemist at Subatech. “This is very interesting for alpha-immunotherapy applications in particular.”

This radiotherapy technique involves introducing molecules which emit specific radioactive radiation—alpha particles—into the body to target cancer cells for example. Since some astatine isotopes are radioactive and emit alpha radiation, the element is considered to be a good choice for alpha-immunotherapy. Moreover, its scarcity stems from its short lifespan: after approximately eight hours, the astatine-210 isotope, which has the longest lifetime, was already half disintegrated.  This characteristic represents a great advantage for treatment, since astatine’s rapid disintegration limits side effects. Yet difficulties remain despite the first encouraging in vitro and in vivo attempts. The revelation of astatine’s potential to form halogen bonds opens new areas to explore with the goal of strengthening the connection between astatine and new biomolecules, which could potentially lead to more effective protocols for alpha-immunotherapy.

Working with the rarest element in the world

To demonstrate the existence of this bond, researchers had to adapt to the chemical element’s constraints. “We worked with isotope 211, which has an even shorter lifetime than isotope 210: after three days there is not enough astatine left for the experiments,” Julie Champion explains. The chemists had to be cunning. First, it is impossible to extract a few grams of astatine from the Earth’s crust; it must be produced artificially. “This is why we work with the Arronax cyclotron in Nantes.  This instrument is a particle accelerator used specifically for the alpha particles we use to bombard a target containing bismuth atoms. The resulting nuclear reaction produces astatine,” the researcher explains. The race against time begins for the synthetic halogen.

It is then extracted in chloroform and transported by truck to Subatech. The precious radioactive cargo must first undergo radiation protection inspections before being inserted into small test tubes which will be used for the radiochemistry experiments. “It is important to understand that we are working at the ultra-trace level,” explains Julie Champion. The quantities are so low that we cannot see the element we are studying and cannot study it using the usual spectroscopic methods.”

How then can astatine’s halogen bond be revealed in this situation? For the solution, the chemists employed techniques from nuclear metrology. These tools make it possible to detect radioactivity within the sample. Two immiscible liquid phases are present in the test tubes. The first is an aqueous phase, containing the chemical species that are soluble in water. The second phase is called organic and contains the chemical species which are not soluble in water. The principle is the same as that of a drop of oil in a glass of water: the two liquids do not mix. Astatine, as it is extracted from the cyclotron, is usually present in the aqueous phase. However, when it forms a halogen bond with a molecule composed primarily of carbon and hydrogen, the astatine returns to the organic phase. By observing the radioactive emissions—in other words astatine’s signature—in both phases, the chemists were able to see astatine transitioning from one phase to the other.

In addition to the alpha-immunotherapy applications, this discovery paves the way for further research. In the experiment that was carried out, the Subatech and CEISAM teams formed a classical bond between astatine and an iodine atom to form a halogen bond with a molecule. Yet iodine can also form a halogen bond! Could it therefore be possible to create two halogen bonds, one with astatine and the other with iodine? This is the type of question that Julie Champion and her colleagues hope to study soon.

 

non-destructive inspection

Medicine for Materials

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Did you know that materials have health problems too? To diagnose their structural integrity, researchers are increasingly using techniques similar to those used in the medical field for humans. X-rays, temperature checks and ultrasound imaging are just a few of the tools that help detection of abnormalities in parts. The advantage of these various techniques is that they are non-destructive. When used together, they can provide much information on a mechanical system without taking it out of service. Salim Chaki is one of the French pioneers in this area. The researcher with IMT Lille Douai explains why manufacturers are keeping a close watch on the latest advances in this field.

 

What is the principle behind a non-destructive inspection?

Salim Chaki: It is a set of techniques that can provide information about a part’s state of health without modifying it. Before these techniques were developed, the traditional approach involved cutting up a defective part and inspecting it to identify the defect. With the non-destructive method, the philosophy is the same as that of human medicine: we use x-rays and ultrasounds, for example, to study what is inside the part, or infrared thermography to take its surface temperature to detect abnormalities. The development of nuclear energy during the post-war period demanded this type of techniques since radioactivity introduced new constraints in handling radioactive objects.

Your research approach involves performing a non-destructive “multi-technical” approach. What is the advantage of this approach?

SC: Historically, engineers would choose to use x-rays, ultrasound or other techniques based on their needs. For several decades, manufacturers did not really consider using several techniques simultaneously, whereas in the medical world a more global approach was already being used, including a clinical examination, blood test, x-rays and possibly further tests to diagnose a patient’s illness. In 2006, we became pioneers by proposing a combination of several techniques to diagnose the structural integrity of composite parts during operation. At that point, manufacturers became very interested, convinced by the high potential of the approach. The possibility of diagnosing a defect without modifying the part and even without taking it out of service represents a major economic advantage. We demonstrated the benefit of the non-destructive multi-technical approach by using infrared cameras, optical cameras for measuring the deformation fields and passive acoustic sensors attached to the structure. These sensors pick up the sound of the vibrations emitted by the part when it cracks. Combining several non-destructive techniques therefore makes it possible to confirm the diagnosis of a part’s condition; it complements the information and improves its reliability.

 

Salim Chaki was one of the pioneers in this field when he began working on non-destructive multi-technical inspection in 2006.

Is it really that difficult for manufacturers who have not yet done this to combine two or more techniques?

SC: Yes, actually implementing several techniques is not necessarily straightforward. There are technical problems in real time related to synchronization: the data collected by one sensor must be able to be correlated both spatially and temporally with the data from the others. This requires them to all be perfectly synchronized during the measurements.  There is also a major “data processing” aspect. For example, the infrared cameras record imaging data that are very big. They then must manage how these data are stored and processed. Finally, the interpretation process requires multiple skills since the data originate from different sensors related to different fields—optics, acoustics, heat science. However, we are currently working on data processing algorithms that would facilitate the use and interpretation of data in industrial settings.

What are the concrete applications of non-destructive multi-technical inspections?

SC: One of the most interesting applications involves pressure vessels—typically gas storage tanks. Regulations require that they be inspected periodically to assess their condition and whether they should remain in use. The non-destructive multi-technical approach not only allows this inspection to occur without emptying the tank and taking it out of service for each inspection, it could also be used to forecast the device’s remaining useful life. This is currently one of the major issues in our research. However, the multi-technique approach is still fairly recent, and therefore not many industrial applications exist. On the other hand, we believe that the future will be more conducive to multi-technical processes which will make this inspection more reliable, an aspect that is repeatedly requested by industrial equipment and plant operators, as well as by the administrative authorities responsible for their safety.

What are your lines of research now that manufacturers have begun adopting these techniques?

SC: First of all, it is important to pursue our efforts in convincing manufacturers of the advantages of multi-technical inspections, particularly the increased reliability of the inspection. There is no universal technique that offers a comprehensive diagnosis of a part’s condition. This introduces another interesting parallel with human medicine: it would be unrealistic to think a single test could detect everything. Also, as I said earlier, we are trying to go beyond the diagnosis by proposing an estimated remaining useful life for a part based on non-destructive measurements carried out while the part is in service. Very soon we will extend this concept to the inspection of parts’ initial health condition. The goal is to quickly predict if a part is healthy or not, starting at the production phase, and determine the duration of its service life. This is known as predictive maintenance.

Is the analysis of the data collected from all of the combined techniques also a research issue?

SC: Yes, of course! Since IMT Lille Douai was founded in 2017, as a result of the merger between Télécom Lille and Mines Douai, new perspectives have opened up through the synergy between our expertise in non-destructive testing of materials and our computer science colleagues’ specialization in data processing. The particular contribution of artificial intelligence algorithms and of big data to processing large volumes of data is crucial in anticipating anomalies for predictive maintenance.  If we could streamline the prognosis using these digital tools it would be a major advantage for industrial applications.

eco-material, Gwenn Le Saout, IMT Mines Alès

What is an eco-material?

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Reducing the environmental footprint of human constructions is one of the major issues facing the ecological transition. Achieving this goal requires the use of eco-materials. Gwenn Le Saout, a researcher in materials at IMT Mines Alès, explains what these materials are, their advantages and the remaining constraints that prevent their large-scale use.

 

How would you define an eco-material?

Gwenn Le Saout: An eco-material is an alternative to a traditional material for a specific use. It has a lower environmental impact than the traditional material it replaces, yet it maintains similar properties, particularly in terms of durability. Eco-materials are used within a general eco-construction approach aimed at reducing the structures’ environmental footprint.

Can you give us an example of an eco-material?

GLS: Cement has a significant CO2  footprint. Cement eco-materials are therefore being developed in which part of the cement is replaced by foundry slags. Slags are byproduct materials from steel processes that are generated when metal is melted. So, interestingly, we now call slags “byproducts”, whereas they used to be seen as waste! This proves that there is a growing interest in recovering them, partly for the cement industry.

Since concrete is one of the primary construction materials, are there any forms of eco-concrete?

GLS: Eco-concrete is a major issue in eco-construction, and a lot of scientific work has been carried out to support its development. Producing concrete requires aggregates—often sand from mining operations. These natural aggregates can be replaced by aggregates from demolition concrete which can thus be reused. Another way of producing eco-concrete is by using mud. Nothing revolutionary here, but this process is gaining in popularity due to a greater awareness of materials’ environmental footprint.

Are all materials destined to be replaced by eco-materials?

GLS: No, the goal of eco-materials is not to replace all existing materials. Rather, the aim is to target uses for which materials with a low environmental impact can be used. For example, it is completely possible to build a house using concrete containing demolition aggregates. However, this would not be a wise choice for building a bridge, since the materials do not have exactly the same properties and different expertise is required.

What are the limitations of eco-materials?

GLS: The key point is their durability. For traditional concrete and materials, manufacturers have several decades of feedback. For eco-materials, and particularly eco-concrete, there is less knowledge about their durability. Many question marks remain concerning their behavior over time. This is such an important aspect of the research: finding formulations that can ensure good long-term behavior and characterizing the existing eco-materials to predict their durability.  At The Civil Engineering Institute (IGC), we worked on the national RECYBETON from 2014 to 2016 with Lafarge-Holcim, and were able to provide demonstrators for testing the use of recycled aggregates.

How can industrial stakeholders be convinced to switch to these eco-materials?

GLS: The main advantage is economic. Transporting and storing demolition materials is expensive. In the city, reusing demolition materials in the construction of new buildings therefore represents an interesting opportunity because it would reduce the transport and storage costs. We also participated in the ANR project ECOREB with IGC on this topic to find solutions for recycling concrete. We must also keep in mind that Europe has imposed an obligation to reuse materials: 70% of demolition waste must be recycled. Switching to eco-materials using demolition products therefore offers a way for companies to comply with this directive.