JEC COMPOSITES MAGAZINE - Issue #42 - July/August 2008 - 58

KNOW-HOW Ecodesign “Eco-characterisation” of composite materials In composite materials design, the performance of a material is assessed in terms of its inherent mechanical properties using technical quality clues, or criteria. Environmental and health impacts are also important criteria, but these have not yet been defined and taken into consideration in characterisation tests. To achieve economic design that is also based on an assessment of the environmental performance, this needs to be done. ductile elastic-plastic material (figure 1). As a result, the stressstrain curve in figure 1 illustrates the linear and non-linear elastic domains, the plastic domain, and the corresponding failure point. However, no information on the material behaviour with respect to the environment and health protection is given. Since our approach is essentially based on this argument, we consider that the absence of such information in the final results may cause serious problems for human health and the environment in the short and/or long term (e.g. asbestos). To overcome these problems and achieve a sustainable development approach, it is imperative to consider the environmental and health constraints in more detail and integrate them into the test results. DR. BRAHIM ATTAF, EXPERT IN COMPOSITE STRUCTURES O ne of the main objectives of designers in the field of highperformance composite structures is to develop lightweight structural components that are strong enough to perform safely in operating conditions, withstand the severe static and/or dynamic loading to which they will be exposed throughout their service life, and hold up to strength, fatigue and stability failure phenomena. Designers also focus their research on how to optimize specific stiffness (E/ρ) and/or specific strength (σ/ρ) to achieve high structural performance coupled with economic design [1-5]. It has been shown that reaching these objectives and fulfilling quality design requirements requires performing characterisation tests early on in the design process to enable choosing the appropriate material for the desired mechanical, thermal, physical or chemical properties. In the case of mechanical characterisation, for instance, the choice of a material is generally based on its mechanical resistance (elasticity, strength, fracture, fatigue, etc.) to adequately meet the anticipated operating conditions. Carrying out this type of characterisation testing in specialized laboratories and applying suitable standard conditions for each type of test is a strong guarantee of these properties. Fig. 1: Stress-strain relation with no information on health and environmental material behaviour To further explain this approach, let us consider a simple, standard material characterisation test under uniaxial mechanical tension, chosen because it is the easiest and most convenient mechanical test. For better understanding and more explicit interpretation, the results are presented in the form of a conventional stress-strain diagram, where the x-axis represents strain ε and the y-axis represents stress σ , but to clearly illustrate the different successive stages of material behaviour, we consider a In the present article, we present an innovative approach that allows deciding very early on in the material selection process whether to approve or reject a proposed material. The approach will bring a considerable advantage to the design process and is based on the elaboration of new criteria on environmental and health conditions, which we call “eco-coefficients”. These are to be inserted into standard technical material characterisation formulae to factor in environmental aspects. When the ecocoefficients are taken into account during material characterisation tests, the term “eco-characterisation” can be considered to apply. JEC Composites Magazine / No42 July-August 2008

JEC COMPOSITES MAGAZINE - Issue #42 - July/August 2008

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