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 (Attaf, 2008). For better understanding and more explicit interpretation, the results are presented in the form of conventional stress-strain diagram, where the x-axis represents strain є and the у-axis represents stress a, but to clearly illustrate the different successive stages of material behaviour, we consider a ductile elastic-plastic material. As a result, the stress-strain curve in Figure 7 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 or long term (e. g., asbestos). To overcome these inconveniences and achieve ecodesign approach, it is imperative to consider the environmental and health constraints in more detail and integrate them into the output results of test.
Fig. 7. Stress-strain relationship with no information on the material behaviour in relation to health and environmental aspects
This approach allows deciding very early on in the material selection process whether to approve or reject a proposed material.
In the stage of material characterisation, the environmental and health impacts are taken into account by considering the eco-efficiency factor X. This factor will be inserted into the standard mechanical characterisation formulae of materials. Hence, Young’s modulus of elasticity, determined by Hooke’s law and derived from experimental results must be adapted to the actual situation by integrating health and environmental considerations into
characterisation tests. Thus, the new Young’s modulus of elasticity will become E "Young’s eco-modulus ". The three dots (л) above the character E are only a brief description of the interaction between Q, H & E as discussed previously in Section 2.2.
In relation to this orientation, the modulus eco-efficiency may be evaluated by measuring the elasticity eco-efficiency factor, defined by the following ratio (Attaf, 2008):
The numerator value of E approaches the denominator value E^0, when X tends towards unity. As it was discussed earlier, if this value does not meet ecodesign requirements, a search for possible new alternatives can be provided to maximise the eco-coefficients until sufficient agreement is achieved. Further investigations on the optimisation of these ecocoefficients are still necessary, however.