JEC COMPOSITES MAGAZINE - Issue #42 - July/August 2008 - 60

KNOW-HOW Ecodesign g…/… “Eco-characterisation” of composite materials The numerator value approaches the denominator value , when the eco-efficiency ratio λ tends towards unity. This ratio may be subjected to an optimisation process with the object of reaching its maximum value. If this value does not meet sustainability requirements, a search for possible new alternatives can be provided by a possible alteration of the principal coefficients until sufficient agreement is achieved. Further investigations on the optimisation of these coefficients are still necessary, however. difference value, which can be minimised to attain the appropriate values requested by standards and ecodesign requirements. The derivation of the mathematical eco-formulations for composite structural analysis is beyond the scope of this article. Conclusion Selecting a composite material based only on technical quality criteria that assess its performance in terms of specific mechanical properties (elastic modulus, ultimate strength, fracture resistance, fatigue resistance, etc.) can cause serious, short- or long-term environment and health problems. We feel that integrating these strict ecological pressures into the material characterisation tests as an essential step in the design process for composite structural elements would be a positive contribution to the world’s socioeconomic well-being. Within this context, we defined and developed new criteria in the form of environmental and health coefficients. These can be factored into characterisation tests for composite materials to allow informed approval or refusal of the proposed material, very early in the design of a composite product. They can also be used in classical lamination theory and integrated into future finite-element computer programs. By comparing output results that take qualitative, health and environmental aspects into account to those that do not, designers can make better use of environmental performance assessment. This innovative approach can help designers and engineers who work in the field of high-strength materials to choose the right materials for manufacturing truly ecofriendly composite products. “Going green” can also help composite companies to survive in the competitive international composite market. Contact: b.attaf@wanadoo.fr Advanced mathematical eco-formulations In high-performance composite structures, structural components are manufactured mainly from unidirectional fibre-reinforced plies, where the ply axes are identified in the principal coordinate system with numbers 1, 2 and 3 [7]. For a unidirectional fibre-reinforced orthotropic ply, the ecoratios related to the engineering constants for the linearelastic mechanical behaviour may be defined, in the principal coordinate system, as: , , (i,j=1,2,3) where , are classical and sustainable moduli of elasticity in the i-direction (where i=1, 2 and 3), , are classical and sustainable shear moduli in the i-j plane (where i-j=2-3, 3-1 and 1-2), are the eco-efficiency ratios of elasticity and shear, is the Poisson’s ratio for transverse strain in the j-direction when stressed in the i-direction. According to generalized Hooke’s law, the stress-strain relations for an orthotropic material (unidirectional ply) may be written in compact matrix form as: References [1] Attaf, B., ‘‘Vibration and Stability Analyses of Stiffened and Unstiffened Composite Plates’’, PhD Thesis, University of Surrey, UK, 1990 [2] Attaf, B., “Effects of Laminate Stacking Sequence on the Free Vibration of Carbon/Epoxy Composite Plates Subjected to In-plane Loads”, La Recherche Aérospatiale, No.2, 1996, pp.149-153 where is the eco-compliance matrix of order 6×6 (6 rows by 6 columns). Furthermore, the eco-stiffness matrix of the ply may be obtained by the inverse of the eco-compliance matrix. Thus, we can write: [3] Attaf, B. and Hollaway, L., “Vibrational Analyses of Stiffened and Unstiffened Composite Plates Subjected to In-plane Loads”, Composites, Vol.21, pp.117-126, March 1990 [4] Attaf, B. and Hollaway, L., “Vibrational Analyses of Glass Reinforced Polyester Composite Plates Reinforced by a Minimum Mass Central Stiffener”, Composites, Vol.21, pp.425-430, Sept.1990 [5] Hollaway, L. and Attaf, B., “On the Vibration of Glass-Polyester Composite With these ecological hypotheses, the constituent equations for a laminated composite structural element can be derived using the classical lamination theory [8]. Thus, the output results (which may be obtained by either classical theory or numerical methods) remain under discussion in practice but acceptable in theory. Moreover, comparing the sustainable results with the classical ones that do not take environment and health considerations into account can yield an estimate Stiffened and Unstiffened Rectangular Plates”, Chinese Society of Aeronautics, 7th Int. Conf. on Composite Materials, pp.435-444, Beijing, Oct. 1989 [6] Attaf, B. ‘‘Towards the Optimisation of the Ecodesign Function for Composites’’, JEC Composites Magazine, n°34, pp. 58-60, July-August 2007. [7] Jones, R.M., ‘‘Mechanics of Composite Materials’’, Scripta Book Company, Washington, D.C., 1975. [8] Saarela, O., ‘‘Computer Programs for Mechanical Analysis and Design of Polymer Matrix Composites’’, Prog. Polym. Sci., Vol.19, pp.171-201, 1994 JEC Composites Magazine / No42 July-August 2008

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

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #42 - July/August 2008