Tailoring Expansion Coefficients of Laminates: A New General Optimal Approach Based upon the Polar-Genetic Method

This paper deals with the problem of design of composite laminates having zero thermal and hygral expansion and/or curvatures coefficients in one or two directions. The problem is stated as a typical non linear optimization problem in the framework of the polar-genetic approach: the formulation is a function of the laminate polar parameters for the representation of tensor quantities, and a genetic algorithm is the solving technique. It is worth noting that the formulation is quite general, as we avoid to take into account any simplifying hypothesis, namely about the type of stacking sequence which is completely undetermined a priori. In addition, thanks to the very general approach previously proposed by the authors for design of elastic properties, the new design problem of thermo-elastic properties of composite laminates can be stated as a unconstrained optimization problem, being possible to include in several design criteria in a unique expression of the objective function. Therefore, we can perform search for laminates not only respecting the condition of having null thermal/hygral expansion coefficients in some directions, but also other requirements such as bending-extension uncoupling, orthotropy and so on, which are necessary conditions to several applications. In this paper we give a detailed description of the theoretical statement of the problem and we show a great number of numerical results.