An experimental validation of the effectiveness of quasi-trivial solutions for composite laminates

In this work the problem of the least-weight design procedure of a multilayer composite plate is addressed. The proposed design method is based on an optimization strategy that uses neither simplifying hypotheses nor standard rules for determining the optimum stack. Indeed, the design task is stated as a constrained non-linear programming problem (CNLPP) wherein requirements of different nature are integrated as optimization constraints. Such constraints include mechanical requirements (i.e. material properties, first buckling load of the plate, membrane stiffness) together with geometrical and technological restrictions on the selected design variables. The proposed strategy follows a two-step approach which first selects the optimum number of plies and then searches the optimum stack in the space of the so-called quasi-trivial solutions. The quasi-trivial optimum sequences have been compared with stacking sequences developed following layup rules typically used in aeronautics: optimized non-standard plates are lighter (about 10%) than standard ones with equivalent or superior mechanical properties. The effectiveness of the developed configurations is proven through an a posteriori experimental campaign of buckling tests conducted at I2M laboratory. The experimental results are in excellent agreement with those provided by numerical simulations.