Thermomechanical Design Optimization of Variable Stiffness Composite Panels for Buckling

Both numerical and experimental research have shown that variable stiffness laminates allow for significant design improvements. Variable stiffness laminates can be manufactured by exploiting the built-in steering capabilities of modern fiber placement machines (FPM). Such variable stiffness panels optimized for buckling were built and tested previously. Test results yielded higher buckling loads than those predicted numerically, which was later found to be related to the residual stresses present after curing. Hence, to benefit fully from the design freedom offered by variable stiffness panels built by FPMs it is essential to include the influence of thermal stresses in the optimization formulation. In this paper, an optimization framework, developed by the authors, is extended to include the influence of thermal loads. Numerical results confirm the importance of including thermal effects in the optimization process. Designs including thermal stresses are found to have improved buckling performance over a larger range of operating temperatures. Proper tailoring of both stiffness and thermal properties allows for ultimate buckling load improvements in the order of four to six times that of the corresponding quasi-isotropic panel.