Response Surfaces for Optimal Weight of Cracked Composite Panels: Noise and Accuracy

Two levels of fidelity are used for minimum weight design of a composite bladestiffened panel subject to crack propagation constraints. The low fidelity approach makes use of an equivalent strain constraint calculated by a closed form solution for the stress intensity factor. The high fidelity approach uses the stress intensity factor directly as the constraint and computes it from the stress distribution around the crack. A number of panels were optimized by both approaches for different values of applied load, crack length, and blade height, and response surface approximations for optimal weight as function of these configuration variables were constructed. Computational cost, noise and accuracy for the results are compared. Introduction An important issue in composite panel design for aircraft structures is crack propagation. However, modeling crack propagation in complex structures entails high computational cost, and may not be feasible for design optimization. Vitali et al. used an equivalent strain constraint for designing a composite stiffened panel with a crack. They employed two levels of model fidelity in the optimization. A low fidelity model that did not include the crack was used with a finite element optimization program GENESIS. A model of higher fidelity including the crack used the STAGS finite element program.