1578. Sensitivity Analysis for Composite Structure Weight

Paper

Abstract

The application of composite material to primary structure introduces new parameters into the strength/weight analysis. Providing weight effects of changes to these parameters is a necessary function in the design process, and frequently this information is an important measure of the worth of such changes. Constituent mechanical properties, unidirectional ply strengths, fiber orientation and volume fraction, and ply ratios can have a significant influence on the macromechanical response and performance and hence the structural weight. To assess the individual effect of material and structural parameters on the structural weight of a stiffened composite panel, as an example, an optimized weight is used as a reference, and the parameters are perturbed by some fraction of their preassigned values to obtain a new minimum weight of or comparison with the reference. A pilot program has been written to perform the basic plate stiffness analysis and stress distribution for a symmetric laminate. Three failure criteria are offered: Tsai-Wu, maximum strain, and modified maximum strain, the latter considering shear strain on a laminate basis for matrix failure. Stringers are treated in a smeared, one-dimensional manner with stringer sweep included. Formal optimization has been reviewed for inclusion in the analysis by linking a routine, based on the method of feasible directions, in which the objective function to be minimized is the sum of the layer thicknesses, and the constraints are based on the failure criteria. Finally, entry to the analysis is possible at the constituent level using micromechanics, as well as the lamina level.