13. Design Optimization and Reliability Analysis of Variable Stiffness Composite Structures

This paper presents a study on the reliability analysis of variable stiffness composites to improve the performance of curved fiber composites in the presence of uncertainties. A comparison to the response of conventional straight fiber composites is presented while assuming the same material properties. To this end, a computational design framework for advanced composites has been developed and implemented and it includes both deterministic and reliability analysis capabilities. The deterministic design module uses the Discrete Material Optimization (DMO) technique, and the reliability analysis module uses the Response Surface Method (RSM) based on the First Order Reliability Method (FORM) and the Monte Carlo Simulation (MCS). Variable Stiffness Composite Laminates (VSCL) are achieved by a continuous change in fiber orientation in the plane of the laminate. The design objective is to tailor and/or maximize the stiffness of the composite structure, and the design variables are the piecewise patch orientations of the fibers in the presence of manufacturing constraints. The manufacturing constraints enforce a bounded change in fiber orientation between adjacent patches in order to ensure fiber continuity to minimize gaps and overlaps. In the reliability analysis, tip deflection and first ply failure are considered separately as the limit state function and the random variables are material properties. The results show that the VSCL are more reliable even in the presence of a high standard deviation compared to the straight fiber composites with low standard deviation assuming the same material properties. It was also observed that the curved fiber composites are more effective in handling concentrated stresses.