Integrated Simulations for the Structural Performance of Composites

Abstract

Fiber-reinforced composites are widely used for structural components in the aircraft, automotive, marine, and other industries due to their low density, high specific stiffness and strength, excellent durability, and design flexibility. During the fabrication of continuous fiber reinforced composite components, fiber direction changes, residual stresses, and out-of-the-mold deformations are unavoidable. As the 2-D fabric is deformed to a 3-D part geometry the fiber tows move, leading to fiber direction changes that result in relative angle changes between the fibers that make up the fabric. These changes have a significant effect on the behavior of the composite material system. The extent of fiber angle change in a non-crimp fabric system is largely dependent on the differences between the 2-D and 3-D geometries and the particular stitching parameters used to manufacture the fabric. In order to better understand the influence of fabrication induced fiber angle change on the performance of structural composite parts, detailed experiments and simulations were conducted. For the experiments, a reinforcement geometry was selected. Due to the complexity of the chosen geometry for draping, several slits were designed at strategic locations to allow the fabric to take the shape without wrinkling. During molding, two patterns were overlaid so that the slit locations after molding were staggered through the thickness to reduce their effect on the structural performance. Detailed draping analyses were performed taking into account the process steps, and the fiber angle changes were calculated using numerical models that were developed previously. Further, the fiber angles following draping were mapped onto the structural performance models used to simulate the crush tests. The predicted stiffness and strength results from the integrated fabrication and performance simulations were compared with the experimental measurements, and the correlations are presented in this paper.