Mechanical Properties of Multidirectional Fiber Composites

An investigation was conducted to systematically evaluate the structure- property relationships in both 3-D and the corresponding 2-D composites. Macroscopic failure modes and microfailure mechanisms in these composites were studied as a function of various material parameters. In particular, the influence of the stitched Z-direction fibers on the mechanical behavior of an otherwise 2-D composite was investigated. The 3-D composites have been found to possess a greater damage resistance than the conven tional 2-D composite materials. The Z-direction (or third-direction) fibers effectively reduce the extent of delamination by increasing the interlaminar surface energy. The total energy absorbed by a composite during impact loading, three-point, and four-point bend ing test is therefore raised without creating an excessive amount of delamination. The third directional fibers are found to have a profound effect on the failure mechanisms.