Fracture behavior in stitched multidirectional composites

Abstract

Abstract Various two-dimensional (2D) and three-dimensional (3D) composite materials in different geometries and compositions were fabricated and examined. The 3D composites were produced by the techniques of stitching. Damage resistance and fracture mechanisms of composites were studied as a function of loading directions at both low and high loading rates. The effects of the type, concentration and distribution of the third-direction fibers on the mechanical behavior of an otherwise 2D composite were investigated. Failure analyses were conducted to determine the failure causes and crack propagation behavior by means of in situ optical microscopy and scanning electron microscopy. Multidirectional composites were found to possess a greater damage resistance than did the conventional 2D composites. The third-direction fibers were found to reduce effectively the degree of delamination and to increase the flexural strength of composites by increasing the interlaminar fracture surface energy. Problems associated with the fabrication of 3D composites were identified and discussed.