The Effect of Crack Length and Bond Strength on the Delamination Process in Borsic-Al Composites

Abstract

The effect of crack length and fiber-matrix bond strength on the delamination process in unidirectional Borsic-Al composites has been examined using Single-Edge-Notch specimens. The transverse tensile strength, σ_T, was used as an indirect measure of the fiber-matrix bond strength, which was altered through variations in hot pressing during composite fabrication. In composites with weak fiber-matrix bonds (σ_T = 3.2 ksi), the net-section stress at delamination, σ _D, was observed to decrease with increasing crack length. Variations in crack length did not significantly alter the basic fracture mechanism in which the delamination process led to notch insensitivity. Increases in the fiber-matrix bond strength (σ_T increased from 3.2 ksi to 13.2 ksi) caused a marked increase in σ_D but did not change the general delamination process. Through the use of cross-plied composites, the transverse strength was raised to 16.6 ksi and delamination was suppressed. This led to notch-sensitive fracture behavior and a substantial decrease in the fracture toughness compared to the composites which delaminated prior to failure.