The Effects of a Single Mode III Loading Cycle on Mode I Crack Initiation and Growth Toughnesses in a Cross-Ply [90°/0°]2s Ti-6A1-4V/SiCf Composite

Abstract

The effects of a single Mode III loading cycle on the subsequent Mode I crack initiation and growth toughnesses in a cross-ply [90°/0°]2 s, Ti-6A1-4V/SiC f composite have been investigated. A Mode III cycle with Δ J III = 8 kJ/m2 was found to have no measurable effect on either the initiation or growth toughnesses. In contrast, a Mode III cycle with Δ J III = 14 kJ/m2 resulted in a significant decrease in the subsequent Mode I crack initiation toughness. It also caused a reduction in the crack growth toughness until the crack had extended beyond the damage zone produced during the Mode III excursion. The results are rationalized on the basis of the fracture mechanisms as well as the deformation field produced by Mode III loading. The Mode III damage effect has implications for failure criteria for composites under multiaxial loading.