INFLUENCE OF CRACK-PROPAGATION DIRECTION ON (110)FRACTURE-TOUGHNESS OF GALLIUM-ARSENIDE

Cleavage of {110} planes in a GaAs single crystal was investigated to study whether propagation direction influences the measured fracture t oughness. The propagation direction for cracks on the (110) plane was varied to be [001], [112], [111], [110] and [00 (1) over bar]. Pre-cra cks were introduced by Vickers hardness indents, and through-thickness -pre-crack bend bars were also tested. One orientation, (110)[(1) over bar 10], tested only with the latter method, had a substantially lowe r toughness than the others, suggesting the existence of one specific 'easy' propagation direction. Possible reasons for toughness differenc es with respect to the propagation direction are discussed. Different testing methods to resolve such issues as firstly direct determination of fracture toughness from indenter cracks, secondly bending fracture toughness experiments from indenter precracks, and thirdly bending fr acture toughness experiments from through-thickness pre-cracks are cri tically compared for their potential to resolve toughness anisotropies .