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 toughness. The propagation direction for cracks on the (110) plane was varied to be [001], [112], [111], [110] and [00 (1) over bar]. Pre-cracks 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 lower toughness than the others, suggesting the existence of one specific 'easy' propagation direction. Possible reasons for toughness differences 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 fracture toughness experiments from through-thickness pre-cracks are critically compared for their potential to resolve toughness anisotropies.