WING CRACKS AND BRITTLE COMPRESSIVE FRACTURE

Uniaxial compression experiments on plates of columnar fresh-water ice have established that out-of-plane extensions or wing cracks develop on inclined cracks which are nucleated at grain boundaries during loading. The wings lengthen in a stable manner as the load rises, eventually splitting the specimen. Compression experiments on cold blocks of PMMA have established that pre-existing, inclined cracks also sprout wings, but that the wings wrap around the inclined crack both through the thickness and along the loading direction eventually converging to approximately the same vertical plane. These observations indicate that a frictional crack sliding model which includes three-dimensional effects can explain compressive fracture. © 1990.