FRACTURE OF BRITTLE MULTIPHASE MATERIALS BY HIGH-ENERGY WATER JETS

High energy water jets are established in processing brittle, inhomoge neous materials like rocks and concrete. Despite their wide field of a pplication, the failure mechanisms of these materials, especially the influence of inclusions, are not well known. This work examines the in fluence of grain inclusions on the fracture behaviour of a multiphase brittle material exposed to high energy water jet processing. The beha viour of the specimens is detected by mass removal measurements, micro scopical observations and the mercury penetration technique. It is fou nd that the failure is based on microcrack growth due to hydrostatic p ressure. The fracture mechanical behaviour of the reference material c hanges considerably with the addition of aggregates. The addition of g rains leads to a reduction of the threshold tool energy for the start of mass removal. On the other hand, the presence of inclusions permits a more reduced and controlled removal progress. The interfaces betwee n matrix and grains are the preferred locations for crack growth and a lso for crack branching. The inclusions act as crack arresters and cra ck branchers. In the case of cracks growing through the grains, a high er amount of fracture energy is absorbed and the fracture performance is weakened.