The fracture patterns associated with the indentation of brittle materials are well known. Two major categories are the Palmqvist system, illustrated in Fig. la, and the radial-median (or half-penny) shown in Fig. lb [1]. Lateral fractures also commonly occur (Fig. lb). Indentation fracture is usually studied in large specimens, which can be considered as effectively semi-infinite, and in which the influence of specimen boundaries other than the plane free surface is negligible. In some cases, however, indentation fracture occurs in much smaller samples, and boundary effects can become important. These include indentation experiments on small particles. Boundary effects will also be important in the erosive or abrasive wear of materials which contain discrete brittle phases, such as metal matrix composites or white cast irons containing massive carbides; complete fracture of the brittle phases would be expected to lead to their removal and consequent rapid wear.
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