The Effect of Stress Nonuniformity and Size on the Strength of Composite Materials

It has long been known that the strength of brittle materials like ceramics depends on the volume of stressed material and the nature of the stress distribution. Both of these effects arise because brittle materials are flaw-sensitive, and flaw severity is generally statistical in nature. As the probability of finding a serious flaw increases with increasing material volume, large brittle bodies tend to fail at lower stress levels than do smaller ones when both are subjected to the same kind of uniform stress field, such as pure tension. The dependence of strength on stress distribution arises because the stress in the region of at least one flaw must equal its critical value for failure to occur. In this paper, we refer to this phenomenon as a “nonuniformity effect.”