Method of Studying Subcritical Cracking of Opaque Materials

Abstract

Since subcritical cracking often precedes catastrophic failure, it is an important engineering consideration, especially if a structure is to be under stress for a long time. A specimen has been developed for laboratory study of subcritical cracking, but it is assumed that crack growth can be observed visually through the specimen. With opaque materials, such observation is generally impractical or impossible. A compliance method of obtaining crack‐growth data is proposed. Experimental examples using polymethyl methacrylate, soda‐lime glass, and an opaque glass‐ceramic show that the method works very well. The usefulness of the method is illustrated for 3 commercial ceramics. It is shown that subcritical cracking occurs over a range of fracture energies for each of these materials.