Fracture Methods in Cement Composites

Contoured double cantilever beams 24 in. (610 mm) long were tested to evaluate the fracture properties of asbestos cement, plain mortar and steel fiber reinforced mortar. The crack extension, the crack opening displacement (COD) and the crack opening of the cantilever's arms at the loading points were experimentally recorded in function of applied loads. Several analytic and experimental techniques were used to determine the fracture properties of the materials including three different analytic approaches to determine the stress intensity factor, the compliance measured strain energy technique, the quasi-static energy measuring technique, and an energy measuring technique defined as the offset fracture energy that takes into consideration the permanent deformation at unloading. It is observed that all techniques give about the same result for asbestos cements. In applying the fracture energy techniques to mortar and fiber reinforced mortar it was found that the compliance measured energy and the quasi-static energy underestimate the true fracture energy of the materials while the offset energy technique gives more realistic results.