1996 Volume 45 Issue 12 Pages 1273-1279
Static strength of polymethyl methacrylate pre-loaded with cyclic high stress was studied. The cyclic pre-loading was carried out using triangle waves of high tensile stress at very low frequencies to avoid the temperature rise in specimens. Fracture in most of the specimens without the cyclic pre-loading started at their surfaces, whereas for a great majority of the specimens subjected to the cyclic pre-loading the fracture started from the inside of the specimens, although a number of visible crazes had been formed on the specimen surface as a result of the cyclic loading. Hence, the cyclic pre-loading of high stress was likely to lessen the role of craze as a stress-raiser or a pre-crack. Moreover, it was deduced from the data of static strength for the specimens pre-loaded with a variation of stress amplitude and frequency that the cyclic pre-loading probably introduced some kind of fracture nuclei inside the specimen. As a possible origin of the inside fracture, development of inhomogeneous distribution of strain energy stored in the specimen during the cyclic loading was proposed.
