Incubation time to crazing in stressed poly(methyl methacrylate)

Crazing is usually a precursor of the brittle fracture of glassy polymers. In this paper, an optical technique is presented to quantify the crazing dominated creep damage that occurs on a stressed transparent glassy polymeric sheet of polymethyl methacrylate (PMMA). The specimens, with various sections, are loaded for a predefined period of time under a constant load at room temperature, and the areal craze densities are obtained as the measurement of creep damage by using an optical microscope. The experimental results show that there is a time lag between load application and the occurrence of the visible crazes, which indicates that craze initiation is a time-dependent phenomenon. Moreover, the time lag decreases with increase in applied stress. Such incubation time to crazing is experimentally obtained and modeled in the present work. r 2007 Elsevier Ltd. All rights reserved.