Fracture surface energy and craze fibril stress in PMMA in water

Abstract
Polymethylmethacrylate (PMMA) is often used as a material for portholes in submarine applications. Therefore, the fracture properties of dry and wet PMMA in water and/or under hydrostatic pressure are of great importance. In this study compact tension specimens immersed in water have been used on a tensile machine and crack tips have been observed by means of optical interferometry during propagation. Fracture stress intensity factors, and plastic zone size have been measured as a function of loading time and crack speed in water. The results have been rationalized in terms of craze stress and craze life time at the crack tip, and in terms of a stress activated process of craze fibril growth and rupture. It has been shown that water increases the fracture toughness, in spite spite of the fact that the microscopic craze stress and craze fibril life time decrease at the crack tip.