Controlled generation of internal cracks in polymethyl methacrylate

A simple technique is presented for generating internal cracks in polymethyl methacrylate (PMMA) using laser irradiation. With precise control of the laser beam, a well-defined single crack can be produced in the matrix. The shape of the crack is flat and regular, close to an ellipse with nearly equal major and minor axes. The size and orientation of the crack can be controlled through the laser energy and the adjustment of the optical system. The laser-induced crack in PMMA consists of three regions: the central damage region caused by direct energy absorption, the intermediate cracking region, and the outer circumferential region associated with crazing. These controlled internal cracks can be used to study crack propagation, interaction, and related problems.