Fracture of Polymethyl Methacrylate

Polymethyl methacrylate specimens were fractured by the static bending, and the speed of the crack propagation was measured by the speed of breaking of the electro-conductive coatings on the surface of the specimens. The rate of crack propagation speed obtained by our method is found to be greater than that which has been obtained by any other investigator.It is found that the fracture morphology is roughly divided into three main classes: (1) the glassy fracture surface containing a number of geometric figures resembling parabolas, (2) the fracture surface having the semicircular“ribs or scallops”of great roughness, and (3) the fracture surface of the greatest roughness at low temperature. It seems that the concentric scallops observed on the fracture surface of the notchless specimens have been produced by the dilatational wave based on the stress release as the crack spreads over the plate.