Surface Characteristics of Fractured Poly(methyl methacrylate)

Abstract

A STUDY of fracture phenomena in poly (methyl methacrylate) has been undertaken, which involves the breaking, in tension, of strip samples, each containing a preformed crack which lies in a plane normal to the long axis (Fig. 1). The samples are extended at fixed rates of elongation until rupture ensues, invariably at the site of the initial crack. It appears by visual inspection that the fracture process occurs in two distinct stages. The crack starts to grow fairly slowly at a velocity which is of the order of 0.1 cm./sec., until a critical stage is reached when the velocity suddenly increases to a value of at least 10⁴ cm./sec. It is not yet known what factor is critical in producing the transition. The final high velocity is possibly the theoretical maximum, limited by the velocity of a longitudinal wave in the medium¹, but no accurate measurements have yet been made. A sharp characteristic audible effect is associated with the rapid stage of crack growth.