The interpretation of impact fractures in glassy polymers

While this study was not exhaustive of the area of impact fractures in glassy polymers, it does demonstrate that there are some significant differences between fractures in polymers and those encountered with glass. Those differences can be summarized as follows: (1) the occurrence of pronounced, highly curved hackle marks, which could in many instances be mistaken for conchoidal marks;(2)the appearance of the beveled edges bordering the cratering on the side opposite origin of force; and (3) a more apparent tendency toward an inverse relationship of muzzle velocity and energy to radial fracture length and degree of curving along crater boundaries. The physical laws applicable to the fracture of glass are identical to those extant in the fracture of glassy polymers; no new forces are at play. All of the differences are capable of being explained in terms of the differences in flexibility and flow between glass and polymers, and the resulting differences in tension development and fracture propagation.