Effect of Crosslink Density on the Critical Flaw Size of a Simple Elastomer Available to Purchase

Tensile experiments have been carried out on a gum, amorphous EPDM elastomer. Samples with various crosslink densities and containing precuts of different lengths were tested. The energy, W_b⁠, per unit volume, to fracture a specimen varied inversely with the length of the precut as predicted by simple tearing energy theory. Values of the inherent flaw size, C_o⁠, of the samples were determined by extrapolation of W_b to that value obtained when no intentional precut was present. Values of C_o decreased with increasing crosslink density. This illustrates the decreasing ability of an elastomer network to blunt the crack tip of a stress-raising flaw as crosslinking is increased. It is suggested that this phenomenon is at least partly responsible for low values of W_b at high crosslink densities.