THE FRACTURE-MECHANICS OF SLOW CRACK-GROWTH IN POLYETHYLENE

The following theoretical equation was obtained for the rate of initiation delta of slow crack growth in polyethylene: delta = sigma(y)K(4)(1 - gamma(2))(2)/eta dE(2) sigma(c)(2), where sigma = applied stress, K = stress intensity, gamma = Poisson's ratio, E = Young's modulus, sigma(c) = stress to produce a craze, sigma(y) = yield point, d = primordial thickness of the craze and eta = the intrinsic viscosity of the fibrils of the craze. The dependence of delta on K agrees with the experimental data. The experimental values of delta vary by a factor of 10(7) depending on the type of polyethylene. This large variation in delta is directly related to intrinsic viscosity eta which evolved from the theory.