Fracture-induced formation of semi-concentric patterns on polymeric films

Using the linear perturbation method, the effect of radial residual-compressive surface stress on the surface evolution of a solid film was analyzed. The result showed that the radial-compressive surface stress can cause the formation of concentric surface waviness on the surface of the film. An analytical relationship was established between the apparent surface stress, the spatial wavelength, and the film thickness. Using a concentrated-loading method, a complementary set of semi-concentric surface ripples was formed on the fracture surfaces of a polymer film which was sandwiched between two glass slides. The amplitude of the semi-concentric ripples first increased with increasing the film thickness and then became independent of the film thickness for the film thickness ranging from 491 nm to 636 nm. Using the derived relationship and the experimental data, the variation of the apparent surface stress with the film thickness was calculated. The magnitude of the apparent surface stress increased with increasing the film thickness.