Surface Effects in Brittle Materials and Internal Length Estimation

The concept of state of degradation is employed as a tool to study the effect of initial material (structure) inhomogeneity and the implications of surface (skin) effects on brittle material response. The initial heterogeneity pattern and its growth under external load is studied experimentally via ultrasonic scanning measurements on prismatic simulated rock samples subjected to mechanical load. Numerical solutions are compared with the experimental results. The skin effects are also studied experimentally through the spatial variation of dissipated energy within the samples tested. In addition, microstructure considerations highlight the skin effect and its implications. The material length for the simulated rock is estimated (for load levels up to peak load) through the experimental observations which yielded 1≃0.24 inches (0.61 cm). The analytical solution of a simple problem including microstructure considerations for the same material yielded 1≃0.21 inches (0.53 cm). This paper integrates and extends the recent work of the author and co-workers.