Rate-Sensitivity of Mode I and Mode II Fracture of Concrete

Abstract

ABSTRACTFor rational and accurate analysis of concrete structures subjected to impact or impulsive loads the knowledge of crack propagation under such dynamic loads is essential. Cracks frequently propagate under mixed-mode (opening and sliding: mode I and mode II) conditions. The rate of loading effects on the mechanical properties have been attributed to the rate sensitivity of crack propagation. The strain-rate effects may be different in mode I and mode II fracture of concrete. Single edge notched beams were subjected to varying rates of loading, to establish the mode I Stress Intensity Factor, KIvs. Crack Velocity, V, relationship for mortar and concrete. Impact tests were conducted using a Modified Instrumented Charpy Impact Test System. The rate of crack growth was obtained using brittle ‘Krak Gages'.Mode I test results lead to the following conclusions. (1) Slow (prepeak) crack growth for concrete is larger than that of mortar, at a given strain rate. (2) Pre-peak crack growth decreases with increase in strain-rate. This could be the reason for decrease in pre-peak non-linearity at higher strain rates. Hence LEFM approach may be valid at high rates of loading. (3) log KI- log V relationship is non-linear especially at the higher rates of loading.