Static and dynamic behavior of damaged concrete and granite in compression

Static and dynamic compression experiments were performed on concrete and g ranite specimens with various levels of induced damage. Damage was induced into the specimens by repeated impacts from a falling weight and quantified as a measure of damage crack surface area per volume using a statistical m icroscopy technique. The static experiments were per-formed following ASTM standard procedures. The static compressive strength of both materials decr eased with increasing levels of damage. The reduction in strength is due to the induced damage causing the activation and propagation of failure crack s in the specimens. The dynamic experiments were conducted using a 50.5 min diameter Split Hopk inson Pressure Bar. The undamaged dynamic compressive strengths of both the concrete and granite were approximately twice their static values at avera ge strain rates of 380/s and 400/s, respectively. However, as the damage le vels were increased, the dynamic compressive strength remained unchanged. F or the dynamic experiments, the strain energy is stored in the specimen fas ter than the cracks can develop and coalesce to completely fail the specime n. Therefore, the relatively small amounts of induced damage did not affect the dynamic compressive strength.