(Received 18 December 2000; accepted 19 June 2001)
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Static and dynamic compression experiments were performed on concrete and granite 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 microscopy technique. The static experiments were performed following ASTM standard procedures. The static compressive strength of both materials decreased with increasing levels of damage. The reduction in strength is due to the induced damage causing the activation and propagation of failure cracks in the specimens.
The dynamic experiments were conducted using a 50.5 mm diameter Split Hopkinson Pressure Bar. The undamaged dynamic compressive strengths of both the concrete and granite were approximately twice their static values at average strain rates of 380/s and 400/s, respectively. However, as the damage levels were increased, the dynamic compressive strength remained unchanged. For the dynamic experiments, the strain energy is stored in the specimen faster than the cracks can develop and coalesce to completely fail the specimen. Therefore, the relatively small amounts of induced damage did not affect the dynamic compressive strength.
Mechanical engineer, Naval Undersea Warfare Center, Newport, R1 02841
Simon Ostrach professor, University of Rhode Island, Kingston,
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