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To evaluate the response of concrete structures subjected to impact or impulsive loading, it is essential to know how cracks propagate under such dynamic loading conditions. Single-edge notched beams were subjected to varying rates of loading to establish the stress intensity factor K1 versus crack velocity V relationship for mortar and concrete. Impact tests were performed using a modified instrumented Charpy test system. During loading, the rate of crack growth was obtained using special brittle Krak gages.
Results indicate the following: (1) For a given strain rate the extent of pre-peak crack growth is larger for concrete than for mortar, and the amount of pre-peak crack growth decreases with increase in strain-rate. (2) Decrease in pre-peak nonlinearity at higher strain rates is probably caused by the decrease in amount of slow (pre-peak) crack growth. Hence, the linear-elastic fracture mechanics (LEFM) approach at high rates may be valid. (3) To obtain realistic size independent value of stress intensity factor, slow crack growth should be included in the calculation for cement composites. (4) The relationship between log K1 and log V is nonlinear especially at the higher rates of loading, for both mortar and concrete.
Graduate research assistant and professor of civil engineering, Northwestern University, Evanston, IL
Stock #: CCA10050J