Abstract
Cracks in SM50A steel for welding structure, chilled to 233 and 193K, were loaded by various stress intensity pulses with durations of 20, 40, and 80 μs to generate experimental data of critical stress intensity levels for crack instability. Fracture surfaces were observed by a scanning electron microscope to examine cleavage nucleation origins ahead of the crack tips. The experimental results are discussed in terms of minimum time criterion and dislocation dynamics. The critical stress intensity obtained by the minimum time criterion was higher at 233K than at 193K, whereas the minimum time was shorter at 233K. The cleavage nucleation origin approached the crack tip as the temperature decreased. Finally, the temperature dependence of the minimum time was interpreted by the dislocation dynamics.
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