Fatigue Strength of Q & T High Strength Steel Plate Under Uniformally Distributed Lateral Load.

Abstract

Experiments were carried out to investigate fatigue strength of plate subjected to uniformally distributed lateral load. Box type models consisting of 7 mm thickness high strength steel plate were introduced and pressurized internally. To investigate fatigue strength of the plate under elastic-plastic large deflection behavior, level of applied load was so high that maximum bending stresses of the plates were about 1.5 and 2.0 times of yield stress according to elastic small deflection theory. There were two kinds of model shape, one was a model with square plate (750×750mm; type A) and another with rectangular plate (750×l500mm; type B). Most of type A models were different from each other in some points expected to affect fatigue strength; such as sidewall thickness, welding operation, initial deflection and corrosion by saltwater. About type B models, two models were introduced, stiffener was fitted to the center of the plate for one model and not for another. Conclusions obtained from these experiments were as follows. (1) Even after 10,000 cycles of loading, no crack initiated when the maximum bending stress of the plate was about 1.5 times of the yield stress. (2) When the maximum bending stress was about 2.0 times of the yield stress, crack initiated at 1,900 cycles and failed at 5,500 cycles. (3) Effects of saltwater corrosion and initial deflection on the fatigue strength were considerable. (4) After initiated at the toe of the stiffener, crack also propagated quickly to the opposite surface.