Behavior of Long Fatigue Cracks in Cellular Box Beam

Abstract

The propagation of long cracks under constant-amplitude cyclic loading is studied in complex welded box beams made of high-strength low-alloy steel. The 8 × 1 × 0.7 m box beams were designed to simulate the cellular structure of a double-hull ship but the results of the experiments are equally applicable to other box systems such as bridges. These experiments were designed to evaluate the residual fatigue life after a significant fatigue crack has formed. After testing, residual stresses were measured on two box beams using the standardized strain-gauge hole-drilling method. The experiment results demonstrated the good crack tolerance of cellular structures. The residual life of a box beam (after a welded detail has failed) was significant. The crack-driving force was evaluated using finite-element modeling. Reasonable correlation between these large-scale tests and the fatigue crack growth rate from small compact specimens was obtained only with models that included the effects of crack closure due to residual stresses. Linear-elastic fracture mechanics proved to be sufficient to predict the behavior of long cracks in this case.