Behavior of long fatigue cracks in cellular box beam

The propagation of long cracks under constant-amplitude cyclic loading is s tudied in complex welded box beams made of high-strength low-alloy steel. T he 8 X 1 X 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 appli cable to other box systems such as bridges. These experiments were designed to evaluate the residual fatigue life after a significant fatigue crack ha s formed. After testing, residual stresses were measured on two box beams u sing the standardized strain-gauge hole-drilling method. The experiment res ults demonstrated the good crack tolerance of cellular structures. The resi dual life of a box beam (after a welded detail has failed) was significant. The crack-driving force was evaluated using finite-element modeling. Reaso nable correlation between these large-scale tests and the fatigue crack gro wth rate from small compact specimens was obtained only with models that in cluded the effects of crack closure due to residual stresses. Linear-elasti c fracture mechanics proved to be sufficient to predict the behavior of lon g cracks in this case.