INFLUENCE OF LOADING PROFILE AND SUPERIMPOSED FLUTTER LOAD FREQUENCY ON THE FRACTURE-BEHAVIOR OF A SUBMARINE HULL STEEL IN SEAWATER

Fracture surface examination is a useful approach in gaining an unders tanding of the fracture behaviour of materials. In this study the frac ture surfaces of submarine hull steel specimens, which failed by corro sion fatigue in seawater, were examined in order to determine the micr omechanics of the fracture process. Results show that the early stage of crack advance, corresponding to an approximate zone of 0.5 mm from crack initiation, was environment-controlled and independent of the lo ading profile and superimposed flutter load frequencies. Beyond this z one the influence of loading profile and superimposed flutter load fre quency on the fracture morphology was clearly in evidence. The changes in the fracture morphology are described. The combinations of loading profile and superimposed flutter load frequency which influenced the cracking behaviour are identified. The influence of cracking modes on the overall fatigue life is also discussed.