In this study, the crack initiation tests under cyclic bending load with large deformation were conducted for carbon steel (JIS SM490C) and aluminum alloy (JIS A5083P-H321) ,where each specimen had a rectangular plate shape. In addition, for SM490C, specimens with stiffener welded joint were also tested. The following results are obtained.
1) In case of that the initial compression displacement range and the cyclic displacement range are equivalent, there is a linear relationship in logarithmic scales between the initial compression displacement range and the number of cycles to crack initiation and, between the initial compression displacement range and the number of cycles to failure.
2) On the surface of the compressive side, the number of cycles to crack initiation is apparently less than that on the tension side surface, in other words, the life on the compression side is obviously shorter compared to that on the tensile side.
3) For the specimens of SM490C with stiffener welded joint, the number of cycles to failure relating to the life is approximately 0.5 to 0.3 times that of smooth specimens of the base metal, that is, in the case with stiffener welded joint, the life apparently becomes shorter.
4) The superior static strength of SM490C to A5083P-H321 leads to the crack resistance of SM490C with smooth specimen being approximately 4 to 10 times stronger in the number of cycles to failure than that of A5083P-H321 under cyclic large bending load.

View full abstract