Fatigue crack extension in four-point bending test for steels imitated heat affected zone

Abstract

To reduce the weight of connecting structures, welding is usually used. In the case of welding thin plates, fatigue cracks often propagate in the heat affected zone (HAZ) rather than base metals. Therefore, it is important to investigate the extension behavior of fatigue crack in HAZ of welding joint. In this study, four-point bending fatigue tests for two high strength steels, an ordinary shipbuilding steel K36A and a shipbuilding steel K36 with low carbon contents by TMCP, were carried out under the stress ratios (R) of 0.1 and 0.8. The specimen with HAZ introduced by thermal cycle simulating the temperature history of HAZ was prepared. The crack extension rate of K36A HAZ specimen is lower than that of the corresponding base metals, especially at small repeating range of stress intensity factor. For R = 0.8 tests imitating tensile residual stress, the crack extension rate much greater than that of R = 0.1.