Akihiro Morimoto

Low-Cycle Fatigue Strength of Notched Low-Carbon Steel Materials

Large structures are usually constructed using the conventional low-carbon steel and often contain many kinds of discontinuous cross sections or initial defects. The fatigue cracks commonly initiate at these sites under repeated loadings. So, the estimation of low-cycle fatigue life for the notched components is one of the most important technologies for the structural metals. In this study, the low-cycle fatigue tests were carried out using the smooth round bar specimens and the notched plate ones with the stress concentation factors Kt = 2.43, 3.26 and 4.25. The strains at the notch root were measured over the fatigue tests. The materials used are the hot-rolled low-carbon steel sheets, SM400A and SM490A. On the basis of test results, the method to estimate the strain on the notched structure using Neuber method, Stowell ones and the fatigue life were considered

Studies on Relation between Low Cycle Fatigue Strength and Fatigue Crack Propagation Rate in Structural Materials.

The estimation of fatigue crack propagation rate in structural materials and the clarification of crack propagation mechanism are extremely important. In this study, a low cycle fatigue test and a fatigue crack propagation test were carried out. Then the relation between the low cycle fatigue strength and the fatigue crack propagation rate was investigated, and the factors affecting the fatigue crack propagation rate were clarified on the basis of a damage accumulation model. Consequently it was found that Youngs modulus E, the fracture ductility ef and the yield strain eN considerably affected the fatigue crack propagation rate da/dN, and the following equation involving the effective stress intensity factor range ΔKeff was proposed in order to consider the effect of material properties on the fatigue crack propagation rate. da/dN=506(ΔKeff/E)2.79/(ef√(ey))