An analytical investigation on fatigue behavior of carbon steel materials subjected to rotating bending loads

An analytical model used to evaluate fatigue behavior of carbon steel materials subjected to rotating bending loads is presented in the paper. The application of the analytical model is aimed at estimating lives of initial crack formation and subsequent crack propagation so that the whole fatigue lives and fatigue crack growth behavior of the investigated carbon steel material can be identified. The lives of initial crack formation are analytically determined according to the value of locally total strain ranges at the critical part of the material. The other lives required by the initial crack to subsequently propagate to its critical size are estimated by utilizing a relationship of stress intensity ranges in the vicinity of the propagating crack tip and crack growth rates as formulated by Paris. The material analyzed is represented by a V-notched round bar sample and it is made of a carbon steel material, which is normally used for the design of transmission shafts, axles, crankshafts, etc. In order to assess the accuracy of the analytical model used, fatigue tests on a number of the same sample design of specimens were carried out under the test loads of rotating bending. The test loads cause the V-notch tip of the tested specimens to be affected by completely reversed stresses with a stress ratio R = -1 and test results obtained are used to verify the analytical-predicted ones. In the paper, the verification of the analytical-predicted results is presented in the form of comparing analytical and experimental behavior of fatigue life (S-N diagrams) and fatigue crack growth (a-N curves). The comparison indicates that the results of the analytical model are very close to the ones of the experimental approach.