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| The model of VHCF crack propagation for high strength steel |
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Abstract When fatigue life is beyond 106, the Wöhler S-N curve was always considered to be asymptotic in horizontal axis, but the fatigue behaviour over 106 cycles can not be neglected. Carburized process hardens surface of structure parts in order to improve wear and fatigue resistance. A piezoelectric gigacycle fatigue machine is employed to the tests in VHCF regime with 20KHz frequency and at stress ratio R=0.1, room temperature. The effects of heat and Carburized treatment on VHCF fatigue strength are investigated by test method. The infrared camera is applied to study the energy dissipation during the tests after calibration by blackbody. The cycle of crack initiation can be determined by the temperature increasing within several cycles near end of test. Through Scanning Electron Microscopy (SEM) analysis, the mainly parameters have been obtained to model the crack propagation (CP) based on Paris law, which permits estimating energy dissipation whose power and position are variable with crack propagation. The temperature distribution and evolution of specimen surface can be calculated by the numerical method FEM. The comparison of test and simulation results shows that the model is good agreement with test in the period of crack propagation.
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Received: 29 December 2009
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2011, Vol. 32 
