| Summary: | 博士 === 中原大學 === 機械工程研究所 === 89 ===
Under cyclic loading condition, the fatigue crack growth rate governed by range of stress intensity factor and stress ratio is well known. Paris’ law, Forman’s equation and Elber’s equation are all the typical formula of this type. However, the effects of loading frequency and temperature on fatigue crack growth rate have also play an important role from many of experimental test. Although, the power law relationship has been used to characterize the effect of loading frequency on fatigue crack growth rate, and thermal activated process has also been used to interpret the effect due to temperature, but, it fail to using a single value of activation energy for lower and higher range of stress intensity factor. James had performed a lot of experiments, through the data regression analysis, an evaluation equation is suggested. In the present study, the mechanical behavior of material is successfully introduced to illustrate the combined effect of loading frequency and temperature on fatigue crack growth rate. By defined dimensionless yielding stress function and dimensionless Young’s modulus, A new FCG rate model that considers the effect of loading frequency and temperature on fatigue crack growth rate for wide-range of temperature and loading frequency has been proposed. By modifying the modified Forman’s equation which was used in the NASGRO and NASGRO 2.0 programs, the effect of loading frequency and temperature can then be taken into account. By comparing with the experimental data and James model, except some of susceptible data, the proposed model shows a good agreement with the experimental results and only a very small difference from James’ predicted value.
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