疲劳裂纹扩展模型中表征裂纹闭合水平参数的确定

Determination of the Parameter Reflecting Crack Closure Development in the Fatigue Crack Propagation Model

借助7075-T 6铝合金、6013铝合金以及0.45w t%碳钢的疲劳试验数据,结合上述材料的力学性能参数,通过非线性最小平方拟合方法,研究了表征裂纹闭合水平参数k对疲劳裂纹扩展率的影响。研究结果表明,对于宏观裂纹范围内的疲劳裂纹扩展,参数k只要大于某个值就对疲劳裂纹扩展率无影响;而对于小裂纹阶段的疲劳裂纹扩展,参数k对疲劳裂纹扩展率的影响较明显,因此参数k的大小主要取决于小裂纹扩展数据。依据0.45w t%碳钢疲劳试验数据,相应参数k的建议值为6 000m-1。

The fatigue crack propagation model with nine parameters proposed by authors can not only account for the effects of initial crack size and load sequence, but also explain various other phenomena of metal fatigue observed in tests. The model would be of great applicability. The parameters in the model can be determined through fitting the experimental data. The effect of the parameter reflecting crack closure development on the fatigue crack growth rate is studied in this paper through the nonlinear least squares fitting method. Results show that for macroscopic cracks the parameter reflecting crack closure development has little effect on the fatigue crack growth rate if the parameter exceeds a certain value. However, when the fatigue crack propagation is in the short crack region, the parameter has obvious effect on the fatigue crack growth rate. Hence, the value of the parameter reflecting crack closure development is mainly determined by the short crack experimental data. According to the fatigue experimental data of 0.45wt% carbon steel, the value of 6000m^-1 is recommended for the corresponding parameter reflecting crack closure development.