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研究裂纹端部三维应力约束、塑性约束和位移约束等对谱载疲劳裂纹扩展的影响。用适于三维应力状态的修正条带屈服模型 ( Modified Strip Yield Model)计算与裂纹扩展有关的三维约束因子。利用所得约束因子的理论解改进 NASA多年来发展的 FASTRAN-II寿命预测软件 ,使其避免了依赖经验确定的约束因子进行寿命预测的局限 ,仅利用一组常幅疲劳裂纹扩展数据和材料的常规机械性能便可预测飞机谱载下的裂纹扩展寿命。对多种谱型、应力水平、过载比和材料的组合情况进行了分析 ,预测寿命与试验结果吻合很好 ,证明本文方法和改进软件可以用于实际结构的寿命预测
The effects of three-dimensional stress, plasticity and displacement constraints at crack tip on fatigue crack growth under spectral loading are studied. The three-dimensional constraint factors associated with crack propagation are calculated using a Modified Strip Yield Model suitable for three-dimensional stress conditions. The theoretical solution of the resulting constraint factor is used to improve NASA’s FASTRAN-II life prediction software, which has been developed over the years, avoiding the limitations of life prediction relying on empirically determined constraints and using only a set of conventional fatigue crack growth data and material conventions The mechanical properties predict the crack propagation life under aircraft spectra. The analysis of multiple spectral types, stress levels, overload ratios and combinations of materials shows that the predicted life expectancy is in good agreement with the experimental results, which proves that the proposed method and the improved software can be used to predict the life expectancy of the actual structure