Modelling of crack tip behaviour was carried out for a nickel-based superalloy subjected to high temperature fatigue in a vacuum and air. In a vacuum, crack growth was entirely due to mechanical deformation and thus it was sufficient to use accumulated plastic strain as a criterion. To study the strong effect of oxidation in air, a diffusion-based approach was applied to investigate the full interaction between fatigue and oxygen penetration at a crack tip. Penetration of oxygen into the crack tip induced a local compressive stress due to dilatation effect. An increase in stress intensity factor range or dwell times imposed at peak loads resulted in enhanced accumulation of oxygen at the crack tip. A crack growth criterion based on accumulated levels of oxygen and plastic strain at the crack tip was subsequently developed to predict the crack growth rate under fatigue-oxidation conditions. The predicted crack-growth behaviour compared well with experimental results.

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一种基于扩散的疲劳氧化条件下裂纹尖端行为建模方法

对在真空和空气中经受高温疲劳的镍基高温合金进行裂纹尖端行为建模。在真空中，裂纹扩展完全是由于机械变形，因此使用累积塑性应变作为标准就足够了。为了研究空气中氧化的强烈影响，采用基于扩散的方法来研究裂纹尖端疲劳和氧气渗透之间的全面相互作用。由于膨胀效应，氧气渗入裂纹尖端引起局部压应力。在峰值载荷下施加的应力强度因子范围或停留时间的增加导致氧在裂纹尖端的积累增强。随后开发了基于裂纹尖端氧和塑性应变累积水平的裂纹扩展准则，以预测疲劳氧化条件下的裂纹扩展速率。预测的裂纹扩展行为与实验结果比较良好。