Abstract Decomposition of the resistance to fatigue crack growth into the intrinsic and extrinsic component is very important for understanding of fatigue failure mechanisms, relation to microstructure and modelling of residual fatigue life. Crack closure for four grades of steel were estimated by the difference between Kmax values and the effective ΔKeff values (measured at the load ratio R = 0.8) corresponding to the same crack growth rate. The results showed that crack closure values obtained by the difference Kmax – ΔKeff were not in agreement with the available crack closure models, both the Newman’s model of plasticity-induced closure and the results from finite element analysis. The discrepancies could not be explained by the effect of mean stress, specimen thickness, loading amplitude or T-stress. Therefore, the application of fracture mechanics to fatigue cracks should be revisited. It was pointed out that ΔKeff may not be a good parameter for quantification of the crack driving force, since the relationship between Kmax – Kcl and the cyclic plastic deformation at the crack tip might not be linear.

中文翻译：

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6经典确定的有效 ΔK 无法量化裂纹扩展速率

摘要 将疲劳裂纹扩展阻力分解为内在和外在分量对于理解疲劳失效机制、与微观结构的关系和残余疲劳寿命建模非常重要。通过 Kmax 值和对应于相同裂纹扩展速率的有效 ΔKeff 值（在载荷比 R = 0.8 下测量）之间的差异来估计四种钢级的裂纹闭合。结果表明，通过差异 Kmax – ΔKeff 获得的裂纹闭合值与可用的裂纹闭合模型不一致，包括 Newman 塑性诱导闭合模型和有限元分析结果。这种差异不能用平均应力、试样厚度、加载幅度或 T 应力的影响来解释。所以，应重新审视断裂力学在疲劳裂纹中的应用。有人指出，ΔKeff 可能不是量化裂纹驱动力的好参数，因为 Kmax – Kcl 与裂纹尖端的循环塑性变形之间的关系可能不是线性的。