This paper presents a damaging stress intensity function ΔK_d for analyzing R-ratio effects on fatigue crack growth (FCG) in metallic materials under constant amplitude loading. The proposed formulation is based on the sum of strain and complementary energy and its role in FCG rate behavior in threshold and Paris region at R-ratios ranging from −2 to 0.97. It doesn’t invoke a crack closure assumption or fitting parameters for R < 0.6. For a high R > 0.7 it utilizes an experimentally determine correction factor, which accounts for the excessive forward plastic zone (FPZ) size and its role on FCG process.

中文翻译：

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用于分析金属材料中 FCG 和 R 比的破坏函数 ΔKd

本文提出了一种破坏性应力强度函数 ΔK _{d ，}用于分析 R 比对恒幅载荷下金属材料疲劳裂纹扩展 (FCG) 的影响。所提出的公式基于应变和互补能的总和及其在阈值和巴黎区域的 FCG 速率行为中的作用，R 比范围为 -2 到 0.97。对于 R < 0.6，它不会调用裂纹闭合假设或拟合参数。对于高 R > 0.7，它利用实验确定的校正因子，该因子解释了过度的前向塑性区 (FPZ) 尺寸及其在 FCG 过程中的作用。