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本文总结了 LY12CZ 铝合金板材在不同应力比 R 下的疲劳裂纹扩展速率、尤其是近门槛区的裂纹扩展速率 da/dN 和裂纹扩展门槛值⊿K_(th)的实验结果,并应用根据裂纹扩展的静态断裂模型导出的公式,对 LY12CZ 这样的疲劳裂纹以典型条带机制扩展的合金中的裂纹扩展,进行定量分析。实验和分析结果表明,在 R=0～0. 5和 da/dN<1. 0×10~(-3) mm/cycle 的范围内,根据裂纹扩展的静态断裂模型导出的公式:da/dN=B(⊿K-⊿K_(th))~2,能很好地拟合 LY12CZ 板材的裂纹扩展的实验结果;式中 B 值可按下式估算:B=1/2π(0. 1E)~2,⊿K_(th)之值可根据裂纹扩展的实验数据进行回归分析求得。在应力比 R=0～0. 5的范围内,⊿K_(th)=9. 3(1-R)~(0. 933) ,da/dN=3. 18×10~(-7) (⊿K-9. 3(1-R)~(0. 933) )~2。
This paper summarizes the fatigue crack growth rate of LY12CZ aluminum alloy sheet under different stress ratios R, especially the experimental results of crack growth rate da / dN and crack propagation threshold ⊿K th (th) near the threshold area, Static fracture model derived from the formula, fatigue crack LY12CZ such as the typical strip mechanism to expand the crack propagation in the alloy for quantitative analysis. The experimental and analytical results show that in the range of R = 0 ~ 0.5 and da / dN <1.0 × 10 ~ (-3) mm / cycle, the formula derived from the static fracture model of crack propagation: da / dN = B (⊿K-⊿K_ (th)) ~ 2, which can well fit the experimental results of crack propagation in LY12CZ sheet. The value of B can be estimated as follows: B = 1 / 2π ~ 2, ⊿K_ (th) values can be obtained by regression analysis based on experimental data of crack propagation. In the range of stress ratio R = 0 ~ 0.5, ⊿K th = 9.3 (1-R) ~ (0.933), da / dN = 3.18 × 10 -7 ⊿K-9. 3 (1-R) ~ (0. 933)) ~ 2.