Near-threshold fatigue crack growth behavior of 2195 aluminum-lithium-alloy—prediction of crack propagation direction and influence of stress ratio
Near-threshold fatigue crack growth behavior of 2195 aluminum-lithium-alloy—prediction of crack propagation direction and influence of stress ratio
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DOI：
10.1007/s11661-000-0164-5
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发表时间：
2000-06
期刊：
影响因子：
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通讯作者：
D. Chen;M. Chaturvedi
中科院分区：
文献类型：
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作者：
D. Chen;M. Chaturvedi
研究了2195-T8铝锂合金在不同应力比下的拉伸性能和疲劳裂纹扩展行为，重点研究了它们与试件取向的关系。测试了与轧制方向成0、15、30、45和90°的试件。该合金具有较强的黄铜型织构和大量的T1(Al2CuLi)相的片状析出物分布在{111}基体面上。拉伸强度和疲劳门槛值都强烈依赖于试件的取向，在与轧制方向成45°的方向上观察到最低值。应力比对疲劳门槛值的影响一般可以用修正的裂纹闭合概念来解释。该合金的疲劳裂纹扩展表现出明显的结晶裂纹，尤其是宏观裂纹偏转。L-T+45°方向的试件偏转角度最小，L-T和T-L方向的试件偏转角度较大。通过考虑由裂纹偏转引起的I型和II型值计算的等效疲劳门槛值，可以合理地解释疲劳门槛值与试件取向的关系。基于施密德定律和特定的晶体织构，提出了预测疲劳裂纹偏转角的四步法。理论预测与实验结果吻合较好。
Tensile properties and fatigue crack propagation behavior of a 2195-T8 Al-Li alloy were investigated at different stress ratios, with particular emphasis on their dependence on specimen orientation. Specimens with orientations of 0, 15, 30, 45, and 90 deg to the rolling direction were tested. The alloy contained a strong brass-type texture and a profuse distribution of platelike precipitates ofT1(Al2CuLi) phase on {111} matrix planes. Both tensile strength and fatigue thresholds were found to be strongly dependent on the specimen orientation, with the lowest values observed along the direction at 45 deg to the rolling direction. The effect of stress ratio on fatigue threshold could generally be explained by a modified crack closure concept. The growth of fatigue crack in this alloy was found to exhibit a significant crystallographic cracking and especially macroscopic crack deflection. The specimens oriented in the L-T + 45 deg had the smallest deflection angle, while the specimens in the L-T and T-L orientations exhibited a large deflection angle. The dependence of the fatigue threshold on the specimen orientation could be rationalized by considering an equivalent fatigue threshold calculated from both mode I and mode II values due to the crack deflection. A four-step approach on the basis of Schmid’s law combined with specific crystallographic textures is proposed to predict the fatigue crack deflection angle. Good agreement between the theoretical prediction and experimental results was observed.