A reexamination of plasticity-induced crack closure in fatigue crack propagation
A reexamination of plasticity-induced crack closure in fatigue crack propagation
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DOI：
10.1016/j.ijplas.2004.11.005
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发表时间：
2005-09
影响因子：
9.8
通讯作者：
Yanyao Jiang;Miaolin Feng;Fei Ding
中科院分区：
文献类型：
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作者：
Yanyao Jiang;Miaolin Feng;Fei Ding
裂纹闭合概念常用于考虑r比和过载对疲劳裂纹扩展的影响。假设当裂纹闭合时，外部载荷对裂纹构件产生的疲劳损伤可以忽略不计。目前的研究提供了一个经常使用的概念的重新评估，重点是塑性诱导的裂纹闭合。对1070钢的中心裂纹试样进行了研究。试件承受平面应力I型加载。采用有限元法对裂纹试件进行弹塑性应力分析。采用常用的单节点/循环解粘方案进行裂纹闭合模拟，结果表明，当扩展裂纹小于塑性区尺寸的4倍时，预测裂纹张开载荷不稳定。所采用的塑性模型对预测的开启载荷有很大影响。将弹性-完美塑性（EPP）应力-应变关系与运动硬化塑性理论结合使用时，发现预测的裂纹张开载荷与有限元网格模型的单元尺寸密切相关。当R=0时，当有限元尺寸变得很细时，预测裂纹张开载荷大大减小。采用双线性（BL）应力-应变关系的运动硬化规律预测裂纹闭合，对元件尺寸的依赖较小。当采用最近开发的循环塑性模型时，单元尺寸对预测裂纹张开水平的影响不显著。虽然裂纹可能会闭合，但研究表明，裂纹尖端附近的材料仍存在循环塑性。当裂纹闭合时，循环塑性降低，但不可忽略。传统方法在疲劳裂纹扩展预测中可能高估了裂纹闭合的作用。
The crack closure concept is often used to consider the R-ratio and overload effects on fatigue crack growth. The presumption is that when the crack is closed, the external load produces negligible fatigue damage in the cracked component. The current investigation provides a reassessment of the frequently used concept with an emphasis on the plasticity-induced crack closure. A center cracked specimen made of 1070 steel was investigated. The specimen was subjected to plane-stress mode I loading. An elastic–plastic stress analysis was conducted for the cracked specimens using the finite element method. By applying the commonly used one-node-per-cycle debonding scheme for the crack closure simulations, it was shown that the predicted crack opening load did not stabilize when the extended crack was less than four times of the plastic zone size. The predicted opening load was strongly influenced by the plasticity model used. When the elastic–perfectly plastic (EPP) stress–strain relationship was used together with the kinematic hardening plasticity theory, the predicted crack opening load was found to be critically dependent on the element size of the finite element mesh model. For R=0, the predicted crack opening load was greatly reduced when the finite element size became very fine. The kinematic hardening rule with the bilinear (BL) stress–strain relationship predicted crack closure with less dependence on the element size. When a recently developed cyclic plasticity model was used, the element size effect on the predicted crack opening level was insignificant. While crack closure may occur, it was demonstrated that cyclic plasticity persisted in the material near the crack tip. The cyclic plasticity was reduced but not negligible when the crack was closed. The traditional approaches may have overestimated the effect of crack closure in fatigue crack growth predictions.