STRESS STATE‐RELATED FATIGUE CRACK GROWTH UNDER SPECTRUM LOADING
STRESS STATE‐RELATED FATIGUE CRACK GROWTH UNDER SPECTRUM LOADING
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DOI：
10.1111/j.1460-2695.1992.tb01307.x
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发表时间：
1992-07
影响因子：
3.7
通讯作者：
G. Wang;B. Palmberg;A. Blom
中科院分区：
文献类型：
--
作者：
G. Wang;B. Palmberg;A. Blom
摘要-使用中心裂纹试样研究了2024-T3和7475-T761铝合金板的疲劳裂纹扩展行为，这些铝合金板经受标准化谱（TWIST和TWSTAFF）。一个带状裂纹闭合模型被用来解释实验数据，并作出预测的裂纹扩展。条带模型是基于Dugdale的概念，但修改，以保持塑性拉伸材料的裂纹表面，使裂纹的张开载荷可以确定，和疲劳裂纹扩展可以分析根据Elber的裂纹扩展假设。与其他同类模型不同，该模型引入了一个可变的约束因子来考虑裂纹扩展引起的裂纹尖端应力状态的渐变。结果表明，裂纹尖端应力状态的转变是引起板料疲劳裂纹扩展异常行为的原因。实验和预测都表明，由于裂纹尖端应力状态的转变，在一定的载荷范围内，裂纹在低载荷下比在高载荷下扩展得快。裂纹尖端的应力状态也有助于观察到的厚度效应的裂纹扩展在板。与实验结果一致，它已被证明，一个平面应力状态将占主导地位，在裂纹尖端的薄板相比，在厚板。平面应力状态导致更高的裂纹张开水平，这导致薄板的更长的疲劳寿命。
Abstract— The fatigue crack growth behaviour in aluminium alloy sheets of 2024-T3 and 7475-T761, subjected to standardized spectra (TWIST and FALSTAFF), was investigated using centre-cracked specimens. A strip crack closure model was used to interpret experimental data, and to make predictions for the crack growth. The strip model is based on the Dugdale concept, but modified to keep plastically-stretched materials on the crack surface so that the crack opening load can be determined, and the fatigue crack growth can be analysed according to Elber's crack growth assumption. Differing from other models of the same kind, a variable constraint factor was introduced to account for the gradual transition of stress state at the crack tip resulting from the crack growth. It has been shown that the transition of stress state at the crack tip causes the unusual behaviour of the fatigue crack growth in sheets. Both experiments and predictions show that a crack may grow faster at a low load than at a higher one in a certain applied load range due to the crack tip stress state transition. The crack tip stress state also contributes to the thickness effect observed for the crack growth in sheets. In agreement with experimental results, it has been shown that a plane stress state will prevail at the crack tip in a thin sheet compared to that in a thick sheet. The plane stress state results in a higher crack opening level which leads to a longer fatigue life for thin sheets.