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本文进行了7475-T7351铝合金板材中心开裂试样恒幅加载宽范围应力比下的疲劳裂纹扩展试验。考虑到裂纹张开应力的确定是基于裂纹闭合概念进行裂纹扩展寿命预测的基础,且在工程应用中需要方便地确定有效应力强度因子变程△K_(ett)。本文通过疲劳裂纹扩展速率da/dN的试验数据导出了所研究材料的裂纹张开应力的经验表达式,进而用有效应力强度因子变程△K_(ett)来联系试验数据,得到对于不同应力比下裂纹扩展行为的统一描述。试验发现,无量纲裂纹张开应力S_(op)/S_(max)随所加最大毛应力水平的提高而降低。 断口分析表明,对于所试验的材料由拉伸型平断口向剪切型斜断口的转变主要受△K_(ett)控制,并注意到由拉伸型向剪切型裂纹增长的过渡对应着S_(op)/S_(max)增加的趋势。
In this paper, the fatigue crack propagation of 7475-T7351 aluminum alloy plate central cracked specimen under constant amplitude and wide range stress ratio was carried out. Considering that the determination of crack opening stress is the basis for predicting the crack propagation life based on the concept of crack closure, it is necessary to easily determine the effective stress intensity factor variation ΔK ett in engineering applications. In this paper, the experimental data of fatigue crack growth rate da / dN were derived and the experimental data of cracked stress of the studied materials were derived. Then the experimental data were connected with the effective stress intensity factor △ K ett, Uniform description of lower crack propagation behavior. It is found that the open stress S op (op) / S max of the dimensionless crack decreases with the increase of the maximum gross stress. Fracture analysis shows that for the tested materials, the transformation from tensile flat fracture to shear oblique fracture is mainly controlled by △ K ett and it is noted that the transition from tensile to shear-type cracks corresponds to S_ (op) / S_ (max) increases.