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用降载、升载和恒幅试验程序测定了LY12CZ铝合金板材在三种应力比 (R =0 . 5,0和 - 1)下的疲劳门槛值及宽范围的裂纹扩展速率。研究结果表明 ,三种应力比的da/dN ΔK曲线上所出现的相同转变点与微观扩展机制、裂纹表面的形貌和材料本身特性有关 ;裂纹闭合效应是引起应力比相关性的重要机制 ;用裂纹闭合模型计算的裂纹张开应力相当好地关联了在宽范围速率 (da/dN =10 8～ 10 2 mm/cycle)内的三种应力比的da/dN与有效应力强度因子范围ΔKeff的关系。
The fatigue threshold and the wide range of crack growth rate of LY12CZ aluminum alloy sheet under three stress ratios (R = 0.5, 0 and -1) were measured by the procedures of unloading, lifting and constant amplitude. The results show that the same transition points on the da / dN ΔK curves of the three stress ratios are related to the microscopic extension mechanism, the morphology of the crack surface and the properties of the material itself. The crack closure effect is an important mechanism that causes the stress ratio to be correlated. The crack opening stress calculated with the crack closure model is fairly well correlated with the da / dN of the three stress ratios over a wide range of rates (da / dN = 10 8 to 10 2 mm / cycle) and the effective stress intensity factor range ΔKeff Relationship.