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=10-8～10-2mm/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.
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