LY12CZ铝合金的疲劳门槛值及宽范围裂纹扩展速率的研究

Investigation of threshold and wide range fatigue crack propagation rates in LY12CZ alloy

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 thresholds and wide range fatigue crack propagation rates in an aluminum alloy,LY12CZ sheet,at three stress ratio(R=0 5,0 and -1) by load decreasing,load increasing and constant load amplitude test procedures were measured The results show that,(1)the da/dN ΔK curves at each stress ratio showed three transitions and these transitions tend to occur at nearly the same crack growth rate for all R ratios tested,(2)the stress ratio against the crack gowth rate relation show a strong correlation,(3)crack closure was found to be the major factor in causing the correlation of stress ratio with crack growth rate The crack opening stress calculated from the closure model was able to correlate fatigue crack growth rate against the effective stress intensity factor range data quite well over a wide range in rates at three stress ratio(R=-1,0 and 0 5) in the LY12CZ alloy