相位角加载条件下2A12铝合金多轴疲劳失效行为

采用SDN100/1000电液伺服拉扭复合疲劳试验机对2A12铝合金进行不同相位角加载条件下多轴疲劳试验研究,通过加载循环曲线和微观断口形貌分析失效机理,对不同损伤累积模型的预测效果进行评价,修正Manson损伤曲线模型以期达到更好的预测效果。结果表明:单级加载条件下,随相位角正弦值的增加疲劳寿命线性递减,当相位角为0°时,轴向硬化、软化交替出现,切向出现循环硬化,90°加载下轴向和切向单独作用效果明显;两级累积路径下,随一级加载周次的增加多轴疲劳寿命延长,0°加载阶段轴向和切向都出现循环硬化现象,两种路径下断口都呈现出多裂纹源特征,在裂纹源区附近观察到台阶状形貌,扩展区存在大量划痕和鳞片状花样;修正后的Manson损伤曲线模型预测误差均在15%以内。

Failure Behavior of Multiaxial Fatigue for 2A12 Aluminum Alloy Subjected to Different Phase Angle Loading Conditions

The multiaxial fatigue behavior of 2A12 aluminum alloy was studied via SDN100/1000 electro-hydraulic servo tension-torsion fatigue tester under different phase angles and the failure mechanism was analysed by cyclic curve of loading and microscopic morphology. The miner model, Manson damage curve model and toughness degradation model were used to evaluate the accuracy of fatigue life prediction, and the Manson damage model would be revised in order to improve the prediction accuracy. The results show that:under the one-stage loading, the fatigue life decreases approximately linear with the increasing of the sine of phase angle. For the phase angle 0°, hardening and softening appear alternately in the axial direction, cyclic hardening shows in torsional direction. The effect of action in axial and torsional direction is significant for the 90° phase angle. The fatigue life prolongs with the cycle of first stage loading increases under the two stage cumulative paths. The hardening appears in axial and torsional directions for the 0° loading, and the multi-crack initiation morphology is observed under the two cumulative paths. The stepped pattern can be detected near the crack initial region, as well as the scratch and scale pattern in the crack extension zone. A prediction error of lower than 15% was achieved for the modified Manson damage curve model.