2198-T8铝锂合金多轴疲劳性能及裂纹扩展行为

Multi-axial fatigue performance and crack expansion behavior of 2198-T8 aluminum-lithium alloy

对2198-T8铝锂合金薄壁管状试样在不同加载条件下进行了拉扭复合疲劳裂纹扩展试验。结果明,随着裂纹扩展阶段的等效应力幅降低,试样的多轴疲劳寿命升高。当应力幅比升高时,多轴疲劳寿命降低,轴向应变变大,扭向应变变小,扭向应变集中滞后于轴向应变集中。结合数字图像相关技术,拟合疲劳裂纹扩展速率模型,并采用两种临界平面模型对裂纹扩展方向进行预测,其中最大正应力平面对裂纹扩展方向的预测效果最好。随着应力幅比的升高,裂纹扩展区微观形貌由磨损形貌变为磨损与疲劳条带共存的形貌,裂纹扩展模式由II型变为I+II型,最终变为以I型为主。

The tensile and torsion fatigue crack propagation tests of thin-walled tubular specimens of 2198-T8 aluminum-lithium alloy under different loading conditions were conducted.The results show that the multi-axial fatigue life of the specimens increases with the decrease of equivalent stress amplitude in the crack propagation stage.As the stress amplitude ratio increases,the multi-axial fatigue life decreases,the axial strain increases,and the torsional strain decreases,and the torsional strain concentration lags behind the axial strain concentration.Combined with the digital image correlation(DIC)technique,the fatigue crack propagation rate model was fitted and two critical plane models were used to predict the crack propagation direction,in which the maximum normal stress plane was the best for predicting the crack propagation direction.With the increase of stress amplitude ratio,the morphology of the crack propagation area changes from wear morphology to the coexistence morphology of wear and fatigue bands,and the crack propagation mode changes from type II to type I+II,and eventually to type I dominated.