平均载荷及载荷幅值对工业纯钛双轴保载疲劳行为影响

Effects of mean load and load amplitude on biaxial dwell fatigue behavior of commercial pure titanium

通过室温双轴保载疲劳试验,研究了不同平均载荷及载荷幅值对工业纯钛双轴保载疲劳行为的影响。结果表明,在相同保载时间下,平均应变及应变速率随着平均载荷和载荷幅值的升高而逐渐增大。当载荷幅值一定时,蠕变应变随着平均载荷的增大而增大,当平均载荷一定时,蠕变应变随着载荷幅值的增大反而减小。分析双轴棘轮与蠕变应变之间交互作用时,发现两者始终相互制约。断口分析表明,随着平均载荷和载荷幅值的增大,疲劳条带特征逐渐消失,韧窝及撕裂棱数量显著增加,断口呈现韧性失效特征。随着平均载荷或载荷幅值的增加,等效应变幅值增加,疲劳寿命逐渐降低。与平均载荷的影响相比,疲劳寿命对载荷幅值的变化更加敏感。分别利用最大主应变、最大剪应变、Mises等效应变、最大主应力及SWT模型进行双轴保载疲劳寿命预测,其中SWT模型预测精度最高。

Based on biaxial dwell fatigue tests at room temperature,effects of different mean loads and load amplitudes on the biaxial dwell fatigue behavior of commercial pure titanium were studied.The results show that the mean strain and strain rate increase with the increase of mean load and load amplitude under the same dwell time.When the load amplitude remains constant,the creep strain increases with the increase of the mean load.However,when the mean load remains constant,the creep strain decreases with the increase of the load amplitude.By analyzing the interaction between biaxial ratcheting and creep strain,it is found that ratcheting strain and creep strain are always restricted by each other.Fracture surface analysis shows that with the increase of mean load and load amplitude,the fatigue strip characteristics disappear gradually,and the number of dimples and tearing ridges significantly increases,exhibiting ductile failure mode.Meanwhile,with the increase of mean load or load amplitude,equivalent strain amplitude is increased,leading to the decrease of fatigue life.Compared with the effect of mean load,fatigue life is more sensitive to the variation of load amplitude.Maximum principal strain,maximum shear strain,Mises equivalent strain,maximum principal stress and SWT models are used to perform biaxial dwell fatigue life prediction,among them SWT model has the highest prediction accuracy.