镁合金管材的热态内压成形起皱行为分析

Analysis of wrinkling behavior in warm hydroforming of magnesium alloy tube

利用数值模拟和塑性理论分析AZ31B镁合金管材的热态内压成形过程的变形机理,找出临界起皱应力、应力状态及皱纹形状的变化规律。结果表明:随着温度升高,管材轴向抗起皱能力下降,其机理是材料的屈服强度和弹性模量随温度升高而下降;皱峰和皱谷处应力轨迹均在环向应变伸长和轴向应变压缩的区域;随着补料量的增大,皱峰处应力向壁厚减薄的方向发展,皱谷处应力向壁厚增加的方向发展;内压与材料屈服强度之比(相对压力)决定初始屈服时皱峰和皱谷处壁厚的变化情况,即温度较高时,相对压力较大,初始屈服时皱峰和皱谷处应力状态越易处于管壁呈减薄趋势的区域;当温度较低时,相对压力较小,初始屈服的皱峰和皱谷处的应力状态越易处于管壁有增厚趋势的区域;随着温度升高,相同加载路径下皱纹的高度和波长增大,皱纹趋向于向中间移动,且波数减少。

The deformation mechanism was analyzed for an AZ31B magnesium alloy tube in warm hydroforming process by numerical simulation and plasticity theory.The critical wrinkling stress,the stress state and the shape of the wrinkles were obtained.It is shown that the yielding strength and the elastic modulus decrease as the temperature rises,which makes the anti-winkling ability of the tube decrease.The stress loci lie at the zone where the circumstantial strain elongates and axial strain is compressive for both the top zone and the bottom zone of the wrinkles wave.The stress at the top zone of the wrinkles wave tends to make the wall thickness thin as the feeding increases.The stress at the bottom zone of the wrinkles wave tends to make the wall thickness thicken.The ratio of the internal pressure to the yielding strength （relative pressure） determines the variation of the wall thickness.If the forming temperature is higher,the relative pressure is greater,which makes the thinning trend of the wall thickness easier at the initial yielding time.If the forming temperature is lower,the relative pressure is smaller,which makes the thickening trend of the wall thickness easier at the initial yielding time.The height and length of the wrinkles wave get larger for the same loading path as the temperature rises.The wrinkles tend to move towards the middle part.The wrinkles wave number decreases.