复合加载工况下PA66的屈服行为研究

Yield Behavior of PA66 Under Combined Loading

利用万能试验机对PA66进行3种应变率加载的单轴压缩、单轴拉伸和复合拉剪的准静态实验。研究表明,各种工况下PA66的屈服行为和硬化行为均表现出明显的应变率敏感性。利用改进的拉剪试样,引入5种不同角度的斜槽(30°,40°,45°,60°,75°),通过对PA66正、剪应力分量的分析可知,随着斜槽角度的增加,拉剪试样的正应力分量逐渐增大,而剪应力分量则逐渐减小。通过对比3种考虑材料静水压相关性和拉压强度不对称性的屈服准则,确定了描述PA66屈服行为的理论模型,并利用材料不同的应变率的实验屈服轨迹对相应应变率的屈服函数进行验证,提出的改进拉剪试样所得实验屈服轨迹与理论屈服函数吻合得很好,进一步验证了复合拉剪测试方法的可靠性。

Compression,tensile and combined tension/shear tests were performed on PA66 at different strain rates by using a universal material testing.The study shows a marked strain rate sensitivity of the yield and hardening behaviors under different loading on PA66.A modified shear-tension specimen(STS)with the material axis inclining to the loading direction at different angles(30°,40°,45°,60°,75°)was presented.The shear stress and normal stress of modified STS were investigated,which indicated that the stress component changes with the angle.Furthermore,by comparing the three yield criteria in present research with experimental yield surface for different stress states,the yield criterion that can describe the asymmetric yield strength of tension and compression and the hydrostatic pressure dependency of PA66 was established.In addition,the yield strength for different strain rates was predicted and the availability was verified by comparing the predicted value under different loading.The experimental yield of PA66 obtained by the shear-tension test method proposed in the present paper agrees well with the theoretical model,which indicates the reliability of the test method.