Research On Anisotropic Multiaxial Fatigue Life Prediction And Fatigue Behavior Of Deformed Magnesium Alloys

Energy shortage and resource depletion are the urgent problems facing the world at present.Energy saving and emission reduction have become the trend of The Times,and the lightweight requirements of materials are more stringent.Magnesium,as the lightest metal structural material,has been widely concerned for its excellent specific strength.Fatigue resistance design is the key to structural component design,and the anisotropic mechanical behavior of deformed magnesium alloys has direct influence on its fatigue properties.Based on the typical model,the fatigue life prediction problem and the influence of anisotropy on fatigue performance under non-proportional loading are studied.The typical models,such as Mises equivalent strain model,GSA model,FS model,MKBM model,Chen-Xu model and SDG model,were used to evaluate the fatigue life under proportional and non-proportional loading,respectively.It is found that the SDG model has a large error in predicting fatigue life under non-proportional loading.Therefore,the equivalent stress correction coefficient is proposed and embedded in the SDG model,and the accuracy of the modified model(M-SDG)is verified by using the fatigue data of seven materials.The M-SDG model does not include this part of the additional strengthening effect,which will appear in the non-proportional loading of magnesium alloy.Therefore,the nonproportional factor is introduced to characterize the additional strengthening effect.In this paper,a new method for calculating non-scaling factors is proposed,and compared with the non-scaling factors defined by Itoh and the modified Itoh non-scaling factors,it is found that the model containing the new non-scaling factors in this paper has higher accuracy.Combined with the new non-scale factors,a new MM-SDG model was proposed by combining the critical surface method with the energy method.The accuracy of the model was verified by using AZ31 and AZ61 magnesium alloys with additional strengthening effect and BT1-0 titanium alloy without additional strengthening effect.Considering the anisotropy factors,the relationship between the fatigue properties and material orientation under the control of stress and strain was analyzed,and the accuracy of the MM-SDG model was verified by the fatigue data of squeezed ZK60 and rolled AZ31 magnesium alloys.Since the triaxial loading fatigue experiment has not been reported,only the biaxial loading fatigue experiment data is used to verify the MM-SDG model.For more complex triaxial loading conditions,the fatigue performance under triaxial loading was analyzed by finite element software,and the accuracy of MM-SDG model was verified by the results of triaxial fatigue simulation.