Fea Fatigue Life Prediction Of Shock Tower Structure Made Of Magnesium Alloys

As an important lightweight material of automobile,magnesium alloy has many advantages such as small density,high specific strength,good thermal conductivity,good performance of absorbing shock and vibration,etc.When magnesium alloy is applied to automobile structure,the most concern is its fatigue life.In order to predict the fatigue life of shock tower structure made of magnesium alloy,stress based fatigue life prediction method is used in this paper to establish three stress-fatigue life(SN)curve based on Von Mises stress,maximum principal stress and structural stress respectively,and by comparing the predicted life of three SN curve with the experimental results,a kind of fatigue life prediction method suitable for this structure jointed by SPR is determined.According to the E466-07 standard of American Society for Testing and Materials(ASTM),the fatigue experiments for five sets of Lap-Shear with single SPR are carried out and the relationship between load and fatigue life is obtained.Then,finite element model of Lap-Shear structures with single SPR based on TIE CONTACT are established and static simulation analysises are carried out to get the unit Von Mises stress and unit maximum principal stress,which are then taken into the fatigue experiment results of Lap-Shear,respectively,getting the relationship between Von Mises stress?maximum principal stress and fatigue life.In addition,finite element model of Lap-Shear structures with single SPR based on ACM(Area Contact Method)are established and Designlife module of nCode is used to obtain the unit structural stress,which are then taken into the fatigue experiment results of Lap-Shear,getting the relationship between structural stress and fatigue life.Then,based on the relationship between the above three stresses and fatigue life,the SN curves based on Von Mises stress,maximum principal stress and structural stress are established in logarithmic coordinates separately.Fatigue tests are carried out for shock tower structure made of magnesium alloy and the fatigue life values of 7 samples are obtained,and also the failure position of the structure is analyzed.Then,the finite element model of shock tower structure made of magnesium alloy is established,and the problems of bolt connection and surface contact optimization during simulation analysis are solved.Then,the finite element analysis of the model is carried out,and Von Mises stress and maximum principal stress at the fatigue failure position are obtained respectively.In addition,the model is analyzed by the Designlife module of nCode,and the structural stress at the fatigue failure position is acquired.Then,respectively,put Von Mises stress,maximum principal stress and structural stress at the fatigue failure locationr into above corresponding three kinds of SN curve,and predicted fatigue life of shock tower structure made of magnesium alloy are obtained based on Von Mises stress,maximum principal stress and structural stress respectively.Then,the predicted fatigue life of three methods are compared respectively with experimental result,and it reveals that the predicted fatigue life based on structural stress is more close to the experimental result than other two predicted fatigue life.Additionally,the difference and the pros and cons for above three stress based fatigue life prediction method are analysed,and the validity is verified for the use of structural stress based fatigue life prediction method to predict fatigue life for shock tower structure made of magnesium alloy.