Safe Fatigue Life Prediction Of SPR-bonded Hybrid Connection Joints With Metallic Sandwich Structures

SPR is a new sheet-material connection technique used for joining new light alloy such as aluminum,which meets the concept of green manufacturing.The connectors are commonly used in automobile manufacturing,aerospace and other relevant fields.As a new light alloy material,aluminum alloy is widely used in modern industry because of its high strength and low density.In practice applications,sandwich structure has been applied wider because it can effectively improve the mechanical properties of joints such as damping,energy absorption and insulation.Foam metal is a commonly used pore structure sandwich which will bring the parts and engineering subjects better mechanical,acoustic performance and safety advantages when it was used as a sandwich structure.Adhesive bonding is also an effective and common connection method to improve the static strength of SPR joints.In this paper,SPR and SPR-bonding hybrid connection technology are used to join sandwich sheet material with metallic foam.The forming quality,statics and fatigue properties of joints are investigated.Meanwhile,the influences of metallic foam and bond line are also researched.Based on the fatigue theory of small mechanical parts,this paper creatively predicts the safe fatigue life of SPR joints,introducing the parameters of data survival rate and confidence coefficient into the terminal prediction formula,and the p-S-N curves are plotted.The main work of this paper is summarized as follows:(1)Feasibility tests and forming analysis are carried out to explore the optimal riveting parameters of joints.The interaction and deformation between rivets and sheets are analyzed.The optimal riveting parameters of SPR are explored for batch riveting,and the forming quality was evaluated by observing the meridian of joint,and then the effect of metallic foam interlayers and bond line on the forming quality was analyzed.(2)Static tests are carried out so that the shear and stripping resistance of the joints can be tested by single lap and cross lap joints respectively.Obtaining the F-N curves of each group of joints,the failure process,peak load,maximum failure displacement and energy absorption are investigated,which affect the failure modes of joints.The accuracy of the results is verified by SEM and EDS scanning.(3)Fatigue tests are carried out to analysis the failure process and failure modes,and the results of fatigue data are processed by statistical methods,that can be verified by scanning electron microscopy and energy dispersive spectrum analysis.The fatigue lives of the joints are predicted by linear fitting,polynomial fitting and three-parameter fitting.Based on the fatigue theory of mechanical small parts,the formula for calculating the safe fatigue life of SPR is explored,and this formula is appropriate for small sample data.In order to obtain a more accurate result,the confidence coefficient and data survival rate are introduced into the prediction formula.