Research On Self-Piercing Riveting Process And Failure Behaviors For Dissimilar Materials

Self-piercing riveting (SPR) is a high-speed mechanical fastening technique for joining sheetcomponents. It has drawn more attention in recent years because it can join some advanced materialsthat are dissimilar, coated and hard to weld. As for it plays a significant role for automotivelightweighting, its strength and durability have also been highly concerned about by the world’sfamous automotive research and development institutions.In this paper, taking self-piercing riveting which is conducted between aluminium and steelsheets as a research subject, it’s forming process, joints static strength and fatigue failure have beenstudied. Aluminium alloy (AA6111T4) and high strength low alloy (HSLA340) steel are used for thisinvestigation.For SPR joints(AA6111T4+HSLA340) process parameters research, this paper presentsexperimental data on the effects of several process variables, such as die diameter (D), die tip height(h) and rivet length (L) and other factors on the static properties of self-piercing riveted joints. Theorthogonal experimental design method has been performed to examine the relative importance ofthese variables on the static performance of the joints.Among the three process parameters investigated, the die diameter (D) is the most dominantfactor for the static strength of such joints, which is followed by rivet length (L) and die tip height (h).Studies have also shown that the Interlock length (IL) which belongs to cross-sectional profile size isa joint static strength indicator. The larger value of IL, the higher the static strength of joint would be.Based on the measurement of cross-sectional profile sizes, the paper determines reasonable formingprocess parameters.In this paper, the riveting process of dissimilar metals SPR joint and its mechanical property forthe lap shear (LP) specimen are studied numerically. At first, rivet material parameters are obtained byinverse material modeling. Then a damage model coupled with the geometrical failure criterion isintroduced into the riveting simulation. Finally, a work hardening coefficient is introduced in thesimulation of LP tests. The results of numerical simulation are satisfactory with experimental ones inthe cross-section profile, force–displacement curves and failure modes of SPR joints. The simulationresults not only contribute to the development of reasonable forminging process parameters, and alsohelp to analyse joint fatigue failure.The paper also carries out SPR lap-shear fatigue tests from two plate thickness combinations. The test results show that there are two fatigue failure modes: sheet fatigue fracture (type I failure)and rivets fatigue fracture (type II failure). Through the analysis of macro and micro joints to fracturesurface, the failure mechanism is determined. The results show that the fatigue life of the joint withtype I failure mode depends primarily on the fatigue crack growth of AA6111T4plate; It has obtaineda good effect using Forman formulas which is based on fracture mechanics model to predict joint life.Concerning type II failure mode, the rivet fatigue life depends mainly on crack initiation. In this paper,Manson-Coffin equation considering the average stress correction is used to estimate the joint fatiguelife which is combined with simulation results. It has achieved good prediction results.