Study Of Self-piercing Riveting Strength Property With Multi-nail Joints

With the rapid development of modern industry,a variety of lightweight metal materials have been widely used in sorts of fields such as automobile manufacturing,whereas difficulties exist in the connection of lightweight metal materials by welding process.As a new-type connection technology,self-piercing riveting(SPR)process with semi-tubular rivet could conquer deficiencies in traditional joining processes effectively,and SPR have been receiving more and more attention.SPR joining strength property of AL5052 aluminum alloy sheets with one or more semi-tubular rivets was studied in this paper and the effect of shot peening strengthening on SPR joint property was analyzed equally.Numerical simulation of SPR process was conducted in DEFORM-3D finite element software.Forming principles of material flow trend,load variation and so on were analyzed during the four forming phase: clamp,penetration,expansion and molding.Also numerical simulation of SPR and tensile process of specimen with multiple rivets was proceeded which could provide reference for the subsequent experiments by analyzing the stress distribution and failure modes of SPR joint.Riveting tests of AL5052 aluminum alloy sheets were done by SPR technology,and the influence of dimension matching on joint cross-section forming quality of SPR was analyzed through intuitive method and profile measuring method.Influences of different process parameters(rivet height,end distance and die shape)on strength property of lap-shear specimen with one rivet were analyzed and optimum matching of parameters was obtained.Based on the optimized parameters SPR and tensile tests of lap-shear and butt joint with multiple rivets were carried out.The impact of rivet quantity and layout form on mechanical property of joint was studied with incorporation of Digital Image Correlation(DIC)system which could analyze the stain around the rivet and deformation of the sheet during tensile test.In addition,the failure modes of SPR joints were summarized.The results show that multi-nail joint could enhance the mechanical property significantly and the position dimension of rivet had evident impact on the static strength property.Also distinct tension and compression region as well as material flow deformation around rivets could be observed.The typical failure mode of SPR joint was the off of rivet tail from sheet and for four-rivet joint that was the fracture of sheet.Finally shot peening process was employed for surface treatment of AL5052 sheets and riveting specimen and it was discovered that shot peening strengthening could develop static strength and failure displacement efficiently.Furthermore,effect of parameters(shot diameter,time of shot peening)on strength property of SPR joint with one and multiple rivets was investigated.The results show that the process parametersadopted had little effect on static strength property and the comprehensive property was better when shot diameter and time of shot peening were 0.3mm and 5 min respectively.