Study On Technology And Shear Mechanical Properties Of Electromagnetic Self-piercing Riveting

Electromagnetic self-piercing riveting(E-SPR)is a new technology based on electromagnetic riveting and self-piercing riveting,which has wide application prospects due to the high quality of joints and its adaptability.In this paper,the E-SPR process was explored preliminarily and carbon fiber reinforced plastics(CFRP),aluminum alloy and high strength steel were used.The quality of E-SPR joined with dissimilar material sheet was investigated from the micro-topography of cross-section and tensile-shear strength.And the structural parameters of rivet were designed.Firstly,the quality of E-SPR joints and pressure self-piercing riveted(P-SPR)joints were investigated by experiments.Results showed that the E-SPR joint had higher undercut and rivet strength after forming compared with P-SPR joint.Meanwhile,the maximum shear load of E-SPR joints was 16.4% higher than that of PSPR,which was confirmed that E-SPR process had better joint quality than P-SPR.Through the failure mode analysis of the joint shear failure,it was demonstrated that the reliability of interlocking structure and the strength o f upper sheet determined the maximum shear strength of E-SPR joints.Then the shear strength of CFRP/aluminum alloy and high strength steel/aluminum alloy E-SPR joints under high-speed loading were compared and analyzed.Experimental results showed that the shear strength of joints could be improved by increasing the strength of sheets.The results at different loading speed demonstrated that the maximum shear load of both joints increased with the increase of loading speed,while the energy absorption decreased with the increase of loading speed.It was determined through the analysis of full filed strain that the failure process of joints was accompanied by the rotation of rivets and flow deformation of the sheet material in the interlocking structure.Finally,the structural parameters of rivet were designed for E-SPR process.Based on the structure of the semi-tubular rivet and the forming method of the expansion deformation,the design methods of rivet edge angle,the depth of the rivet leg and the inner diameter of rivet leg were established.The cross-section micro-topography and shear strength of dissimilar materials joints joined with nine kinds rivet were investigated respectively.Results showed that the edge angle and inner diameter of rivet leg had a large influence on the joint strength.Based on the analysis of the correlation between the maximum shear load and energy absorption and the reference value,the optimum shear strength of rivet No.2 for E-SPR of dissimilar materials were determined.