Abstract
Neutron diffraction was used to describe the residual stress distributions in self-piercing riveted (SPR) joints. The sheet material displayed a compressive residual stress near the joint, and the stress gradually became tensile in the sheet material far away from the joint. The stress in the rivet leg was lower in the thick joint of the softer steel sheet than in the thin joint of the harder steel sheet. This lower magnitude was attributed to the lower force gradient during the rivet flaring stage of the SPR process curve. This study shows how the residual stress results may be related to the physical occurrences that happened during joining, using the characteristics curve. The study also shows that neutron diffraction technique enabled a crack in the rivet tip to be detected which was not apparent from a cross-section.
Highlights
Self-piercing riveting (SPR) is a cold forming joining technique used to fasten sheet material by mechanical interlock
Compressive residual stresses were observed in measurement points 4, 5, 6, and 7 along line AA which are situated between −5.5 mm and 5.5 mm from the rivet axis
It is evident from results presented that the neutron diffraction method can successfully quantify residual stress variations in the rivet leg and detect cracking inside the joint
Summary
Self-piercing riveting (SPR) is a cold forming joining technique used to fasten sheet material by mechanical interlock. Automotive industries are increasingly adopting this technique because of the growing use of light weight or dissimilar metal (such as galvanized steel, aluminium, and magnesium alloys) that is difficult to weld. During SPR joining, a mechanical interlock is created between the sheets by flaring of the rivet in the bottom sheet under the guidance of rivet internal geometry and a die (Figure 1). The SPR process is capable of joining multiple material stacks and dissimilar materials because of the formation of the mechanical interlock. The process requires plastic deformation of the rivet in the bottom sheet without cracking. The ability of a rivet to pierce and deform in a ductile manner becomes more limited with the introduction of higher strength lightweight materials
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