The damage investigation of wedge-shaped electromagnetic riveting structure of CFRP/aluminium alloy

In the aircraft industry, electromagnetic riveting is now widely used in the riveting of wedge-shaped aluminium-alloy structure and carbon-fibre- reinforced polymer (CFRP), but damages to the CFRP often happen. To investigate the reason for the damages, methods of C-scan, x-ray, Compton backscatter scanning (CBS), metallography, and thermal deply were applied to study the wedge-shaped riveting structures. The study indicates that the composites by the tail of the rivets, which are close to the edge of the structure, are almost comminuted, and those rivets expand uniformly along the shaft and interference fit with the structure, and at the same time curve toward the edge. The composites around the rivets, which are away from the edge of the structure, are slightly damaged, and these rivets deformed not so uniformly, most of them clearance fit with the structure, and in some joints interference fit and clearance fit occur alternatively. The investigation shows that, in the joints close to the edge, the balance of constraints from the aperture to the rivet is broken by the slope around the tail of the rivet, results in a rightward force working on the rivet tail. The integration of this force and the riveting force curves the rivet instantaneously, which comminutes the right-side composites of the rivet tail. For the rivets away from the edge, the deformation becomes more buckled the longer the rivet, which causes the instability of the fit situation and reduces the damage to the composites.