Numerical investigation on the effects of circuit parameters on the plastic deformation of fastener holes in thin aluminum alloy via electromagnetic expansion process

The size of the plastic deformation zone caused by fastener hole strengthening is a critical indicator of the strengthening performance. In this study, 2A12-T4 aluminum alloy specimens with a hole diameter of 6 mm and thickness of 1.5 mm were strengthened by Lorentz force through the electromagnetic strengthening method. The numerical results show that the Lorentz force can introduce tensile stress in both hoop and radial directions in the specimen during the strengthening process and produce a high compressive hoop residual stress around holes without serious axial deformation compared with the conventional cold hole expansion process. The simulation results are experimentally validated by the grid method in verifying the residual strain, and the fatigue life can be improved by several times after strengthening. Furthermore, under the same discharge energy, there is an optimal capacitance of around 40 μF in this work to achieve the maximum size of the plastic deformation zone. In addition, a larger crowbar resistance can cause a stronger radial inward Lorentz force during the unloading process and result in lower residual stress; therefore, the crowbar resistance should be as small as possible.