Abstract
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.
Highlights
For the purpose of jointing the fasteners in aircrafts, automobiles etc., it’s unavoidably to drill holes in these engineering structures and components
Cracks during cycling loads are much more preferred to initiate around holes owing to the severe stress concentration issue, which would significantly reduce the fatigue life of the fasteners [1]
When the external load is removed, the plastic deformation zone(PDZ) would be compressed by the spring-back of the surrounding elastic area, the compressive residual stress is produced, and the larger PDZ, the stronger compressive residual stress [8]. This compressive residual stress would reduce the service tension stress, which could suppress the initiation of the crack and extend the fatigue life [9]
Summary
For the purpose of jointing the fasteners in aircrafts, automobiles etc., it’s unavoidably to drill holes in these engineering structures and components. Conventional hole strengthening methods, named cold working, such as direct cold expansion [2], split sleeve cold expansion [3,4,5,6] and shot peening [7], have already been developed The principle of these methods is to push the hole wall radially outward, the elastic/plastic deformation is occurred. When the external load is removed, the plastic deformation zone(PDZ) would be compressed by the spring-back of the surrounding elastic area, the compressive residual stress is produced, and the larger PDZ, the stronger compressive residual stress [8] This compressive residual stress would reduce the service tension stress, which could suppress the initiation of the crack and extend the fatigue life [9]
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