Fatigue fracture mechanism and life prediction of steel-aluminium clinched joints under different stress ratios

Vehicle bodies are subject to complex random loads during travelling, making it imperative to investigate the effects of different stress ratios on the body joining structure. To investigate the fatigue performance of steelaluminium clinched joints under different stress ratios, fatigue experiments were conducted on these joints subjected to different load levels at stress ratios of -0.4, 0.1, and 0.4. The fracture mechanism of steel-aluminium clinched joints under different stress ratios was investigated through analysis of the joint's fracture morphology and the composition of abrasive chips using Scanning Electron Microscope and Energy Dispersive Spectroscopy. A fatigue life prediction model for steel-aluminium clinched joints was developed by employing the modified Paris formulation of the Wallker equation. The results indicate that joint failure can be classified into three main forms: lower sheet fracture, upper sheet pull-off accompanied by lower sheet fracture and reaching infinite life (2 million times). The lower sheet of a fatigue failure specimen in a steel-aluminium clinched joint exhibited a novel form of fretting damage known as lower sheet inter-plate fretting wear. Furthermore, the application of Walker's improved Paris formula proved to be highly effective in accurately predicting the fatigue life of steel-aluminium clinched joints under different stress ratios, with the predicted results demonstrating excellent agreement with experimental findings.