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Laser shock hole-clinching is a high–strain rate mechanical joining process in which the metal foils are joined together based on plastic deformation generated by a laser-induced shock wave. In the process, fracture is a typical defect and seriously influences the clinching quality and production efficiency of joints. However, the classification and variation of fracture modes in laser shock hole-clinching are of less concern. In this study, the fracture mode of Cu-Fe joints in laser shock hole-clinching was experimentally investigated. Both optical microscopy and scanning electron microscopy were adopted to analyze the fracture surface morphology of clinched joints. The influence of laser power density, laser spot diameter, the initial grain size and thickness of metal foil, and spacer height on the fracture mode of joints was evaluated. It is revealed that the temperature increase caused by high–strain rate plastic deformation has no impact on the fracture behavior of the joining partners. Fracture always occurs on joining partner I, and it can be divided into four modes, including bottom surface fracture, bottom corner fracture, neck fracture, and mixed fracture. It is found that fracture on the bottom surface is seldom seen but mixed fracture accounts for most of the cracked specimens. Neck tensile fracture rarely appears alone, and it usually exists accompanied by fracture on the bottom corner. The fracture mode varies from a tensile fracture mode on the bottom corner to a mixed fracture mode and then to a shear fracture mode on the neck with the enhancement of laser power density. In addition, the initial grain size of joining partner I has a significant impact on the fracture mode of clinched joints. The fracture mode varies from bottom corner fracture to mixed fracture in relation to the change of mechanical properties of metal foil with an enlarged grain size. However, the mixed fracture mode always appears with the enlargement of both laser spot diameter and spacer height. [ABSTRACT FROM AUTHOR]

Laser shock hole-clinching is a novel mechanical joining process in which the shock wave pressure induced by a high-energy pulsed laser is employed as a punch. This process is quite suitable for the joining of two dissimilar materials with significant differences in plasticity and strength. However, the effect of key process parameters on the forming quality of joints by laser shock hole-clinching is less concerned. In this study, the influence of laser power density, spacer height, number of laser pulse, and initial grain size of metal foils on the forming quality of Cu-Fe joints was experimentally investigated. The characteristics of interlock value and thinning rate distribution under various process parameters were systematically examined. It is revealed that laser shock hole-clinching process can be divided into the confined bulging and interlock formation stages. Based upon the examination of substandard joints, the defects in laser shock hole-clinching process are classified which contains no interlock, nonuniform interlock, bottom and neck fracture. It is found that the thinnest position of joints locates at the region in contact with the upper corner of the joining partner II in which extensive plastic deformation occurs related to the force acting during clinching process. The interlock value increases significantly as the enlargement of initial grain size, whereas the deviation also becomes larger due to the inhomogeneous plastic deformation for the metal foil with coarse grains. Moreover, the ratio of spacer height to the thickness of the joining partner II affects the thinning rate distribution and interlock value of joints. The spacer height equaling to the thickness of the joining partner II is recommended within the given parameters. [ABSTRACT FROM AUTHOR]