Connections between steel and aluminium using adhesive bonding combined with self-piercing riveting: Testing, modelling and analysis
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The multi-material design of modern car bodies requires joining technologies for dissimilar materials. Adhesive bonding in combination with Self-Piercing Riveting (SPR) is widely used for joining steel and aluminium alloys. In the crash design, an efficient numerical model of this hybrid joining technology is required to guarantee crashworthiness and reliability. Idealised models are applied to describe the mechanical behaviour of the connection and its calibration depends directly on the material combination. A multitude of different metals and thicknesses are joined in a modern car body. Consequently, an experimental calibration of all connections is not feasible. In this work, a virtual test procedure was developed to establish the mechanical connection behaviour without the need for extensive experimental tests. Furthermore, the interaction between the adhesive and SPR connection was studied to provide a better understanding of this hybrid joining technology. The virtual test procedure consisted of three Finite Element (FE) models. First, the SPR process was simulated using a 2D axisymmetric model. Large deformations in the top and bottom sheet were handled by an adaptive mesh. Separation of the top sheet was modelled by element erosion. The joining process model was successfully applied to establish the geometry and strain history of the connection. From the results, a 3D mesoscopic model was created. Here, the geometry of the connection was discretise by a fine mesh of solid elements. The mechanical behaviour of SPR, adhesively bonded and hybrid connections under various loading modes was established using the mesoscopic model. The idealised model of SPR connections was then calibrated virtually from the established mechanical behaviour. Development and calibration of the numerical models was supported by a multi-scale testing approach. The material characterisation involved tests on the applied steel and aluminium sheets, adhesive and self-piercing rivets. Various tests were performed on SPR, adhesively bonded and hybrid connections to characterize the joints. Furthermore, a new component test was developed and tested under quasi-static and dynamic loadings. The results were applied to validate the virtual test procedure at loading conditions comparable to a vehicle crash. Here, the virtual test procedure proved to be a promising approach as the number, location and failure sequence of all failed SPR connections was predicted accurately.