The following is an excerpt.

In the body of a modern car, there is a multitude of dissimilar materials. The joining of these materials is a crucial challenge in car body design. 

Accurate and efficient numerical models of the applied joining technologies are essential for the design and crash analyses. These challenges are the motivation behind the PhD-work of Matthias Reil, carried out at SFI CASA and the Department of Structural Engineering.

Reil defended his thesis at NTNU Thursday 21 November. The title of the thesis is «Connections between steel and aluminium using adhesive bonding combined with self-piercing riveting: Testing, modelling and analysis».

SFI CASA will bring another story on Matthias Reil´s work later. In the meantime, enjoy the following abstract:

«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 discretised 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».

Aluminium-Steel connection combined with adhesive bondingThe following Assessment Committee assessed Matthias Reil´s thesis:

• Professor Eric Markiewicz, Universite Polytechnique Hauts-de-France

• Professor Katia Mocellin, Mines Paris Tech, France

• Professor Arild Holm Clausen, Department of Structural Engineering, NTNU

Professor Clausen was the Administrator of the Committee. The subject for Reils trial lecture was

“Challenges and opportunities in the design of electric cars”.

Associate Professor David D. Morin, Department of Structural Engineering, has been the candidate’s main supervisor. Professor Magnus Langseth, Department of Structural Engineering and Researcher Octavian Knoll, Department of Structural Engineering, have been the candidate’s co-supervisors.