The following is an excerpt.
The body of a modern car is like a gigantic 3D Puzzle, with a multitude of different materials, parts and pieces. The joining of all those mixed parts is a crucial challenge in today´s design of car bodies.
The automotive industry is out on a never-ending hunt to reduce time, weight and cost in vehicle development. At the same time, the complexity is increasing a lot.
«Virtual testing is one important tool in solving this conflict of interest», states Matthias Reil.
These challenges are also the motivation behind his PhD-work, carried out at SFI CASA and the Department of Structural Engineering.
In the development of a passenger car, numerical methods are applied to design the car body.
«Numerical simulations substitute cost and time-consuming real-world tests. In order to develop and calibrate the numerical models, we need to have an accurate understanding of all the applied materials and joining technologies», Matthias Reil states.
HOW TO MODEL A HYBRID CONNECTION IN A CRASH SIMULATION
Just a few decennials back, car bodies consisted primarily of steel parts joined by welding. The joining of today´s dissimilar materials is very challenging. Welding is often not an option.
Matthias Reil focuses on numerical models to describe the behaviour of adhesively bonded self-piercing riveting connections between steel and aluminium (Test specimen on photo right). This method is common for joining steel to aluminium in modern car bodies.
«My objective was to develop an efficient and reliable way of modelling such a hybrid connection in a vehicle crash simulation», he explains.
Reil wrote his Master thesis at BMW on the structural analysis of carbon fibre reinforced plastic materials. At that time, BMW was already a partner of SFI CASA. When he had finished his thesis, BMW offered him a position as a PhD candidate.
SHARED CANDIDATE BETWEEN CASA AND BMW
«Doing the PhD as part of SFI CASA came almost naturally as it offered great benefits for all parties. For me as a PhD candidate, access to excellent supervision, cutting edge testing facilities and especially the possibility to do research abroad was desirable», he says.
Furthermore, for BMW, having a shared PhD candidate, had the benefit of having someone at the heart of the research project, enabling a good backflow of information. According to Reil, for SFI CASA to have input regarding the needs of the industry and industrial implementation were very useful.
Reil defended his thesis on 21 November. In total, he has spent 18 months in Trondheim. Reil finds the change between Germany and Norway a nice variety. He also thinks it has been vital for the success of his doctoral work.
MOTIVATED BY THE INDUSTRY´S NEED FOR RESEARCH
«At BMW, I was working at a colossal R&D Facility with thousands of engineers & other developers. The work environment was quite busy and professional. The input from colleagues at BMW was vital. It helped to keep the needs of the industry and the industrial implementation in mind. Furthermore, experiencing how the industry needs the research helped to keep up the motivation».
At SFI CASA there are fewer people and smaller offices. He says that this fact gave the space needed for really digging deep into the scientific aspects of the thesis.
«Having so many other PhD candidates around, who are in the exact situation, was very important, both from a professional side, but even more so from a social. Furthermore, performing all the experiments was very straight forward and did not require much administrative overhead».
SAFE, RELIABLE AND COMPETITIVE CARS
Matthias Reil underlines our need for a deep understanding of the mechanical behaviour of all the materials and joining technologies applied in the car body. Simply, without this understanding, we would not be able to design safe, reliable and competitive cars.
«Having an accurate numerical representation of adhesively bonded self-piercing riveting connections is one important piece of the puzzle».
He says that the macroscopic models describe the mechanical connection behaviour with reasonable accuracy and cost. Therefore, they can apply in full-scale crash simulations.
The motivation behind his PhD work came both from BMW and SFI CASA. BMW car bodies widely use self-piercing riveting and adhesive bonding. They join a great variety of materials and thickness combinations. To establish the mechanical behaviour of these connections through testing is very expensive. Also, it requires much time.
«Substituting the experimental characterization by a virtual approach was therefore especially important for BMW», Matthias Reil says.
In SIMLab there had already been investigations on self-piercing riveting connections. However, research on adhesive was scarce – even though the hybrid joining technology is quite standard in modern car bodies. Also, the literature provides only very little information about it. Reil says that from an SFI CASA and research point of view, studying the interaction between both joining technologies was especially important.
BMW is a co-founder of Reil´s project, as well as his employer. At the same time, CASA has four other automotive partners that are BMW´s competitors. When asked how the paries handle all this and on possible conflict of interests, Reil answers:
«Conflict of interest was not a big problem as the guidelines are quite clear. All the partners share the research performed, as well as the knowledge gained from SFI CASA. Of course, by working directly at BMW I also had access to some confidential information. I had to make sure not do disclose any of this information. However, such confidential information was not directly part of my research, so I was able to share all the information regarding my work.
RESEARCH THAT MAKES A DIFFERENCE
«In which way will you -eventually- say that your research is a significant step forward»?
«By establishing the mechanical behaviour of self-piercing riveting, adhesively bonded and especially hybrid connections. By the developed methodology for the virtual test procedure. Highlighting the benefits of a virtual test procedure as well as establishing utterly new application fields is also of great importance. Also, the development and successful validation of a novel component test».
The automotive industry aims to half the number of physical crash tests. CASA aims to contribute to this through the virtual lab. Reil describes CASA as a player on the forefront of virtual testing. He says that the applied virtual approaches, both for materials and joints, show promising results.
«I am convinced they will contribute to reducing cost and time in the vehicle development».
AS CLOSE AS POSSIBLE TO AN ACTUAL VEHICLE CRASH
The fresh doctor´s research presents a brand-new test setup for adhesively bonded and point-wise connected components. He explains: «With a test on the component level you want to validate your numerical models at conditions as close as possible to an actual vehicle crash. That is, with reduced effort and precise control of the boundary conditions and loadings. The new component test enables us to do precisely that. It can be performed under quasi-static and dynamic conditions and allows us to control the loading in the connections precisely. Furthermore, we can identify the exact moment and the sequence when failure takes place».
«Do you think that your research makes a difference for the automotive industry»?
«I am convinced that my research will contribute to safer and lighter car bodies. However, modern passenger cars are highly optimized and very complex products. The sum of the work performed by all researchers and engineers is what makes the big difference».
RESEARCH PUT TO USE BY CAR MAKERS
Experimental results from Reil´s research is already in use to calibrate numerical models applied in vehicle crash simulations. The virtual test procedure is currently under validation for different material combinations. After the successful validation, the virtual test procedure can apply in the development process of car bodies.
The now fresh doctor started working in the development of high voltage batteries for electric vehicles at BMW this summer.
«The development of electric cars is a pressing issue for all car manufacturers which means that the work is very inspiring and fun but also quite challenging», he says.
The title of Matthias Reils thesis is: « Connections between steel and aluminium using adhesive bonding combined with self-piercing riveting: Testing, modelling and analysis». His supervisors have been Associate Professor David D. Morin (main) Professor Magnus Langseth, and Octavian Knoll at BMW have been his co-supervisors.