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Research into the use of Plexiglas for vehicle glazing

In cooperation with partners from universities and industry, TECOSIM has brought the SimPlex project sponsored by the Hessen Agentur agency to a successful conclusion. The aim of the project was to develop a new simulation method to calculate crash behaviour in Plexiglas vehicle glazing. The final presentation took place on 12 November in the ETA Factory of the Technical University (TU) of Darmstadt.

The now complete research project was launched in 2017 in cooperation with the Institute for Mechanics and Materials Research (IMM) at the Mittelhessen University of Applied Sciences, the TU Darmstadt and industrial partners. Its purpose was to investigate whether the use of polymethyl methacrylate (PMMA) acrylic glass is feasible in terms of crash capability. “The material promises to reduce weight by up to 50 percent compared directly with conventional car window glazing. What's more, it will also improve acoustics and breaking strength significantly,” says Prof. Dr. Stefan Kolling from the Mittelhessen University of Applied Sciences, explaining the motivation behind the project.

Scientists from the participating institutes and engineers from TECOSIM jointly developed a process that enables the material to be used in the digital vehicle development process and compared with conventional mineral glass. “Using a realistic simulation method, we can now create a virtual prototype and simulate various crash scenarios that are a reliable indicator. This paves the way for the use of Plexiglas in vehicle production,” declares Damaso Lopez Ruiz, CAE Manager at TECOSIM. “Together with partners in industry, our next step is to intensify discussions with customers about using this material in the field,” adds Martin Westerwald, Managing Director of TECOSIM GmbH.

Statistical analysis of fracture behaviour
During the research project, the partners developed a material model for PMMA and established the necessary material parameters in experiments. At the heart of the research was a statistical analysis of fracture behaviour, as this is what largely determines the risk of injury, especially in the case of head impact (Figure 1). Therefore, first of all the injury probability was quantified with the aid of a validation model. Finally, the material models were deployed in overall vehicle simulations in side impact and lateral pole crash scenarios (Figure 2).

Figure 1: Simulation model of head impact and the influence of breaking strength with a large scatter on injury probability.

Figure 2: Comparison of side window material ESG versus PMMA or AG100. The influence of the side window in the overall vehicle lateral pole test.

 

An analysis of simulations using conventional glass PMMA produced comparable results. What’s more, a PMMA and TPU film composite was also developed in this project, so that the consortium was able to evaluate composite windscreens and side windows as well.

Moreover, using a side window of PMMA, the researchers demonstrated the importance of stochastic material behaviour for vehicle design. The extent of injury probability ((known in passive safety as Head Injury Criterion (HIC)) reacts very strongly to breaking strength with scatter. The stochastic simulation and establishment of suitable dependent variables (the 95 percent limit in Figure 1, for example) will therefore be extremely important in future.

As part of the research project, the team were able to make use of simulation data from TECOSIM’s self-developed Reverse Engineering process, TEC|BENCH. Vehicles freely available on the market are scanned and the geometry data prepared in CAE models for crash simulation.

Demand for lightweight design solutions is unabated
The demand for lightweight design solutions continues unabated in the automotive industry. In the interests of vehicle electrification, longer range and to further lower CO2 emissions, experts are constantly searching for ways to further reduce weight. Glazing accounts for up to five per cent of overall vehicle weight, so transparent thermoplastic windows offer great potential. The study is not making a mere direct comparison of mass, however; overall weight will be reduced at a uniform level, such as in side windows or sunroofs. This allows the vehicle's centre of gravity to be lowered to ensure improved driving dynamics. Plexiglas glazing provides better protection against impact from stones than mineral glass windows thanks to its greater breaking strength. It also delivers improved acoustics due to its insulation properties, making driving more agreeable.