MATERIAL VALUES FROM HIGH-SPEED TENSILE TESTS FOR CRASH SIMULATION

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MATERIAL VALUES FROM HIGH-SPEED TENSILE TESTS FOR CRASH SIMULATION
17 August 2007 - Bayer MaterialScience AG

Crash tests are complex and costly. Developers in the car industry therefore try to keep the numbers of such tests to a minimum and instead are making increasing use of simulations. This also applies to plastic components such as front ends, bumpers, and fenders. Finite element method simulations are used to analyze the crash behavior of these components at typical speeds. The material values required can be derived from high-speed tensile tests.

Bayer MaterialScience AG provides this service to its customers in the automotive industry through the Thermoplastics Testing Center. This accredited test center has a servohydraulic high-speed tensile testing system that enables material properties to be tested at tensile speeds of up to 20 meters per second. “At the heart of the system is a high-speed video camera. This enables us to monitor very precisely the local elongation of the test body at a maximum recording speed of one megahertz,” explains Dr. Jens Stange, head of the TTC testing department. “We can then draw up material cards for non-reinforced and glass-fiber-reinforced plastics of this type, where deformation and failure occur in a window of less than 100 microseconds.”

The tensile tests can be performed with pull forces of up to 20 kilonewtons and at temperatures of –40 °C to 200 °C (controlled test chamber). Using the force measured in each case and the local elongation determined on video, force-deformation graphs can be created for various tensile speeds and temperatures. Reverse engineering is then used to determine the values for the material card. This information can then be used with standard crash-simulation programs such as LS-Dyna or PAM-Crash to calculate the strength, energy absorption, and dynamic load-bearing properties of the plastic component and to reliably assess its crash behavior.

“Thanks to the video camera’s extremely high resolution of 640 x 512 pixels and image frequencies of up to one MHz, we can record a larger number of images even at very high speeds and thus with very short test durations. As a consequence, sufficient measuring points from the deformation phase and the moment of material failure can be obtained. The values obtained are therefore very precise, which in turn benefits the forecast quality of the crash simulations,” says Stange.

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About: Bayer MaterialScience AG
Bayer Corporation, headquartered in Pittsburgh, is part of the worldwide Bayer Group, an international health care, nutrition and innovative materials group based in Leverkusen, Germany. Bayer employs 23,300 in North America with net North American sales of 8.8 billion euros in 2003. Bayer’s three operating business areas – HealthCare, CropScience and MaterialScience, improve people’s lives through a broad range of essential products that help diagnose and treat diseases, protect crops and advance automobile safety and durability.

Bayer MaterialScience AG is one of the world's largest producers of polymers and high-performance plastics. The main customers for Its innovative developments in coatings, adhesives, insulating materials and sealants, polycarbonates and polyurethanes are the automotive and construction industries, the electrical/electronics segment and manufacturers of sports and leisure goods, packaging, and medical devices.

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