With the increasing requirement for more optimized vehicle crashworthiness analysis from the automotive industry, tensile testing of sheet steels under dynamic conditions is becoming imperative. Positive strain rate sensitivity, wherein strength improves with strain rate, shows promise for improved energy absorption in the event of crash.
Requirement for a Recommended Practice
A variety of testing methods are used to acquire information under dynamic conditions, each representing a specific range of strain rates and generating a specific type of data. Drop weight systems, Single Bar (SB) system¸ compression Split Hopkinson Bar system, tensile Split Hopkinson Bar (SHB) system, and servo-hydraulic system are some of the testing methods widely used.
Moreover, in recent years, many new systems have been created in order to fulfill the ever growing demand for dynamic tensile testing. Nevertheless, there are no guidelines available as to the testing techniques, measurement devices, specimen dimensions, and other key issues that are vital to the quality of test results. Consequently, it is often not possible to compare the data from different labs. Moreover, the quality of the test results is typically not satisfactory, requiring signal damping and curve smoothing to make them usable.
Development of a Recommended Practice
Since tensile steel stress-strain data at dynamic conditions is increasingly becoming important, WorldAutoSteel initiated in the development of a Recommended Practice for Dynamic Tensile Testing for Sheet Steels by commissioning a team of testing experts from steel company members of WorldAutoSteel in March 2003.
As part of the initiative, the team drafted a recommended practice by compiling the data on the sheet steel know-how of key testing laboratories, including University of California at San Diego, University of Dayton Research Institute, ThyssenKrupp Stahl, Technical University of Aachen, Sumitomo Metals, POSCO, Nippon Steel Corporation, JFE, Ispat Inland, Colorado School of Mines, and ArcelorMittal. After developing a draft of the recommended practice, a Round Robin test program was conducted from early 2004 through early 2005. Based on the Round Robin test program results, the recommended practice was revised and the specimen geometry was further improved.
Conclusion
The final Recommended Practice for Dynamic Tensile Testing for Sheet Steels comprises data on the scope of the project, some specifications about machine types, high strain rate testing, specimen geometry, input methods, measurement devices, clamping methods, and an evaluation and improvement of data quality.
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This information has been sourced, reviewed and adapted from materials provided by WorldAutoSteel (World Auto Steel).
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