Recommended Practice for Dynamic Testing for Sheet Steels - Development and Round Robin Tests

Tensile properties of sheet steels at dynamic conditions are becoming more important for automotives in recent years due to the positive strain rate effect of steels which significantly improves energy absorption capability during crash events. However, several testing techniques are used by different testing laboratories, no testing standards are available, and the quality of data generated by different laboratories is often not comparable. In order to improve the data quality at high strain rate testing conditions and thus to improve the accuracy of crash simulation results, The International Iron and Steel Institute (IISI) initiated a project to develop the “Recommendations for Dynamic Tensile Testing of Sheet Steels”. The document provides guidelines for key elements of high strain rate testing, testing techniques, input methods, specimen geometry and stress/strain measurement instrumentations. A Round Robin test program was launched afterwards to evaluate the current status of testing quality with 10 laboratories participating from Europe, Japan, Korea and North America. The Round Robin test program showed that not only the equipment used are different, specimen dimensions are also vastly different from different testing laboratories. This paper describes the development of the document, key issues of the high strain rate testing, and Round Robin test results. An example is also given showing how data quality was significantly improved by careful refinement of the testing procedures including specimen geometry.