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Recently the University of Dayton Research Institute (UDRI), the Society of Automotive Engineers (SAE), and the High Strain Rate Plastics Committee (HSRPC), participated in a cooperative research effort to develop and assess the precision statistics of a Practice Guide for High Strain Rate Testing of Polymers. Development of the practice guide included collaborative research, surveys and an interlaboratory test program. This practice guide was incorporated into the draft SAE-J Standard (SAE J2749 High Strain Rate Tensile Testing of Polymers) and will be approved as a standard in 2008. SAE-J2749 addresses instrumentation and data analysis issues associated with measuring load. Information regarding strain measurement methods during high strain rate testing of polymers was obtained through the interlaboratory test program.

Tensile tests were performed on DP600 and DP780 dual-phase steels to determine the relative effects of bake-hardening on the static and dynamic material response. The quasi-static test variables were prestrain level, specimen orientation (longitudinal, transverse), and heat treatment (as-received, bake hardened). Dynamic tests were performed at rates ranging from 0.001/s to 500/s, with variables of prestrain level and heat treatment. Increases in the ultimate and yield strength for both DP600 and DP780 were mainly due to prestrain and strain rate effects. The bake-hardening effects varied with the material, amount of prestrain, and strain rate. Crush tests were also performed on DP780 tubes in the as-received and bake-hardened conditions at rates ranging from quasi-static up to 7250 mm/s. The energy absorption was similar regardless of the rate.

Crash simulation models require dynamic material property data to produce realistic predictions. The models often have to simulate multi-layered components that can contain polymers, foams, and metals. This paper describes a pilot study on the dynamic tensile properties of energy absorbing foams. The first phase consisted of the development of tensile test procedures suitable for high rate testing of foams. The second phase involved dynamic tensile tests on foams at rates up to 3.0 m/s. A half-scale ASTM D1623 Type A cylindrical tensile dog-bone was used for the dynamic tests. The pilot study showed that dynamic tests on foam were possible. The dynamic ultimate tensile strength, failure strain, and stiffness of three foams at various rates were measured. The groundwork has been laid for the development of a foam tensile test standard for the automotive industry, with the potential of generating shared databases.

The American Chemistry Council sponsored program to optimize a specimen design for use in high strain rate testing of long fiber-reinforced thermoplastics (LFRT) was experimentally validated through testing of injection molded long glass-filled polypropylene (LGFPP) and long glass filled Nylon ® (Nylon). It was demonstrated that the dynamic specimen geometry generated valid results for LFRT tensile tests in the quasi-static through 400/s regime. Optimum specimen size depended on the maximum test rates and end use of the data. The program results provide a basis to select specimen parameters to appropriately represent LFRT or similar materials for comparison or material property testing. Tests established the effects of injection technique; strain rate (nominal 0.1/s to 400/s); fiber fill content (20wt%, 30wt%, 40wt%), specimen type and width, panel thickness, distance to the fill gate, flow orientation, and material homogeneity.

Material testing standards for quasi-static rates are relatively well established. The increasing need for high strain rate material properties is now focusing the engineering community's attention on the test methods used to generate data. Differences in procedures and analysis may yield information in apparent conflict with other published data. The lack of industrial standards for high strain rate testing makes it vital that the end-user understands the valid applications and limitations of high strain rate material data. Current test methods, proper specimen selection, strain measurement methods, data analysis techniques, and interpretation of high strain rate data are reviewed.