Currently, there are discussions going on concerning high strain rate testing methods and data needed to be optimised for the use of steel in Finite Elements Analysis (FEA) models. Crash models results show strain rates of up to 1000s-1 and therefore material data up to this strain rate level is needed. Not only the strain rate but also the temperature has an influence on the mechanical properties. Therefore, the combination of strain rate and temperature effects is of great interest. Indeed, it is well known that high temperature leads to a decrease of the mechanical characteristics, while high stain rate leads to an increase. A balance of the latter effects is important since the location of some crash relevant parts close to the engine leads to temperatures close to 80°C. With regard to the steel grades produced in the ARBED group and used for car body applications, in this study the strain rate sensitivity is investigated in the temperature range from –40°C to +80°C for different steel grades: Interstitial Free High Strength Steel IFHSS260, micro-alloyed steel ZStE420, galvanized Dual Phase steel DP500G and austenitic stainless steel 301LN. MATERIALS AND TESTING PROCEDURE Investigated materials The mechanical properties were measured in rolling direction (RD) according to the standard EN10002 on a common tensile test-bench at room temperature with a strain rate of 5⋅10-3s-1 (see Table 1). TABLE 1 MECHANICAL PROPERTIES OF THE INVESTIGATED STEEL GRADES IN ROLLING DIRECTION Grade Thickness mm YS MPa TS MPa A80 % n0 r0 IF HSS 260 1.20 260 394 36.6 0.201 1.37 ZStE 420 1.13 431 495 26.0 0.166 0.65 DP500G 1.15 368 558 25.0 0.151 0.84 301LN annealed condition 1.20 378 752 50.8 0.35-0.6 0.92 Dynamic tensile testing facilities The dynamic tensile tests were performed in RD on a servo hydraulic high-speed tensile machine up to a strain rate of 10s-1 for 3 temperatures based on the automotive standards, i.e. -40°C, 20°C and 80°C. Flat tensile specimens with a 40mm gauge length were used at ram speeds up to 400mm/s. In order to complete the strain rate range up to ε& = 1000s-1, tensile tests were performed on a split Hopkinson tensile bar set-up developed at the University of Ghent but only at room temperature. The experimental test facility consists of a 6m long input bar and a 3.15m long output bar, between which the test specimen is fixed, as schematically presented in Figure 1. Figure 1: Schematic representation of a split Hopkinson tensile bar setup Both the aluminium input bar and output bar have a diameter of 25 mm. The 5mm wide, flat steel sheet specimen has a gauge length of 10 mm. The anvil at the outer end of the input bar is hit by an impactor, which is pneumatically accelerated. The pneumatic accelerator has a capacity of 5kJ. A tensile wave with a duration of 1.2 msec is generated by the impact and propagates along the input bar towards the specimen.
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