Abstract
The determination of material properties under high speed loading is a challenge. The system ringing in a conventional servo-hydraulic tensile testing machine deteriorates the quality of force measurement, which makes a precise determination of yield locus, strain hardening and fracture strain difficult. In this work, the system ringing effect of the entire tensile testing system were analyzed. It was determined that the ringing of the system is location and geometry dependent. A new type of tensile sample has been developed. Beside of the usual major plastic deformation area, it has an additional elastic area, within which a locally restricted secondary minor plastic deformation takes place. This very small plastic deformation absorbs the elastic vibrations in this area. Therefore, the deformation forces can be measured by strain gauge without any ringing effect. The plastic deformation behavior of materials can be determined for a wide range of strain rate of 0.0001 - 1000 /s exactly. To explain the functionality and the physical background of the new sample, based on the equations for one-dimensional stress waves and theory of the stress wave attenuation due to dislocation motions, a simplified beam model with analytical formulations could be established und programmed in MATLAB. Verifications show a good prediction of sample geometry using this simplified model.
Highlights
Stress wave propagation and ringing free force measurementBased on the positive effect determined in [7] for force measurement in the lower area above the sample clamping area of the ISO 26203-2 sample (elastic measurement area [EMA] in Fig. 1a), Li and Fang performed an extensive FE analysis on high-speed tests using a hydraulic machine [9], where the entire hydraulic tensile machine (Zwick Company, type HTM5020) was modeled using LS-DYNA (see Fig. 1d)
Introduction and state of the artDuring a vehicle crash event, large multi-axial plastic deformation with strain rate in the range of 10−4 − 103 /s occurs
Other researchers [5,6,7] reported that forces are measurable with reduced oscillations when strain gauge sensors (SGS) for force measurement are placed on the lower sample shoulder area above the sample clamping area at a strain rate of up to 200 /s
Summary
Based on the positive effect determined in [7] for force measurement in the lower area above the sample clamping area of the ISO 26203-2 sample (elastic measurement area [EMA] in Fig. 1a), Li and Fang performed an extensive FE analysis on high-speed tests using a hydraulic machine [9], where the entire hydraulic tensile machine (Zwick Company, type HTM5020) was modeled using LS-DYNA (see Fig. 1d). The force oscillation in the elastic measurement area (EMA) was reduced comparing to the ISO sample In this work, it was found, that the force oscillation is very large in the area of hydraulic jack and sliding bar for the sample loading, large in the area of load cell in the lower part of the test system, and nearly zero in the area of plastic deformation (GL area of the sample). It was found, that the force oscillation is very large in the area of hydraulic jack and sliding bar for the sample loading, large in the area of load cell in the lower part of the test system, and nearly zero in the area of plastic deformation (GL area of the sample) Based on these findings, many attempts were conducted to further reduce the force oscillations in the EMA between S1 and the second shoulder (S2) of the Gen. I specimen (Fig. 1b). Tests on different steel grades (DC04, HC340, DP1000, CPW1000) and Aluminium (Al 6082) show the same positive results
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