PSI - Issue 60

5

Vaibhav Gangwar / StructuralIntegrityProcedia00(2024)000 – 000

Vaibhav Gangwar et al. / Procedia Structural Integrity 60 (2024) 123–135

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Fig. 9. Plot of strain rate reached with strain gauge

3.2 High strain rate tensile test The high strain rate tensile test is then performed on another sample with strain gauge implemented in INSTRON CEAST 9350 test setup. Fig.(5) depicts the voltage vs. time signal for this at a velocity of 3m/s but the signal obtained is too much noisy so the signal must be properly filtered first to reduce noise. Because the maximum noise (frequency) must be known for filtering, the FFT (Fast Fourier transform) algorithm is used to convert it into frequency domain. After determining the maximum noise level, a low-pass filter is applied to cut off the upper frequency. The signal left after filtering is shown in Fig.(8); this is the actual voltage that comes out due to strain gauge displacement. The voltage signal is then multiplied by calibration constant (0.087) to obtain the strain signal. The engineering strain vs. time plot is shown in Fig.(9). The force vs. time is shown in Fig.(10). The engineering stress-strain diagram is then plotted as seen in Fig.(11). The true-stress vs. true plastic strain curve obtained from engineering stress-strain diagram. True-stress vs. true plastic strain curves for different velocities are determined from experiment in a drop-weight impact machine and are smoothened by curve fitting and shown in Fig. (12). The true-stress vs. true plastic strain curves obtained from both the servo-hydraulic machine (tested elsewhere) and drop weight impact machine at almost similar strain rates are shown in Fig.(13). The matching in the response is continued upto ultimate stress. MJC material parameters are then extracted from experimental results of tensile tests at different strain rates. Initially, MJC material parameters are extracted from experimental results of tensile test from servo-hydraulic test upto 500 s -1 strain rate and listed in Table 1. Then MJC material parameters are extracted from the test data obtained from drop-weight machine and are listed in Table. 2. The tensile test data from drop weight machine are available upto 570 s -1 . The accuracy in FE simulation of tensile tests depends on the accuracy of material parameters, which depends on the pool of test data. In this case, FE simulation of tensile tests at high strain rates are performed with two sets of material parameters as listed in Table. 1 and Table. 2 and compared with experimental results to assess the accuracy of the material parameters.