Study of Dynamic Loading Tests on Low-Impedance Specimens

The key problems of the effective acquisition of low-impedance transmitted signals and the stress equilibrium in the Hopkinson bar loading tests on low-impedance specimens with high strain rates, were investigated. Based on the previous research fundaments, low-impedance elastic transmitted bars were introduced to replace the traditional metal transmitted bar, the in-situ calibrated semiconductor strain gauge technology was used to amplify weak transmitted signals, and the low-impedance specimens were tested with high precision. Reconstruction and calculation of the stress wave loading process were conducted to get the stress equilibrium history and the influential factors’ sensitivity. The trapezoidal incident wave was proposed to realize stress equilibrium and achieve constant strain rate loading on specimens as early as possible. The results show that, low impedance polymethyl methacrylate bars/tubes as transmitted bars along with semiconductor strain gauges can acquire weak signals as low as several Newtons. The stress equilibrium history of the low-impedance specimen depends on the elastic wave velocity. Under the trapezoidal incident wave loading, the stress equilibrium and constant strain rate loading can be achieved at 2 characteristic periods. Based on the design of specimen thicknesses, the critical effective strain consistency can be achieved under different stress rate loadings.