Dynamic compressive testing

High-strain-rate compression tests were performed using a Split Hopkinson Pressure Bar (SHPB) at ambient temperature (298 K). In the SHPB setup used in this study, the specimen is sandwiched between the incident bar and the transmission steel bar. The contact end of the specimen/pressure bar was covered with a silicone grease to minimize friction. A high-pressure chamber was used to launch a striker bar, which impacts one end of the incident bar and generates an elastic wave pulse. Strain gauges were bonded on the surface of the incident and transmission bars to detect the propagation of stress waves. Because the stress equilibrium in the specimen was confirmed by the measured stress waves, one wave analysis was conducted in this study. Strain rate ε˙(t), stress σ(t), and strain ɛ(t) were calculated using the following equations⁴⁰.

where C_B, E_B and A_B are the elastic wave speed, elastic modulus and cross-sectional area of the bars, respectively; L₀ and A₀ are the length and cross-sectional area of the specimen; ε_R is the reflected strain, ε_T is the transmitted strain, and ε˙ is the strain rate. The average strain rate was measured to be 1.4 × 10³ s⁻¹ for a specimen of 5.0 mm height. For each composition, 5 tests were performed to ensure consistency in the results.