258 S.K. Roy et al. Fig. 31.5 Typical target plate after impact (Test ID 1000-024) Table 31.1 Physical measurement of target plates after impact Spall crack details Test ID MPDV system details Target Plates Impact velocity, km/s Crater diameter, mm Penetration depth, mm Bulge, mm Diameter, mm Width, mm 1000-024 9 Probe A36 5.708 17.2˙0.3 7.7˙0.3 3.1˙0.3 21.4˙0.2 1.9˙0.1 1000-025 4.763 15.4˙0.3 6.5˙0.3 1.4˙0.1 14.5˙0.2 0.2˙0.1 1000-088 11 Probe 304L 6.583 17.3˙0.2 6.4˙0.3 2.4˙0.1 n/a n/a 1000-089 HY100 6.698 16.5˙0.3 6.4˙0.2 3.0˙0.3 n/a n/a 1000-090 12 Probe HY100 6.743 15.5˙0.1 4.5˙0.3 3.3˙0.1 n/a n/a 1000-091 304L 6.758 15.5˙0.2 3.9˙0.1 3.2˙0.2 n/a n/a 1000-026 25 Probe A36 4.823 15.1˙0.2 6.5˙0.5 1.5˙0.1 n/a n/a 1000-027 5.088 16.9˙0.8 7.0˙0.4 2.3˙0.2 n/a n/a 1000-028 5.157 15.9˙0.4 6.5˙0.5 1.7˙0.2 18.5˙0.1 0.7˙0.1 at times up to 15–20 s from typical 9-probe, 11-probe and 25-probe MPDV experiments are presented in Fig. 31.6. It should be noted that due to the similar type of velocity profiles for 304L and HY100 steels in 11-probe and 12-probe MPDV experiments, only 11-probe velocity profiles are presented in Fig. 31.6. In general, all A36 and 304L steel showed a twowave structure velocity profile in compression: an elastic wave followed by a relatively sharp plastic wave. Because of known material properties differences between steel and stainless steel, subtle differences do exist in the measured wave profiles. The velocity peak for the plastic wave was proportional to the impact velocity. Velocity profiles also showed a second velocity peak and a spall signature in the form of a ‘pullback velocity’ signal within the first 5 s. Supposedly, all low carbon alloy steels should show another wave rise after the plastic wave due to the’$"phase transition [13] similar to what was observed in shocked iron [14, 15]. However, in the case of HY100 steel, the signature of ’$" phase transition is not prominent in our gas gun experiments at the rear surface. We suspect this could be due to the complex, asymmetric nature of the stress wave at that location in the target plate, and the relatively low stress amplitude of the wave at the rear surface of the target plate. Fundamental shock compression experiments that do observe the phase transition wave have all been done with a condition of uniaxial strain, which is not the case for the stress wave we observe. In all MPDV experiments, the impact center is within ˙3.0 mm from the nearest PDV probe. Therefore, probes located closest to the impact center showed the earliest arrival of the free surface velocity signal and showed the highest peak velocities in general; but there were certain exceptions. While the exact reason of these anomalies is not yet understood completely, possible reasons may include the complex asymmetric nature of the stress wave. 31.4 Conclusion Gas gun experiments were performed to measure the plastic deformation of steel plates during high-velocity impact and an MPDV system was used to measure free surface velocity during these experiments on the back of the target plate. Plastic deformation as represented by bulge of the target plates and crater damage were proportional to impact velocity. Velocimetry data captured by MPDV systems provide information on the comparative dynamic behavior of target plates made of different materials. Although, significant efforts are still needed to analyze these MPDV data accurately, implementation of MPDV system in high-velocity impact experiments certainly provides a new horizon for the researchers to explore. Work is ongoing to interpret the results of these experiments.
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