repetitions resulted from firing the same charge-standoff configuration against the two target types (e.g. tests 1 and 6). This confirms the stability of the jet tip velocity and the average velocity measurement should be a good estimate of the jet velocity prior to impact with the target. For the NWS charge the average jet velocity was 4.32 km/s. This increased by 14 % to 4.91 km/s for the SWS charge. The CWS case resulted in an average velocity of 6.3 km/s, which represents a 46 % increase in jet velocity over the NWS charge and a 28 % increase over the SWS charge. Thus, a significant increase in the jet velocity with the enhanced wave shaping techniques was observed that emphasises the cumulative effect and pressure increase from the geometrical convergence of the detonation waves. Details of the experimental and numerical analyses of the SC liner collapse can be found in [6, 7]. The damage common to the PC targets consisted of the following: very limited damage around the hole on the front face of the target; extensive spallation on the rear face of the target; and the borehole produced by the shaped charge jet. Thus the observed external damage can be separated in two distinct zones for the present tests: the borehole and the spallation zone. For the first one, the tapering borehole with the borehole diameter Bs at the front surface of the target, reduces gradually to the minimum borehole diameter Bmat, conventionally, the depth of penetrationDp. For the spallation zone, the damage can be roughly approximated by a cone of diameter, Ds (diameter of the maximum spallation zone), with the base at the rear surface of the target. The height of the coneHp is such that in the case of complete penetrationDp + Hp ¼W,whereWis the target height. If the borehole does not penetrate all the way through, as observed in test #1, Dp + Hp <W. The values of the target damage parameters for all ten tests listed in Table 39.1 are summarised in Table 39.2. Due to the general lack of spallation for the UHPC targets the parameters Ds andHp cannot be defined in the tests #6–#10. In this case, the remarks for the Ds parameter are: MC refers to minor cracking, C—cracking and S to almost spallation with the plug attached to the main body of the target. The borehole damage zone was measured by inserting rods with consecutively reduced diameters. Keeping the scale of the measurements for the borehole zone, the results of the measurements are graphically depicted in Fig. 39.2 for each of the tests. The scales in the radial and depth directions for the borehole cavity are different but independently to scale. The scale for the spallation zone is not preserved and the zones are shown schematically with indication of partial or complete penetration for the PC tests or cracking for the UHPC tests. An example of damage to the PC targets is shown in Fig. 39.3. From the damage summary, it follows that all of the jets from the charges with wave shaping (simple or complex) penetrated the 300 mm deep plain concrete targets, whereas the NWS charge jet did not fully penetrate, as shown in Fig. 39.3a, b. Complete penetration depends on both the borehole produced by the jet and the level of spallation on the rear face of the target. The CWS charge had the highest jet velocities (as recorded by the make screen gauges), however, the SWS charges produced the largest rear face spallation depths against the plain concrete targets. This may be a result of the jet formation and shape, which for the CWS charges produces a more localised penetration effect similar to those produced by small-angled high-density SC metal liners. On the contrary, for the SWS and NWS charges, extensive scabbing effects were produced (possibly without penetration) which are typical for Table 39.2 Target damage summary # 1 2 3 4 5 6 7 8 9 10 Bs 29.9 35.5 29.9 35.5 29.9 25 25 21.8 25 25 Bm 7.9 19.5 26.4 19 24.3 7.9 7.9 7.9 7.9 7.9 Ds 500 550 520 400 550 MC C C S C Hp 90 140 125 95 115 – – – – – Dp 177 160 185 205 185 138 185 190 182 192 Fig. 39.2 Schematic depiction of damage zones in the PC (#1–#5) and UHPC (#6–#10) targets. Borehole (top)—to scale and spallation (bottom)—not to scale. The estimated spallation markings for the UHPC tests indicate minor cracking detached from the borehole damage area 270 A.D. Resnyansky and S.A. Weckert
RkJQdWJsaXNoZXIy MTMzNzEzMQ==