shallow low-density metal SC liners. The damage images in Fig. 39.3 correspond to the NWS charge where the jet did not fully penetrate the target, and the SWS charge at 134 mm standoff distance (test #3). The latter result is typical for the rest of the set of tests against the plain concrete. The damage results reported here for the UHPC targets relate to the five tests #6–#10 as described in the testing schedule of Table 39.1. The typical damage to the front face of the UHPC target for the SWS and CWS charges is shown in Fig. 39.4a, c. The level of scabbing around the hole was similar for all of the charge-standoff combinations; approximately 100 mm diameter and 12–20 mm depth. These dimensions are less than those for the PC targets due to the increased strength of theUHPC. The rear face damage to the UHPC targets exhibited some variation. It varied from very subtle cracking for the NWS charge, through to some cracking for the SWS charge (Fig. 39.4b) and almost spallation for the CWS charge (Fig. 39.4d). The SC jet did not achieve complete penetration through the 300 mm deep UHPC targets, except for the CWS charge in similar previous testing [6, 7] with a more powerful Composition B solid explosive. The boreholes produced by the two CWS charges at the two standoff distances were very similar, including the initial width of the hole, the hole depth and degree of tapering with depth, despite the difference in standoff and jet formation time. Comparatively, the boreholes produced by the two SWS charges at the two standoffs showed a similar trend to that achieved with the PC targets. At the reduced standoff, the jet has less time and space to form and thus impacts the target surface with a larger area of interaction (wider jet). This is shown by the initially larger borehole for the SWS charge at the reduced standoff. However, this comes at the expense of greater tapering of the borehole with depth due to not developing a fully formed SC jet. Summarising the results of the SC jet impact against the UHPC targets, it should be noted that rear spallation was rarely observed, except for the CWS charge at the smaller standoff. The rear face damage was mostly limited to cracking with the degree of cracking increasing for the SWS and CWS charges. Also, less damage surrounding the borehole at the impact surface was noted for the UHPC compared with the PC. Rear surface damage in the form of spallation for the UHPC targets requires a sustained energy deposited over some minimum area of projectile–target interaction (a discussion on this issue can be found in [5]). Possibly, the reduced area of interaction and higher compressive strength of the UHPC is a reason for the borehole diameter not increasing with standoff distance in contrast to the PC targets. The reduced area of interaction also Fig. 39.3 Damage to the plain concrete targets: NWS charge (test #1)—front face (a), rear face (b); and SWS charge (test #3)—front face (c), rear face (d) Fig. 39.4 Damage to the UHPC targets at 86 mm standoff; SWS charge (test #7)—front face (a), rear face (b); and CWS charge (test #9)—front face (c), rear face (d) 39 Damage of Two Concrete Materials due to Enhanced Shaped Charges 271
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