Stand-off-dependent penetration-damage trends in finite-thickness concrete under scaled shaped charge loading: Experimental evidence for model calibration and protective assessment

Abstract

Concrete remains the predominant construction material for military and protective infrastructure due to its structural robustness and cost-effectiveness. This study investigates the penetration behaviour of concrete targets subjected to scaled shaped charge detonation, with emphasis on stand-off distance effects. Controlled experiments were conducted using small-scale shaped charges with oxygen-free copper liners. Jet formation and tip velocity were characterised using flash X-ray radiography, incorporating magnification factor corrections for enhanced accuracy. Concrete targets (compressive strength 43.8 ± 1.87 MPa, n = 3) were tested at stand-off distances of 30-150 cm (11 tests total: n = 3 at 150 cm; n = 2 at each remaining distance), assessing observed perforation occurrence, crater diameter, and surface damage extent. Results indicate that increasing stand-off distance is associated with reduced observed perforation occurrence and generally increased surface damage area and crater diameter within the tested configuration. At shorter stand-off distances, concentrated jet momentum produces deeper penetration; at larger stand-off distances, jet breakup and energy dispersion yield broader but shallower damage zones. This study provides three primary contributions: (i) a reproducible experimental benchmark with fully specified charge geometry, target properties, and measurement procedures; (ii) uncertainty-aware crater and perforation metrics reported as mean ± standard deviation with explicit sample sizes at each stand-off; and (iii) preliminary experimental evidence of a stand-off-dependent transition trend that can support calibration and validation of high-fidelity hydrocodes. The observed damage pattern is consistent with the hypothesis that, as stand-off distance increases, part of the effective jet energy shifts from axial penetration toward broader surface cracking and spall formation. The results are therefore framed primarily as an experimental benchmark for model calibration and comparative protective assessment rather than as direct full-scale design guidance.