Calculation of Initial Parameters for Concrete Damage Induced by Spherical Cased Charge Blast

To quantitatively evaluate the destructive effects of a cased charge on concrete structures, this research combines theoretical analysis with numerical simulations to determine the initial blast wave parameters impacting the concrete surface with high precision. It further analyzes the influence of casing thickness on damage outcomes. Applying Newton′s second law, the research derives the governing equation of motion for the spherical shell by accounting for the simultaneous influences of detonation pressure, concrete resistance forces, and circumferential shell stresses. The governing equation was numerically solved using MATLAB, enabling a systematic investigation of the effects of casing thickness(2~8 mm) on the radial expansion velocity distribution. Through application of particle velocity continuity conditions at the shell-concrete interface, closed-form solutions were derived for both initial particle velocity and shock pressure at the concrete borehole wall surface. Numerical simulations were conducted for a representative scenario featuring composition B explosive(density is 1.6 g/cm, detonation velocity is 7.80 10³ m/s, charge radius is 23.3 mm) encased in 45# steel shell(density is 7.85 g/cm³, yield strength is 3.55 10² MPa) detonating within concrete medium(density is 2.4 g/cm³). The results demonstrate that the maximum shell velocity exhibits an inverse relationship with shell thickness, decreasing by 43.8% from 1.44 10³ m/s(2 mm shell) to 8.08 10² m/s(8 mm shell). Correspondingly, the pressure transfer ratio(P_mx/P_m) at the borehole wall declines from 0.82 to 0.46 with increasing shell thickness. This research establishes that reducing the shell thickness effectively enhances energy transfer efficiency and improves the blast damage effect on concrete, whereas increasing the shell thickness significantly reduces energy transfer efficiency but improves the projectile′s structural integrity and penetration capability, which is necessary for penetrating hard targets. These findings underscore the necessity of balanced ammunition design that considers both penetration requirements and blast effectiveness.