New correlations for evaluating the equivalent bare charge mass for a cased charge

Abstract

Munitions contain casings that consume explosive energy. The blast load (e.g., peak overpressure and maximum impulse) intensity generated by ammunition explosion will be lower than that generated by a bare charge with equal mass. To evaluate the blast load of a cased charge under different conditions, the equivalent bare mass needs to be calculated. However, the accuracy of existing correlations strongly depends on the empirical determination of relevant controlling parameters and lacks theoretical clarification. In this paper, new correlations are proposed based on a more rigorous theoretical derivation, considering both the mechanical behaviors of the casing’s material and the change of the polytropic exponent during the expansion process of the explosion products. The controlling parameters are attributed to the rupture radius ratio and the polytropic exponent of detonation products expansion to casing rupture state. The reasonability is validated by both comprehensive numerical simulations with dynamic mechanical constitutive model and theoretical derivations. The results calculated by the new correlation show better agreement with the experimental results than those calculated by previous correlations, and the results difference is explained in more consistency with the thermos-physical properties of the charge and mechanical behaviors of casing material. Furthermore, the correlation of the cased-to-bare impulse ratio is also theoretically improved, providing a more accurate theoretical basis for both the equivalent bare mass and impulse evaluation for a cased charge.

Keywords

• Cased charge
• Energy conservation
• Equivalent bare charge
• Fracture strain
• Polytropic exponent