Abstract
The acceleration characteristics of fragments generated from explosively-driven cylindrical shells are important issues in warhead design. However, there is as yet no reasonable theory for predicting the acceleration process of a specific metallic shell; existing approaches either ignore the effects of shell disintegration and the subsequent gas leakage on fragment acceleration or treat them in a simplified manner. In this paper, a theoretical model was established to study the acceleration of discrete fragments under the combined effect of shell disintegration and gas leakage. Firstly, an equation of motion was developed, where the acceleration of a cylindrical shell and the internal detonation gas was determined by the motive force impacting the inner surface of the metallic cylinder. To account for the force decrease induced by both the change in fragment area after the shell disintegrates and the subsequent drop in gas pressure due to gas leakage, the equation of motion was then associated with an equation for the locally isentropic expansion of the detonation gas and a modified gas-leakage equation. Finally, theoretical analysis was conducted by solving the associated differential equations. The proposed model showed good agreement with experimental data and numerical simulations, indicating that it was suitable for predicting the acceleration of discrete fragments generated from a disintegrated warhead shell. In addition, this study facilitated a better understanding of the complicated interaction between fragment acceleration and gas outflow.
Highlights
Cylindrical shells filled with explosive charges are typical structures in conventional warhead design and can be sorted into the continuous shell and the preformed-fragment shell
There are several possible explanations for this point of view. It can be inferred from Equation (12) and Equation (14) that the acceleration of the discrete fragments generated from the disintegrated shell is determined by the inner surface of the fractured shell S0, the gas pressure inside the disintegrated shell P0, and the ratio of the leaked charge mass to the total mass C0 /C
For our theoretical calculations on natural fragment acceleration, we choose to replicate the experiment conducted by Wang et al [4], because the shell disintegration and acceleration process of an AISI 1045 steel cylinder were captured clearly and the place where Photonic Doppler Velocimetry (PDV) located for fragment velocity measurement was free from end effects
Summary
Cylindrical shells filled with explosive charges are typical structures in conventional warhead design and can be sorted into the continuous shell and the preformed-fragment shell. Lindsay et al [19] separated the roles of the two factors and established a two-component model to fit the shell expansion data obtained from a copper-cylinder expansion test Their formulas neglect shell disintegration and gas leakage, and the post-disintegration acceleration of the shell is again not derived or described reasonably. Zhang and Sun [23] built a model for predicting the fracture radius of a cylindrical shell and the corresponding rupture velocity, based on yield conditions, continuous equations, and equations of motion These models have contributed successfully to the understanding of the failure and fracture behavior of continuous warhead shells, but it remains challenging to calculate the specific fragment acceleration process because gas leakage is much too complicated and challenging to analyze. The detailed fragment-acceleration process and final fragment velocities agreed well with experimental data and numerical simulations, indicating that the proposed model is applicable to calculate the acceleration of discrete fragments produced by a warhead shell
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