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2 Journal of KONES

2 2015

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Selected aspects of modelling a phenomena occurring with very large strain rates on the example of the shaped charge jet stream forming process and explosive formed projectiles

Panowicz R., Konarzewski M., Borkowski J., Milewski E.

Journal of KONES

2015

Vol. 22, No. 3

187--192

During the process of the shaped charge jet stream formation and creation of the explosive formed projectiles, we have to deal with strain rates reaching level of 107 1/s and strains larger than in other dynamic phenomena. Therefore, the correct numerical analyses of such problems are especially demanding, both in terms of preparation of the numerical model and time needed for obtaining the solution. For their execution, both meshfree and Euler description based computational methods are used. Due to very large deformations and associated with them numerical analyses errors, computational methods based on the Lagrange description are not used. Description of the materials behaviour has to take into account influence of the strain rate in wide range of parameters. In most cases, it is realized by using in computational analyses Johnson-Cook or Steiberg-Green constitutive models. These models provide an accurate description of the material parameters not only in the wide range of strain rates, but also in large scope of strains and temperatures. Article presents results of the numerical analyses concerning the influence of selected numerical and geometric parameters of the system on the process of shaped charge jet stream formation and creation of explosive formed projectile.

Analysis of the influence of the finite elements mesh density on the determined shaped charge jet parameters

Panowicz R., Konarzewski M., Borkowski J., Milewski E.

Journal of KONES

2015

Vol. 22, No. 3

329--335

Article presents results of numerical analyses of the finite elements mesh density influence on the shaped charge jet stream formation process and its selected parameters. Authors considered classical shaped charge, which consists of the plastic explosive material, copper liner and aluminium case. To properly described, material properties of the liner and case of the shaped charge, the Johnson-Cook material model was used. Detonation process was described using burn model approach. Behaviour of the detonation process products was described by commonly used John-Wilkins-Lee equation of state. Due to the nature of the presented phenomenon, in which we are dealing with large strains and strain rates, for its modelling authors utilized Euler description, implemented in the LS-Dyna software. In these method material flows by the finite elements and mesh is not deformed. Such approach allows for modelling phenomena where large and very large deformations occur. Unfortunately, it can result in a destabilizing of the systems energy balance. In order to minimize dissipation processes, in calculations was used second order scheme because of the spatial variables and time. Analyses were performed in axially symmetric setup, which was possible due to the symmetry of the analysed system. Influence of the finite elements size on the process of jet stream formation and its selected parameters was analysed.