The role of Kelvin-Helmholz instabilities on shaped charge jet interaction with reactive armour plates

• Reactive armor panels have been used for many years as very efficient add-on armoragainst shaped charge warheads. The main features of the defeat mechanisms of thearmor are therefore well known. The origin of the irregular disturbances on the shapedcharge jet, which leads to the severe fragmentation and scattering of the jet, is howevernot described in literature. As this scattering of the jet provides the main protectionmechanism of the armor, it is of interest to understand the details of the interaction andthe origin of the disturbances. Some experimental observations have been made showingthat the backward moving plate often displaces the jet relatively smoothly while it is theinteraction with the forward moving plate that causes the disturbances that leads tofragmentation and scattering of the jet. In this work, a mechanism for the interaction isproposed based on the theory of Kelvin–Helmholtz instabilities, which explains the originof the disturbances on the jet due to the interaction with the forward moving plate.Numerical simulations have been performed to show the difference in the mechanisms ofbackward and forward moving plates when interacting with the jet. The impact angle ofthe plate seems to be the dominant parameter for the onset of instabilities. A parametricstudy has also been performed on how different interaction and material parametersinfluence the development of instabilities of the interface between the jet and the armorplate. The parametric study shows that low-strength jets promote development of instabilities,a tendency that is amplified by frictional forces between the materials. Theinfluence of the plate strength is more complex due to the influence of the structuralstability on the contact forces. The effect of friction and melting of the metals in theboundary layer to the development of the instabilities is discussed. A microscopic study ofthe edge of the penetration channel has been made, which shows that the materials havebeen melted during the interaction between the plate and the jet.

Keyword

TECHNOLOGY

TEKNIKVETENSKAP

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ref (subject category)

art (subject category)