uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
The role of Kelvin-Helmholz instabilities on shaped charge jet interaction with reactive armour plates
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
2010 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 77, no 5, 051805- p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2010. Vol. 77, no 5, 051805- p.
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-132941DOI: 10.1115/1.4001738OAI: oai:DiVA.org:uu-132941DiVA: diva2:359769
Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2011-01-13Bibliographically approved
In thesis
1. Interaction between High-velocity Penetrators and Moving Armour Components
Open this publication in new window or tab >>Interaction between High-velocity Penetrators and Moving Armour Components
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work was aimed at understanding mechanisms of importance for the design of weight-efficient armour against long-rod projectiles (LRP) and shaped charge (SC) warheads. The focus was on how to achieve effective mechanical disturbances on the threat before it hits the target.

Methods were developed for laboratory tests in full and reduced scale, and for registration and evaluation of the fast and violent events involved. For numerical simulations, the Xue-Wierzbicki fracture model was implemented and used for the LRP in order to allow fractures due to shear load without extensive damage of the entire projectile. In order to reproduce the scattering of the SC jet after interaction with reactive armour, use was made of a very fine computational mesh.

Severe disturbances and fractures of the penetrators (LRP and SC jet) originate from the interaction phase in which a plate slides along the penetrator. In the case of an SC jet, this sliding contact results in severe scattering of the SC jet due to instabilities of the same kind as those between two fluids in contact, moving in parallel with different tangential velocities (Kelvin-Helmholtz instabilities). The generation of such instabilities is caused by the very high velocity (in the order of 10000 m/s) and the relatively low material strength of the SC jet in combination with the high contact pressure and the motion of the plate. In the case of an LRP, the high strength of the material of the projectile and its low velocity (in the order of 2000 m/s) relative to that of an SC jet, prevent the generation of KH-instabilities. Instead, fractures of the projectile may occur due to abrupt change of contact pressure at the exit of the plate. The positive pressure gradient and longer interaction time of forwards moving plates compared to backwards moving plates make the former plates more effective. A side-hitting steel rod gives approximately the same effect on an LRP as that of a steel plate with the same thickness, velocity and angle of obliquity.

The results obtained can be used for assessment and optimisation of reactive armour modules and active protection systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 65 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 784
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid Mechanics
urn:nbn:se:uu:diva-132922 (URN)978-91-554-7940-4 (ISBN)
Public defence
2010-12-15, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 714Available from: 2010-11-24 Created: 2010-10-29 Last updated: 2011-03-21Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text
By organisation
Applied Mechanics
In the same journal
Journal of applied mechanics
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 493 hits
ReferencesLink to record
Permanent link

Direct link