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Interaction between High-velocity Penetrators and Moving Armour Components
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
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. , p. 65
Series
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
Identifiers
URN: urn:nbn:se:uu:diva-132922ISBN: 978-91-554-7940-4 (print)OAI: oai:DiVA.org:uu-132922DiVA, id: diva2:359770
Public defence
2010-12-15, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Note
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
List of papers
1. Effect of thin oblique moving plates on long rod projectiles: a reverse impact study
Open this publication in new window or tab >>Effect of thin oblique moving plates on long rod projectiles: a reverse impact study
2006 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, no 10, p. 1696-1720Article in journal (Refereed) Published
Abstract [en]

The geometry and motion of long rod projectiles after penetrating thin obliquely oriented and moving armour plates were studied. Plates moving in their normal directions towards as well as away from the projectile (scalar product of velocities negative and positive, respectively) were considered. The influences of plate velocity and obliquity (angle between the normal of the plate and the axis of the projectile) were investigated through small-scale reverse impact tests with tungsten projectiles of length 30 mm and diameter 2 mm, and with 2 mm-thick steel plates. The obliquity (30°, 60° and 70°) and the plate velocity (300 to −300 m/s) were varied systematically for a projectile velocity of 2000 m/s. The disturbing effect of the plate on the projectile was characterised in terms of changes in length, velocity, angular momentum, linear momentum and kinetic energy. Plates with obliquity 60–70° moving away from the projectiles with velocity 200–300 m/s were found to cause extensive fragmentation of the projectile and to have large disturbing effects in terms of all measures used.

Keywords
Oblique plate, Reactive armour, Long rod projectile, Residual projectile, Reverse impact, Test, Experiment
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-70699 (URN)10.1016/j.ijimpeng.2005.02.004 (DOI)
Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2017-11-21Bibliographically approved
2. Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Numerical simulations
Open this publication in new window or tab >>Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Numerical simulations
2012 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 40-41, p. 35-45Article in journal (Refereed) Published
Abstract [en]

Simulations have been performed to evaluate the possibility of reproducing the fragmentation of a long-rod projectile impacted by a moving oblique plate. When the moving plate slides along the projectile, fractures due to shear loading may occur in the projectile. Therefore, a fracture model suggested by Xue–Wierzbicki was used for the projectile together with the Johnson–Cook strength model. This fracture model is based on an equivalent plastic strain of fracture which depends on a stress triaxiality and a deviatoric stress parameter. The results of the simulations were compared with experimental results of a preceding study in which the impact conditions were varied in such a way that the projectile fractured in some but not all tests. The comparisons show that the simulations reproduced the fractures in the projectile well. Also, the transition from a deformed non-fractured to a severely fractured projectile was captured. The benefit of including the deviatoric stress parameter and the mechanisms leading to fragmentation of the projectile are discussed.

Keywords
Reactive armour, Oblique plate, Long-rod projectile, Fracture model, Numerical simulation
National Category
Engineering and Technology
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-132940 (URN)10.1016/j.ijimpeng.2011.09.003 (DOI)000298460600005 ()
Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2017-12-12Bibliographically approved
3. Influence of side impacting dynamic armour components on long rod projectiles
Open this publication in new window or tab >>Influence of side impacting dynamic armour components on long rod projectiles
2007 (English)In: / [ed] Francisco Gálvez, Vicente Sánchez-Gálvez, 2007Conference paper, Published paper (Refereed)
Abstract [en]

(LRP) before they hit the basic armour is a weight efficient way of in-creasing the protection of lighter vehicles. In this study, the effect of moving armour components, in the form of one or three cylindrical rods, hitting the side of the LRP, was investigated. The rods were hit-ting the side of the LRP at an angle of attack of 60 degrees. Rod ve-locities of 200 and 600 m/s and hitting points in the front and in the middle of the LRP were studied. The velocity of the LRP was 2000 m/s. The study is based on small scale reverse impact experiments and continuum dynamic simulations.To break the LRP, high rod velocities must be used. One rod hitting the LRP at 200 m/s gives approximately the same effect (some yaw but no fracture) as that of a moving oblique plate having the same ve-locity and angle of obliquity. Increasing the velocity of the rod to 600 m/s resulted in fracture of the LRP closely behind the hitting point both when hitting the front and the middle of the LRP. When using three rods, fracture was only obtained when the hitting points of the rods were closely spaced.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132939 (URN)
Conference
International Symposium on Ballistics,23rd International Symposium on Ballistics, Tarragona, Spain, 16-20 April 2007
Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2016-04-07Bibliographically approved
4. Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Experimental test
Open this publication in new window or tab >>Deformation and fracture of a long-rod projectile induced by an oblique moving plate: Experimental test
2011 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 38, no 12, p. 989-1000Article in journal (Refereed) Published
Abstract [en]

The influence of projectile length to diameter ratio (15, 30 and 45), plate thickness (0.5, 1 and 2 projectile diameters), projectile velocity (1500, 2000 and 2500 m/s) and plate velocity (−300 to 300 m/s) on the interaction between long-rod tungsten projectiles and oblique steel plates (obliquity 60°) was studied experimentally in small-scale reverse impact tests. The residual projectiles and their motions were characterised in terms of changes in length, velocity, angular momentum, linear momentum and kinetic energy. The parameters found to have the largest influence on the disturbance of the projectile were the plate velocity, in particular its direction, and the thickness of the plate. In the ranges studied, the influence of length to diameter ratio and of projectile velocity were found to be less important.

Keywords
Reactive armour, Oblique plate, Long-rod projectile, Small scale, Reverse impact
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132938 (URN)10.1016/j.ijimpeng.2011.07.002 (DOI)000296680700007 ()
Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2017-12-12Bibliographically approved
5. The role of Kelvin-Helmholz instabilities on shaped charge jet interaction with reactive armour plates
Open this publication in new window or tab >>The role of Kelvin-Helmholz instabilities on shaped charge jet interaction with reactive armour plates
2010 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 77, no 5, p. 051805-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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132941 (URN)10.1115/1.4001738 (DOI)
Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2017-12-12Bibliographically approved

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