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Johnsson, Fredrik
Publications (3 of 3) Show all publications
Elofsson, M., Johnsson, F., Forsman, B. & Liwång, H. (2016). Riskanalys för att fatta bättre beslut. Tidskrift i sjöväsendet, 2, 130-141
Open this publication in new window or tab >>Riskanalys för att fatta bättre beslut
2016 (Swedish)In: Tidskrift i sjöväsendet, ISSN 0040-6945, Vol. 2, p. 130-141Article in journal (Other academic) Published
Place, publisher, year, edition, pages
Tyresö: Kungl. Örlogsmannasällskapet, 2016
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Military Technology
Identifiers
urn:nbn:se:fhs:diva-6247 (URN)
Available from: 2016-07-06 Created: 2016-07-06 Last updated: 2019-08-26Bibliographically approved
Johnsson, F. & Vretblad, B. (2015). Full-scale experiments to determine shaped charge penetration in sandbag constructions from long standoff distances. In: 16th ISIEMS International Symposium on the Interaction of the Effects of Munitions with Structures: . Paper presented at 16th ISIEMS International Symposium on the Interaction of the Effects of Munitions with Structures, 2015.
Open this publication in new window or tab >>Full-scale experiments to determine shaped charge penetration in sandbag constructions from long standoff distances
2015 (English)In: 16th ISIEMS International Symposium on the Interaction of the Effects of Munitions with Structures, 2015Conference paper, Published paper (Refereed)
Abstract [en]

Protective measures must often be established during explosive ordnance disposal (EOD) operations to reduce the effects of unexploded ordnance (UXO). Adequate models for the design of protective constructions against the jet from shaped charge ammunition are lacking. Two conditions are unique for EOD operations on shaped charges: constructions built from sandbags and long standoff distances. For these conditions, verified test data are very limited.

 

To study these conditions, full-scale experiments have been conducted at the Swedish EOD and Demining Centre (SWEDEC) with the objective to generate data for the development of a useful tool for EOD operations. Three series of five shots using a 107 mm warhead have been fired against both sandbag and homogenous sand/gravel targets, at standoff distances from 10 to 100 calibers.

 

The result indicates that the hydrodynamic penetration theory, based on the Bernoulli equation, is not suitable for these target materials and these standoff distances. The actual penetration was more than twice what was expected from calculations based on this theory. Furthermore, the penetration was found to be significantly smaller when the sand/gravel was packed in sandbags – a result in contradiction to the same theory.

 

Standoff curves which also take into account if the target material is packed in sandbags or not have been developed. The general shape of these curves is different from what is characteristic for materials such as metals and concrete. Increasing standoff decreases penetration only marginally.

 

The jet is fully fragmented into smaller segments when it hits the target, but still has good penetration capability in these target materials. This phenomenon is related to the cut-off velocity, the lowest jet velocity that gives a contribution to the penetration, which is considerably lower than for more resistant target materials. Combining the influence of the cut-off velocity with the hydrodynamic penetration theory is used in the explanatory model in the paper.

 

The experiments also demonstrated that the target material surrounding the jet moved forward, resulting in a growing penetration channel after the jet was fully consumed. This is related to phase three penetration. The contribution to the total penetration is considerable and gives a plausible explanation as to why sandbags give better protection.

 

The results have been used to develop a new model for the design of protective measures against jet penetration. The military utility for EOD operations has been the main criteria during all development phases. The final result is a simple tool that can be used under field conditions. Approximately one year after the first experiments, the result has been implemented in regulations and training for EOD personnel in the Swedish Armed Forces.

Keywords
Shaped Charge, Penetration, Sandbag, Explosive Ordnance Disposal, Protective Measures, Military Utility
National Category
Other Engineering and Technologies
Research subject
Military Technology
Identifiers
urn:nbn:se:fhs:diva-5813 (URN)
Conference
16th ISIEMS International Symposium on the Interaction of the Effects of Munitions with Structures, 2015
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2019-08-26Bibliographically approved
Johnsson, F., Vretblad, B. & Sivertun, Å. (2012). Shaped Charge Calculation Models for Explosive Ordnance Disposal Operations. Journal of Military Studies, 3(1), 1-24
Open this publication in new window or tab >>Shaped Charge Calculation Models for Explosive Ordnance Disposal Operations
2012 (English)In: Journal of Military Studies, ISSN 1799-3350, Vol. 3, no 1, p. 1-24Article in journal (Refereed) Published
Abstract [en]

The clearance of unexploded ordnance (UXO) and other explosive remnants of war (ERW) containing shaped charge warheads poses a particular technical hazard to consider for explosive ordnance disposal (EOD) personnel. The wide use of light anti-tank weapons, such as rocket propelled grenades and the scattering of sub-munitions in different conflict areas have made the clearance of shaped charge ammunition a frequent task. However, unlike other hazards, for shaped charges, EOD personnel lack adequate means for the establishment of the maximum hazardous area and for the design of measures for hazard confinement against the shaped charge effect.

In this article two different models are suggested, which together give guidance for protective measures during clearance of shaped charge ammunition. The development of these models is based on their military utility, by consideration of the limited information availability, the short time frames, the working methods and the technology level that are characteristic for EOD operations. The two suggested models are developed further into a complete set of design rules for protective measures, giving a versatile tool to replace today´s rough estimates and guesswork, in these safety-related decisions.

Place, publisher, year, edition, pages
Helsinki: National Defense University, Finnish Society of Military Sciences, 2012
Keywords
shaped charge, jet penetration depth, hazardous area, explosive ordnance disposal, protective measures
National Category
Engineering and Technology
Research subject
Military Technology
Identifiers
urn:nbn:se:fhs:diva-4142 (URN)
Available from: 2013-08-28 Created: 2013-08-28 Last updated: 2019-08-26Bibliographically approved
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