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BETA
Vretblad, Bengt
Alternative names
Publications (10 of 16) Show all publications
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
Militärteknik
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: 2017-08-01Bibliographically approved
Johnsson, F. & Vretblad, B. (2015). Risk: Is That Really a Technical Issue?. In: ISMS2015: . Paper presented at ISMS Annual Conference, 13-15 October 2015, Helsinki, Finland.
Open this publication in new window or tab >>Risk: Is That Really a Technical Issue?
2015 (English)In: ISMS2015, 2015Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Life is full of risks – in war and peace. Risks that we often try to avoid, eliminate or - at least - reduce. Military activities often include risks – in war requiring excessive countermeasures but also in peacetime situations and during international military missions where competent risk reducing actions must be searched for.

Military Technology within SNDU focuses research on military utility as a measure when evaluating technical systems for military purposes. The definition of military utility often must be different for different applications and measured in different units, e.g. economic costs, cost in time to complete a task or costs in human lives - or even combinations of units for different systems.

A recent research program at SNDU handles risks in explosive ordnance disposal (EOD) operations based upon the military utility.

The wide use of light anti-tank weapons and the scattering of sub-munitions have made clearance of unexploded ordnance containing shaped charge warheads - a frequent task for EOD personnel.

Several circumstances are characteristic for EOD operations and have to be taken into consideration when evaluating the military utility: the limited information availability, the short time frames, the working methods and the technology level.

Protective measures such as evacuation of a hazardous area or building of a protective construction often have to be executed to reduce risks.  Two conditions are unique for protective constructions in EOD operations on shaped charge ammunition: constructions built from sandbags and long standoff distances.

As has been shown in earlier ISMS annual conferences measures to handle risks were identified and acted upon in the SNDU program[i],[ii].  

The result up until now is a tool meeting the military requirements - e.g. which can be used under field conditions, within a limited time frame and without access to advanced calculating equipment. The format is a simple diagram included in a complete design tool.

This tool is now being implemented in regulations and training for EOD personnel in the Swedish Armed Forces.

The result reached so far fill a gap, but it does not represent the ultimate solution for risk handling –it rather form a step forward within EOD operations. The tool, however transparent and based upon verified tests, only handles the two cases: either full countermeasures or no countermeasures. This binary approach to risk factors is not unique for this situation, many methods and tools are designed for extrema, nothing in between.

To establish a protective construction that completely eliminates the risk is often not possible, simply because the large dimensions require resources or time to complete the construction that are not available.

What if only partial protection is possible– what risk does that leave us with?

The surroundings also affect the actual risk. Infrastructure, terrain formations and vegetation can both decrease and increase the effects from the ammunition. Furthermore, what influence do different render safe procedures and applied clearance charges have on the risk? Only suitable tools that consider the actual influence of these aspects will provide the necessary foundation for estimation of a more correct risk. Here we are still without rules to apply.

Basic questions like “What risk is acceptable?”, “During what conditions?” and “How do we reach acceptable risk levels?” remain to be answered. Furthermore, we have to develop how we communicate the risk to decision makers, particularly in extreme situations. If a risk described in mathematical format is not rightly understood by everyone other formulations that are perfectly clear must be used.

We know that the attitude towards risks varies with individuals, with the situation and over time but we do not have vehicles to give us adequate quantitative measures. The answers to questions on acceptable risk not only relate to technical issues but also comprise military judgement, leadership and communications as well as they have judicial and ethical dimensions.

The objective for future research in the field is a dynamic risk management model comprising also other situations than those studied up until now and to evaluate and appreciate alternative mitigation measures along the chain of clearance activities.

A dynamic risk management concept developed for EOD operations should be a step in the handling of the general threat from explosive remnants of war, i.e. land mines, UXO:s  and IED:s, which often have significant impact on a military operation as a whole. These threats exist on all levels of conflict and their constantly changing character requires a dynamic approach when it comes to risk handling.

War fighting is evolving, with a continuous struggle between our measures and the opponents countermeasures. There is no clear distinction between friend and foe, peace and war or danger and safety - military activities take place in a grey-zone. Supportive programs have to be adapted to this reality and methods for dynamic risk management tailored for military operations. The military utility of such a concept is obvious with good possibilities to generalisation, a worthwhile starting point for dynamic risk handling methods for other military activities.

The paper is focused on a dynamic risk management concept where not only technical issues are dealt with, but also other military concerns are addressed with the military utility as a basic measure.

 

[i]Johnsson, F, Vretblad, B & Sivertun, Å, Shaped Charge Calculation Models for Explosive Ordnance Disposal Operations. International Society of Military Sciences (ISMS) 2012 Annual Conference. Kingston, Canada, 2012.

 

[ii]Johnsson, F & Vretblad, B, Experimentally developed model for the design of protective measures against shaped charge jet penetration during EOD operations. International Society of Military Sciences (ISMS) 2014 Annual Conference. Vienna, Austria, 2014.

Keywords
Dynamic Risk Management, Military Utility, Explosive Ordnance Disposal, Protective Measures, Shaped Charge
National Category
Other Engineering and Technologies
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-5814 (URN)
Conference
ISMS Annual Conference, 13-15 October 2015, Helsinki, Finland
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2016-11-07Bibliographically approved
Lindström, R. O., Vretblad, B., Janzon, B., Christensson, A. & Sjöland, M. (2014). En studie rörande nolltolerans mot förluster vid internationella insatser: Årlig redovisning från KKrVA Avd IV den 4 december 2013. Kungl Krigsvetenskapsakademiens Handlingar och Tidskrift, 1:Bihäfte(1)
Open this publication in new window or tab >>En studie rörande nolltolerans mot förluster vid internationella insatser: Årlig redovisning från KKrVA Avd IV den 4 december 2013
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2014 (Swedish)In: Kungl Krigsvetenskapsakademiens Handlingar och Tidskrift, ISSN 0023-5369, Vol. 1:Bihäfte, no 1Article in journal (Other academic) Published
Abstract [en]

The Royal Swedish Academy of War Sciences, Division of Military Technology, presents its annual report on the theme "Zero Tolerance for Losses in International Operations". Focus has been on own personnel and losses by combat action.) The study primarily concerns the land arena and the time span 2020-2030. Weapons development continues. The availability of weapons – even advanced ones – increases, also for non-state belligerents. Zero tolerance will require more and more efficient protection solutions to be developed – and to be used to meet increasing threats. Available technology offers many options. Zero tolerance requires high skills of the planner and purchaser, to ensure long-term research and development, timely acquisition and training, and ability to understand potential, limitations, and to adjust tactics accordingly. Holistic systems thinking will be required before, during and after interventions, including staff recruitment, advanced leadership, adequate equipment and high quality training in order to be able to fulfil a difficult mission in the highly complex environment in which the operation will occur.

National Category
Engineering and Technology
Research subject
Militärteknik; Ledningsvetenskap
Identifiers
urn:nbn:se:fhs:diva-4534 (URN)
Note

Bihäfte, Kungl Krigsvetenskapsakademiens Handlingar och Tidskrift

Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2019-08-01Bibliographically approved
Johnsson, F. & Vretblad, B. (2014). Experimentally developed model for the design of protective measures against shaped charge jet penetration during EOD operations. In: ISMS Annual Connference 2014: Armed Forces for 2020 and beyond Roles. Paper presented at ISMS Annual Conference 2014.
Open this publication in new window or tab >>Experimentally developed model for the design of protective measures against shaped charge jet penetration during EOD operations
2014 (English)In: ISMS Annual Connference 2014: Armed Forces for 2020 and beyond Roles, 2014Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The wide use of light anti-tank weapons, such as rocket propelled grenades and the scattering of sub-munitions lead toa greatnumber of explosive remnants of war (ERW) containing shaped charge warheadsin different conflict areas. A serious problem is that, the explosive ordnance disposal (EOD) personnel lack adequate means for the design of protective measures against the jetfrom clearance of shaped charge ammunition. In this paper, based on a master thesis in military technology,a previously suggested calculation model1, is developed further. The objectiveis to create a tool that can be applied to EOD operationsand meet military requirements by consideration of the limited information availability, the short time frames, the working methods and the technology level that are characteristic for such operations.

Full-scale experiments have been conducted to clarify the effects of conditions that are typical for EOD operations: protective measures built from sandbags with a long standoff distance to the ordnance. The results indicate that the hydrodynamic penetration theory is not suitable for these conditions,and,furthermore, thata sandbag construction provides significantly better protection against the jet than a homogeneous gravel construction.

By disturbance analysis, the sensitivity of the individual parameters in the model is studied for typical errors. Subsequently, Monte Carlo simulation has been used to analyse the cumulative effect these errors can cause. The simulation results have then been the used to determine the model ́s margin of safety.

To achieve the desired military utility it should be possible to use the model under field conditions, with limited time frames and without access to advanced calculating means. This has resulted in a simple diagram included in a completedesign tool.It is proposed to implement the toolin regulations and curricula for EOD operations in order to remedy today’s lack of decision support

National Category
Aerospace Engineering
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-5145 (URN)
Conference
ISMS Annual Conference 2014
Available from: 2015-01-12 Created: 2015-01-12 Last updated: 2015-11-26Bibliographically approved
Lindström, R., Vretblad, B., Christensson, S. A., Janzon, B. & Sjöland, M. (2013). En studie rörande nolltolerans mot förluster vid internationella insatser.
Open this publication in new window or tab >>En studie rörande nolltolerans mot förluster vid internationella insatser
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2013 (Swedish)Report (Other academic)
Publisher
p. 44
National Category
Other Engineering and Technologies
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-4343 (URN)
Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2017-01-04Bibliographically approved
Axberg, S., Andersson, K., Bang, M., Bruzelius, N., Bull, P., Eliasson, P., . . . Vretblad, B. (2013). Lärobok i Militärteknik, vol. 9: Teori och metod (1ed.). Stockholm: Försvarshögskolan (FHS)
Open this publication in new window or tab >>Lärobok i Militärteknik, vol. 9: Teori och metod
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2013 (Swedish)Book (Other academic)
Abstract [sv]

Ämnet militärteknik utgår från att tekniska system är officerens arbetsredskap och att en förståelse för och kunskap om dessa verktyg är central för att kunna utöva professionen framgångsrikt. Denna nionde volym av Lärobok i Militärteknik, benämnd Teori och Metod, behandlar centrala begrepp, teorier och postulat samt metoder för värdering av teknik och består av ett antal texter författade av 16 forskare och lärare vid den militärtekniska avdelningen. Volymen riktar sig främst till de som inlett sin officersutbildning och utgörs till stora delar av ett kompilat av publicerade och opublicerade militärtekniska texter och kan sägas utgöra militärteknikens ”state of the art”.

Place, publisher, year, edition, pages
Stockholm: Försvarshögskolan (FHS), 2013. p. 146 Edition: 1
Series
Lärobok i militärteknik, ISSN 1654-4838 ; 9
Keywords
militärteknik, militär nytta, risk, system, militär förmåga, teknikens inverkan
National Category
Other Engineering and Technologies not elsewhere specified Other Social Sciences not elsewhere specified
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-4381 (URN)9789186137236 (ISBN)
Available from: 2014-01-10 Created: 2014-01-10 Last updated: 2017-08-07Bibliographically approved
Vretblad, B. & Johnsson, F. (2013). Tool for Clearance of Shaped Charge Ammunition Designed for Military Usefulness. In: : . Paper presented at 15th International Symposium on Interaction of the Effects of Munitions with Structures (ISIEMS), 17-20 September 2013, Potsdam, Germany.
Open this publication in new window or tab >>Tool for Clearance of Shaped Charge Ammunition Designed for Military Usefulness
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Evaluation and assessment of weapons and weapon systems should be based upon military usefulness. The military usefulness should, similarly, be a basis for the assessment of procedures and processes used for military activities. Even advanced systems may fail when meeting military usefulness criteria.

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 scientifically based procedures for the design and establishment of protective measures do not exist. Procedures applied in the field are more often than not based upon ad hoc solutions.

 

To close the gap and find adequate methods for clearance of shaped charge ammunition, a tool has been developed at NDC to meet criteria from military usefulness and adopted to the prevalent operational conditions applicable to military missions, in particular:

 

    *   Complexity should be low bearing in mind the expertise available in the field.

    *   The time factor is essential both from strictly military aspects and from economic point of view.

    *   Information access. Data needed may be obscured or lacking.

    *   Simple construction that may be used with locally available material and equipment.

In addition to meeting the criteria for military usefulness, such a tool should address the different effects from shaped charges e.g. blast and fragments and – in particular - effects from the jet generated.

 

The principles for the tool are described in the paper. Of particular interest is the influence of the stand-off distance for the risk reducing methods.

 

The risks from different effects at different distances and in different directions are analyzed and discussed. In particular, the slug from the jet is shown to be decisive for the hazardous area when protective measures are inadequate.

Keywords
shaped charge, jet penetration, stand-off distance, explosive ordnance disposal, protective measures, danger area
National Category
Engineering and Technology
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-4339 (URN)
Conference
15th International Symposium on Interaction of the Effects of Munitions with Structures (ISIEMS), 17-20 September 2013, Potsdam, Germany
Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2015-06-04Bibliographically 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
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-4142 (URN)
Available from: 2013-08-28 Created: 2013-08-28 Last updated: 2017-08-01Bibliographically approved
Johnsson, F., Vretblad, B. & Sivertun, Å. (2012). Shaped Charge Calculation Models for Explosive Ordnance Disposal Operations. In: International Society of Military Sciences (ISMS) 2012 Annual Conference: . Paper presented at International Society of Military Sciences (ISMS) 2012 Annual Conference.
Open this publication in new window or tab >>Shaped Charge Calculation Models for Explosive Ordnance Disposal Operations
2012 (English)In: International Society of Military Sciences (ISMS) 2012 Annual Conference, 2012Conference paper, Oral presentation only (Refereed)
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 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 danger area and for the design of measures for hazard confinement against the shaped charge effect. This shortcoming limits the responsible EOD officer to rough estimates and guesswork without scientific support, in these safety-related decisions.

This paper is based on a SNDC military technology thesis, (1). In the thesis two different models, which together give guidance for protective measures during clearance of shaped charge ammunition, are suggested. 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 first model is intended for use in the design of measures for hazard confinement against jet penetration. The suggested model is derived from a combination of two existing models for the shaped charge effect. A model for shaped charge penetration in single layered media developed by the Swedish Defence Research Agency (FOI) is used as the basis for the model. This is then combined with a modified model that describes how the penetration depth decreases with an increasing stand-off distance. Together they give a simple model for calculating the minimum thickness of barricades and mounds to withstand the penetration of shaped charges at varying distances.

The second model is for estimation of the maximum hazardous area generated by the shaped charge jet. This calculation model is based on the trajectory of the most critical jet segment, i.e. the slug. By defining typical values for those parameters that EOD personnel normally do not have information about, this model can be described with a simple graph. The graph gives the maximum hazardous area based only on the calibre and the elevation of the ordnance. The slug may be stable or unstable in its trajectory - the former giving a significantly larger hazardous area. As the conditions for or the probability of which will apply in a particular case is, currently, not supported by adequate scientific data, figures are given both for a stable and a tumbling slug segment. The use of the figures for an unstable slug will lead to a smaller area at the expense of higher risk.

The two suggested models are developed further into a set of "tools" for the design of protective measures. These tools are adapted to the unique nature of EOD operations, and consist of a complete set of design rules giving a versatile tool to replace today´s rough estimates and guesswork.

Keywords
shaped charge, jet penetration, stand-off distance, explosive ordnance disposal, measures for hazard confinement, protective measures, danger area
National Category
Other Engineering and Technologies
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-2866 (URN)
Conference
International Society of Military Sciences (ISMS) 2012 Annual Conference
Available from: 2012-12-12 Created: 2012-11-14 Last updated: 2017-08-02Bibliographically approved
Johannesson, P. & Vretblad, B. (2011). Byggformler och tabeller (11ed.). Stockholm: Liber AB
Open this publication in new window or tab >>Byggformler och tabeller
2011 (Swedish)Book (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Stockholm: Liber AB, 2011. p. 177 Edition: 11
Keywords
Matematik, Mekanik, Hållfasthetslära, Byggstatik, Dimensioneringsregler, Geoteknik, Grundläggning, Träkonstruktioner, Betongkonstruktioner, Stålkonstruktioner, Hydraulik
National Category
Other Natural Sciences
Research subject
Militärteknik
Identifiers
urn:nbn:se:fhs:diva-3088 (URN)978-91-47-10022-4 (ISBN)
Available from: 2012-12-20 Created: 2012-12-20 Last updated: 2013-08-12Bibliographically approved
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