1998-04 Proceedings of the Third International Symposium on Technology and the Mine ProblemThe results of a feasibility test using Rigid
Polyurethane Foam (RPF) as an operational antipersonnel
mine counter-mine technique are presented.
RPF, at a given density and thickness, can withstand the
explosive effects of anti-personnel blast mines and mitigate
or neutralize the effects of surface laid anti-vehicular
mines. A 12-inch thick, 4 pound per cubic foot foam block
completely contained a 10-gram explosive charge of PETN
while a 30-inch foam block with the same density
contained a 30-gram charge. A 24-inch thick pad
supported 50 passes of an M88A2 Recovery Vehicle,
crushing the foam no more than 2-3 inches throughout the
length of a 56 foot foam roadway. Underneath this
roadway, simulated land mines set at 14 psi were not
triggered by the passage of an M88A2 and a HMMWV.
Our experiments indicate that RPF can provide additional
traction in muddy conditions and set-off explosives
connected to trip wires. The pressure and trafficability
experiments were conducted jointly with Sandia National
Laboratories and the Waterways Experiment Station,
Vicksburg, MS in July-August 1997, and the explosive
experiments were conducted by Sandia National
Laboratories at the Energetic Materials Research and
Testing Center (EMRTC), Socorro, NM in August and
October 1997

Alba, A.

Maruyama, X.

Mason, G.

Schmidt, C.

Woodfin, R.

Calhoun, Institutional Archive of the Naval Postgraduate School

Calhoun: The NPS Institutional ArchiveFaculty and Researcher Publications Faculty and Researcher Publications Collection1998The Use of Rigid Polyurethane Foam as a LandmineBreaching TechniqueAlba, A.http://hdl.handle.net/10945/484671THE USE OF RIGID POLYURETHANE FOAMAS A LANDMINE BREACHING TECHNIQUEA. Alba1, X. Maruyama1, R. Woodfin2, C. Schmidt3, G. Mason41 Naval Postgraduate School, CA2 Sandia National Laboratories, NM3 Los Alamos Technical Associates, NM4 Waterways Experiment Station, MSAbstract --The results of a feasibility test using RigidPolyurethane Foam (RPF) as an operational anti-personnel mine counter-mine technique are presented.RPF, at a given density and thickness, can withstand theexplosive effects of anti-personnel blast mines and mitigateor neutralize the effects of surface laid anti-vehicularmines. A 12-inch thick, 4 pound per cubic foot foam blockcompletely contained a 10-gram explosive charge of PETNwhile a 30-inch foam block with the same densitycontained a 30-gram charge.  A 24-inch thick padsupported 50 passes of an M88A2 Recovery Vehicle,crushing the foam no more than 2-3 inches throughout thelength of a 56 foot foam roadway.  Underneath thisroadway, simulated land mines set at 14 psi were nottriggered by the passage of an  M88A2 and a HMMWV.Our experiments indicate that RPF can provide additionaltraction in muddy conditions and set-off explosivesconnected to trip wires.  The pressure and trafficabilityexperiments were conducted jointly with Sandia NationalLaboratories and the Waterways Experiment Station,Vicksburg, MS in July-August 1997, and the explosiveexperiments were conducted by Sandia NationalLaboratories at the Energetic Materials Research andTesting Center (EMRTC), Socorro, NM in August andOctober 1997.IntroductionMines, both anti-tank and anti-personnel, have beencombat multipliers in past and present battlefields.  Whenproperly employed, mines can drastically reduce a unit's abilityto maneuver its forces and synchronize its efforts on thebattlefield.  Currently, our land forces have breach in-stridetechniques and countermine systems that can reduce a 300-meter long obstacle within ten minutes, but these techniquesand weapon systems are slowly becoming obsolete against therapidly evolving mine technology and techniques.  It has beenargued that the United States has made very little countermineprogress since World War II, instead, the focus has been ondeveloping fuzing, lethality, and emplacement technologies[Ref. 1].  This study presents new results using RigidPolyurethane Foam (RPF) to improve current breachingtechniques.  The scope of this study is centered on anti-personnel mines, however this report also includes results ofexperiments that can be extended to anti-tank mines.The purpose of this study is to determine if rigidpolyurethane foam can be used to either neutralize orefficiently attenuate the explosive effects of  surface orsubsurface laid anti-personnel mines [Ref. 2, 3].  It will alsodetermine if the foam is a viable system for operational use onthe modern day battlefield.  Feasibility experiments in theareas of trafficability, traction effects, trip wire reduction,foam repair, and explosive cavity formations provideinformation [Ref. 9] to determine the foam's applicability inmilitary operations.  One possible application is to spray thefoam on a minefield and allow a combat unit to continuethrough the obstacle field with speed and avoid losses to thecovering enemy unit.  Rigid Polyurethane Foam could also beused  as a temporary walkway as part of humanitarian effortsto protect civilian populations from mines left behind after aconflict.Rigid Polyurethane FoamThe RPF [Ref.4] chosen for these feasibility experiments,NCFI 811-91, is a two-part liquid which can expand up to 60times its original volume.  The amount of expansion willdepend on the desired strength of the foam.  Because of thisconsiderable volume expansion, this foam can be transportedin minimum bulk for possible military applications.  The twochemicals are 1,1-Dichloro-1-flouroethane (CH3CCl2F orHCFC-141b) and Polymethylenepolyphenylisocyanate(Polymeric MDI).  The first chemical is the Polyol resin andthe second chemical is the isocyanate.  The mix ratio of thechemicals by volume is one part resin to one part isocyanate.The mix ratio by weight is 100 parts resin to 106 partsisocyanate.  It has a cream time of 55-65 seconds and a risetime of 3-4 minutes [Ref. 5, 6]. Polyurethanes are formed from the reaction of a polyolwith an isocyanate [Ref. 7].  The polyol, which means multiplealcohols or multiple OH groups, reacts with isocyanate, whichis the N-C-O combination of atoms.  When these twomonomers combine, a more stable molecular structure resultsfrom the molecular rearrangement.RPF has been used in a variety of applications, such as inthe automotive and building industries, but it has been2primarily used for thermal insulation, specifically for frozencontainers fitted for trains, trucks, aircraft, and ships.  In theautomotive industry, RPF is used to fill longitudinal runners,motors, and trunk hoods in order to provide additionalstiffening.  The building industry uses RPF to fill gaps betweendoor casings and walls [Ref. 8].• Dr. Ronald Woodfin of the Exploratory Sensors andFusing Department of Sandia National Laboratories conductedextensive experiments on RPF from November 1995 throughFebruary 1996.  His results are contained in SAND96-2841.This Phase I report focuses on the "development of a foam thatcan neutralize mines and barriers and allow the safe passage ofamphibious landing craft and vehicles" [Ref. 9].  Phase Iconcentrated on the following areas:• Laboratory characterization of foam properties• Field experiments with prefabricated foam blocks inorder to determine its capability  to carry military traffic• Flammability characteristics• Response to bullet impact• Toxicity• Explosive cavity formation from surface and subsurfaceshotsFeasibility ExperimentsThe feasibility experiments were conducted at twolocations.   The initial experiments were conducted jointly withSandia National Laboratories and the Waterways ExperimentStation, Vicksburg, MS at Duckport, LA [Ref. 10] while theexplosive tests were conducted by Sandia NationalLaboratories, Albuquerque, NM, at EMRTC, Socorro, NM.Waterways conducted a Concept Evaluation Program inorder to determine the trafficability of a foam roadway, theability of the foam to distribute the load of a static and movingvehicle, the effects of laying foam on trip wires, and finally theeffects on sub-surface laid mines.  These experiments wereconducted at Duckport, LA between 25 July - 07 August 1997.The Sandia experiments concentrated on the explosiveeffects on Rigid Polyurethane Foam blocks [Ref. 11, 12, 13].Failure criteria of the foam based on density, explosive charge,and foam thickness were explored.  The final experimentswere conducted to determine the possibility and efficiency ofrepairing damaged blocks.Both experiments were part of an integrated plan withSandia National Laboratory playing the lead role.  Becausethese were operational feasibility tests, mixed English andmetric units are reported.Trafficability TestsThese experiments were conducted in order to investigatethe foam's ability to carry military traffic.  A tracked vehicle,M88A2 Hercules Tank Retriever, and a wheeled vehicle,M998 High Mobility Multi-purpose Wheeled Vehicle(HMMWV), were used for these tests.  The M88A2 weighed138,000 lb and was fitted with an M60 track which produced acontact pressure against the road bed of 17.4 psi.  TheHMMWV weighed 9,490 lb with a front tire pressure of 25 psiand a rear tire pressure of 35 psi.  The contact pressures on theground were 20 psi and 26 psi respectively [Ref 2].Set-up:  An RPF roadway with dimensions, 51' X 26' X 2' wasconstructed on a flat plastic clay soil surface. The foamdispensing machine was a Decker Industries commercialmodel applicable to the building industry.   This machine canonly dispense foam at a maximum rate of 90 lb/min, which isnot quick enough to dispense large quantities of foam in therequired time for an in-stride breach.  In order to construct the24-inch thick roadway, the foam had to be dispensed inapproximately four layers with each layer no more than 6inches thick.  When the layers were poured larger than sixinches thick, the internal temperature in the foam increased.This heat buildup caused the foam to split.  (The choice offoam composition for this experiment was not optimized forland use,  but was dictated by use for other applications underwater.)Experiment:  The M998 HMMWV and M88A2 TankRetriever were driven over the 24- inch deep, 4 lb/ft3 foamroadway for a total of 50 passes each. Indentationmeasurements of the foam were taken after each pass, whichwas one length of the roadway.Results:  After the first five passes, the HMMWV vehiclebarely indented the foam. In some areas where the foam wasslightly higher, small cracks developed.  After 50 passes, thefoam was indented no more than 1/4 inch. The M88A2’s firstpass created an indentation up to an inch in depth in someportions of foam.  After the second pass, the M88A2 began topack the foam underneath the tracks and the debris began tosettle on top of the worn surface.  After 50 passes, the M88A2crushed the foam between 2-3 inches throughout the length ofthe roadway.Conclusions: The minimal damage created by 50 passes of theM88A2 would suggest that the foam roadway will be able tocarry the passage of at least an entire battalion before repairswould have to made on the foam.Trip Wire ExperimentsSet-up:  Five trip wires were positioned on the northern end ofthe roadway.  Three of the trip-wires were M-1, 7 lb pulldevices while the remaining two were string tensionpotentiometers.  Each wire was anchored on one end to awooden stake while the other end was attached to a trippingmechanism  set at 7 lb.  The wires were approximately twoinches above the ground.3Experiment:  The  foam was poured into the trip wire areawith  a west to east fill pattern.  The goal was to achieve a totalfoam depth of 24 inches.Results:  The foam immediately encapsulated the trip wiresand the expansion of the foam caused the wires to rise. All fivetrip wire devices were tripped by the expanding foam.Conclusions:  RPF provides an operational means oftriggering trip wire triggered devices prior to the passage offoot and vehicular traffic.Effects on Sub-surface laid MinesSet-up:  Eight M15 training mines and eight pressure cellswere employed under the same roadway used for thetrafficability tests.  Four of  the pressure cells were rated at 50psi and used for the HMMWV lane while the remaining fourcells were rated at 100 psi and used for the M88A2 lane.  Themines were buried approximately 2 inches deep and were setto be tripped after experiencing a load of 14 psi.  The pressurecells were buried approximately 3 inches in depth and placedadjacent to the M15 mines in order to provide the loading datafor each pass of a vehicle.Experiments:  Load sensor data was taken for each of the 50passes of the M88A2 and HMMWV.Results:  Without the use of the foam, the M88 was calculatedto have a surface contact pressure of 17.4 psi while theHMMWV had a contact pressure of 20 psi for the front tiresand 26 psi for the rear tires.   The load sensors indicated anaverage load of 5.4 psi for the M88A2 and 0.34 psi for theHMMWV.  The Phase I report by SNL calculated similarvalues, 5.0 psi for the M88A2 and 0.5 psi for the HMMWV[Ref. 11:p. 109].  None of the simulated mines were triggeredby any of the 100 passes over the foam roadway.Conclusions:  RPF was able to neutralize the effects ofsubsurface laid M-15 training mines.Explosive Effects on RPFSet-up: A twelve-inch thick layer of fine sand was placed ontop of solid ground.  Sand was chosen in order to provide alevel surface for the foam blocks.  Sand bags were placed ontop of the foam blocks to ensure that the foam remained on topof the sand during the explosion.  The smaller foam blocks willtend to elevate, thus causing a considerable air gap during thepropagation of the explosive shock.  The explosive used forthese experiments was PETN, pentaerythritol tetranitrate,which is commonly used in grenades, small caliber projectiles,and demolition devices [Ref. 3:p. 6.13].  PETN has aconversion factor of 1.45 when scaled to TNT, i.e. 10 g PETNhas the explosive effect of 14.5 g TNT. A patty-shapedexplosive was chosen over a spherical shape in order to closelyreplicate the explosive geometry in an anti-personnel mine.A two-part polyurethane dispensing machine made byDecker Industries, Florida, was used to make the 15 foamblocks for this experiment.  This was also the same machineused to create the foam roadway for the trafficabilityexperiments.  The machine was dispensing  3.5-4.0  lb/ft3 foamat an average rate of 55 lb/min.  Cream time, which is theamount of time elapsed before the mixture reached a cream-like consistency, took place after 55-65 seconds.  The foamreached its maximum expansion after a rise time of 3-4minutes.Experiment: Two different block sizes, 65" X 65" and 85" X85", were used in order to investigate edge effects.  The PETNexplosive was positioned directly underneath the geometriccenter of each foam block.  The top of the explosive was madeflush with the sand surface in order maintain direct contactwith the block.  Nonel Primadet chord, a non-electric blastingdevice, was used to detonate the charge.  The chord madecontact with the bottom of the PETN and was routedunderneath the sand towards the triggering mechanism.  Aftereach shot, measurements were taken of the ground crater,entrance cavity, exit cavity, and depth of penetration in thefoam.Results:  The 30- gram explosive perforated through all butthe 30-inch foam block.  The failure of the foam block wascontained to the cavity, and there were no cracks observedlaterally to either side of the foam.  Two modes of failure wereobserved on the blocks that were perforated.  The direct blastfailure results in the crushing of the foam cells near the entrypoint of the explosive while the foam's mechanical failureresults in a shear plug.  The shear plug creates an exit cavitysignificantly larger than the entry cavity.  Figure 1 shows ageneric sketch of the explosive effects on an RPF block.Figure 1.  Sketch of the explosive effects on an RPF block.Using the cube-root scaling equation,D AW= 1 3/where D is the cavity depth in inches, A is a constant withunits in/g1/3, and W is the yield in grams, we can calculate theconstant, A, in order to predict cavity depths from larger4yields.  For the 4 lb/ft3 foam, A has a value of 3.26 in/g1/3.This constant allows us to predict both the cavity depth andcavity diameter based on our experimental results.  Using thesepredictions for the 4 lb/ft3 foam, a VS - 1.6 anti-tank mine,which has 1.7 kg of TNT, would create a 31-inch cavitydiameter with a cavity depth of 35 inches.  Similarly, the M19anti-tank mine, which has 9.5 kg of Comp B, would  create a61-inch cavity diameter with a cavity depth of 67 inches.These numbers suggest that in order to completely contain ananti-tank mine similar to the M19, the foam roadway wouldhave to be much greater than 67 inches thick.  Additionalexperiments will have to be conducted  in order to obtain afoam density that can provide an operationally capable foamroadway.Repair of Damaged RPF BlocksSet-up: The damaged foam blocks used for these experimentswere the blocks used for the cavity formation experiments.Experiments:  These experiments were conducted todetermine the most efficient method of repairing a damagedfoam block and its subsequent strength. By pouring the foamdirectly into the damaged cavity, some of the foam escapedthrough the bottom.  Once the foam began to rise, it quicklyadhered to the interior of the block.Results: The foam not only filled the cavity, but it also seepedthrough the smaller cracks in the interior wall.  Cold jointswere formed at the boundary between the new and old joints.Follow-on experiments will determine the resulting strength ofthese repaired foam blocks.ConclusionsThe test results gathered from the Waterways ExperimentStation indicate that a 24-inch thick, 4 lb/ft3 RigidPolyurethane Foam roadway adequately supported multiplepasses of a track and wheeled vehicle. More importantly, thefoam roadway was able to neutralize the mines buriedunderneath the foam and activate all trip wire detonateddevices in the breach lane.  Traction tests revealed that thefoam did not improve traction for the M88A2 and only slightlyincreased the traction of the HMMWV.  As for its use as abreaching technique for anti-personnel mines, the foamroadway itself serves as a very efficient breach lane, but itcurrently can not be employed in the timely manner needed forbreaching exercises.  The current dispensing machine can notdispense large enough quantities of foam in the required timefor a in-stride breach.The explosive cavity formation tests by Sandia NationalLaboratories indicate that a blast anti-personnel mine with 30grams of PETN can be adequately contained by a 16-inchthick, 4 lb/ft3 foam block.  A 10 gram PETN charge can becontained by a 14-inch thick, 4 lb/ft3 foam block  Thisthickness is reduced when the foam is statically loaded.The combined results of the two test sites indicate that thesame 24-inch thick foam roadway constructed by Waterwaysshould be able to withstand the explosive effects of a 30-gramPETN charge.  Based on cube root scaling laws, the 24-inchfoam roadway should be able to completely contain a 10-gramPETN charge, and the 30-gram data suggests that the foamroadway could contain a significantly larger charge.  Energyabsorption experiments are currently being conducted bySandia National Laboratories in order to determine the amountof energy that is mitigated by the foam.  The amount of foamneeded to contain a specific explosive can be determined fromthe energy absorption properties of the foam.These feasibility experiments indicate that RigidPolyurethane Foam, at a given density and thickness, canwithstand the explosive effects of anti-personnel blast minesand mitigate or neutralize the effects of surface laid anti-tankmines.The work described here is a summary of a thesissubmitted to the Naval Postgraduate School for a Master ofScience Degree in Applied Physics. [Ref.14]LIST OF REFERENCES1. Hambric, H. and W. Schneck, The Anti-personnel MineThreat, Night Vision  Electronic Sensors Directorate, 1994.2. Bailey, A and S. Murray, Explosives, Propellants &Pyrotechnics, Brassey's (UK),Ltd., 1989.3. Coppens A. and R. Reinhardt, Explosives and Explosions,Naval Postgraduate School, 1995.4, Archulete, M. and W. Stocum, Toxicity Evaluation andHazard Review for Rigid  Foam, Sandia NationalLaboratories, 1994.5. North Carolina Foam Industries, MSDS:  AromaticIsocyanate, NCFI, 1996.6.  North Carolina Foam Industries, MSDS:  Polyol ResinSystem, NCFI, 1996.7. Strong, B., Plastics, Materials and Processing, Prentice-Hall Inc., 1996.8. Hespe, H., Guide to Engineering Plastic Families:Thermosetting Resins, Mobay Corporation, 1983.9. Woodfin, R., Rigid Polyurethane Foam (RPF)Technology for Countermine (Sea)Program - Phase 1, SandiaNational Laboratories, Albuquerque, NM, 1997.510. Mason, G. and K. Hall, Rigid Polyurethane FoamCountermine and Traction Concep Evaluation Program,Waterways Experiment Station, 1997.11. Rand P. and B. Hance, Foam for Barrier Crossing:Initial Properties, Sandia  National Laboatories, 1995.12.  Rand P. and B. Hance, Foam for Barrier Crossing:Mechanical Properties as a Function of Density,Temperature, and Time After Pour, Sandia NationalLaboratories, 1995.13.  Rand P., private communication, September 11, 1997,SNL.14. Alba, Albert L., “Rigid Polyurethane Foam as a BreachingTechnique for Anti-Personnel Mines”, Masters Thesis, NavalPostgraduate School, Monterey, CA, December 1997.

The Use of Rigid Polyurethane Foam as a Landmine Breaching Technique

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The Use of Rigid Polyurethane Foam as a Landmine Breaching Technique

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