ARMY RESEARCH LABORATORY

Fire-Resistant and Fragment

Penetration-Resistant Blankets for the

Protection of Stored Ammunition

Wai K. Chin

Thomas J. Mulkern

Archibald Tewarson

Approved for public release; distribution is unlimited.

ARL-TR-2285 SEPTEMBER 2000
i

Army Research Laboratory

Aberdeen Proving Ground, MD 21005-5066

_____________________________________________________________________

ARL-TR-2285 September 2000

_____________________________________________________________________

Fire-Resistant and Fragment PenetrationResistant Blankets for the Protection of

Stored Ammunition

Wai K. Chin

Thomas J. Mulkern

Weapons & Materials Research Directorate, ARL

Archibald Tewarson

Factory Mutual Research Corporation

_____________________________________________________________________

Approved for public release; distribution is unlimited.

_____________________________________________________________________
ii

_____________________________________________________________________

Abstract

_____________________________________________________________________

Large quantities of munitions stored in the open are vulnerable to a

host of initiation threats, both inadvertent and intentional in nature.

An experimental flame- and fragment-resistant blanket was

developed to protect such munitions and prevent sympathetic

reactions when the blanket is used in concert with earthen barricades.

The blanket, which consists of aramid and ceramic fibers, passed

several rigorous tests in both the laboratory and in the field. The

ballistic performance of the blanket offered protection from 300-g and

454-g fragments traveling at velocities of 140 m/s and 60 m/s,

respectively. The blanket also provided flame protection from high

temperature gas jets, as well as burning JA2 and M30 propellant,

when the temperatures exceeded 1200° C for 10 seconds.

This final report combines the research efforts of the fragment

penetration study and the flame and heat blocking with fire blankets for

munition protection study: U.S. Army Research Laboratory (ARL)

technical report, “Fire Blanket for Munition Protection: Flame- and

Heat-Blocking Properties of Advanced Materials,” to be published by

ARL, Aberdeen Proving Ground, Maryland.
iii

ACKNOWLEDGMENTS

The authors would like to thank Mr. Duane Scarborough and Mr. Robert Rossi of the

U.S. Army Defense Ammunition Logistics Activity for funding this research

program. We would also like to thank Mr. Vincent Boyle, Dr. Robert Frey, Dr. John

Starkenberg, Dr. Warren Hillstrom, Mr. Anthony Canami, Mr. Thomas Adkins,

Ms. Dawnn Saunders, and Mr. Gould Gibbons of the Explosive Technology Branch,

Weapons and Materials Research Directorate, U.S. Army Research Laboratory, for

the use of the experimental facilities and the coordination of the plans.
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INTENTIONALLY LEFT BLANK
v

Contents

1. Introduction and Background ........................ 1

2. Experimental...................................... 6

2.1 Fibers/Fabrics ................................... 6

2.2 MST Blanket Specimens ............................ 6

2.3 Flammability .................................... 7

2.4 Flame Penetration Experiments ....................... 7

2.5 Heat Penetration Experiments ........................ 8

2.6 Determination of Exposure Conditions .................. 12

2.7 Resistance to Fragment Penetration..................... 17

3. Results and Discussion .............................. 22

3.1 Flame Penetration Experiments ....................... 22

3.2 Heat Penetration Experiments ........................ 25

3.3 Ballistics and Arena Experiments...................... 36

3.4 Blanket Design Considerations........................ 52

4. Conclusions ...................................... 53

4.1 Flammability .................................... 53

4.2 Phase 1 Ballistics ................................. 55

4.3 Phase 2 Ballistics ................................. 55

4.4 Sub-Scale Arena Experiments ........................ 56

4.5 Issues and Concerns............................... 56

References ............................................. 57

Distribution List ........................................ 59

Report Documentation Page ............................... 61

Figures

 1. Heat Penetration Apparatus Use in the Experiments for Sample MST

Blankets .......................................... 10

 2. Measured Radiant Heat Flux at the Sample Surface Versus Distance

Between the Surface and the Radiant Heater in the Heat Penetration

Apparatus......................................... 11

 3. Arrangement of the Sample MST Blanket With Three Layers of

Kevlar Fabric at the Back of the Sample MST Blanket on the

Horizontal Platform of the Heat Penetration Apparatus ......... 11

 4. Average Front and Back Surface Temperatures Above Ambient at

the Center of 20-mm Thick Sample No. 8 .................... 15

 5. Average Front and Back Surface Temperatures Above Ambient at

the Center of 5-mm Thick Sample No. 3..................... 16

 6. Average Front and Back Surface Temperatures Above Ambient at

the Center of 5-mm Thick Sample No. 4..................... 17

 7. Front View of Ballistic Clamp Fixture ...................... 19
vi

 8. Modified Remington 700 Rifle With 40-mm Smooth Bore Fragment

Launcher Attachment ................................. 20

 9. Modified Remington 700 Rifle Assembled and Secured in Firing

Bracket Next to Doppler Radar Head ...................... 20

10. Average Front and Back Surface Temperatures Above Ambient at

the Center of 5-mm Thick Fabric No. 1...................... 26

11. Average Front and Back Surface Temperatures Above Ambient at

the Center of 5-mm Thick Fabric No. 2...................... 26

12. Average Front and Back Surface Temperatures Above Ambient at

the Center of 15-mm Thick Fabric No. 5..................... 27

13. Average Front and Back Surface Temperatures Above Ambient at

the Center of 20-mm Thick Fabric No. 5..................... 27

14. Average Front and Back Surface Temperatures Above Ambient at

the Center of 20-mm Thick Fabric No. 7..................... 28

15. Average Front and Back Surface Temperatures Above Ambient at

the Center of 25-mm Thick Fabric No. 9..................... 28

16. Back Surface Temperatures Above Ambient at the Center of 5-mm

Thick Sample No. 1 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 29

17. Back Surface Temperatures Above Ambient at the Center of 5-mm

Thick Sample No. 2 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 29

18. Back Surface Temperatures Above Ambient at the Center of Back

Center of 5-mm Thick Sample No. 3 Versus That of the Kevlar

Fabric Backing Layers 1, 2, and 3 ......................... 30

19. Back Surface Temperatures Above Ambient at the Center of Back

Center of 5-mm Thick Sample No. 4 Versus That of the Kevlar

Fabric Backing Layers 1, 2, and 3 ......................... 30

20. Back Surface Temperatures Above Ambient at the Center of 15-mm

Thick Sample No. 5 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 31

21. Back Surface Temperatures Above Ambient at the Center of 20-mm

Thick Sample No. 6 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 31

22. Back Surface Temperatures Above Ambient at the Center of 20-mm

Thick Sample No. 7 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 32

23. Back Surface Temperatures Above Ambient at the Center of 20-mm

Thick Sample No. 8 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 32

24. Back Surface Temperatures Above Ambient at the Center of 25-mm

Thick Sample No. 9 Versus That of the Kevlar Fabric Backing

Layers 1, 2, and 3.................................... 33

25. Pusher Plate and 1-lb Steel Fragment With Polymer Foam Sabots

Attached on Both Ends ................................ 38
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26. Blanket Clamped in Frame Impacted by a 454-g Steel Fragment .... 39

27. Typical Damage on a Ply of Kevlar as a Result of Impact by a 454-g

Steel Fragment ...................................... 39

28. Typical Damage on an Inner Ply of Silica Oxide as a Result of Impact

by a 454-g Steel Fragment .............................. 40

29. Fully Assembled Sub-scale Prototype MST Blanket ............. 40

30. Live Propellant Experiment on an Uncovered Inert Acceptor

Ammunition Crate ................................... 41

31. Side Burn Propellant Experiment (0.5 kg JA2) on a Covered Inert

Acceptor Ammunition Crate ............................ 41

32. Temperature Profile of a Covered Acceptor Ammunition Crate..... 42

33. Temperature Profile of an Uncovered Acceptor Ammunition Crate .. 43

34. Typical Charred Remains of a Top-Burn Live Propellant Experiment. 43

35. Setup of Bonfire Experiment Before Ignition .................. 44

36. Bonfire Experiment Several Minutes After Ignition.............. 44

37. Bonfire Experiment After the Flames Self-Extinguished .......... 45

38. Temperature Profile of a Bonfire Experiment ................. 45

39. Setup of Uni-charge Experiment, in Which Four Uni-charge Packages

Were Placed Inside the Steel Tube......................... 46

40. Setup of Uni-charge Experiment, Showing Stand-off Distance...... 46

41. Results From a Uni-charge Experiment...................... 47

42. Back Surface of a Blanket Subjected to a Hot Gas Jet Emitted From

Four Uni-charge Packages .............................. 47

43. Temperature Profile of the Back Surface of a Blanket From a

Uni-charge Experiment ................................ 48

44. Uni-charge Placed on Top of a Covered Inert Acceptor Before

Ignition ........................................... 49

45. Uni-charge Placed on Top of a Covered Live (Uni-charge) Acceptor

Before Ignition ...................................... 49

46. Typical Results From the Ignition of a Uni-charge on Top of an MST

Blanket ........................................... 49

47. Temperature Profile Results From the Ignition of a Uni-charge on

Top of an Undamaged MST Blanket (four plies of Kevlar ) ....... 50

48. Temperature Profile Results From the Ignition of a Uni-charge on

Top of an Undamaged MST Blanket (five plies of Kevlar )........ 50

49. Temperature Profile of a Live Acceptor Under a Torn Blanket With

a Uni-charge Ignited onTop (four layers of Kevlar )............. 51

50. Temperature Profile of a Live Acceptor Under a Torn Blanket With

a Uni-charge Ignited onTop (five layers of Kevlar ) ............. 51

51. Instrumented Acceptor Stack of Ammunition After Several

Experiments........................................ 52
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52. The Effect of Stitching on the Brittle Ceramic Felt Material ........ 52

53. Composite Sandwich Schematic Showing Different Layers of

Material .......................................... 53

Tables

 1. Thermal Properties of NASA’s Thermal Protective System for

Atmospheric Entry and Hypersonic Cruise Vehicles ............ 3

 2. Commercially Available Fabrics for Use in Sample MST Blankets ... 5

 3. Organic Ballistic Fiber Material Properties ................... 6

 4. Sample MST Blankets Used in the Flame Penetration Experiments .. 9

 5. Sample MST Blankets for the Heat Penetration Experiment ....... 13

 6. Baseline Experiments With Short Exposure Duration of the

Unpainted Sample Surface.............................. 14

 7. Flame Penetration Into a Thick Wood Block With a Smaller Sample.. 23

 8. Flame Penetration Into a Thin Wood Block With a Smaller Sample

for 10 Seconds’ Exposure............................... 24

 9. Flame Penetration Into a Thin Wood Block With Larger Samples

for 10 Seconds’ Exposure............................... 25

10. Maximum Temperature of the Front Surface of the Sample and Back

Surface of the Third Kevlar Fabric Layer.................... 34

11. Estimated Effective Thermal Diffusivity Values of Sample MST

Blankets .......................................... 35

12. Estimated Back Surface Temperatures of the Third Layer of Kevlar

Fabric ............................................ 37

13. Areal Density of Kevlar Ballistic Blankets................... 37

14. Typical Fragment Velocities, Calibration Data of Fragment Launcher,

and Penetration Data ................................. 38

15. Weight and Cost Estimates for MST Blanket, BPS Blanket, and a

BPS-Ceramic Hybrid Solution............................ 54
1

FIRE-RESISTANT AND FRAGMENT PENETRATION-RESISTANT

BLANKETS FOR THE PROTECTION OF STORED AMMUNITION

1. Introduction and Background

Munitions stored in the open are vulnerable to a host of threats, both friendly

and hostile in nature. The U.S. Army Defense Ammunition Logistics Activity

(AMMUNITIONLOG) tasked key players at the U.S. Army Research Laboratory

(ARL) to design and evaluate a protection scheme comprised of a rapidly

deployable system of barricades and fire-inhibiting blankets as a part of the

Munitions Survivability Technology (MST) program. These barricades and

blankets will prevent the propagation of reactions and fire between stacks of

stored munitions.

When large quantities of ammunition are stored outdoors, the deflagration of

one stack can lead to the detonation of adjacent stacks by various mechanisms

such as direct fragment impact from high velocity low trajectory projectiles, blast

pressure, rapid deformation, and burning because of fire propagation.

In order to prevent most of these mechanisms, the individual stacks of

ammunition can be separated by either large distances or earthen barricades,

which will prevent direct fragment impact. Although a barricade may separate

stacks of ammunition, detonations may still occur by indirect means such as hot

fragments, firebrands, and burning propellant from the donor stack. These

become high trajectory low velocity projectiles and may land on neighboring

acceptor stacks of ammunition. If the acceptor stack contains easily ignitable

material such as propellant, ammunition crates constructed of wood, or

combustible cartridge cases, a fire and subsequent low order detonations are

possible. A domino effect can destroy large stores of munitions in the course of

hours or even days. In order to protect against these indirect mechanisms, a fireblocking and heat-blocking blanket with a specific level of ballistic protection can

be used to cover the ammunition stack.

There is an extensive historical database to justify this research effort, some of

which is mentioned in ARL-TR-2030 [1]. Frey and Starkenberg cite instances

when sequential detonations led to the loss of entire storage depots of

ammunition. These depots were lost because of alleged sympathetic detonation

from neighboring ammunition stacks that tend to expel firebrands,

unexploded/armed warheads, and assorted hot fragments. These fire initiators

can be thrown great distances, even farther than the mandated minimum safe

distances for ammunition storage. Because of this, there is the potential for long

burn periods for an ammunition depot fire when firebrands are randomly
2

thrown toward neighboring stacks. The earthen barricades and blankets

evaluated in the MST program should greatly increase the overall survivability

of an ammunition depot if they are used in concert and properly implemented.

This document only illustrates the work performed in the development of the

fire- and heat-blocking/ballistic blanket portion of the program. Past studies that

looked at the usefulness of fire-blocking materials demonstrated mixed results

for the effectiveness of blankets in preventing fire propagation [2]. This study,

however, was not specifically focused on a blanket solution, and a full spectrum

of experiments was not performed to adequately assess a blanket’s effectiveness

in preventing fires and sympathetic detonations.

Through laboratory scale flammability study and sub-scale field experiments,

ARL hoped to develop a lightweight MST blanket to protect stored munitions

from low velocity, high trajectory ballistic threats as well as an assortment of fire

threats when the blanket is used in conjunction with a barricade system.

In order to develop this blanket, a number of design issues had to be taken into

consideration. The blanket should protect against a wide range of low velocity

ballistic as well as multiple thermal threats. These threats were determined,

based on best guess estimates from empirical data as well as real-world events,

but because of the statistical nature of an exploding munitions stack, all the

potential combinations of threats could not be evaluated. The system had to be

flexible enough to conform to any size pallet of munitions, so a modular

approach to the design was chosen. The individual pieces from this modular

design had to be easily handled and assembled by soldiers in the field. The

system also had to be durable and manufactured from high performance, low

cost materials. Based on these requirements, a large number of candidate

materials had to be evaluated to develop the most robust and cost-effective

solution.

A literature search was performed for the pertinent information about the

resistance to flame and heat penetration of single and multiple layers of various

organic and inorganic fiber-based fabrics. A total of about 150 relevant papers

and reports were found. Many studies indicated that resistance to flame and

heat penetration increased when layers of fabrics made from fibers of organic

and inorganic polymers were used [3-14].

An example of the use of a combination of inorganic fiber-based fabrics is the

heat-blocking system used by the National Aeronautics and Space

Administration (NASA) for the thermal protection of atmospheric entry and

hypersonic cruise vehicles [7]. The front and the back surfaces of the heatblocking system consist of four layers of alumino-borosilicate (ABS) fabric with a

fifth inner layer of silica fabric and thread. The core consists of a combination of

layers of the following materials: (a) silica felt (98.5% SiO2), (b) ABS (62% Al2O3,
3

14% B2O3, and 24% SiO2), (c) silica felted fiber mat (99.9% SiO2), (d) alumina mat

(95% Al2O3, 5% SiO2, and (e) silica felt (98.5% SiO2). The thermal properties of the

five layers that constitute the core are listed in Table 1.

Table 1. Thermal Properties of NASA’s Thermal Protection System for

Atmospheric Entry and Hypersonic Cruise Vehiclesa

__________________________________________________________________

 Heat Thermal Thermal

Density Capacity Conductivity Diffusivity

Layers Material (kg/m3) (kJ/kg-K) (kW/m-K) x 105 (mm2/s)b

__________________________________________________________________

1 Silica felt 96 0.349 1.58 0.47

(98.5% SiO2)

2 ABS (62% 96 0.388 2.16 0.58

Al2O3, 24%

SiO2, 14% B2O3)

3 Silica felted 136 0.258 1.87 0.53

fiber mat (99.9%

SiO2)

4 Alumina mat 96 0.336 1.80 0.56

(95% Al2O3,

5% SiO2)

5 Silica felt 96 0.349 1.58 0.47

(98%SiO2)

__________________________________________________________________

a

taken from [5]; b: thermal diffusivity = thermal conductivity/(density)(heat capacity)

The data in Table 1 indicate that thermal diffusivity values for inorganic fiberbased fabrics are between 0.47 to 0.58 mm2/s. The inverse of thermal diffusivity

can be considered as a parameter expressing resistance to heat penetration. The

combination of alumina- and silica-based fabrics would be a likely candidate for

sample MST blankets, since the combination has low thermal diffusivity values.

An example of the use of combination of organic and inorganic polymer fiberbased fabrics is the system used for the Columbia space shuttle [9]. The system

consisted of silicone-impregnated fiberglass batting, sewn in covers of reinforced

polyimide film, with alternate layers of perforated polyimide film and

Dacron (polyethylene terephthalate [PET]) net, and a polyimide film cover. This

combination had also been considered for high temperature filtration, flameresistant upholstery for commercial passenger vehicles, and aircraft crew

uniforms.

Combinations of organic and inorganic fibers are also used to enhance resistance

to fuselage “burn-through” in aircraft fuel fires [15]. Fuselage burn-through

refers to the penetration of an external post-crash fuel fire into an aircraft cabin.
4

The time to burn through is critical because, in survivable aircraft accidents, the

hazards of burning cabin materials ignited by burn-through from an external fuel

fire may incapacitate passengers before they are able to escape.

There are typically three barriers that a fuel fire must penetrate in order to burn

through to the cabin interior: the aluminum skin (30 to 60 seconds’ resistance,

depending on thickness), the thermal acoustical insulation, and the interior side

wall and floor panel combination. Thermal acoustical insulation, typically

comprised of fiberglass batting encased in a polyvinylfluoride ([PVF], Tedlar )

moisture barrier, provides 60 to 120 seconds’ protection as long as it is not

dislodged from the fuselage structure. Honeycomb sandwich panels used in the

side wall and floor areas of transport aircraft offer a substantial barrier to fire.

The efficiency of preventing or delaying burn-through of modified fiberglass

batting or replacement insulation materials has been examined in full-scale fire

experiments with a reusable fuselage rig [15]. The use of polyimide (Kapton )

film (an organic polymer) in place of PVF (Tedlar ) film improved the burnthrough resistance. A layer of Nextel (tightly woven ABS fabric) is placed inside

each of the insulation batts, and all are encapsulated in the standard metallized

PVF (Tedlar ) film; this prevented burn-through for nearly 7 minutes. Most of

the Nextel remained in place except for one area about 20 inches by 20 inches

(0.51 m by 0.51 m), which had been penetrated.

Additional organic and inorganic polymer fibers as insulation materials

evaluated in full-scale fire experiments with a reusable fuselage rig consisted of

[15]

• Curlon - a heat-treated, oxidized polyacrylonitrile fiber (OPF) (70%

carbon, 20% nitrogen, and 10% oxygen). Curlon was extremely effective

in resisting flame penetration for at least 5 minutes during several full-scale

experiments.

• Solimide AC-430 System - the system consisted of rigid polyimide foam,

with Quartzel , a vitreous silica wool barrier. This system, however, was

less effective than the system with NextelTM-enhanced fiberglass and the

Curlon .

• AstroquartzII System - the system consisted of an AstroquartzII ceramic

mat with a thin layer of NextelTM ceramic fiber paper. This system resisted

flame penetration for more than 8 minutes.

The Federal Railroad Administration [9] has also successfully tested glass fiber,

ceramic fiber, and mineral fiber blankets for the thermal protection of aluminum

railroad tank cars from torch and pool fires.
5

The use of organic and inorganic fiber-based fabrics has now been

commercialized for variety of applications [10-14]. Table 2 lists some

commercially available fabrics that could be considered for the sample MST

blankets. The amount of organic polymer fibers is very small compared to

inorganic polymer fibers. For example, NextelTM 312 sewing threads are a

combination of NextelTM 312 ceramic fibers and rayon fibers (10% by weight)

[13]. The list is not a comprehensive list; it is only an example of commercially

available fabrics for use as sample MST blankets for thermal protection. Please

note that these fabrics do not provide protection from ammunition penetration.

Table 2. Commercially Available Fabrics for Use in Sample MST Blankets

__________________________________________________________________

Fabrics and Exposure Temperature Limita Ref

__________________________________________________________________

1) Zetex , T 593o C (inorganic fibers); 2) Zetex Plus , T 1093o C 10

(inorganic fibers)

1) Kao-TexTM 2000 cloth, T 1093 o C (inorganic fibers); 2) calcium 11

magnesium silicate, T 958 o C; 3) Kaowool ceramic fiber, B Blanket,

T 958 o C (inorganic fibers); 4) Cerawool , T 958 o C (inorganic fibers);

5) Kaowool blanket S, T 1230 o C (inorganic fibers); 6) Cerachem

blanket, T 1430 o C (inorganic fibers)

1) DurabackTM, T 958 o C (inorganic fibers); 2) Durablanket 2600, 12

T 1430 o C (inorganic fibers)

1) NextelTM 312 ceramic fibers, T 1430 o C (aluminoborosilicate); 13

2) NextelTM 440 ceramic fibers, T 1648 o C (aluminoborosilicate)

RM Therma-Shield insulation materials: 1) SuperSpan welding cloth; 14

2) FluorelTM-coated ceramic cloth 1093 o C; 3) Therma-Shield 2400

(alumina silica fiber with binders) 1288 o C

__________________________________________________________________

aDetailed chemical compositions of the fabrics are not available, as they are proprietary materials.

Temperature specifications are from the manufacturer’s brochures.

There were several options from which to choose in off-the-shelf technology for

high performance fibers, which may be used in a flexible blanket for ballistic

applications. These fibers include para-aramid fibers and ultrahigh molecular

weight polyethylene (PE) fibers. DuPont (Kevlar®) and Acordis (Twaron ) both

produce para-aramid fibers, while Honeywell (Spectra ) and Toyobo

(Dyneema ) produce PE fibers. Both families of fibers offer unparalleled strength

and stiffness-to-weight ratios (see Table 3) and are widely used in ballistic

applications [17-18].
6

Table 3. Organic Ballistic Fiber Material Properties

__________________________________________________________________

Tensile

Upper Use Density Tenacity Strength Elongation Cost

Material Temp (°C) (g/cc) (g/den) (MPa) (percent) ($/lb)

__________________________________________________________________

Aramid 300 1.44 23 to 26 2760 2.4 to 3.6 30

Polyethylene 120 0.97 28 to 38 3000 3.0 to 4.5 30

Nylon 150 1.14 9 76 10 5 to 10

__________________________________________________________________

These fibers need to be woven into the proper architecture in order to see their

full benefits. Mackiewicz [19] examined the performance of several different

weave architectures and determined that the Kevlar® 29 Style #745 [20] weave

provided optimal protection from overhead artillery blasts and associated

fragments. Based on this research, the U.S. Army developed a ballistic protective

system (BPS) to protect materiel [21] from ballistic threats. This BPS blanket was

chosen as a starting point for the MST blanket, but since it offered too much

ballistic protection and too little flame protection, modifications had to be

implemented.

2. Experimental

2.1 Fibers/Fabrics

Because of the diverse performance requirements of the blanket, several organic

and inorganic fibers/fabrics had to be examined in a composite sandwich

construction whereby the optimal properties of each material could be exploited.

Some of the materials evaluated had to meet certain ballistic requirements; these

include several fabrics woven from high performance organic fibers such as

ballistic nylon, para-aramid, and polyethylene fibers. Other materials needed to

meet the high temperature requirements of the blanket; they consisted of several

candidate fabrics woven from inorganic fibers, including fiberglass and ceramic

fibers. Several other materials and/or coatings had specific performance

requirements such as flame resistance, abrasion resistance, water resistance, and

camouflage properties.

2.2 MST Blanket Specimens

The specimens evaluated in this study fell into three categories in size and

construction. Small (< 305 mm by 305 mm) coupons were constructed of several

layers of fabric stacked to achieve a desired thickness. These samples were

typically used in small-scale laboratory flammability studies, where they were
7

clamped in some type of fixture and exposed to a thermal threat. Large

(>610 mm by 610 mm) specimens were also fabricated for ballistic study. These

composite blankets of varying thickness consisted of multiple layers of organic

and inorganic fabrics, which were mounted in a frame for fragment penetration

experiments. The third type of specimen fabricated consists of a sub-scale

finished product, which was designed to cover a generic ammunition crate that is

915 mm wide by 915 mm long by 305 mm high. These sub-scale demonstrators

were constructed of five pieces (one top and four sides) that are held securely

together with a series of straps and buckles to completely cover the ammunition

crate.

2.3 Flammability

The objective of the study was to examine the resistance to flame and heat

penetration by a combination of inorganic and organic fiber fabrics. A literature

search indicated that inorganic fiber-based fabrics have high fire resistance and a

combination of organic and inorganic fiber-based fabrics in layers is effective for

thermal and weather protection. Contact was made with several high

performance blanket manufacturers who are using technology developed by

NASA. Consequently, some of these manufacturers supplied ARL with some of

these high performance fabrics that have a thickness of 5 mm (defined as thin in

this report) and 15 to 25 mm (defined as thick in this report). These high

performance fabrics are identified as sample MST blankets in this report. The

resistance of each sample MST blanket to flame and heat penetration was

assessed in the following types of experiments:

2.3.1 Flame Penetration Experiments

An oxyacetylene torch flame was used in the experiments. The top surface of the

sample MST blanket wrapped around a wooden block was exposed to the

oxyacetylene flame. The extent of burn-through of the sample blanket and wood

and the charring and flaming of wood were used to assess the extent of flame

penetration through the sample MST blanket.

2.3.2 Heat Penetration Experiments

The front surface of the sample MST blanket on top of three layers of Kevlar

fabric (as a backing fabric) was exposed to a known external heat flux value.

Temperatures measured at the center of the front and back surfaces of the sample

MST blanket and back surfaces of each layer of the Kevlar fabric were used to

assess the extent of heat penetration through the sample blanket.

2.4 Flame Penetration Experiments

In the flame penetration experiments, a sample surface mounted on a block of

wood was exposed to an Airco oxyacetylene torch with a No. 144-2 cutting tip. In

some experiments, a black powder propellant or M9 propellant was placed

between the sample and wood surface. The oxygen and acetylene gas pressures
8

on the torch were set at 276 kPa and 34 kPa, respectively. The tip of the flame

was kept between 13 and 25 mm above the center of the sample surface. Some

samples ignited as soon as the oxyacetylene flame was brought close to the

surface. In these experiments, samples were allowed to burn for about

10 seconds. Flame penetration depths and visual observations were made during

the study of the samples. Three sets of experiments were performed in which

samples dimensions, the thickness of the wooden block, and the mode of

attachment were varied:

2.4.1 First Set of Experiments (thick wooden block, metal frame)

In this set of experiments, 152-mm square samples were used. The samples were

mounted on top of a 152-mm square and 51-mm thick block of pine. A 6-mm

thick metal picture frame fixture with a 102-mm square opening was placed on

top of the sample surface to keep it stable during the experiment. The sample

was studied until failure for 3 to 80 seconds.

2.4.2 Second Set of Experiments (thin wooden block, metal frame)

In this set of experiments, 152-mm square samples were used. The samples were

mounted on top of a 190-mm square and 19-mm thick blocks of pine. A 6-mm

thick metal picture frame fixture with a 102-mm square opening was placed on

top of the sample surface to keep it stable during the experiment. The sample

surface was exposed to the flame for 6 to 10 seconds.

2.4.3 Third Set of Experiments (larger sample area, thin wooden block, and no

metal frame)

In this set of experiments, 254-mm square and 152- by 356-mm rectangular

samples were used. The samples were stapled on top of 190-mm square and

19-mm thick and 140- by 152-mm and 38-mm thick blocks of pine, respectively.

The sample surface was exposed to the flame for 6 to 10 seconds. The sample

MST blankets used in the flame penetration experiments are listed in Table 4.

2.5 Heat Penetration Experiments

For the heat penetration experiments, the sample MST blankets, which consisted

of combinations of mostly alumina, silica, and ceramic-based fabrics (inorganic

fabrics) with a backing made of three layers of Kevlar fabric (organic fabric),

were used. The selection of sample MST blankets was based on the data from the

flame penetration experiments and background information from the literature.

Spectra PE material was excluded from these experiments because of inherently

poor flammability properties. The sample MST blanket was evaluated in a heat

penetration apparatus shown in Figure 1.
9

Table 4. Sample MST Blankets Used in the Flame Penetration Experiments

__________________________________________________________________

Sample Namea Descriptiona

__________________________________________________________________

A Silica cloth 94% silica; service temperature: as hot as 2000° F

399C-1 (continuous heating) and 3000° F (short term heating);

weight: 18 oz/yd2; thickness: 0.030 in. Cotronics Corp.,

Brooklyn, NY

B Felt insulation Silica fibers; service temperature: as hot as 2300° to

370-1 3000° F; density: 12 lb/ft3 for a thickness of 0.13 in. and

8 lb/ft3 for a thickness of 0.25 in. Cotronics Corp.,

Brooklyn, NY

C HTX-1000-9N 94% silica similar to A but thicker - a woven

continuous filament amorphous silica fabric with a

proprietary coating; service temperature: as hot as

1800° F; weight: 33 oz/yd2; thickness: 0.046 in. Amatex

Corporation, Morristown, PA.

D Nextel 312 Woven from continuous alumino-borosilicate fibers;

(AF 40) service temperature: as hot as 2200° F (continuous) and

2600° F (short term); weight: 25.0 oz./yd2; thickness:

0.039 in.; melting point: 3272° F. 3M Company, St.

Paul, MN.

E Siltemp 96% silica high temperature insulation made from

25M Mat amorphous silica; service temperature: as hot as 2000° F;

density: 13 lb/ft3; nominal thickness of 0.23 in.

Ametek, Wilmington, DE

F Kevlar®/fiber Medium weight aramid fiber blends over a

glass 22PT30 fiberglass yarn; service temperature: as hot as 650° F;

weight 22 oz/yd2; thickness: 0.060 in. Amatex

Corporation, Morristown, PA.

G Nomex® III Weight: 7.5 oz/yd2. Southern Mills, Union City, GA

aramid blend

H Fiberglass Woven ceramic fibers; weight: 24 oz/yd2; thickness:

0.025 in. JPS Glass Company, Slater, SC

I Silicone-coated 94% silica woven continuous filament amorphous silica

silica cloth fabric with silicone rubber coating on one side; service

HT 1000-9N-SRI temperature: as hot as 1800° F; weight: 42 oz/yd2;

thickness: 0.054 in.; Amatex Corporation, Morristown, PA.

J NorFab Kevlar - glass style 30PT20DC, 30 oz/yd2

K 3M Nextel fabric style 440

L Ceramic fabric style 399C-2

M Ceramic fiber batting 370-1; 1/8 in.

N Ceramic fiber batting 370-4; 0.5 in.

O Ballistic blanket - 13 layers of Kevlar fabric

P Kevlar -Nomex fabric style 5450; 9.2 oz/yd2

Q Amatex mineral-coated glass style G26T33-7B; 9.2 oz/yd2

R Carbon fiber batting; 7 oz/yd2

__________________________________________________________________

aNames and information are from the manufacturers’ brochures; the units are the same as reported

in the brochures.
10

Heater

Scale

Horizontal

Sample Holder

Sample

Infrared

Heater

(8 cm x 25 cm)

0.67 m

1.5 m

Thermocouple

Crank

Side View

Figure 1. Heat Penetration Apparatus Used in the Experiments for Sample MST

Blankets.

The heat penetration apparatus consisted of a single infrared heater (Model 5208-

10, Research Inc., Minneapolis, MN) attached at the top of a 1.5-m high, 0.67-m

long, and 0.67-m wide metal frame with wheels. The heater had a cross section of

80 mm by 250 mm. A controller (Model 5620, Research Inc., Minneapolis, MN)

was used to adjust the output of the radiant heater.

A horizontal platform was used to hold the sample MST blanket. The platform

was moved in a vertical direction to change the external heat flux value at the

sample surface. A Medtherm heat flux gauge was used to calibrate the heat flux

from the radiant heater to the sample surface. The calibration is shown in

Figure 2. The heat flux increases with decreasing distance between the sample

surface and the radiant heater and reaches a maximum of about 200 kW/m2 for a

distance of 30 mm between the sample surface and the heater.

In each experiment, the sample MST blanket with three layers of Kevlar fabric at

the back was placed on top of the horizontal platform, as shown in Figure 3. Five

thermocouples at the center of each layer were used to measure (a) the front and

back surface temperatures (Ts and Tu, respectively) of the sample MST blanket,

and (b) the back surface temperatures of each layer of the Kevlar fabric (Tk1, Tk2,

and Tk3). A water-cooled shield was used to block the heat exposure of the

sample blanket until the radiant emission from the heater was stabilized

(20 seconds).
11

1

10

100

1000

10 100 1000

Distance of Sample Blanket Surface Level from the Heater (mm)

Radiant Flux (kW/m

2

)

Figure 2. Measured Radiant Heat Flux at the Sample Surface Versus Distance

Between the Surface and the Radiant Heater in the Heat Penetration

Apparatus.

Infrared lamps

3

2

1

Sample Blanket

Thermocouples

Three

Kevlar

Fabrics

R

Water cooled

Reflector Unit

Thermocouple

146 mm

76 mm

 76 mm

Clamp Sample Blanket

Water Cooled Shield

Kevlar FabricR

Figure 3. Arrangement of the Sample MST Blanket With Three Layers of Kevlar

Fabric at the Back of the Sample MST Blanket on the Horizontal

Platform of the Heat Penetration Apparatus.

For the temperature measurements, K-type thermocouples (Omega) were used,

which were attached to the fabric surfaces with a high temperature adhesive. The

thermocouples were connected to a data processor (Analog Device, Signal

Processor Model 5B47-K-04). The data processor was connected to a data logger

(DL1, prototype unit) interfacing with a Gateway 2000 PC with Windows 95
12

operating system through its serial communication port. A software package

LITEUP was used to instruct the hardware to read the data. The software

package LITESHOW was used to stop the data acquisition and transfer the data

into a data file. The software package XLITE was used to convert the data file to a

text file. The K-type thermocouple data were imported as voltages and converted

to degrees C (conversion factor of degrees C per 40 microvolts).

The experiment was started by placing the sample MST blanket on the horizontal

platform, turning on the data processor, data logger, and the Gateway 2000 PC,

and initiating the software package LITEUP with the name of the data file. The

heater was then turned on with the water-cooled shield in place to block the heat

exposure of the sample MST blanket. The heater was allowed to stabilize for

20 seconds, at which time, the water-cooled shield was moved away and the

sample MST blanket surface was exposed to the preset heat flux value. In each

experiment, the sample blanket was exposed to heat flux for a fixed exposure

time (between 10 to 120 seconds). The temperature was measured every

0.05 second at five locations (at the center of the front and back surfaces of the

sample MST blanket and back surfaces of the three layers of Kevlar fabric).

At the end of the exposure, the heater was turned off. The software application

LITESHOW canceled the data acquisition and transferred the data into a data

file. The PC was then booted in DOS (disk operating system), and the software

XLITE converted the data file into a text file. The PC was then reverted to

Windows 95 and the text file was read into a Microsoft Excel template

worksheet. The thermocouple data imported as voltages were converted to

degrees C and recorded into the Microsoft Excel temperature worksheet as a

1-second running average (temperature was recorded every 0.05 second and thus

averaged 20 data points).

The sample MST blankets evaluated in the heat penetration apparatus are listed

in Table 5. Note that the samples consist of layers of alumina, silica, and other

inorganic materials. These fabrics were similar to those listed in Tables 1 and 2.

Combinations of numbers 1000, 800, and 600 designate various types of

fiberglass. CH represents silica fiber. Nextel consists of woven aluminoborosilicate (ABS) fibers.

Four sample MST blankets were thin (5 mm) and five sample MST blankets were

thick (15 to 25 mm). The manufacturers did not provide detailed chemical

compositions of the samples because they were assembled from proprietary

combinations of fabrics.

2.6 Determination of Exposure Conditions

The goal of the sample MST blanket exposure experiments was to expose the

surface to a high enough temperature for longer times, without ignition, and to
13

be able to use the data for extrapolation to higher temperatures (possibly as high

as 3000° C) and exposures as long as 60 seconds.

Table 5. Sample MST Blankets for the Heat Penetration Experiment

__________________________________________________________________

Sample Fabric Fabric Thickness/

 No. Arrangement LayersaSide Exposed

__________________________________________________________________

Thin sample MST blankets

 1 Shiny 1000/600 aluminum; 5 mm thick

 AF – 62 Nextel 1000/600

Shiny aluminum

 2 Beige 188 CH; 0.13-in. Kaowool 5 mm thick beige

 paper rubberized silica

Black

 3 Light green Zetex 10615-1860; 5 mm thick

 0.13-in. Kaowool paper; Zetex

Gray 84 GHS

 4 Ceramic fabric 399C-2 5 mm thick

Creamy 0.13-in. ceramic blanket

Creamy Ceramic fabric 399C-2

Thick sample MST blankets

 5 Shiny 1000/600 aluminum- 15 mm thick beige

 Copper knit 500; 188 CH

Beige

 6 Silver silica 1000/500 stainless steel foil 20 mm thick beige

 0.5-in. Kaomat ; 188 CH

Beige

 7 Orange silicone 1000/500 OSb; 0.5-in. 607 20 mm thick beige

 Superwool ; 188 CH

Beige

 8 Shiny 1000/800 aluminum; 0.5-in. 20 mm thick beige

 Kaowool–S ;188 CH

Beige

 9 Fiberglass weave 1000/800 stainless steel foil; 25 mm thick

 0.5-in. 607 Superwool ; fiberglass

Shiny 1000/600 aluminum

__________________________________________________________________

aSample details are from the manufacturer’s catalogue.

bOS = orange silicone
14

Several preliminary experiments were performed to set the exposure conditions

without the ignition of the sample. For the initial experiments, two thin sample

MST blankets (No. 1, 3, and 4) and a thick sample MST blanket (No. 8) were

used. The experiments were performed with unpainted surface and with a flat

black painted surface. The sample surface was exposed to 20, 50, and 84 kW/m2

for short (10 to 20 seconds), intermediate (100 seconds), and longer (120 seconds)

exposure, when there was no ignition of the sample.

The first set of baseline conditions is listed in Table 6. The experiments were

started with the short exposure to avoid the possibility of igniting the sample

blanket. The sample blanket’s surface was not coated. The short exposure of 10 to

20 seconds was found unsatisfactory as the temperature rise at the front surface

of the sample MST blanket was quite low and the back surface temperature was

close to ambient. Exposure for 100 seconds was also unsatisfactory.

Table 6. Baseline Experiments With Short Exposure

Duration of the Unpainted Sample Surface

__________________________________________________________________

Experiment Number Sample MST Blanket Heat Flux (kW/m2)

__________________________________________________________________

1 1 20

2 1 20

3 1 50

4 4 20

5 4 50

6 4 50

7 4 84

__________________________________________________________________

The second set of baseline experiments used unpainted and black painted sample

surfaces exposed to 84 kW/m2 for 120 seconds. In the second set of experiments,

samples 3, 4, and 8 were used. There was no sample ignition in any of the

experiments. The data are shown in Figures 4 through 6.

The surface temperature for the black painted surface is higher; the steady state

is of longer duration, without the ignition of the sample. Data for the unpainted

surface are unsatisfactory because of the low surface absorptivity. For example,

an examination of the temperature profile for sample No. 8 in Figure 4 indicates

that the surface temperature of the beige side (188 CH) is about 1.5 times the

temperature of the shiny side (1000/800 aluminum, Figure 4a). Thus, an

exposure of 84 kW/m2 for 120 seconds of a flat, black painted surface was

selected for the heat penetration investigation.
15

0

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180

Time (second)

Average Temperature (o C)

Front

Back

a. Unpainted shiny side (1000/800 aluminum) was exposed to 84 kW/m2 for 120

seconds.

0

50

100

150

200

250

300

0 20 40 60 80 100 120 140 160 180

Time (second)

Average Temperature (

o C)

Front

Back

b. Unpainted beige side (188 CH) was exposed to 84 kW/m2 for 120 seconds.

0

100

200

300

400

500

0 20 40 60 80 100 120 140 160

Time (seconds

Average Temperature (

o C) 

Front

Back

c. Black painted beige side (188 CH) was exposed to 84 kW/m2 for 120 seconds.

Figure 4. Average Front and Back Surface Temperatures Above Ambient at the

Center of 20-mm Thick Sample No. 8.
16

0

50

100

150

200

250

300

350

0 20 40 60 80 100 120 140 160 180

Time (second

Average Temperature (

o C)

Front

Back

a. Unpainted surface was exposed to 84 kW/m2 for 120 seconds.

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (o C)

Front

Back

b. Black painted surface was exposed to 84 kW/m2 for 120 seconds.

Figure 5. Average Front and Back Surface Temperatures Above Ambient at the

Center of 5-mm Thick Sample No. 3.
17

0

40

80

120

160

200

240

280

0 20 40 60 80 100 120 140 160 180

Time (second

Average Temperature (

o C)

Front

Back

a. Unpainted surface was exposed to 84 kW/m2 for 120 seconds.

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (

o C)

Front

Back

b. Black painted surface was exposed to 84 kW/m2 for 120 seconds.

Figure 6. Average Front and Back Surface Temperatures Above Ambient at the

Center of 5-mm Thick Sample No. 4.

2.7 Resistance to Fragment Penetration

Two series of ballistic experimentation were performed in order to determine the

ballistic performance of the hybrid blankets. The complete results of Phase 1

ballistic experimentation are documented in ARL-TR-2122 [22]. The results from

the Phase 2 ballistics are presented in this report. This report also documents

small-scale arena experiments in which these blankets were assessed against live

propellant threats.
18

2.7.1 Phase 1 Ballistics

For this phase of ballistic experimentation, a 0.3-kg right circular cylinder was

used as a fragment simulator. This simulator was 170 mm long and 17 mm in

diameter. The fragment size was based on a series of experiments in which two

Composition B (Comp-B) loaded M107 155-mm rounds were simultaneously

nose detonated [22]. The resulting fragments were on the order of 0.3 kg and had

an aspect ratio of 10. A right circular cylinder fragment simulator was chosen for

ease of manufacturing and ease of launching.

The projectile fragments were launched from a 25-mm inner diameter smooth

bore compressed gas gun. A polyethylene foam sleeve acted as a sabot to center

the projectile in the gun barrel during firing. A polypropylene pusher plate made

was used to provide a tight seal along the edges for efficient/repeatable

projectile launching. The projectile velocity, which was based on the terminal

velocity of a 0.3-kg falling body, was approximately 146 m/s. The velocity of the

projectile was measured with break screens and high speed timers.

All the targets used for the Phase 1 ballistic study were fabricated from multiple

layers of Kevlar 29 fibers. The inorganic fabrics were not expected to contribute

to the ballistic performance of the system; therefore, they were not used in this

phase of evaluation since the objective was to determine the blankets’ ballistic

effectiveness. Two different panel constructions were investigated, each with a

different areal density, and are designated as ARL and FFF (Federal-Fabrics

Fibers). All samples were stitched together with aramid thread and supported

securely in a picture frame fixture according to MIL-C-44050A for fragment

penetration experiments.

The 13.6-oz/yd2 17 by 17 (yarns/inch by yarns/inch) plain weave fabric used in

the ARL targets was purchased from Hexcel-Schwebel (Anderson, South

Carolina). The Style No. 745 fabric was woven from 3000-denier (weight in

grams of a 9000-m-long end) Kevlar 29 yarn. The fabric was also treated with a

waterproofing compound.

The Kevlar 29 yarns (fiber bundles) used in the fabrication of the FFF blankets

were first bathed in a mixture of organic binder and vermiculite for flame

resistance. After drying, the yarns were woven into a fabric for blanket

construction and evaluation. This fabric was produced from 1500-denier yarns;

therefore, the number of plies needed to achieve an equivalent areal density was

more than enough. This weaving process resulted in a loose plain weave fabric,

which was not as tightly woven as the ARL fabric. The areal weight of these

fabrics with the vermiculite coating is approximately 4 oz/yd2, about one-third

that of the ARL fabrics. Therefore, additional layers of FFF material were added

to compare the blankets, based on equivalent areal densities.
19

All targets were secured between two 25-mm thick aluminum frames with

C-clamps (see Figure 7). The samples were evaluated for ballistic performance

with three shots per target in a diagonal array as illustrated. A 0.05-mm 2024-T3

aluminum sheet was used as a witness plate, and a “catch box” was positioned

behind the target in order to stop any projectiles that completely penetrated the

target..

Figure 7. Front View of Ballistic Clamp Fixture.

2.7.2 Phase 2: Ballistics and Sub-Scale Arena Experiments

Based on the Phase 1 ballistics and the preliminary thermal evaluation, a plan for

the Phase 2 ballistics and sub-scale arena experiments was developed. This

would demonstrate the ability of aramid fiber/ceramic fiber blankets to provide

flame protection and low velocity impact protection to co-located munitions

from firebrands discharged by violent reaction of nearby ammunition stores.

Phase 2 ballistics and sub-scale arena experiments were subdivided into three

areas of effort to reach the objective. These controlled experiments were chosen

because of the statistical nature of these events. If these blankets were set up in a

full-scale arena experiment, any type of fragment impact or interaction with a

thermal threat could not be guaranteed. In a controlled experiment, we could

guarantee interaction and record all the appropriate data.

The first subdivision involved the Phase 2 ballistic investigation, in which

different areal density Kevlar /silica oxide fabric targets were evaluated in order

to determine an effective ballistic limit. This was performed with a larger

fragment simulator traveling at a lower velocity than used in Phase 1 ballistics.

The second and third subdivisions comprise the sub-scale arena experiments.

The second subdivision involved static flame experiments with live propellant

threats found in the field to determine a specific level of protection thermal

threats. The third subdivision is a controlled dynamic experiment to simulate an

actual detonation of an ammunition stack and the effects received by a
20

neighboring stack. All the experiments were recorded with high speed

photography and Doppler radar. Temperature data were collected with type K

thermocouples.

In the first subdivision, a 454-g steel rectangular slab with sharpened edges was

chosen as a simulated fragment threat and is representative of fragments that are

produced from a reacted stack of munitions. A black powder charge was used to

propel the fragment from a modified gun system (see Figure 8). The fragment

velocity was fixed at 60 m/s, and the gun was calibrated to produce repeatable

velocities of 60 ±1 m/s. The velocity data were obtained with the use of Doppler

radar (see Figure 9).

Figure 8. Modified Remington 700 Rifle (top) With 40-mm Smooth Bore

Fragment Launcher Attachment (bottom).

Figure 9. Modified Remington 700 Rifle Assembled and Secured in Firing

Bracket Next to Doppler Radar Head.

Five separate blankets consisting of three plies of ceramic fabric sandwiched

between four plies of Kevlar® were used. A maximum of three fragments was
21

fired at each sample. If any of the blankets failed, additional plies of Kevlar®

fabric were added to increase the areal density. If any blanket passed a three-shot

experiment, the number of Kevlar® plies was reduced until a failure was

observed. Plies of Kevlar® were added and removed in pairs in order to maintain

blanket symmetry. As in Phase 1, successful blankets were evaluated for ballistic

properties with a wood backing to simulate a packaged ammunition stack. This

will ensure that the blanket provides adequate ballistic protection in

unsupported and supported configurations in the field.

The investigation was considered a success if the fragment did not completely

penetrate the final ply of Kevlar®. Subsequent laboratory experiments

determined the size of the damage zone in the ceramic. Flammability studies

determined any loss in thermal protection because of impact damage to the

ceramic material.

2.7.3 Sub-Scale Arena Experiments

The second subdivision involved the use of live propellant threats to determine

the thermal properties of the blankets and their ability to protect stored

munitions in case of a fire or explosion. The flame penetration and heat

penetration results reduced the number of candidate materials for the required

thermal protection by means of a hot gas jet. Several blankets were used to cover

live and inert sub-scale acceptor stacks of ammunition. The Phase 1 and Phase 2

ballistic results dictated the final blanket construction in which ceramic layers

were sandwiched between a specific number of Kevlar® plies.

The blankets were exposed to realistic threats of propellant and burning debris

(wood and plastic). Unprotected acceptor stacks of ammunition were exposed to

the same threats. The temperature profiles of both the top and bottom surfaces of

the blanket as well as the internal crate temperatures were monitored with

thermocouples. Based on these results, the number of ceramic plies is adjusted

until a satisfactory solution is resolved. The investigation is considered a success

if the blanket prevents scorching of the inert acceptors and/or ignition of the live

acceptor materials.

The third subdivision subjected larger scale blankets to a simulated dynamic

thermal event whereby fragments were propelled at several co-located acceptor

stacks covered with prototype blankets. Each sub-scale prototype blanket was

subjected to a volley of 0.45-kg projectiles, which produced varying degrees of

damage to the blanket. The blankets were then placed on live acceptor stacks and

a thermal threat was ignited on top. Any decrease in the flame/heat protection

may be attributed to the damage received from fragment impact. The experiment

is a success if the blanket prevents severe scorching and ignition of the live

acceptor materials.
22

3. Results and Discussion

3.1 Flame Penetration Experiments

In the experiments, a sample surface was exposed to an oxyacetylene flame for a

fixed time duration. Samples were mounted and secured on top of a pine wood

block by a metal frame or were stapled. Black powder and M9 propellant were

placed on top of the sample and between the sample and the pine wood surface.

Three different sets of experiments were performed:

1. First Set of Experiments (thick wooden block, metal frame): Samples A

to I (see Table 4) and their combinations;

2. Second Set of Experiments (thin wooden block, metal frame): Samples

J to O (see Table 3) and their combinations; and

3. Third Set of Experiments (larger sample area, thin wooden block, no

metal frame): Samples J, P, Q, and R (see Table 4).

3.1.1 Results from the First Set of Flame Penetration Experiments

In the experiments, samples were mounted on thick pine wood blocks with a

metal frame. The sample surface was exposed to an oxyacetylene flame for 3 to

80 seconds. The results are listed in Table 7.

The data in Table 7 indicate that a combination of silica-based samples is more

effective in resisting flame penetration. The silica-based sample combinations

that appear to be effective are

• Silica cloth (#A)-felt insulation (#B) combination for exposures of less than

60 seconds;

• Silica cloth (#A)-felt insulation (#B-silica fibers)-silica cloth (#A)

combination for exposures of less than 80 seconds;

• Siltemp (#E-silica insulation) combination for exposures of less than 40

seconds;

• HTX-1000-9N (#C, silica similar to #A)- Siltemp (#E-silica insulation)

combination;

• Silicone-coated silica cloth (#I)- Siltemp (#E-silica insulation) for

exposures as long as 30 seconds.
23

Table 7. Flame Penetration Into a Thick Wood Block With a Smaller Sample

__________________________________________________________________

Exposure

Experiment Sample MST Blanket on Duration Wood

 Number Wooden Block Surface (seconds) Behavior

__________________________________________________________________

1 No sample, wood surface exposed 3 Charring

2 SiO2 cloth (#A) 6 Charring

3 Silica cloth (#A) heated to 767 oC 20 Outgassing

4 Silica cloth (#A) over black powdered 11 Charring of

propellant on wood surface. wood and

Propellant exploded in 11 seconds cloth

5 1/8-in. silica felt (#B) 10 Charring

6 #A/#B layer heated to 700° C 60 Charring- no

flaming

7 #A/#B/#A layer heated to 750° C 80 Third layer

slightly browned;

wood slightly

charred

8 Nextel (#D) 6 Burn throughcharred wood

9 #D/#D 6 Less severe burnthrough than

Experiment 8

10 Siltemp (#E) 40 Bottom charred

11 Kevlar /fiber glass (#F) heated to 775° C 5 Burning of wood

12 Kevlar /fiber glass (#F) heated to 700° C 4 Burn through

13 Nomex III aramid (#G) 3 Burn through

14 HTX1000-9N silica (#C) heated to 800° C 15 Burning of wood

15 #C/#E 54 Wood did not char

16 Woven ceramic fibers/Fiberglas (#H) 7 Burn through

17 Silicone-coated silica cloth (#I) 10 Slightly charred

18 #I/#E 30 No char

19 #C/#E + propellant on top of Propellant No char

blanket ignited

immediately

20 #C/#E + propellant between the Propellant Wood and bottom

sample and wooden block ignited blanket charred

immediately

21 #I/#E + propellant on top of blanket Propellant No char

ignited

immediately

22 #I/#E + propellant between the Propellant Wood and bottom

sample and wooden block ignited blanket charred

immediately

ignition

__________________________________________________________________
24

3.1.2 Results from the Second Set of Flame Penetration Experiments

In the experiments, samples were clamped to thin pine wood blocks with a metal

frame. The sample surface was exposed to an oxyacetylene flame for 10 seconds.

The results are listed in Table 8.

Table 8. Flame Penetration Into a Thin Wood Block With

a Smaller Sample for 10 Seconds’ Exposure

__________________________________________________________________

 Flame

 Penetration

Experiment Sample Combinations Into Wood (mm) Comments

__________________________________________________________________

23 Kevlar -glass (#J) over 13 64-mm square hole

ceramic fiber batting (# N) on the sample surface

24 Ceramic fiber batting (# N) 9 51- by 64-mm hole on

the sample surface

25 Nextel fabric (#K) over 6 51- by 64-mm hole on

ceramic fiber batting (#M) the sample surface

26 Nextel fabric (#K) over 5 51- by 64-mm hole on

ceramic fiber batting (#N) the sample surface

27 Ceramic fabric (#L) 5 25- by 19-mm hole on

the sample surface

28 Ceramic fabric (#L) over None No hole

ceramic fiber batting (#M)

29 Ceramic fabric (#L) over None No hole

ceramic fiber batting (# N)

30 Kevlar ballistic blanket (#O) 3 13- by 15-mm hole on

the sample surface;

76- by 89-mm wood

burned

31 Kevlar ballistic blanket (#O) None 2-mm penetration

over ceramic fabric (#L) into sample

32 Ceramic fabric (#L) with None No penetration into

ceramic fiber batting (#M) over sample

Kevlar ballistic blanket (#O)

__________________________________________________________________

Observations in Table 8 show that ceramic-based samples are able to resist flame

penetration. Sample combinations that are effective in preventing flame

penetration are (a) ceramic fabric (#L) over ceramic fiber batting (#M and #N),

(b) Kevlar ballistic blanket (#O) over ceramic fabric (#L), and (c) ceramic fabric

(#L) with ceramic fiber batting (#M) over Kevlar ballistic blanket (#O).
25

3.1.3 Results from the Third Set of Flame Penetration Experiments

In the experiments, large, mostly organic fiber-based fabric samples were stapled

on thin pine wood blocks. The sample surface was exposed to an oxyacetylene

flame for 10 seconds. The results are listed in Table 9.

Table 9. Flame Penetration Into a Thin Wood Block With

Larger Samples for 10 Seconds’ Exposure

__________________________________________________________________

 Flame

 Penetration

Experiment Sample Combinations Into Wood (mm) Comments

__________________________________________________________________

33 Kevlar -Nomex fabric 10 Sample burned off

(# P) on 38-mm thick

wooden block

33 Kevlar -glass (#J) on 13 25- by 64-mm hole on

38-mm thick wooden block the sample surface

34 Amatex mineral-coated glass 10 64- by 76-mm hole on

(#Q) on 38-mm thick wooden the sample surface

block

35 Two layers of Kevlar -glass 9 13- by 19-mm hole on

(#J) on 19-mm thick wooden the sample surface

block

36 Two layers of (Kevlar -glass 14 13- by 25-mm hole on

(#J) + carbon fiber batting the sample surface

(#R)) on 19-mm thick wooden

block

37 Two layers of (Kevlar -glass 14 10- x 19-mm hole on

(#J) + two layers of carbon the sample surface

fiber batting (#R)) on 19-mm

thick wooden block

__________________________________________________________________

The information in the table shows that none of the organic fiber-based fabrics as

single or multiple layers prevented flame penetration into wooden block. Thus, it

is necessary to use fabrics with a combination of organic and inorganic layers or

only inorganic layered fabrics.

3.2 Heat Penetration Experiments

In the experiments, a single layer of each sample MST blanket on top of three

layers of Kevlar fabric were exposed to an external heat flux of 84 kW/m2 for

120 seconds. Temperatures versus time measurements were made at the center of

the front and back surfaces of the sample and at the center of the back surfaces of

the three layers of the Kevlar fabric.
26

3.2.1 Front and Back Temperatures at the Center of the Sample

The measured data for the front and back temperatures at the center of the

sample are shown in Figures 4c (No. 8), 5b (No. 3), 6b (No. 4), and in Figures 10

through 15.

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (o C)

Front

Back

Figure 10. Average Front and Back Surface Temperatures Above Ambient at the

Center of 5-mm Thick Sample No. 1. (The black painted surface was

exposed to 84 kW/m2 for 120 seconds.)

0

100

200

300

400

500

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (o C)

Front

Back

Figure 11. Average Front and Back Surface Temperatures Above Ambient at the

Center of 5-mm Thick Sample No. 2. (The black painted surface was

exposed to 84 kW/m2 for 120 seconds.)
27

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (

o C)

Front

Back

Figure 12. Average Front and Back Surface Temperatures Above Ambient at the

Center of 15-mm Thick Sample No. 5. (The black painted surface was

exposed to 84 kW/m2 for 120 seconds.)

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (

o C)

Front

Back

Figure 13. Average Front and Back Surface Temperatures Above Ambient at the

Center of 20-mm Thick Sample No. 5. (The black painted surface was

exposed to 84 kW/m2 for 120 seconds.)

An examination of the front and back surface temperature profiles in the figures

indicates that the delay in the rise of back surface temperature depends on the

sample thickness and composition. For thin samples (thickness = 5 mm, No. 1, 2,

3, and 4), the rise in the back surface temperature was started between ~20 to

60 seconds. For thicker samples (thickness = 20 to 25 mm, No. 6, 7, 8, and 9), the

rise in the back surface temperature started between ~80 and 130 seconds. For

Sample No. 5 (15 mm thick), there was a negligible increase in the back surface

temperature.
28

0

100

200

300

400

500

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (

o C)

Front

Back

Figure 14. Average Front and Back Surface Temperatures Above Ambient at the

Center of 20-mm Thick Sample No. 7. (The black painted surface was

exposed to 84 kW/m2 for 120 seconds.)

0

100

200

300

400

500

0 20 40 60 80 100 120 140 160

Time (second)

Average Temperature (

o C)

Front

Back

Figure 15. Average Front and Back Surface Temperatures Above Ambient at the

Center of 25-mm Thick Sample No. 9. (The black painted surface was

exposed to 84 kW/m2 for 120 seconds.)

3.2.2 Back Surface Temperature of the Sample and Kevlar Fabric Backing

Three layers of organic polymer-based Kevlar fabric were placed behind the

sample as a backing. In the experiments, temperatures were measured at the

center of the back surface of the sample and each layer of Kevlar fabric as

shown in Figure 3. The measured surface temperatures are shown in Figures 16

through 24.
29

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350 400

Sample Temperature ( oC)

Kevlar Fabric Temperature (

o C) 

1

2

3

Figure 16. Back Surface Temperature Above Ambient at the Center of 5-mm

Thick Sample No. 1 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 400° C.)

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Sample Temperature ( oC)

Kevlar Fabric Temperature (

o C)

1

2

3

Figure 17. Back Surface Temperature Above Ambient at the Center of 5-mm

Thick Sample No. 2 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 440° C.)

The average back surface temperature of each layer of Kevlar fabric was lower

than the average back surface temperature of the sample. The average back

surface temperature of the bottom third layer of Kevlar fabric was lowest,

indicating that Kevlar fabric does provide thermal protection as was found in
30

the flame penetration experiments (see Table 8, combinations of samples L, M,

and O). It is necessary, however, to use at least three layers of Kevlar fabric.

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140 160 180 200 220 240

Sample Temperature ( oC)

Kevlar Fabric Temperature (

o C)

1

2

3

Figure 18. Back Surface Temperature Above Ambient at the Center of Back

Surface of 5-mm Thick Sample No. 3 Versus That of the Kevlar

Fabric Backing Layers 1, 2, and 3. (The maximum temperature of the

front surface of the sample was 550° C.)

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

Sample Temperature (oC)

Kevlar Fabric Temperature (

o C)

1

2

3

Figure 19. Back Surface Temperature Above Ambient at the Center of 5-mm

Thick Sample No. 4 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 490° C.)
31

0

4

8

12

16

20

24

0 5 10 15 20 25 30

Sample Temperature ( oC)

Kevlar Fabric Temperature (

o C)

1

2 3

Figure 20. Back Surface Temperature Above Ambient at the Center of 15-mm

Thick Sample No. 5 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 450° C.)

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70

o

1

2

3

Sample Temperature (° C)

Figure 21. Back Surface Temperature Above Ambient at the Center of 20-mm

Thick Sample No. 6 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 475° C.)
32

0

2

4

6

8

10

12

0 2 4 6 8 10 12 14 16 18 20 22 24

Sample Temperature (° C)

1

2

3

Figure 22. Back Surface Temperature Above Ambient at the Center of 20-mm

Thick Sample No. 7 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 430° C.)

0

4

8

12

16

20

24

28

0 5 10 15 20 25 30 35 40 45 50 55 60

Sample Temperature ( oC)

Kevlar Fabric Temperature (

o C)

1

2

3

Figure 23. Back Surface Temperature Above Ambient at the Center of 20-mm

Thick Sample No. 8 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 444° C.)
33

0

4

8

12

16

20

24

28

32

36

40

0 10 20 30 40 50 60 70 80

Sample Temperature ( oC)

Kevlar Fabric Temperature (

o C)

1

2

3

Figure 24. Back Surface Temperature Above Ambient at the Center of 25-mm

Thick Sample No. 9 Versus That of the Kevlar Fabric Backing Layers

1, 2, and 3. (The maximum temperature of the front surface of the

sample was 440° C.)

Maximum temperatures of the front sample surface and back surface of the third

layer of Kevlar fabric are summarized in Table 10. Data in Table 10 indicate that

there is a significant decrease in the temperature of the third layer of Kevlar

fabric when compared with the front surface temperature of the sample. For a

significant reduction in the flame and heat penetration, there is, however, a need

to use at least 15- to 25-mm thick layers of inorganic fiber-based fabrics and at

least three or more layers of Kevlar fabrics for backing.

3.2.3 Resistance to Heat Penetration

As discussed in the background section, effective thermal diffusivity of a fabric

system can be considered as a parameter for expressing resistance to heat

penetration. The thermal diffusivity of a fabric system can be estimated from the

following expression [16]:

 

Tu = Ts[erfc(x/2 t)] (1)

in which Tu is the steady state back surface temperature above ambient of the

sample (oC), Ts is the steady state temperature above the ambient of the front

(exposed) surface of the sample (oC), x is the thickness of the sample (mm), t is

the exposure time used in the experiments (120 s), and is the effective thermal

diffusivity of the sample (mm2/s). Effective thermal diffusivity is expressed as

k/ cp, in which k is the thermal conductivity (kW/m-K), is the density (g/m3),

and cp is the heat capacity (kJ/g-K). The expression is used to calculate

temperatures inside a material satisfying a thermally thick condition, at various
34

distances from a hot surface, assuming conduction to be the dominant mode of

heat transfer [14].

Table 10. Maximum Temperature of the Front Surface of the Sample

 and Back Surface of the Third Kevlar Fabric Layer

__________________________________________________________________

Maximum Temperature (oC)

 Front Back Surface

Thickness Sample of Third

Sample Fabric Layers (mm) Surface Kevlar Layer

__________________________________________________________________

Thin Sample MST Blankets

1 1000/600 aluminum ; 5 400 120; increasing

AF – 62 Nextel ; 1000/600

Aluminum

2 188 CH; 0.13-inch 5 440 40; increasing

Kaowool paper;

Rubberized silica

3 Zetex 10615-1860; 5 550 70; increasing

0.13-inch Kaowool

paper; 84 GHS

4 Ceramic fabric 399C-2 5 490 50; no increase

0.13-inch ceramic blanket

Ceramic Fabric 399C-2

Thick Sample MST Blankets

5 1000/600 aluminum; 15 450 22; increasing

Copper knit 500; 188 CH

6 1000/500 stainless steel 20 475 < 22; increasing

foil 0.5-in Kaomat ; 188 CH

7 1000/500 OS; 0.5-inch 607 20 430 < 22; no increase

Superwool ; 188 CH

8 1000/800 aluminum; 20 444 < 22; no increase

0.5-inch Kaowool-S ; 188 CH

9 1000/800 stainless steel 25 440 30; increasing

foil; 0.5-inch 607 Superwool ;

1000/600 aluminum

__________________________________________________________________

The thermal conductivity values for various fabrics selected for the heat

penetration experiments are listed in the manufacturers’ brochures and range

from about 0.5 by 10-4 to 4 by 10-4 kW/m-K. The thermal diffusivity values are

generally not listed, except for few fabrics. For example, 3M Company has

performed heat conduction experiments with Nextel 312 fabric in a 1093° C
35

furnace. The temperature inside was measured as a function of time for 1, 3, 6,

and 9 layers. Each layer was 0.965 mm. The estimated effective thermal

diffusivity values from Equation 1 range from 0.5 mm2/s at 120 seconds to 3.2

mm2/s at 720 seconds. The effective thermal diffusivity value at 120 seconds is

comparable to the values listed in Table 1 for similar types of fabrics.

In the heat penetration experiments, Tu and Ts values were measured as

functions of time at the center of the sample surfaces. All other information is

available to estimate the effective thermal diffusivity of the fabric systems used

in the experiments. The effective thermal diffusivity values for the sample MST

blankets estimated from the average temperatures measured at the center of the

black painted front and back surfaces in the heat penetration experiments are

listed in Table 11. The estimated effective thermal diffusivity values for 5-mm

thick sample MST blankets agree well with the values listed in Table 1 for similar

materials and for values for Nextel 312 fabric.

Table 11. Estimated Effective Thermal Diffusivity

Values of Sample MST Blankets

__________________________________________________________________

 Thermal

Sample Blanket Fabrics and Fibers in diffusivity

(thickness in mm) Layers of the Sample Blanket (mm2/s)

__________________________________________________________________

 2 (5 mm) 188 CH; 0.13-inch Kaowool paper; 0.40

Rubberized silica

 3 (5 mm) Zetex 10615-1860; 0.13-inch Kaowool 0.64

paper; 84 GHS

 4 (5 mm) Ceramic fabric 399C-2 ; 0.13-inch ceramic 0.51

blanket; Ceramic Fabric 399C-2

 5 (15 mm) 1000/600 aluminum; copper knit 500; 2.66

188 CH

 6 (20 mm) 1000/500 stainless steel foil; 0.5-in Kaomat ; 4.25

188 CH

 7 (20 mm) 1000/500 OS; 0.5-inch 607 Superwool ; 188 CH 4.13

 8 (20 mm) 1000/800 aluminum; 0.5-in Kaowool-S ; 5.51

188 CH

 9 (25 mm) 1000/800 stainless steel foil; 0.5-inch 607 6.46

Superwool ; 1000/600 aluminum

__________________________________________________________________

The effective thermal diffusivity values of 15- to 25-mm thick sample MST

blankets containing metal fibers range between 2.66 and 6.46 mm2/s, which are

significantly higher than the values of 5-mm thick samples without the metal

fibers.
36

The estimated effective thermal diffusivity values listed in Table 11 can be used

to extrapolate the data measured in the heat penetration experiments to higher

temperatures and to estimate the back surface temperature of the third layer of

the Kevlar fabric backing. In the estimations, the temperatures of the front

surface of the sample were assumed to be in the range of 500° to 3000° C, with

the actual thickness and estimated effective thermal diffusivity values of the

sample MST blankets and heat exposure of the front surface for 10, 30, and

60 seconds. These estimations are listed in Table 12. Note that 15- to 25-mm thick

samples resist heat penetration effectively until 3000° C for 60 seconds.

3.3 Ballistics and Arena Experiments

3.3.1 Phase I Ballistics

Thirty fragment-impact experiments were conducted with the fragments and

blanket materials previously described. In most of the experiments, the blankets

were secured in a fixture without any backing material. In seven experiments,

the blankets were secured in the fixture and backed by a 19-mm thick pinewood

panel to simulate a wooden ammunition crate. Other experiments were

conducted, backed and unbacked, with a modified right circular cylinder where

a pointed tip was fashioned onto the end, thereby concentrating the initial impact

force over a smaller area of the blanket.

Two different areal density FFF blankets and three different areal density ARL

blankets were evaluated as illustrated in Table 13. The sample identification (ID)

describes the type of sample, the number of layers of Kevlar® it contains, and a

sequential number to identify the sample. Accordingly, FFF 20-2 is a FederalFabrics Fibers sample with 20 plies and is the second sample in the 20-ply series.

Multiple iterations of fragment experiments were performed in order to

determine the proper blanket areal density. Based on this phase of ballistic

investigation, approximately four to six layers of the ARL, Style #745 Kevlar® 29

were needed to stop a 300-g right circular cylinder fragment. An equivalent areal

density of FFF materials failed to stop the fragment. This is primarily because of

the loosely woven construction of the fabric. None of the blankets evaluated

were able to stop the pointed fragment from penetrating; again, this is because of

the woven architecture of the blanket whereby the fragment was able to slide

past rather that engage the yarns. In general, this phase of fragment experiments

was a worst case scenario in which all fragments impacted “end on”

(horizontally) and at a high velocity. An experiment was needed to incorporate a

fragment’s natural propensity to tumble in flight and strike a target at several

different orientations.
37

Table 12. Estimated Back Surface Temperatures of

the Third Layer of Kevlar Fabric

__________________________________________________________________

Temperature Above Ambient (oC)

Assumed Third Bottom Kevlar Fabric Layer

 Front 10-second 30-second 60-second

Sample MST Sample Exposure Exposure Exposure

blanket Surface Tk3 Tk3 Tk3

__________________________________________________________________

2; x = 5 mm; 1000 11 42 65

 = 0.40 mm2/s 2000 21 85 130

3000 32 127 195

3; x = 5 mm; 1000 36 93 126

 = 0.64 mm2/s 2000 72 186 251

3000 108 278 377

4; x = 5 mm; 1000 25 79 113

 = 0.51 mm2/s 2000 51 158 225

3000 76 237 338

5; x = 15 mm; 1000 4 25 43

 = 2.66 mm2/s 2000 8 50 86

3000 13 75 129

6; x = 20 mm; 1000 0 3 6

 = 4.25 mm2/s 2000 1 7 12

3000 6 18 25

7; x = 20 mm; 1000 1 9 15

 = 4.13 mm2/s 2000 2 13 23

3000 3 26 46

8; x = 20 mm; 1000 1 5 8

 = 5.51 mm2/s 2000 2 10 17

3000 3 16 25

9; x = 25 mm; 1000 3 24 43

 = 6.46 mm2/s 2000 7 48 87

3000 10 72 130

__________________________________________________________________

Table 13. Areal Density of Kevlar® Ballistic Blankets

__________________________________________________________________

10-ply FFF 20-ply FFF 4-ply ARL 8-ply ARL 13-ply ARL

__________________________________________________________________

Average 1.30 2.64 1.81 3.71 6.16

Areal Density

(kg/m2)

Standard 0.01 0.03 0.00 0.01 0.04

Deviation 
38

3.3.2 Phase II Ballistics

As mentioned previously, the fragments used in Phase 2 ballistics were 454-g

steel slabs with sharpened edges (see Figure 25). These fragment simulators were

launched from a modified Remington 700 rifle with Paradox powder. A

sampling of the data is tabulated to show the repeatability of the launching

mechanism with the amount of charge used (see Table 14). Once the gun was

calibrated, the velocity measurements were no longer recorded. Multiple

iterations of fragment experiments were performed in order to determine the

proper blanket areal density. Based on this phase of ballistic investigation, four

plies of Hexcel-Schwebel Style #745 Kevlar® 29 were sufficient to stop the

projectile.

Figure 25. Pusher Plate (left) and 1-lb Steel Fragment With Polymer Foam Sabots

Attached on Both Ends. (The pusher plate and sabots are 40 mm in

diameter.)

Table 14. Typical Fragment Velocities, Calibration Data of

Fragment Launcher, and Penetration Data

__________________________________________________________________

Blanket Propellant Velocity Plies

No. (grains) Plies (m/s) Penetrated

__________________________________________________________________

 1 39 4 64.0 0

 2 39 4 60.2 0

 3 39 4 57.8 0

 4 39 4 59.2 0

 5 39 4 62.6 0

 6 39 4 59.6 0

 7 39 4 64.2 1

 8 39 4 59.8 1

 9 39 4 58.9 1

 10 39 4 59.9 0

 11 39 4 58.7 1

 12 39 4 60.7 3

 13 39 4 59.9 0

 14 39 4 63.2 1

__________________________________________________________________
39

Because of fragment impact (see Figure 26) on the target, a number of damaged

fibers could easily be observed on the surface, but the investigation was still

considered a success since a complete penetration did not occur. A postmortem

of the blankets revealed tears in the Kevlar® several layers deep and a small area

of damage in the ceramic layers (see Figures 27 and 28). This damage may or

may not affect the thermal performance of the blanket.

Figure 26. Blanket Clamped in Frame Impacted by a 454-g Steel Fragment.

Figure 27. Typical Damage on a Ply of Kevlar as a Result of Impact by a 454-g

Steel Fragment.
40

Figure 28. Typical Damage on an Inner Ply of Silica Oxide Fabric as a Result of

Impact by a 454-g Steel Fragment.

3.3.3 Sub-Scale Arena Experiments

A number of sub-scale arena experiments were performed in order to adequately

simulate potential real-life events. The results from both the ballistic fragment

penetration experiments and flame/heat resistant experiments were promising.

Static flame experiments were performed with several types of propellant (JA2

and M30) and burning debris. Each represented a fast burning, high temperature

threat and a long burning, low temperature threat, respectively. In each

experiment, a blanket was used to completely cover a generic ammunition crate

(see Figure 29). Thermocouples were placed on top of the blanket, under the

blanket, and inside the crate for temperature data collection. Similar experiments

were conducted on uncovered inert ammunition crates (see Figure 30).

Figure 29. Fully Assembled Sub-scale Prototype MST Blanket.
41

Figure 30. Live Propellant Experiment on an Uncovered Inert Acceptor

Ammunition Crate.

Several different amounts of propellant (0.5, 1, 2.5, 5 kg), which represented a

short duration, high temperature threat, were placed on the top of the blanket

and next to the blanket (see Figure 31). The propellant was ignited with an

electric match, while thermocouples and live video were used to capture the

event in real time.

Figure 31. Side Burn Propellant Experiment (0.5 kg JA2) on a Covered Inert

Acceptor Ammunition Crate.

For the 0.5-kg experiment, the propellant reached a temperature of more than

2000° C and burned for about 5 seconds. The back surface of the blanket and the

interior of the wooden crate did not increase in temperature significantly. Similar
42

results were observed with the 2.5-, 5-, and 10-kg experiments, in which the

propellant was ignited, flared, and quickly extinguished, while the back surface

of the blanket and the interior of the wooden crate did not increase in

temperature substantially. An increase of 50° to 100° C above ambient for short

durations were typical values. This was true for both the top-burn and the sideburn experiments. A typical temperature profile (see Figure 32) through the

thickness showed a significant difference between the front surface of the blanket

and the back surface. The uncovered ammunition crate temperature profile

shows a spike in the internal temperature (see Figure 33), which may have easily

ignited the contents of a live acceptor. This spike may be attributed to flame

penetration between adjacent boards on the crate. A photograph of the blanket

(see Figure 34) that covered the acceptor stack shows several layers of scorched

nylon and Kevlar®, but the wooden packaging was unperturbed while the

uncovered inert crate was totally scorched from the ignited propellant.

Figure 32. Temperature Profile of a Covered Acceptor Ammunition Crate.

During these static flame experiments, the only time a failure was observed was

when the blanket did not completely cover the crate and flames were allowed to

penetrate the blanket at a seam and ignite the combustible material underneath.

In these instances, the ammunition crate ignited and sustained a burn for an

extended length of time. In an actual depot fire, this type of behavior could

possibly lead to the sympathetic detonation of neighboring stacks.
43

Figure 33. Temperature Profile of an Uncovered Acceptor Ammunition Crate.

Figure 34. Typical Charred Remains of a Top-Burn Live Propellant Experiment.

Bonfire experiments were performed in order to evaluate the effectiveness of

these blankets against a lower temperature longer duration thermal threat.

Several pounds of JA2 were used to ignite the wood and debris (see Figure 35).

Once these items ignited, a blanket-covered ammunition box was placed next to

the fire (see Figure 36). The burning embers were then piled on the side of the
44

blanket and allowed to burn until the flames extinguished (see Figure 36). The

temperature profile (see Figure 37) shows that the blanket was effective in

retarding heat transfer to the wooden crate for extended periods of time. The one

temperature spike observed (see Figure 38) was attributable to the penetration of

flames through one of the seams of the blanket. Sandbags were employed in

order to prevent any future occurrence. Again, care must be used when these

blankets are installed. If the stack is not completely covered by the blanket,

flames can easily penetrate and cause a catastrophic failure.

Figure 35. Setup of Bonfire Experiment Before Ignition.

Figure 36. Bonfire Experiment Several Minutes After Ignition.
45

Figure 37. Bonfire Experiment After the Flames Self-Extinguished.

Figure 38. Temperature Profile of a Bonfire Experiment.

Another arena experiment, which evaluated the blanket in extreme

temperatures, simulated the ignition of a tubular storage container of 155-mm

artillery uni-charge packages. Four uni-charge packages were placed in a

155-mm steel tube, which was blocked at one end with a steel plate (see
46

Figure 39). The blanket-covered target was placed approximately 1 m from the

opening of the tube to ensure direct contact with the hot gas jet (see Figure 40).

Figure 39. Setup of Uni-charge Experiment, in Which Four Uni-charge Packages

Were Placed Inside the Steel Tube.

Figure 40. Setup of Uni-charge Experiment, Showing Stand-off Distance.

The first uni-charge was ignited with an electric match and the other three

successively auto-ignited during the experiment. The blanket was subjected to a

tremendous gas jet for approximately 2 minutes. The flames ablated the

protective outer cover, and several layers of Kevlar® (the ceramic inner layers)

were also heavily damaged (see Figure 41) during the event.
47

Figure 41. Results From a Uni-charge Experiment.

The back surface of the blanket was still intact (see Figure 42), and the

temperature profile illustrates the blanket’s ability to protect stored munitions

from a severe thermal threat (see Figure 43). The charred edge is where some

flames were able to breach the blanket, which resulted in a temperature spike on

one of the thermocouple channels. Again, the temperature spike was attributable

to flame migration through a seam and not to a failure from a complete burnthrough of the blanket. If this blanket had been made entirely of Kevlar®

, as in

the BPS, this experiment would have surely been a failure with a total burnthrough the thickness of the blanket. The inorganic layers of ceramic fabric

provided the required high performance for an aggressive threat such as this.

Figure 42. Back Surface of a Blanket Subjected to a Hot Gas Jet Emitted From

Four Uni-charge Packages.
48

Figure 43. Temperature Profile of the Back Surface of a Blanket From a Unicharge Experiment.

In the next arena experiment, the sub-scale blankets were subjected to a volley of

six 454-g fragments in which several small tears in the blanket that were similar

to previously illustrated tears were observed (see Figures 27 and 28). These

blankets were then placed on acceptor stacks, which consisted of inert wooden

packaging material and live, loose uni-charge packages (see Figures 44 and 45).

Generally, the outer layer of nylon and the first layer of Kevlar® were charred

(see Figure 46) and the back surface increased about 75° C above ambient. The

two curves in Figures 47 and 48 represent experiments in which two different

types of blankets were placed on the wooden packaging material. The curves

illustrate the blanket’s ability to protect the wood packaging and ammunition

from heat and flame. As expected, the more insulation present (i.e., layers of

Kevlar®), the lower the back surface temperature.

There were no visible signs that flames were able to penetrate the blanket,

although holes were present. This may be attributed to the shifting of individual

layers to cover holes in neighboring plies. This phenomenon eliminates a direct

path for the fire and heat to penetrate.
49

Figure 44. Uni-charge Placed on Top of a Covered Inert Acceptor Before Ignition.

Figure 45. Uni-charge Placed on Top of a Covered Live (Uni-charge) Acceptor

Before Ignition.

Figure 46. Typical Results From the Ignition of a Uni-charge on Top of an MST

Blanket.
50

Figure 47. Temperature Profile Results From the Ignition of a Uni-charge on Top

of an Undamaged MST Blanket (four plies of Kevlar®).

Figure 48. Temperature Profile Results From the Ignition of a Uni-charge on Top

of an Undamaged MST Blanket (five plies of Kevlar®).
51

The next two curves (see Figures 49 and 50) are from experiments in which the

damaged blankets were placed on top of a live acceptor and a uni-charge was

ignited on top of the blanket. The uni-charge was positioned directly above the

acceptor and temperature data were collected (see Figure 51). Again, a small

increase in the back surface temperature was observed but the blankets appear to

have been effective in preventing ignition of the acceptor propellant.

Figure 49. Temperature Profile of a Live Acceptor Under a Torn Blanket With a

Uni-charge Ignited on Top (four layers of Kevlar®).

Figure 50. Temperature Profile of a Live Acceptor Under a Torn Blanket With a

Uni-charge Ignited on Top (five layers of Kevlar®).
52

Figure 51. Instrumented Acceptor Stack of Ammunition After Several

Experiments.

3.4 Blanket Design Considerations

A manufacturing effort needs to address several issues, including (a) the

formation of a seamless blanket that prevents flame/heat penetration and (b) the

long-term durability of some of the ceramic materials. Seamless construction will

improve the effectiveness since the flame cannot penetrate the seam between

adjacent segments. Improvements in the stitching process may reduce the

fracture of the ceramic felt material along the stitched locations of the blanket.

This felt fracture (see Figure 52) might be detrimental to the thermal performance

of the blanket over time because of rough handling.

Figure 52. The Effect of Stitching on the Brittle Ceramic Felt Material.
53

These blankets were configured so that they provided optimal protection from

ballistic and thermal threats. A composite construction was chosen because of the

unique requirements of the blanket (see Figure 53). The number of layers of

Kevlar® was established, based on the low velocity ballistic experiments. The

number of layers of ceramic fabric was dictated by the results of the heat/flame

penetration experiments.

Figure 53. Composite Sandwich Schematic Showing Different Layers of Material.

From the total number of layers in the blanket, an areal density can be

determined. Based on areal density, the blanket cost and appropriate weight per

section can be established. Table 15 illustrates some sample calculations to

determine some of these parameters which compare the MST blanket, a BPS

blanket, and a BPS with ceramic material added to the system.

Based on the requirements for the MST blanket, it is apparent that the BPS cannot

be substituted for the MST blanket because of its poor flame penetration

properties, nor could the ceramic material be added to the BPS in its current

configuration because of cost and weight issues.

4. Conclusions

4.1 Flammability

• Literature information and flame and heat penetration data from this study

suggest that the use of a combination of commercially available inorganic

(alumina, silica, and ceramic) and organic (Kevlar ) fiber-based fabrics in

multiple layers is effective in enhancing the resistance of the fabric systems

to flame and heat penetration.
Table 15. Weight and Cost Estimates for MST Blanket, BPS Blanket,

and a BPS-Ceramic Hybrid Solution

_________________________________________________________________________________________________________

 Area Weight Total Ply Total

Covered per Ply No. Weight Cost/ply Weight Total Thickness Thickness

Material (m2) (kg/m2) Plies (kg/m2) ($/m2) (kg) Cost ($) (mm) (mm)

_________________________________________________________________________________________________________

MST Blanket

Kevlar 29 46.50 0.44 4 1.76 19.78 81.82 3680 0.64 2.54

Ceramic Fabric 46.50 0.64 2 1.27 27.96 59.09 2600 0.64 1.27

Ceramic Felt 46.50 0.73 1 0.73 13.98 34.09 650 3.18 3.175

Cordura Cover 46.50 0.24 2 0.49 4.95 22.73 460 0.38 0.762

Labor/Misc.

9 4.25 66.67 197.73 7390 7.747

BPS

Kevlar 29 46.50 0.44 13 5.72 19.78 265.91 11960 0.64 8.255

Ceramic Fabric 46.50 0.64 0 0.00 27.96 0.00 0 0.64 0

Ceramic Felt 46.50 0.73 0 0.00 13.98 0.00 0 3.18 0

Cordura Cover 46.50 0.24 2 0.49 4.95 22.73 460 0.38 0.762

Labor/Misc.

15 6.21 66.67 288.64 12420 9.017

BPS+Ceramic

Kevlar 29 46.50 0.44 13 5.72 19.78 265.91 11960 0.64 8.255

Ceramic Fabric 46.50 0.64 2 1.27 27.96 59.09 2600 0.64 1.27

Ceramic Felt 46.50 0.73 1 0.73 13.98 34.09 650 3.18 3.175

Cordura Cover 46.50 0.24 2 0.49 4.95 22.73 460 0.38 0.762

Labor/Misc.

18 8.21 66.67 381.82 15670 13.462

_________________________________________________________________________________________________________
55

• Several combinations of the inorganic fiber-based fabrics with three layers

of Kevlar fabric backing were used as sample MST blankets. Data from the

study suggest that to prevent heating of the back surface of the sample MST

blanket, the front layers of the inorganic fiber-based fabrics need to be

greater than 5 mm in thickness and at least three layers of Kevlar fabric

layers need to be used as backing layers.

• Effective thermal diffusivity values of sample MST blankets provide a

useful parameter to estimate their effectiveness in preventing flame and

heat penetration in the back of the sample MST blankets.

• A procedure has been developed to obtain effective thermal diffusivity of

the sample MST blankets from the measured average steady state

temperatures at the center of the front and back surfaces, thickness, and

exposure time duration. The effective thermal diffusivity values of the

sample MST blankets are in good agreement with the literature values for

generically similar fabric systems.

4.2 Phase 1 Ballistics

• The shape of the fragment and its orientation at impact have a large effect

on the degree of blanket penetration.

• For approximately the same areal density, the ARL style #745 Kevlar®

tightly woven blanket is more effective for stopping fragments than the FFF

1500-denier, loosely woven material. Approximately four to six layers are

required to prevent penetration of a flat-faced, cylindrical steel fragment

that weighs 0.3 kg, is 170 mm long and 17 mm in diameter, and is traveling

at a velocity of 146 m/s.

• A modified conical nosed fragment penetrated all ARL and FFF blankets

studied.

• The addition of wood panels behind the blanket gave mixed results for

fragment penetration protection.

4.3 Phase 2 Ballistics

• Four layers of Kevlar® style #745 were sufficient to prevent a 454-g

rectangular slab fragment traveling at 60 m/s from penetrating an

ammunition stack in both supported and unsupported configurations.

Therefore, the addition of a wood panel behind the blanket did not affect

the performance of the blanket.

• Small holes were observed in both the Kevlar® and the ceramic fabric, but

complete penetration did not occur.
56

4.4 Sub-Scale Arena Experiments

• Prototype blankets consisting of four or five layers of Kevlar 29®, two layers

of nylon, and three layers of silica felt/fabric passed a variety of fragment

penetration experiments and heat/flame experiments. The specifications

for each layer are listed in Table 15.

• The materials evaluated should protect stored ammunition from low

velocity fragments and assorted thermal threats, provided that the blanket

is manufactured correctly, assembled correctly, and used in concert with

earthen barricades.

4.5 Issues and Concerns

• One issue that needs to be addressed is an effective way to ensure that the

blanket totally covers the stored ammunition. The materials evaluated in

this research effort are extremely effective in preventing the ignition and

detonation of an ammunition stack, but if a firebrand is able to penetrate a

seam or migrate under a pallet, the blanket will not be effective. More work

needs to be done to make the individual segments perform as a single

seamless unit.

• The effect of stitching on the fabrics needs to be addressed in a

manufacturing effort. The felt ceramic is an effective insulator but is brittle

and may fracture during rough handling and blanket fabrication. Other

materials may be substituted, which combine the same ceramic felt material

in a flexible organic matrix but at an increased weight.

• Another recurring issue with the designs studied was the continued

burning/smoldering of the nylon protective outer cover. Although it is

advertised as a flame-retardant material, it is not completely flame

resistant. This material ignites at a higher temperature than non-flameretardant nylons, but once it is ignited, it may continue to burn slowly. A

silicone-coated fiberglass, which was evaluated in this study but rejected

because of weight and cost issues, may be an appropriate substitution for

this protective outer cover.
57

References

Frey, R.B., and J. Starkenberg, “The Vulnerability of Ammunition Stacks to Small

Fragments,” ARL-TR-2030, U.S. Army Research Laboratory, Aberdeen

Proving Ground, MD, August 1999.

Finnerty, A.E., “Fire Tests of Ammunition in Wooden Boxes,” BRL-MR-3936,

Ballistics Research Laboratory, Aberdeen Proving Ground, MD, August 1991.

Shanley, L.A., B.L. Slaten, P. Shanley, R. Broughton, D. Hall, and M. Baginski,

“Thermal Properties of Novel Carbonaceous Fiber Battings,” Journal of Fire

Sciences, 12, 238, 1994.

Myers, R.E., and E. Licursi, “Inorganic Glass-Forming Systems as Intumescent

Flame Retardant for Organic Polymers,” Journal of Fire Sciences, 3, 415, 1985.

Lem, K.W., Y.D. Kwon, H.B. Chin, H.L. Li, and D.C. Prevorsek,

“Spectra Composite That Withstands Torch Flame Test,” Journal of Fire

Sciences, 1, 147, 1993.

Saad, M.A., and R.L. Altman, “Thermal Protection Studies of Plastic Films and

Fibrous Materials,” Journal of Fire Sciences, 6, 250, 1988.

Kourtides, D.A., W.C. Pitts, M. Araujo, and R.S. Zimmerman, “High

Temperature Properties of Ceramic Fibers and Insulations for Thermal

Protection of Atmospheric Entry and Hypersonic Cruise Vehicles,” Journal of

Fire Sciences, 6, 313, 1988.

Damant, G.H., “Use of Barriers and Fire Blocking Layers to Comply with Full

Scale Fire tests for Furnishings,” Journal of Fire Sciences, 14, 3, 1996.

Polymer News, 8, 177, 1996.

Newtex, 8050 Victor-Mendon Road, Victor, NY.

Thermal Ceramics, P.O. Box 923, Augusta, GA.

Christy Refractories Company, 4641 McRee, St. Louis, MO.

3M Ceramic Materials Department, 3M Center Building St. Paul, MN.

RM Engineered Products Inc, 4854 O’Hear Avenue, North Charleston, SC.

Marker, T.R., “Full-Scale Test Evaluation of Aircraft Fuel Fire Burn-through

Resistance Improvements,” Final Report DOT/FAA/AR-98/52, Office of

Aviation Research, Washington, DC, July 1999. National Technical

Information Service, Springfield, VA 22161.

Carslaw, H.S., and J.C. Jaeger, Conduction of Heat in Solids, Second Edition,

Oxford at the Clarendon Press, Oxford, England, 1959.

Dupont Kevlar® Literature H-77877 1998.
58

Allied Signal Spectra Shield Literature AS-PF-PS9A 1999

Mackiewicz, J.F., “Development of Protective Ballistic Covers,” ARL-TR-86, U.S.

Army Research Laboratory, Aberdeen Proving Ground, MD, February 1993.

Hexcel-Schwebel High Performance Fabric Literature 1997.

Natick SBCCOM Ballistic Protective System Fact Sheet March 15 2000.

Boyle, V.M., A.L. Bines, and W.B. Sunderland, “Munitions Survivability

Technology: A Comparison of Two Different Blanket Designs for Protecting

Against an Indirect Fragment Threat,” ARL-TR-2122, U.S. Army Research

Laboratory, Aberdeen Proving Ground, MD, Nov 1999.
59

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INTENTIONALLY LEFT BLANK
Cerachem , Cerawool , Kaomat , and Kaowool are registered trademarks of Thermal

Ceramics.

Curlon is a registered trademark of Orcon Corporation.

Dacron , Kapton , Kevlar , Nomex , and Tedlar are registered trademarks of

E.I. DuPont de Nemours & Co., Inc.

DurabackTM is a trademark of Unifax Corporation.

Durablanket is a registered trademark of Unifax Corporation.

Dyneema is a registered trademark of Toyobo Japan.

FluorelTM is a trademark of Fluorel SA.

Kao-TexTM is a trademark of Thermal Ceramics.

Microsoft is a registered trademark of Microsoft Corporation.

NextelTM is a trademark of 3M Corporation.

Quartzel is a registered trademark of Saint-Gobain Industrial Ceramics.

Siltemp is a registered trademark of Amatek Chemical Products.

Solimide is a registered trademark of Inspec Foams.

Spectra is a registered trademark of Honeywell.

Superwool is a registered trademark of Morgan Materials Technology Ltd, England

Twaron is a registered trademark of Acordis.

WindowsTM is a trademark of Microsoft Corporation.

Zetex and Zetex Plus are registered trademarks of Newtex Industries, Inc.

The findings in this report are not to be construed as an official Department of the Army

position unless so designated by other authorized documents.

Citation of manufacturer’s or trade names does not constitute an official endorsement or

approval of the use thereof.

Destroy this report when it is no longer needed. Do not return it to the originator.
Cerachem , Cerawool , Kaomat , and Kaowool are registered trademarks of Thermal

Ceramics.

Curlon is a registered trademark of Orcon Corporation.

Dacron , Kapton , Kevlar , Nomex , and Tedlar are registered trademarks of

E.I. DuPont de Nemours & Co., Inc.

DurabackTM is a trademark of Unifax Corporation.

Durablanket is a registered trademark of Unifax Corporation.

Dyneema is a registered trademark of Toyobo Japan.

FluorelTM is a trademark of Fluorel SA.

Kao-TexTM is a trademark of Thermal Ceramics.

Microsoft is a registered trademark of Microsoft Corporation.

NextelTM is a trademark of 3M Corporation.

Quartzel is a registered trademark of Saint-Gobain Industrial Ceramics.

Siltemp is a registered trademark of Amatek Chemical Products.

Solimide is a registered trademark of Inspec Foams.

Spectra is a registered trademark of Honeywell.

Superwool is a registered trademark of Morgan Materials Technology Ltd, England

Twaron is a registered trademark of Acordis.

WindowsTM is a trademark of Microsoft Corporation.

Zetex and Zetex Plus are registered trademarks of Newtex Industries, Inc.

The findings in this report are not to be construed as an official Department of the Army

position unless so designated by other authorized documents.

Citation of manufacturer’s or trade names does not constitute an official endorsement or

approval of the use thereof.

Destroy this report when it is no longer needed. Do not return it to the originator.