QUARTERLY

Volume 7, Number 1–2003 

AMPTIAC is a DOD Information Analysis Center Administered by the Defense Information Systems Agency, Defense Technical Information Center and Operated by IIT Research Institute

Increasing the 

Performance of

GEARS

Plus...

Composite Airfield Matting

Hydraulic Fluid 

Contamination

YBCO 

Superconductors

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About the cover: From gears to superconductor-levitated trains, this issue of the 

AMPTIAC Quarterly highlights some exciting advances in processing techniques and 

materials development. (Photography of gear manufacturing courtesy of Arrow 

Gear Company, Downers Grove, IL, www.arrowgear.com)
The AMPTIAC Quarterly, Volume 7, Number 1 3

INTRODUCTION

Friction and wear between two sliding surfaces are in large 

part dependent upon the finish of the surface. In particular 

the roughness of the surface has a strong influence on the coefficient of friction. Overcoming friction, especially in high 

performance applications, involves stringent lubrication

requirements. Examples of applications requiring exceptional

surface finish include gears and bearings. A new surface finishing technology, known as Superfinish, has proven to be effective at reducing gear wear while at the same time reducing

lubrication requirements. This revolutionary technology was

developed as part of the Power Transfer Systems Manufacturing

(PTSM) program, sponsored by the US Army Aviation and

Missile Command (AMCOM) at Redstone Arsenal.[1] While

the initial research focused upon gears, it has the potential to be

applied to other high performance machinery components that

are subjected to frictional forces.

PTSM is managed under contract by Alion Science and

Technology. The goals of the PTSM program are to reduce the

DOD’s operating and support costs, thus making weapon 

systems and military vehicles more affordable. PTSM’s investigation of superfinished gears was conducted to determine

whether this technology would enable improvements to helicopter drivetrain operation and reliability. Recent efforts by

the PTSM program have focused on improving the performance of helicopter transmissions. The high performance

demands of aerospace gears dictate the stringent requirements

placed upon the metallurgical quality, geometry, and surface

finish of these components. To meet these requirements, gears

are often continuously operated near the upper bounds of

their design envelope.

IMPROVING GEAR LIFE: THE ROAD SO FAR

One of the seven basic machines of antiquity[2], gears are

essential components in most mechanical devices – classical 

or contemporary. Most modern mechanical power transfer 

systems utilize intermeshed gears as their mode of transfer (see

sidebar “Gears Basics” on page 8 to learn more about gears).

Military vehicles and equipment are no exception to this rule,

as they are also driven by similar powertrains. Gear-driven 

systems are used in a wide variety of hardware; including fixedwing and rotary-wing aircraft, ground support equipment, 

missile guidance and launch systems, artillery, and land vehicles. In high-performance applications friction and bending

resulting from the contact of opposing gear faces cause wear,

which in turn reduces driveline efficiency. 

Metal gears are manufactured to their rough dimensions by

some combination of metallurgical and machining steps. They

are then heat treated to anneal the metal. The annealing process

alters the gear’s dimensions slightly, which is why standard

industry practice calls for finishing operations to follow the

heat treatment. Finally, gears are precision-ground after heat

treating to obtain the necessary final tolerances required to provide higher power density levels without increasing component

size or weight.

However, the grinding processes used to finish gears leave

microscopic surface features that influence gear life. Therefore,

additional processes are needed to eliminate these features

while preserving the required geometric accuracy and surface

finish. Recent experimental results indicate that improved part

surface finish can reduce pitting fatigue in gears, as well as

enhance the bending fatigue life of their teeth. Such improvements reduce the amount of frictional losses inherent in any

power transfer system.

Through PTSM’s predecessor, the Instrumented Factory for

Gears (INFAC) program (also Army-sponsored), Alion[3], in

partnership with Army helicopter manufacturers, designed

experiments and conducted tests to evaluate the effect of various surface treatments and thin film solid coatings (also

referred to as vapor deposition coatings or VDC) on the pitting

fatigue life and load bearing capability of precision gears.[4]

The surface treatment processes used for the INFAC experiments included two superfinishing methods, hard shot 

peening, and ausforming[5]. The technical feasibility of the 

Paul Niskanen, PTSM Program Manager 

and 

Ali Manesh

AMPTIAC Technical Staff

Chicago, IL

and

Raymond Morgan

US Army Aviation and Missile Command

Redstone Arsenal, Huntsville, AL
thin film solid coating processes selected for this study had

already been demonstrated in the tooling and automotive parts

industries. The coatings selected included:

• Amorphous boron carbide (B4C) deposited by physical

vapor deposition (PVD) at Bodycote’s Diamond Black facility in Conover, NC. This coating is known to have a high

hardness (93-95 Rockwell C Scale, HRC), and good lubricity (a coefficient of friction, COF, equal to 0.2). It is also

unreactive to lubricating oils. The coating is deposited at low

temperatures (~250°F) at a thickness range of 1 to 4 microns.

• Diamond-like carbon (DLC) deposited using the RF plasma

process; by the Diamonex Division of Morgan Advanced

Ceramics Inc., Allentown, PA. This coating is a mixture of

sp3- (diamond-type) and sp2- (graphite-type) bonded carbon

with no long-range crystal order. The coating can be deposited to a mirror smooth finish, has high hardness (>93 HRC),

and good lubricity (COF = 0.1). Coating thickness is also

held between 1 to 4 microns.

• A new coating made of amorphous carbon with tungsten carbide inclusions (referred to as WC/C coating). This coating

was applied by Balzers Tool Coating Inc, North Tonawanda,

NY, using a reactive sputtering process. Like the others the

coating thickness was held between 1 to 4 microns. Hardness

is around 1000 HV50 (Vickers Hardness Scale, 50 gm load)

and the COF is between 0.1 and 0.2.

IMPROVING GEAR DURABILITY: 

COMPETING SURFACE TREATMENTS ARE EVALUATED

Preliminary tests were conducted on sample coupons using the

Rolling/Sliding Contact Fatigue (R/SCF) test technique

(Figure 1). R/SCF is a coupon screening test; designed to determine contact fatigue resistance while simulating contact stresses experienced by gear teeth under load. This method allows

evaluation of test coupons at significantly lower costs than actual gear testing. In order to draw a clear conclusion, all surface

treated samples were tested, and the results were compared to

those from samples fabricated using conventional processing

methods (baseline). The results of the R/SCF tests indicated

the statistical lifespan for the VDC specimens exceeded that of

the baseline (conventionally processed unpolished/uncoated)

specimens by an average of 22%. The best test specimen outperformed the best baseline specimen by a factor of three. The

uncoated superfinished specimens were virtually indestructible

in this test. These specimens exhibited a statistical lifespan that

exceeded the baseline by an average of 950%. They also

demonstrated the capability of carrying 28% higher contact

stresses for at least three times the life of the baseline specimens.

Subsequent testing on actual VDC gear samples also gave

excellent results. The unpolished VDC-processed specimens

out performed the baseline specimens by exhibiting an

improvement in average lifetime in excess of 500%, while 

also demonstrating the ability to withstand at least 8% higher

contact loads.

Although R/SCF testing is often used as a screening test to

evaluate how materials would perform in a gear application,

flight safety requirements dictate rigorous component testing.

Consequently, the very encouraging R/SCF results led the

PTSM evaluation team to down-select the superfinish process

for testing on actual aerospace-quality gears, and to compare

results to those obtained on conventionally processed gears.

SUPERFINISHING BECOMES THE PROCESS OF CHOICE

Two superfinishing methods, both employing vibratory polishing techniques, were evaluated. The first method used 

aluminum oxide particles as an abrasive. The particles were

mixed with small zinc cylinders (chopped wires), water, and

detergents. The process provided the desired surface finish, but

required a longer processing time than the second method.

Additionally, the samples did not perform as well as the other

superfinished specimens.

The second polishing method is a process known as

Chemically-Accelerated Vibratory Surface Finishing (subsequently referred to as Isotropic Superfinishing, or Superfinish). The

process uses ceramic media, along with reagents that chemically convert the metallic surface being polished. The process was

developed and patented by REM Chemicals, Brenham, TX. 

How Does Superfinish Work?

Gear surfaces are processed to provide a very hard surface layer

– this is sometimes called case hardening. For the gears used in

this program, this was done through a heat treat process known

as carburizing. This treatment results in a hard, but less ductile

surface that penetrates to a depth of about 0.040 inches. The

hard surface provides the needed wear resistance for the gear

teeth, while leaving the core of the gear with the needed ductility and fracture toughness. While this surface hardness is

desired for gear performance, it would hinder conventional 

finishing operations.

4 The AMPTIAC Quarterly, Volume 7, Number 1

a) R/SCF Test Rig

b) R/SCF Test Specimens

c) Schematic of the R/SCF Test (GRI)

Figure 1. Rolling/Sliding Contact Fatigue (R/SCF) Test. (Photos

and Schematic Courtesy of the Gear Research Institute (GRI))

56 Tooth Gear

Load Roller Speed

(5” Diameter)

Upper Shaft

Lower Shaft (Motor End)

Lower Shaft with

16 Tooth Gear

Specimen 

(1” Diameter)

Specimen Speed 1330 RPM

(Surface Velocity 348 FPM)

Load Roller Speed = 1330 x 16/56 = 380 RPM

(Surface Velocity = 497 FPM; 

1.43 x Surface Velocity of Specimen)
The AMPTIAC Quarterly, Volume 7, Number 1 5

This is what sets the Superfinish method apart from other

approaches - The REM process results in a very shallow softening of the hard case, allowing the ceramic media to gradually

remove the now-softened peaks on the surface. This soft layer

is referred to as a conversion coating (converted from hard to

soft). The ceramic media will not abrade the hard surface of the

metal, but it will rub off the soft layer. When the soft layer is

removed, exposing the harder metal surface below, the conversion process starts again (thus it is self-restoring). In this way,

the Superfinish process keeps removing the peaks, until it

reaches the valleys. Knowing the material removal rate of the

alloy and process used, as well as the starting surface finish

parameters, one can calculate how long to run the process.

When the process has resulted in the desired surface finish, the

conversion process is terminated by the addition of other

chemicals (soap), and the parts are allowed to burnish until

bright surfaces are achieved.

The Superfinish Process

The Superfinish process utilizes conventional vibratory 

finishing equipment, as seen in Figure 2. This equipment, in

combination with high density finishing media, can produce

isotropic[6] surface finishes with an Arithmetical Mean

Roughness (Ra)[7] value as low as 1.0 μin[8]. The Superfinish

process is illustrated in Figure 3. At the start of the process

(Step 1), the original metal surface reacts a first time with the

chemical polishing mixture, forming the first conversion coating (Step 2). The vibratory machine and polishing media 

produce an effective rubbing motion on the surface of the

metal part(s) (Step 3), exposing the peaks of the metal surfaces

to a second reaction (Step 4) and re-forming the complete 

conversion coating. The process of conversion coating reformation and removal (Step 5) is continued through many

successive cycles. The whole process is continued until the metal

parts are smoothed to the required surface finish quality. At this

point, the chemical mixture used during the smoothing stage is

drained away, and a neutral, burnishing soap is introduced into

the vibratory machine. The burnish removes all remaining 

conversion coating (Step 6) from the surface of the part(s), 

producing a mirror-like appearance and imparting a mild rust

preventive to the surface. The part(s) are then ready for unloading and the Superfinish process is complete. A photograph of a

gear before and after superfinishing is shown in Figure 4.

Initially selecting the proper polishing media (in terms of

shape, size, and mixture) is critical to successfully superfinishing gears. Since gears are polished in a viscous slurry of ceramic particles and chemicals subjected to high frequency vibration

(with no direct mechanical rubbing applied to the individual

abrasive particles), the particle sizes and shapes remain stable

over time. As a result, the polishing media has a low attrition

rate, and can be used repeatedly with the same results.

An example of the expected change in surface finish resulting

from Superfinish processing is as follows:

Starting Ra = 8 to 16 μin Typical Final Ra = ~ 2 μin

Starting Rz = 90 to 120 μin[9] Typical Final Rz = ~ 30 μin

For aerospace gears, the Superfinish process typically removes

70 to 100 μin. of stock per hour. Thus, if parts have a starting

Rz of 120 μin the required processing time will be about 1.5

hours. 

SUPERFINISH IS INTRODUCED TO PRODUCTION GEARS 

With a goal of ultimately implementing the technology, a 

project technical advisory

team composed of experts

from the helicopter industry was formed to determine what component

testing was required.

Based on the advisory

team’s recommendations,

the testing included:

• Evaluation of the effects

of superfinish processing

on both gear geometry

and contact profiles.

This was accomplished

by comparing gear surface features using a coordinate measuring machine (CMM)

on both superfinished and conventionally processed spiral

bevel gears. 

Figure 2. Superfinish Equipment Cell

Installed at the PTSM Facility, Chicago,

IL. (Equipment Courtesy of REM

Chemicals)

Figure 4. Spiral Bevel Gears Before

and After (right) Superfinish

Processing.

Figure 3. Isotropic

Superfinish Process

Schematic. (Courtesy

of REM Chemicals)

Table 1. Baseline Hardness & Surface Roughness Measurements.

Pyrowear® X53

AISI 9310 Spiral Bevel Gears Spur Gears

Component Gear Pinion (smaller gear) Gear

Hardness 50-61 HRC 57-62 HRC 59-62 HRC

Ra 7-12 μin 6-9 μin 8-13 μin

Rmax[11] 63-150 μin 55-130 μin 65-119 μin

1. Original Surface

2. Conversion Coating Formation

3. Coating Removal by Media

4. Coating Re-forms

5. Process Continues

6. Burnish Removes Coating
6 The AMPTIAC Quarterly, Volume 7, Number 1

• Power circulating pitting and bending fatigue tests conducted on baseline and superfinished AISI 9310 alloy spiral bevel

gears and spur gears made from Pyrowear® X53 alloy.

Geometry and Profile Evaluation

For the gear geometry and profile evaluation, twelve spiral

bevel gear sets (AGMA Quality Q12[10]) were used. These

gears were untested remnants of another test program, and

were provided by Army Research Laboratory (ARL) personnel

assigned to NASA’s Glenn Research Center. Alion personnel

conducted hardness and surface roughness testing on all parts,

both before and after superfinish processing. Table 1 displays

the results of the tests on the baseline specimens. Results from

the superfinished specimens will be reported later.

Parts were also inspected on a Zeiss/Höfler CMM by Arrow

Gear Company (Downers Grove, IL) to determine if the

superfinish process resulted in any appreciable changes in tooth

thickness, overall geometry, or contact profile. Results from the

CMM inspections determined the following:

• Superfinishing removed an average of 0.00015 inches from

the tooth surface of both the pinion and gear, resulting in an

average tooth thickness change of 0.0003 inches. There was

also an average of 0.0001-inch change in tooth geometry.

• Superfinished gears remained within the specified tolerances.

• AGMA Quality Class was maintained.

Power Circulating Pitting (contact) Fatigue Testing

Eight sets of spiral bevel gears made from AISI 9310 steel, the

most common aerospace gear material, were selected to evaluate the effects of superfinishing. Power circulating (contact)

fatigue tests on these samples, conducted by ARL at NASA

Glenn, indicated that superfinished gears performed at least as

well as the baseline samples and that no deleterious effects were

observed. The availability of existing samples at ARL provided

a fast and economical look at the effects of superfinishing on

aerospace gear materials, and guided decisions on the remaining test plan. However, these samples were not considered useful for a statistical validation study. Gears fabricated from the

same lot of material had been previously tested on another ARL

program, and were considered suspect due to erratic results.

However, the advisory team determined that since a significant

database already exists for AISI 9310 ground gears they would

be suitable for initial comparison screening tests. The goal of

the initial testing at NASA was to save time and money, and yet

demonstrate that superfinished gears performed no worse than

the baseline.

ARL also conducted the same tests on Pyrowear® X53 gears.

Fifteen sets of spur gears were made. Of these, eight sets were

tested as baseline (conventionally processed) samples and seven

sets were tested after superfinishing. The test setup allowed half

of the tooth surfaces on a single face to be engaged during the

test and as a result, up to four data points could be collected

from each gear set (two sides of both the front and back of each

tooth). Figure 5 illustrates the fatigue test apparatus. Fifteen

tests comprising 1.5 billion stress cycles were completed on the

conventionally processed (as-ground) Pyrowear® X53 spur

gears, and all tests resulted in surface fatigue on one or more

teeth. For the superfinished spur gears, ten tests were completFigure 5. NASA Glenn Research Center Gear Fatigue Test

Apparatus. 

Figure 6. Plot of Surface Fatigue Data.

Table 2. Power Circulating (Contact) Fatigue Testing.

Gear Finishing Process As Ground Superfinished

Ra (Flank) 9-12 μin 2-3 μin

Tests Ending with 15 of 15 8 of 10

Surface Fatigue

Number of Tests 0 1 @ 600 million cycles – no failure

Suspended 1 @ 333 million cycles – no failure

Average Time-on-Test 100 million cycles 300 million cycles

(300% improvement)

b) Schematic View

a) Cutaway View

Oil-seal Gas Flow

Viewing Port

Test-gear Cover

Test-lubricant

Inlet

Test-lubricant Outlet

Temperature Measurement

Location

Slave-system

Oil Inlet

Drive Shaft

Shaft Oil Seal

Load Pressure

Loading Vane

Slave Gear

Oil

Seal

Nonactuating

Slave Gear Test

Gears Drive Shaft

Belt Pulley

Offset Actuating

Slave Gear

Shaft

Seal

Load

Pressure

Shaft

Torque

Slave-gear

Torque

Loading Vane

A

A

View 

A-A

Loading

Vane

Ground

Superfinished

Regressions

Suspended Test

6 8 10 20 30 40 60 80100 200 300 400 600

Cycles to Failure (Millions)

Percent of Population Failed

99

95

90

50

20

10

5

2

1
ed comprising a total of 2.9 billion stress cycles, and eight of

the ten tests resulted in surface fatigue on one or more teeth.

Table 2 and Figure 6 display the results of these tests.

Analysis of the test results indicate that superfinishedprocessed gears run longer without incurring damage when

compared to as-ground gears. The as-ground gears also exhibit

a more pronounced run-in[12] as compared to the superfinished gears. It should be noted that data from this study, as is

consistent with most high-cycle fatigue data, have a large degree

of scatter, even though nominally identical specimens were tested using carefully controlled conditions. However, an analysis

of the data revealed the superfinished gears experience a 300%

improvement in life when compared to baseline. This improvement has been statistically calculated to the 90-percent confidence level.

Optical Inspection of Gear Teeth

Photographs of typical gear tooth conditions resulting from the

surface fatigue tests are shown in Figure 7. Inspection of these

photographs reveals that only one quarter of the tooth area

(when considering both the front and back of a tooth) experienced wear during any single test. The Army researchers who

conducted these tests determined that the

damaged contact areas for both the asground and superfinished gears were similar.

When comparing one specimen to another

the location and degree of damage varied

somewhat, but generally they appeared

roughly the same. The important thing to

note is not the actual damage but rather the

number of cycles required to damage the

specimen. The superfinished gears all experienced significantly more stress cycles before

damage occurred and the test was stopped.

The photograph on the far right is an extreme example. This

test on a superfinished gear was suspended after 605 million

stress cycles, about three times as long as the longest surviving

as-ground specimen. Very little wear was noted on this gear.

Power Circulating Bending Fatigue Testing

The Gear Research Institute (GRI) at Penn State conducted

power circulating bending fatigue tests (see Figure 8) on spur

gears made from Pyrowear® X53. For this test, 28 spur gears (14

sets) were made. These gears were specifically designed with special undercuts at the root of each gear tooth to assure failure in

bending rather than from contact stresses. Seven tests were conducted with specimens having as-ground root fillets. Seven additional tests were conducted with specimens having ground and

superfinished root fillets. To obtain reasonable S/N curves, these

gears were tested at various stress levels. As-ground gear sets were

tested at the following stress levels: one at 153 ksi, four at 158

ksi, one at 164 ksi, and one at 175 ksi. The number of cycles to

failure ranged from 0.1 to 11 million cycles. The superfinished

gear sets were tested at 186 ksi (one set) and 175 ksi (six sets),

and the number of cycles to failure ranged from 0.2 to 8 million. One sample was still running after 9 million cycles.

Testing at Penn State resulted in frequent premature failures

related to surface defects rather than bending loads. These failures were consistent with the presence of large non-metallic

inclusions. Therefore, the failures prevented rigorous statistical

analysis of the results. However, since all of the specimens were

made from the same bar of material, the tests did reflect an

improvement in bending performance that can be achieved via

superfinishing.

The surface finish of 14 of the bending fatigue samples was

inspected. In the as-ground condition, the average surface

roughness on flanks was 9-12 μin, and was 12-16 μin in the

root area. The original superfinishing cycle preferentially treated the tooth flanks, and had little affect in the root areas.

However, since the finish in the root area affects bending

fatigue performance, parts were reprocessed to improve finish

in the root. After the second processing, the surface roughness

in the root was 6-9 μin. 

Results reported by GRI, indicate that even small surface finish improvements in the root fillets result in reduction of stress

concentrations caused by machining marks. This reduction was

sufficient to eliminate these marks as fracture origin sites.

Although the data was insufficient for statistical validation,

results indicated that superfinishing increased bending fatigue

resistance by at least 10%. GRI also reported that Superfinishing virtually eliminated wear. A photograph of a typical

bending failure observed at GRI is shown in Figure 9.

CONCLUSIONS

Superfinishing has thus far demonstrated itself to be an exciting and promising material processing technology. When

brought to full maturity, this process has the potential to greatly enhance the performance of gears for use in the military and

beyond. It is a formidable part of a greater effort to lengthen

service life and reduce sustainment costs. While the focus of

this article has concerned gears, it should be noted that

Superfinishing may be beneficial for other applications that are

subjected to high degrees of wear due to contact with other

moving components.

The AMPTIAC Quarterly, Volume 7, Number 1 7

Figure 7. Typical Surface Fatigue Failures: left - as Ground,

center - Superfinished, right - Superfinished, Suspended Test.

(Photo Courtesy of the Army Research Laboratory)

Figure 8. 

Power Circulating

Fatigue Test Rig.

(Photo Courtesy

of the Gear

Research Institute)

Figure 9. Typical Bending Failure of

a Spur Gear as Observed at GRI

(Fractured Tooth is Missing). 

(Photo Courtesy of the Gear

Research Institute)
Gear Basics

Gears are one of the most fundamental of all

machines. They may be manufactured in any 

number of shapes, sizes, geometries, and configurations. Simply put, gears transfer power from one to

another by their direct mechanical interaction

(intermeshing). Not only do they transfer power, 

but different configurations can also change the

direction of transfer, convert circular motion to 

linear motion, or linear motion to circular

motion. While there are numerous

types of gear geometries, this

guide is limited to those relevant to our feature article -

spur gears and bevel gears.

Spur Gears

Spur gears are wheels with mating teeth cut in their surfaces, such

that one turns the other without slippage. When the mating teeth are

cut so that they are parallel to the axis of rotation, the gears are called

straight spur gears. Figure 1 shows an example of intermeshed straight

spur gears and relevant gear anatomy.

When two gears of unequal size are meshed together, the smaller of

the two is called a pinion. Regardless of the size difference between a

gear and a pinion, the teeth of both must be the same size to mesh

properly. Straight spur gears are the most common type. Another type

of spur gear, the helical spur gear, is very common in military hardware and vehicles. In helical gears the teeth are cut slantwise across

the working face of the gear. Therefore, one end of

the tooth lies ahead of the other; with each having

a leading and trailing end (Figure 2).

For intermeshed straight spur gears, the entire

widths of mating teeth come in contact simultaneously. However, with helical (also know as spiral)

gears, contact between two teeth starts first at the

leading end and moves progressively across the gear

faces until the trailing ends are in contact. This type

of meshing action keeps the gears in constant 

contact with one another. As such, there is more 

efficient power transfer and smoother, quieter

action. One disadvantage of helical spur gears is the

tendency to thrust or push axially on its shaft (due

to the conversion of radial force to axial force

caused by the slant of the teeth). Typically, special

thrust bearings are installed at the end of the shaft

to counteract axial thrust.

8 The AMPTIAC Quarterly, Volume 7, Number 1

Isotropic superfinishing is a repeatable and robust process. 

It improves both surface and bending fatigue resistance of 

aerospace-quality gears without affecting the AGMA gear 

classification. Superfinishing is able to remove grinding marks

on finished gears and provide equal surface roughness values of

about 2 micro-inches, when measured in perpendicular directions. In gear tests, the Superfinish process demonstrated the

ability to improve surface fatigue resistance by 300 percent, and

it improved bending fatigue by at least 10 percent when compared to the baseline ground samples. The benefits of the

superfinish process will translate into lighter transmissions for

new designs (due to increased bending fatigue limits permitting

gear teeth with a reduced section modulus) and improved 

system durability for both existing and new designs.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the support of US Army

Aviation Missile Command, and the contributions made to

this work by the following organizations and individuals: Mark

Michaud, REM Chemicals; Bob Handschuh & Tim Krantz,

ARL(NASA-Glenn); Douglas McPherson & Aaron Isaacson,

Gear Research Institute; Jim Corwin, James Corwin Associates.

REFERENCES & NOTES

[1] Power Transfer Systems Manufacturing Program, US Army

Aviation and Missile Command, Redstone Arsenal, Contract

No. DAAH23-00-C-R232

[2] The seven basic machines: Inclined Plane, Wedge, Screw,

Gear, Pulley, Wheel, and Lever. The earliest known treatment

Figure 1. Basic Gear Anatomy (Straight Spur).

PINION

GEAR

Line of

Centers

Circular

Pitch (D)

Root Diameter

Line of

Action

Pressure

Angle (φ)

Outside Diameter (Do)

Top Land

Root

(Tooth)

Filet

Whole Depth

(ht

)

Tooth

Profile Outside Diameter (Do)

Center

Distance

(C)
Bevel Gears

Bevel gears are used to change the direction of transfer in a power transfer

system. The working face of a bevel gear is cut at angle. This type of gear

can connect shafts lying at any given angle because the gears have been

specifically beveled to manifest the needed angle. Like spur gears, the teeth

of bevel gears may be either straight or helical.

Figure 3 shows several examples of bevel gears. When the sweep angle of

the bevel gears equals 90°, it is referred to as a miter gear. By visual inspection, it is obvious that the bevel angle for an individual gear is half of the

intended sweep angle. For example, the gear faces for a miter gear are

beveled at 45° angles. Helical bevel gears are also very common. They are

used for all the same reasons of efficient transfer, and noise and vibration

reduction as in helical spur gears.

Figure 3. Straight and Helical Bevel Gears.

Figure 2. Helical Spur Gear.

C. Helical Bevel Gear

A. Miter Gear B. Bevel Gear

The AMPTIAC Quarterly, Volume 7, Number 1 9

of the subject is attributed to the Greek mathematician

Archimedes (who is sometimes credited with the development of

the modern versions of the gear and the screw)

[3] Then IIT Research Institute (IITRI). The bulk of IITRI

became Alion in December 2002

[4] Enhanced Surface Protection of Precision Gears, March 2001,

and Nose Gearbox Spiral Bevel Pinion and Gear Surface Enhancements, March 2001, US Army Aviation and Missile Command,

Redstone Arsenal, Contract No. DAAJO9-95-C-0546

[5] A low temperature thermomechanical process. More

information on the ausforming process can be found at

http://www.arl.psu.edu/areas/ausform/ausform.html

[6] Isotropic – Surface topographical features are roughly the

same in all directions and along all axes

[7] Ra is the Arithmetical Mean Roughness (measured by DIN

4768)

[8] μin = micro-inches (10-6 in.)

[9] Rz is the Mean Peak-to-Valley Height (measured by DIN

4762)

[10] American Gear Manufacturers Association Quality Q12 –

This is an industry standard that defines the quality level of the

gears tested

[11] Rmax is the difference between the highest peak and the

lowest valley

[12] Run-in: Similar to break-in. As a new gear is initially run in

mesh, slight wear occurs, resulting in a smoothing and polishing

of the contact areas of the gear teeth

(Photography of Gear

Manufacturing Courtesy of Arrow

Gear Company, Downers Grove, IL,

www.arrowgear.com)
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The AMPTIAC Quarterly, Volume 7, Number 1 11

Material EASE

UNDERSTANDING AND REDUCING THE EFFECTS OF CONTAMINATION ON HYDRAULIC FLUIDS AND SYSTEMS

Brigitte Battat

(formerly AMPTIAC Technical Staff)

and

Wade Babcock

AMPTIAC Technical Staff, Rome, NY

INTRODUCTION

At least 75% of all hydraulic systems degrade and fail due to contaminated or

aging hydraulic fluid.[1] Contamination causes aging/degradation of fluids

and ultimate failure of hydraulic systems for a number of different reasons. In

addition to increasing internal leakage (which lowers the efficiency of pumps,

motors, and cylinders,) it also decreases the ability of valves to control flow and

pressure accurately, thus wasting horsepower and generating excess heat.

Furthermore, it causes parts to stick due to sludge or silting, or they can seize

when large amounts of contaminants accumulate in the clearances. Sources

of contamination can include: (1) the manufacturing process, (2) hydraulic

fluids, (3) environmental exposure, (4) system wear, (5) and servicing.[2]

Many military systems rely on hydraulics, and as such these systems are

put to work in every conceivable environment and are among the highest contributors to maintenance and service workloads. This ubiquity is a doubleedged sword; the systems’ ever-present nature exposes them to continuous use

making them a common maintenance item, and the common maintenance

and diverse operational environments offer many opportunities for contamination. In this issue of MaterialEASE, we seek to present some of the basics

regarding hydraulic fluids and how they become contaminated, and expand

upon the deleterious effects this contamination has on hydraulic systems. We

will also present some of the chief causes of fluid contamination, and the 

relatively simple measures which can be taken to lessen the problem. 

Contaminants

While hydraulic system contaminants can be either solid particles or liquids,

water is the most common. Solid particles contaminate by chemically reacting

with the fluid, or fouling the system through accumulation. For instance, a

new hydraulic fluid can contain 500,000 particles per 100 mL that are 5 μm

or larger, which exceeds the level recommended by most manufacturers for

normal operation.[3] Worse than this, 0.5 μm particles can be harmful to

most systems. Due to the wide range of hydraulic fluids, there are many 

standards for cleanliness which compounds the problem. For example, 

MIL-H-5606F requires that in 100 mL of fluid there be no more than 10,000

particles ranging in size between 5-15 μm, no more than 1,000 particles

between 16-25 μm, and no more than 5 particles over 100 μm.[4] 

The behavior of water as a contaminant varies from system to system.

Water sometimes forms an emulsion with the fluid, or it might be partially

immiscible, floating on the surface or settling to the bottom of the fluid

depending on the relative density. The presence of water ultimately causes 

corrosion of the system components and resultant contamination of the fluid

by corrosion products. Water ingress may be caused by design flaws, service

environment, maintenance activities, internal generation, and methods of

fluid servicing. Improper storage of open fluid containers and inadequate

transfer of fluid to the system may cause serious contamination problems.

Contaminants also enter hydraulic systems through the reservoir breather

(when used) and contaminated replacement components. Environmental

contamination enters the system through ingestion, and can be prevented

through use of (1) sealed reservoirs (2) vacuum breakers (relief valves),

and/or (3) high efficiency breather filters (such as desiccators) in places where

humidity is high enough to become hazardous.[5] Contamination from

stored containers may be avoided through proper storage and handling procedures. Large containers are likely to include a high level of particles; hence,

fluid filtering is suggested prior to use.

In general, moisture is deleterious to hydraulic systems, with the exception

of aqueous-type hydraulic fluids and the systems designed to utilize them.

Moisture enters waterproof containers through “breathing” caused when a

container is exposed to wide temperature ranges. Therefore, containers stored

outdoors should be placed on their sides to prevent water from accumulating

on their tops. Furthermore, container lids should be periodically checked for

tightness.

Hydraulic systems may even be degraded by the additives included in

them to fight environmental attack and corrosion (i.e., through corrosion by

galvanic action, or due to slime and ultimate malfunctioning). For example, an additive in certain MIL-H-5606 fluids contains a contaminant that 

is soluble in the additive itself but is not soluble in the finished hydraulic 

fluids.[6] Hydraulic fluids containing corrosion inhibitors will often form a

slime when moisture is introduced. Some mahogany sulfonate rust

inhibitors containing calcium chloride and calcium sulfate (inorganic

water-soluble salts) cause degradation of hydraulic systems, through staining and galvanic corrosion of steel.

Contamination with liquid other than water can occur with both miscible

and immiscible fluids. Contamination of this type takes place when one

hydraulic fluid is replaced with another without thoroughly cleaning the 

system. Nevertheless, certain military specifications indicate when two fluids

are compatible and may be mixed. The two mixing fluids are compatible in

the sense that together they do not form resinous gums, sludges, or insoluble

solid materials, but they are still contaminated because in a mixture they do

not preserve the properties they have individually. Individual characteristics

may still be required in applications that need pure fluids.

Microbiological contaminants grow in fluids where other contaminants

are present (e.g., water). This problem can be reduced or eliminated with the

use of biocides, but the source of the contamination must be removed.

21 AMPTIAC
APPROACH TO FLUID CONTAMINATION – EXAMPLE ONE

Naval Air Technical Data and Engineering

Service Command (NATEC)

The Naval Air Technical Data and Engineering

Service Command (NATEC) carried out a contaminant analysis through automatic particle

counting.[15] Particle counters used by the Navy

study included devices such as (1) HIAC Royco

8011, (2) HIAC Royco 8012, (3) UCC

CM20.9090.USN, (4) Millipore Patch Test Kit,

and others. These are electronic particle counters

that provide the number of particles of various

sizes. Counts exceeding the maximum allowable

in any size range render the fluid unsuitable for

use. The class of contamination is based upon

the total number of particles in any size range

per 100 ml of hydraulic fluid. 

Sampling techniques employed during these

tests were based on “flushing away” the contaminants in both the sampling line and those generated by mechanical operations, by allowing an

initial quantity to flow into a waste receptacle.

Without interrupting the flow of the tested fluid,

the sampling bottle was rinsed with various

amounts of the fluid that were discarded.

Inspection of the samples for free water, cloudiness, haziness, visible particulate or a pink condition was conducted. Samples exhibiting any of

the abovementioned conditions were considered

unsatisfactory. Fluid was resampled to verify this

condition, before taking corrective action. Table

1 contains the cleanliness standards established

by the Navy (hydraulic fluid contamination SAE

749 D Navy Standard Class).

Contamination was defined according to the

following rules:

• Class of contamination was based on the total

number of solid particles in any size range,

per 100 ml. If the allowable particle count in

any size range was exceeded, the next higher

class level was usually assigned.

• Class 5 represented the highest acceptable

level of contamination.

• Class 5 level of acceptability had to be met at

the inspection interval specified for the equipment under test.

On the basis of this approach to contamination control, the NATEC program concluded that

the factors affecting the accuracy of solid particle

counts include (1) the type and cleanliness of the

container, (2) the sampling technique, (3) the

sample preparation, (4) the Standard Operating

Procedure (SOP), and (5) the calibration.

Calibration methods are changing due to a halt

in the production of Air Cleaner Fine Test Dust

(ACFTD, size-graded particulate) and because

the US Military is using standards of cleanliness

not used by the international community.

12 The AMPTIAC Quarterly, Volume 7, Number 1

Material EASE

CONTAMINATION EFFECTS 

The effects of contamination typically begin with the hydraulic fluid,

extend into the system, and can even continuously worsen in a closed or

sealed system. The primary initiator is corrosion products (chips and particles) that cause wear on internal components, exposing clean surfaces

that subsequently become corroded.[6] Additionally, contaminants such

as water, other liquids, and even purposely added chemicals (additives)

can cause solids or slime to accumulate in the system, gradually reducing the performance of valves and other tight-tolerance components.

These vicious cycles will continue to quietly rob a hydraulic system’s performance, long after decontamination measures are taken.

Solid particles cause damage according to their size. High concentrations of small particles (≤10 μm) form silt which erodes the interior

mating surfaces of valves and renders them inoperable. Contaminating

solid particles that are equal in size to the clearance between two moving

surfaces can cause both jamming and wear. Cycling the valve may clear

this contamination, but when it jams clearance can only be achieved by

disassembly. Larger contaminating particles block ports and orifices, and

can cause transient malfunction (“coincident jamming”) when they are

trapped by a mechanism moving from one position to the next (e.g., a

Table 1. Hydraulic Fluid Contamination Classes (according to SAE 749 D[13]).

Number of particles per 100 ml of oil

Contaminant Exceeding

Class 5-10 μm 10-25 μm 25-50 μm 50-100 μm 100 μm

0 2700 670 93 16 1

1 4600 1340 210 28 3

2 9700 2680 380 56 5

3 24000 5360 780 110 11

4 32000 10700 1510 225 21

5 87000 21400 3130 430 41

6 128000 42000 6500 1000 92
A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY

The AMPTIAC Quarterly, Volume 7, Number 1 13

AMPTIAC

particle trapped between a poppet and its seat prevents the closing of a relief

valve).

System malfunctions caused by contamination may be classified into the

following three broad categories:

• degradation (gradual changes over time in pump flow rates, valve leakage,

and wear of cylinder barrels causing cylinder speed decline, etc.)

• transient (intermittent failures)

• catastrophic (complete failure of a system or component)

All of these can be reduced through a well-planned contamination control program.

Removal of contaminants is planned according to the sensitivity of the system to contamination. The various components are rated according to this

sensitivity, also known as the omega rating of the components. It is often more

efficient to use a filter dedicated to the entire system which meets the specifications of the system’s most sensitive component.

SOLUTIONS TO CONTAMINATION

In order to solve the contamination problem, contamination analysis is first

needed to identify the type and concentration of the contaminant. A comprehensive discussion on methods for contamination analysis is beyond the scope

of the present article. However, a few methods deserve being pointed out.

Methods for gauging solid particle contamination involve counting, sizing,

and/or weighing of the particles contained in a given volume of fluid.

Microscopic particle counting is conducted according to standards such as SAE

ARP-598[7] and ASTM F 312.[8] Automatic particle counting is conducted

according to a national (ANSI B 93.28M) and an international (ISO 4402)

standard that calibrates systems and establishes reproducibility of counters in

various laboratories within 6%.[9] 

Liquid contaminant measurement is difficult, especially if the contaminant is soluble or miscible in the hydraulic fluid. As water is the most common

liquid contaminant of hydraulic fluids, it can be separated from the fluid (if

present at a high concentration) through dilution with a solvent that makes

the water immiscible. This technique includes Federal Test Method 3001[10]

and ASTM D 95.[11]

Chemical analysis and accurate recording of contaminant concentrations over the life of the hydraulic systems can identify abnormal 

conditions and potentially predict failing components. The following

procedures for extracting fluid samples and analyzing them for contamination have been well-established and even standardized: 

1. Proton-Induced X-Ray Emission (PIXE) is a nondestructive technique that

analyzes simultaneously all samples (i.e., powders, soil, aerosol filters, etc.)

and assesses particles up to 150 μm in size.[12]

2. Infrared analysis is commonly used to identify chlorine or fluorine in the

hydraulic system corrosion products.

3. Gas chromatography

4. Spark source mass spectrometry

5. Energy dispersive X-ray scanning electron microscopy

STEPS TO REDUCE CONTAMINATION AND FUTURE WORK

While the issue of contamination in hydraulic systems will not go away, there

are measures which can be employed to lessen its deleterious impact. Many of

these are relatively simple handling and storage processes, and involve paying careful attention to fluids and fluid combinations specified in systems.

The long-term performance of critical systems depends upon placing a

renewed emphasis on maintenance and handling procedures which are often

taken for granted.
APPROACH TO FLUID CONTAMINATION – EXAMPLE TWO

Breakdown of Preservative Fluid 

MIL-PRF-46170 in Aircraft Hydraulic

Systems[14]

Several aircraft programs have linked the formation of organic material and uncommanded

flight control events to the presence of preservative fluid in the hydraulic systems. Examples

include F-14 and F/A-18 aircraft where the

hydraulic filters have shown buildup of organic

materials. The V-22 hydraulic systems are preservative-free, and the filters have no organic

buildup. Also, the V-22 pumps stored for several

years have shown no corrosion damage. By comparing aircraft with and without fluid preservatives several programs have decided to eliminate

the preservatives from their hydraulic systems.

Other problems attributable to preservative

fluids include F/A-18 E/F hydraulic filters becoming prematurely clogged with green organic

material. (Navy engineers have suspected fluid

breakdown and Boeing engineers have assumed

that copper played a key role in filter clogging.)

The incompatibility of the preservative fluid with

the hydraulic system at elevated temperatures, the

impossibility of drip draining actuators, and the

validation of hydraulic fluids as lubricants for

corrosion protection were but a few of the issues to

be solved. As a result of these problems, the “Red

Team” made of government and industry experts

(representing the Navy, the Air Force, Boeing,

Northrop, Vickers, Honeywell/Allied Signal, PTI

Industries, and Pall) was formed. At the initial

meeting, the members of the team suggested the

14 The AMPTIAC Quarterly, Volume 7, Number 1

Material EASE

Proper Fluid Selection

Maintainers must pay careful attention to choosing the proper fluid 

specified for use in a particular system. It is critical to use the proper

fluid, and to avoid mixing fluids in a system. Even when a system specifies that more than one fluid may be used, maintenance personnel

should try to always use only one fluid in that system and not mix fluids.

If a different fluid must be used, the system should be drained and

flushed before adding the new fluid. Keep in mind that even if two fluids

are miscible, the mixture may not perform with the ideal properties of

either component separately. Also, the combination of some fluids and/or

their additives may be deleterious to the system.

System manufacturers and suppliers must be diligent in specifying

appropriate fluids for a system. These specifications should be clear about

potential incompatibilities if multiple fluids are used, and should recommend proper system maintenance procedures for all environmental

conditions. Fluids should also be chosen with proper regard to environmental and hazardous materials regulations.

Proper Fluid Handling and Storage

Hydraulic fluids should be kept in their sealed containers until ready for

use. Both new and partially used containers should be handled and

stored very carefully. Lids should be checked routinely and secured tightly, and drums should be kept in a relatively benign environment. Large

temperature swings cause the containers to “breathe” from expanding

and contracting air and liquid inside. This, combined with moisture

from rainfall or humidity, can cause the ingress of water into the container. Some fluids are hygroscopic, meaning that they absorb moisture

readily when exposed to humid air, and thus require extra measures to

be taken to lessen the chance of them becoming contaminated.

System Maintenance

Hydraulic systems, because of their prevalence, are often in need of

repair just because they are used so much. Standard operating procedures should be carefully checked for fluid contamination opportunities, and system maintenance procedures should be similarly diligent in

keeping contaminants from systems. Much of this may be accomplished

through procedural changes identifying which fluids are appropriate for

which systems, and the proper handling of those fluids and systems.

Additionally, procedures should be adjusted to spell out what must be

done to replace a fluid or change from one specified fluid to another. In

general, the system should be flushed of all the old fluid and potentially cleaned prior to installation of the new or replacement fluid.

Future Work

Plans for future hydraulic fluids include research to reduce their fire risks

and the development of thermally stable hydraulic fluids. These will meet

the challenges of increased pressures and electro-hydrostatic actuation

due to higher temperatures. Novel purification methods that would

enable the reuse of hydraulic fluids are also under consideration. The

continuation of laboratory simulations of the conditions that caused

stuck valves in helicopters, hydraulic pump tests, and toxicity are expected to be included in future programs.[2] 

Table 1. Fluids Used for Aircraft Storage.*

Type of fluid Type of aircraft/engine

MIL-H-5606 B1B, C-130, C-135, E-3, E-4, E-6, F-5, P3C, U2R

MIL-PRF-83282 F-110 (F-16, actuator), F-404, H-60, H-64, S-60

MIL-PRF-6083 C-5A/B, F-117, F-16

MIL-H-46170 AV-8, C-17, S-3A, B-2, F-15, E2C, F-18, H-53, H-60, S-60, V-22

*Information from Parker Aerospace
REFERENCES

[1] Norvelle, D.F., An Introduction to Fluid Power, West Publishing Company, St.

Paul, MN, 1991

[2] Gschwender, L., Snyder, C.E. Jr., Sharma, S., Flanagan, S, (Materials

Directorate, Wright Patterson Air Force Base), Advances in US Air Force

Hydraulic Fluids, JSL 16-1 35 ISSN 0265-6582

[3] Moore, L.C., The Cleanliness of New Hydraulic Fluids, Basic Fluid Power

Research Journal, vol. 11, Oklahoma State University, Stillwater (October 1977)

[4] MIL-H-5606F, Hydraulic Fluid Petroleum Base: Aircraft, Missile, and

Ordnance, 26 August 1991

[5] MIL-HDBK-118, 22 September 1993, pp. 7-3 to 7-22

[6] Deane, T.N., The Effect of Contamination on Fluids and the Effect of the

Ingredients of the Fluids on Contamination, Proceedings of Aerospace Fluid

Power Systems and Equipment Conference, Society of Automotive Engineers,

Warrendale, PA, 1965

[7] SAE ARP 598B-86, Determination of Particulate Contamination in Liquids

by the Particle Count Method, Society of Automotive Engineers, Warrendale, PA,

1986

[8] ASTM F 312-69, Method for Microscopical Sizing and Counting Particles

from Aerospace Fluids on Membrane Filters, American Society for Testing and

Materials, Philadelphia, PA, 1969

[9] ISO 4402-77, Hydraulic Fluid Power – Calibration of Liquid Automatic

Particle Count Instruments – Method Using Air Cleaner Fine Test Dust

Contaminant, International Organization for Standardization, Stockholm,

Sweden, 1977

[10] Federal test Method 3001.8, “Water in Petroleum and Other Bituminous

Materials”, Federal Test Method Standard No. 791C, Methods of Testing

Lubricants, Liquid Fuels, and Related Products, 30 September 1986

[11] ASTM D 95-83, Standard Test Method for Water in Petroleum Products

and Bituminous Materials by Distillation, American Society for Testing and

Materials, Philadelphia, PA, 25 March 1983

[12] Eleftherakis, J.G., “Accurate Analysis and Description of Field-Induced and -

Generated Contaminants”, Paper No. 901678, SAE Technical Paper Series, Society

of Automotive Engineers, Warrendale, PA, September 1990

[13] Zdrojewski, W.S., NOAP Spectrometer Technical Report, Automatic Particle

Counting, Military Aerospace Hydraulic Fluids Workshop Proceedings, August

2000

[14] Moorman, J.W. (Naval Air Systems and Flight Controls), Breakdown of

Preservative Fluid MIL-PRF-46170 in Aircraft Hydraulic Systems, Military

Aerospace Hydraulic Fluids Workshop Proceedings, August 2000

[15] Ohlson, J. (Sabre Systems), F/A-18E/F Hydraulic System Red Team,

Military Aerospace Hydraulic Fluids Workshop Proceedings, August 2000

[16] Gschwender, L., Elimination of Barium Containing Fluids in DOD

Aircraft Systems-Pollution Prevention Research Program, Military Aerospace

Hydraulic Fluids Workshop Proceedings, August 2000

The AMPTIAC Quarterly, Volume 7, Number 1 15

AMPTIAC A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY

following issues to investigate:

• The Navy discussed the premature clogging of

F-18 E/F filters with organic plaque.

• The Air Force presented data from in-service

breakdown of preservative additive in Army

helicopters.

• Boeing presented data on Scanning Electron

Microscopy (SEM) analysis of filters, demonstrating that filters showed organic material

bound to filter fibers, and that the material

could be removed with toluene/xylene (the

same solvent used by the Air Force to clean

valve deposits in Army helicopters). 

At later meetings, team members demonstrated that the rust inhibitor barium dinonylnaphthalene sulfonate (BSN) in MIL-PRF-46170 is a

major contributor to filter clogging. As a result of

these meetings, the Red Team recommended

eliminating the use of MIL-PRF-46170 as a preservative hydraulic fluid in F/A-18E/F aircraft

hydraulic systems (and all other Navy Aircraft

Hydraulic Systems), and the use of operational

fluid MIL-PRF-83282 for system operation and

shipping/storage of components. Table 1 contains

a summary of fluids used in military aircraft.

Currently, BSN is successfully used as a 

corrosion inhibitor in two military fluids, MIL-H6083 and MIL-H-46170. They are utilized operationally by the Army in ground vehicles and as

storage fluids for components in the Air Force 

and Navy. The Environmental Protection Agency

limits the concentration of barium to 100 mg/l

according to the handbook 40 CFR, 261.24. Any

amount beyond this limit must be disposed of as

a hazardous material.

Further efforts by the Red Team established

the need to initiate a pollution prevention research program to remove barium compounds

from fluids in DOD aircraft systems. The main

catalysts to this program included:

• The aircraft components are stored with four

different fluids

• Lack of documented reasons to use fluids with

corrosion inhibitors such as barium

• Inventory is reduced, hence components have

shorter shelf life

• Cost savings

The expected payoffs through the implementation of this program include (1) the

elimination of hazardous waste disposal, (2)

curbing of operational problems from barium

contamination, (3) reduction of AF inventory

by two fluids, (4) reduction of storage space,

(5) saving charges passed on by component

suppliers and overhaulers.
16 The AMPTIAC Quarterly, Volume 7, Number 1

2003 Spring IEEE Conf. on Technologies

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05/07/03 - 05/08/03

Cambridge, MA

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Email: tradeshows@socplast.org

Web Link: www.npe.org

2003 Electronic Materials Conference

06/25/03 - 06/27/03

Salt Lake City, UT

TMS

184 Thorn Hill Road

Warrendale, PA 15086 

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Composite Materials 2003

07/02/03 - 07/04/03

Deutsche Gesellschaft 

fur Materialkunde e.V.

Hamburger Allee 26

Frankfurt 60486 Germany; 

Phone: +49 69-7917-745

Fax: +49 69-7917-733

Email: verbund@dgm.de

Web Link: www.dgm.de/verbund

Microfluidics Design and Analysis

07/14/03 - 07/15/03

Cary, NC

Coventor

4001 Weston Parkway

Cary, NC 27513 

Phone: 919.657.8102

Email: Gail.massari@coventor.com

Web Link: www.coventor.com

14th Intl. Conf. on Composite

Matls.(ICCM-14)

07/14/03 - 07/18/03

San Diego, CA

Society of Manufacturing Engineers

One SME Drive

Dearborn, MI 48121 

Phone: 800.733.4763

Fax: 313.271.2861

Web Link: www.sme.org

2003 Meeting of the Military Sensing

Symposia (MSS) Specialty Group on

Active E-Œm%

08/25/03 - 08/28/03

Boulder, CO

Infrared Information Analysis (IRIA) Ctr.

Veridian Systems Division, Inc

PO Box 134008

Ann Arbor, MI 48113-4008 

Phone: 734.994.1200

Fax: 734.994.5550

Email: mss@veridian.com

Web Link: www.iriacenter.org

Mark Your Calendar
BACKGROUND: MISSION REQUIREMENTS

To achieve the Air Force’s vision of Global Vigilance, Reach,

and Power, deployment and sustainment of forces are extremely important. Being able to respond quickly and decisively

anywhere in the world relies on a myriad of combat support

activities that occur on the ground. Many aircraft sorties 

are typically required to bring in equipment, supplies, and 

personnel when the Air Force deploys to a remote location. As

the operation or conflict continues and intensifies, available

parking space at these remote locations is quickly exhausted.

Therefore, expanding aircraft parking aprons to increase the

Maximum on Ground (MOG) requirements at airfields supporting contingency operations is critical. Lightweight airfield

matting, rapid soil stabilization, or a combination of both will

significantly increase the Air Force’s contingency operation

capability by providing the means to rapidly expand aircraft

parking aprons and increase MOG at all types of airfields 

supporting contingency operations. 

One major consideration for assessing airfield capabilities is

the number of aircraft that can be parked at the airfield, i.e.,

MOG. The two categories of MOG are based on parking

requirements and working requirements. The parking MOG

refers to the number of aircraft that can be parked at an airfield

and depends upon the specific mission. Bare base planning 

factors require a specific area for each type of aircraft. For 

example, a squadron of fighter aircraft requires more than

200,000 square feet. If these requirements are not met, there is

a high probability of compromising the mission. The working

MOG requirement is dependent on the available parking space

and the size and type of crews and equipment available to 

service the aircraft. Working MOG has a significant impact on

the overall speed in which a bare base can be established. The

rate at which materials and equipment can be airlifted into a

site is directly related to the working MOG.

The type of airfield can compound the problem of providing

MOG. Airfields are typically separated into four categories:

expedient airfields, temporary airfields, semi-permanent airfields, and main operating bases or commercial airfields. A wide

variety of airfields are used during contingency operations and

often the use of non-Air Force airfields in austere or underdeveloped locations is required. These optimally positioned airfields are selected primarily based on proximity to the theater of

operations and not necessarily with regard to current airfield

conditions. Therefore, these airfields often require improvements or expansion to meet mission requirements. See Table 1

for a comparison of airfield classifications.

Consequently, the type of airfield and the mission requirements dictate the MOG needs, which in turn determine the

amount of parking area expansion needed. These factors determine the manpower and time required for installation of the

mat system. 

EXISTING SYSTEM: AM-2 AIRFIELD MAT

AM-2, the current airfield mat system, has been used by the 

Air Force for over 40 years. At one time AM-2 was the primary

tool for rapid runway crater repairs but has now been relegated

to repair and expansion of taxiways and parking aprons. It is a 

1-1/2 inch thick aluminum panel fabricated from an extruded

main section and extruded end connectors. (See Figures 1 and

2.) The end connectors are welded to each end of the main panel

section, prongs up at one end and prongs down at the other end,

forming a complete panel. The sides of the panels are manufactured to interlock in a rotating motion, as seen in Figure 3. The

key features of AM-2 are summarized in Table 2.[1]

A simple rectangular area large enough to support a fighter

squadron, requiring only matting, key locks, and edge

clamps, requires 480 pallets of matting. This encompasses a

volume of 39,066 cubic feet weighing a total of 1,274,316

Dean Foster

Materials and Manufacturing Directorate

Air Force Research Laboratory

Wright-Patterson AFB, OH

Mark Anderson, Ph.D, P.E.

Materials and Manufacturing Directorate

Air Force Research Laboratory

Tyndall AFB, FL

The AMPTIAC Quarterly, Volume 7, Number 1 17
18 The AMPTIAC Quarterly, Volume 7, Number 1

pounds and would fill up 48 C-130 transport aircraft.[1] One

crew working 12-hour shifts takes 5 days to install it, and that

does not account for assembly problems due to alignment

shifts, dirt, sand, and debris inside the panel connectors (AM2 is made to fit loosely together). Another concern is damage

to the panel from shipping. As can be seen in Figure 1, the

end and edges are complex shapes. If damaged, the panels are

rendered un-usable, thus requiring more time and material to

complete the surfacing of the project area.

The AM-2 connection system between mats is also complicated, requires many additional parts, and does not allow for

individual panel removal for repair or replacement. Its joint

also acts as a hinge, flexing in- and out-of-plane, and does not

transfer load across panels. Consequently, this “pumping”

action causes subgrade repairs to be a common maintenance

problem. 

AM-2 matting, although robust and multifaceted, is a very

heavy, complicated, time consuming, and difficult to maintain

system to provide expansion of taxiways and parking areas. Not

only is it cumbersome to transport, but it also requires numerous pieces of support and maintenance equipment, which

reduce its ability to respond quickly and decisively anywhere in

the world. The Air Force needs the capability to expand aircraft

parking aprons, connecting taxiways, and maintenance areas

rapidly. This could be a significant factor in the Air Force’s 

ability to conduct contingency operations from bare bases or

austere airfields. 

The Department of Defense estimates that there are more

than 1,200 airfields worldwide that have potential use during

contingency operations. The state of these airfields ranges from

extremely austere dirt strips to commercial airports and fixed

military installations. Many of these airfields do not have 

adequate aircraft parking aprons to support large contingency

operations. Compound this problem with the unknown soil

types at these potential sites and the current system for providing airfield expansion to meet the vision of the Air Force is 

rendered obsolete. 

PROPOSED SYSTEM: COMPOSITE MATERIALS

Enter the new age of materials having strengths up to ten times

greater than conventional materials with unit weights less than

half and we’re talking about composite materials. Due to

advances in manufacturing technologies, composite materials

are seeing expanded use in a wide range of applications, from

military and aerospace, to sporting goods. Due to these unique

qualities, a project has been undertaken by the Deployed Base

Table 1. Types of Airfields.

Airfield Class (Subclass) Typical Location Runway Surface Taxiways/Parking Aprons Duration of Use Aircraft Accommodated

Expedient Airfield Forward Soil If Available at All, ~4 Weeks or Less C-17, C-130

(Small Austere Airfields) Tactical Areas They Are Soil Surfaced

Expedient Airfield Forward Unpaved, Perhaps If Available at All, 1 – 6 Months C-141, C-130, C-17, 

(Support Area Airfields) Tactical Areas With Membrane or They Are Soil Surfaced Various Tactical Aircraft

Mat Surfacing

Temporary Airfields Forward or Asphalt or Concrete, Some Available, 6 – 24 Months Most Transport 

Rear Areas Perhaps in Need Soil Surfaced and Tactical Aircraft

of Improvement

Semi-Permanent Rear Areas Only Concrete or Asphalt; Paved and Available, More than 2 Years Entire Fleet of Aircraft 

Airfields Maintained but not enough Available 

for Contingency Ops for the Mission

Main Operating Bases Rear Areas Only Concrete or Asphalt; Paved and Plenty More than 2 Years Entire Fleet of Aircraft 

(also Commercial Well Maintained Available, but Perhaps Available 

Airports) not Enough for the Mission

for Complete Ops

Table 2. Features of the AM-2 Matting System.

• Panels come in two sizes, a full-length 2’ x 12’ panel and 

a 2’ x 6’ half-length panel; all are 1 1/2” thick

• Panels painted Marine Corps Green; top surface is coated 

with nonskid of the same color

• Panels weigh 6-lbs/ft2

• Panels cost ~ $18/ft2

• Several types of key locks, connector bars, locking bars, and 

associated hardware are needed for full assembly

• Installation requires at least a 16-person crew consisting of a

supervisor, alignment leader, 2 prybar handlers, and 6, 2-person

mat installation teams.

• Panels are laid in a brick pattern, building both widthwise and

lengthwise away from the starting point.

• Key-locks are installed every 100’ in the longitudinal 

direction to facilitate the removal of panels for repair of matting 

or subgrade

• Ramps are used to transition from the subgrade surface to the mat

• Edges are anchored into the ground to prevent the mat from 

sliding and buckling.
The AMPTIAC Quarterly, Volume 7, Number 1 19

System Branch of the Air Force Research Laboratory

(AFRL/MLQD) to ascertain the feasibility of a composite mat

that will meet the Air Force’s future requirements. (Design

goals for the composite matting system are outlined in Table 3.)

AFRL/MLQD is working with two contractors, Ebert

Composite Corporation of Chula Vista, California and

Webcore Technologies Incorporated of Dayton, Ohio, to 

develop the composite matting to replace the current AM-2. 

Material choices have centered on a glass fiber in a vinyl-ester

matrix. Popular forms of glass fibers range from unidirectional

roving to woven fabrics both in prepreg and dry states, depending on the manufacturing method used to produce the matting.

A prepreg has glass fibers impregnated with resin, creating a 

pliable, tacky tow or fabric. It is stored below the curing temperature of the matrix and is easily formed into the desired

shape or placed in the designed direction. If the fibers are 

bundled together in a tow or woven in a fabric with no resin,

but ready for the matrix to be applied either through a resin

bath process or through a resin transfer molding (RTM)

process, then the material is supplied in a dry state.

The vinyl ester resin offers good corrosion resistance and

excellent mechanical properties at elevated temperatures. This

is because reaction sites of the vinyl ester are at the ends of its

Table 3. Goals for Composite Airfield Matting System.

• 3-lbs/ft2

• 1 1/2” thick panels

• Cost equal or less than AM-2

• Installation rate of 800 ft2/labor-hour

• Initial panel dimensions nominally 4’ x 8’, but shall be optimized later

• Connection systems shall be rugged but simple for:

• efficient installation and breakdown

• rapid replacement of damaged panels

• reuse of mats and connection accessories at other deployment locations

• Capable of handling loads from present and near-future cargo and fighter aircraft operations on a low strength subgrade

• Capable of withstanding shear stress from braking and turning actions of aircraft traveling at taxiing speeds

• Performance in all weather conditions and temperatures from -25 ̊F to 125 ̊F

• Capability of being cleared of snow and dirt using standard airfield plows, vacuum sweepers and towed sweepers

• Resistant to ultraviolet degradation

• Ability to be anchored to restrain movement under normal operating conditions including uplift forces caused from winds or jet and propeller

blast from aircraft

• Do not exceed current AM-2 transportation footprint aboard C-130 aircraft

Figure 1. AM-2 Matting Stacked for Shipment.

Figure 2. Extruded AM-2 Panels’ Cores are Filled for Added Stiffness.

Figure 3. Deploying the AM-2 Matting Requires a 16-Person Team.
20 The AMPTIAC Quarterly, Volume 7, Number 1

polymer chains resulting in fewer sites for chemical decomposition. Although vinyl ester resins have a lower cross-link 

density (compared to high-performance resins like epoxies,)

they have improved toughness characteristics such as impact

strength and interlaminar shear.

To achieve the weight reduction while maintaining the thickness requirement, the proposed matting has utilized a sandwich

construction, integrating a core material in the mat’s structure.

Composite plies (also called skins or face sheets) are bonded

completely around the core providing the required structural

properties of the sandwich panel. Utilizing this concept provides greater stiffness than that of the individual pieces making

up the sandwich panel. The composite skins provide the necessary means to carry the bending loads, while the core provides

the means to handle the shear loading requirements. The composite plies of the skins may also be oriented to maximize the

structural properties for specific loading applications, thus

making the structure even more efficient.

Benefits of sandwich construction include high strength-toweight and rigidity-to-weight ratios, good damage, impact and

fatigue resistance, high durability, and the capability to imbed

fasteners and other hardware into the panel. Core material

choices vary widely from structural foam, non-structural foam,

and balsa wood. Foams are typically polystyrene, phenolic,

polyurethane, polypropylene, polyvinyl chloride, and

ploymethacrylimide to name a few. Core materials also allow

for different manufacturing methods such as RTM, structural

reaction injection molding, vacuum infusion or vacuum assisted resin transfer molding (VARTM), and pultrusion. 

This project employs two separate panel designs, each utilizing different manufacturing methods. One type of panel is

made with a VARTM process, constructing the panel’s fiber

reinforcement in a dry state around the core material and

impregnating the dry reinforcement with resin by pulling it

through the panel with a vacuum, as described in the flowchart

in Figure 4.[2] The other style of panel is made with a pultrusion process, where dry fiber on material creels is pulled

through a resin bath, then through a die which imparts the

final shape and cures the part. Cut-off saws follow the die and

cut parts to the desired length. A simplified process flowchart is

provided in Figure 5.[2]

An important part of the composite matting system being

developed is the panel-to-panel connection and joint. The 

proposed connection, shown in Figure 6, is simpler than 

AM-2 and has the ability of transferring load. It utilizes a 3-part

cam-lock system, shown in Figure 7. The bottom piece of the

cam-lock can be embedded into the panel reducing the number of loose parts. This type of connection allows for removal

of a minimum number of panels to facilitate subgrade and

panel repairs. The joint also overlaps adjoining panels, creating

a load transfer path. This joint design can minimize or possibly

eliminate the need for subgrade preparation and repair. 

Figure 4. VARTM Flowchart.

• Tooling table covered

with release film or

peel ply to prevent

panel from adhering

to tooling

• Dry composite plies

applied to form first face

sheet; aligned and oriented

to meet the structural

design requirements

• Core material

is placed • Dry composite plies applied to

form other face sheet; again

aligned and oriented to meet the

structural design requirements

• Face sheets are wrapped

around the edges of the core

• Various combinations of peel,

bleeder, and breather plies, as

well as caul plates are put in

place, depending upon the specific

vacuum system being used and

characteristics of the resin system

• Vacuum bag is placed

around the entire part,

sealing it to the tooling

table

• Several ports in the bag

may be used to apply vacuum, depending upon the

size of the panel and the

resin system used

• Resin system is drawn into

the bag through ports

opposite the vacuum, and

begins impregnating the

dry lay-up panel

• Once the part has been

fully impregnated, the resin

flow is shut off

• Vacuum is maintained

while the resin cures, ensuring uniformity of skin thickness and consolidation of

resin and fibers.

• Vacuum bag is removed and

completed part is released
The AMPTIAC Quarterly, Volume 7, Number 1 21

Figure 5. Pultrusion Flowchart.

EVALUATIONS AND FUTURE EFFORTS

As mentioned before, the installation rate goal of the proposed

system is double that of the existing AM-2 system. This will be

achieved through a simpler installation process where the connection is incorporated into the panel and the panels are made

to be independent of installation direction. The proposed panel

will be manufactured with an 8” lip that is half the thickness of

the overall panel and can be seen clearly in Figures 6-8. When

connected together, the lips form a joint capable of transferring

load. Simple cam-lock connection pieces will be embedded

into the lips requiring only the mating piece to secure the panel

together. The goal is to lay panels in any direction by starting

with an end or edge panel with the panel lips on the bottom.

Forming the first row of edge panels by mating the end lips

together, the next row is placed mating the side lips together

with the adjoining panel, aligning the cam-locks as shown in

Figure 8. Locking the embedded cam-lock pieces together with

the locking device makes the panel-to-panel connection. This

procedure is repeated until the area required is covered. It’s

anticipated the required crew for installation will be approximately 4 to 6 people. Additional time is reduced by incorporating a ramp into the end or edge panel as opposed to

installing the ramp required for the AM-2 matting. When combined, these features should reduce the installation time to the

target range, as well as reducing overall weight of the system.

Initial evaluation of the proposed system will be based on a

single wheel load of 30,000 pounds, a 350 psi tire pressure, and

a low strength subgrade. (This loading situation is equivalent to

an F-15.) Traffic will be normally distributed in a 70-inch traffic lane to simulate a taxiway traffic pattern and the panels will

be laid out in a brickwork pattern over a sample subgrade. The

panels and subgrade will be continuously monitored with strain

gages attached to the bottom of the panels and pressure gages

buried in the soil. Mat surface deflection will also be measured.

The composite mats will be trafficked in line with AM-2 to

compare performance. Failure criteria for AM-2 matting is a 

1-inch deflection and breaks or tears in the mat that exceed 

6 inches. The testing series will commence in December 2003,

with results and a down-select occurring about 4 to 6 months

afterward. Future evaluations will be based on loads representing C-17 aircraft over various subgrades. The proposed joint

will be evaluated based on the joint’s flexural strength and 

tensile load transfer. The flexural strength, tested according to

ASTM C393, will determine the flexural properties of the 

bolted joint under load. If the joint is significantly more 

flexible than the panel, it will create rutting and pumping,

resulting in subgrade failure. The tensile load transfer test in

accordance with ASTM D3039 will determine the ability of

• Fiber material creels are set up with

either unidirectional tows or fabric

• Unidirectional fiber tows are used if 

the part utilizes fibers oriented along 

its longitudinal axis

• Fabric is used if the part requires 

fibers at an off axis orientation

• Inserts and embedded

items are placed into the

manufacturing process just

after the material creels

• Dry fibers are pulled

through a resin bath,

becoming soaked in

resin

• Fiber/resin mix is pulled

through the forming die

• Typically made of tool steel 

at a specific hardness

• Typically come in various 

pieces, bolted together to 

form the required crosssectional shape

• May also be coated to 

prevent degradation due to 

pH differences between it 

and the resin

• Forming die is heated to the desired temperature for

the curing cycle of the resin system

• Can employ several thermal gradients through the 

length of the die to create the required cure cycle

• Out-gassing of the curing part may also be required, 

since a particular resin system may evolve gasses • due to its chemical reaction during cure Secondary tooling may also

be added down the pultrusion

line to achieve the desired

part configuration

• Parts are cut to length by traveling saws following

the cured material exiting the dies

• Pultrusion process is fully automated and can 

be run at various speeds depending on the 

material system used and the required cure cycle
22 The AMPTIAC Quarterly, Volume 7, Number 1

Figure 7. Lap Joint and Keylock Assembly of Proposed

Composite Matting.

Figure 8. Close-up View of Keylock Assembly (Underside) in Proposed

Composite Matting.

Figure 6. Section of the Proposed Composite Mat Joining Surface Showing

Overlapping of Adjacent Mats.

the joint to transfer tensile loads across the joint interface. The

joint must be at least as strong as the panel itself in order to

achieve adequate load transfer. 

Once the down-select occurs, Phase II will focus on optimizing the panel performance against its weight. The joint

and connection details will be further refined to ensure load

transfer occurs under all possible conditions. The connection

hardware will be scrutinized against all possible attacks from

corrosion and material interaction, and appropriate material

selection will be undertaken to reduce these effects.

Manufacturing will also be optimized for efficiency and costs.

CONCLUSION

This project will cut across all military branches for improved

mobility in adverse terrain. The Army and Navy have recently

evaluated a number of mat systems under the Joint Logistics

Over The Shore (JLOTS) program. This program assessed 

mat performance under heavy truck traffic and subgrade conditions representative of beach and marine environments. 

Mat systems evaluated in this program ranged from an 8 feet

wide by 14 feet wide high-density polyethylene thermoplastic

weighing 9 1bs/sf to a 0.35-inch thick 4-ply woven chopped

fiberglass mat weighing approximately 3 lbs/sf, to engineered

lumber. While many of these mats work well for truck traffic,

none meet the Air Force goals of weight, installation rate, and

structural capacity required for aircraft operations. The Army’s

Joint Rapid Airfield Construction (JRAC) program is another

area where the Air Force’s lightweight structural mat will be a

big player. One of the main JRAC research areas is MOG

expansion through improved matting technology and soil 

stabilization. Consequently, mobilization for future military

operations will be greatly enhanced by providing a system 

for universal use that covers a wide range of uses without 

costly and complicated installation. Composite materials may

provide the only realistic solution to all these considerations.

REFERENCES

[1] NAVAIR 51-60A-1, AM-2 Airfield Landing Mat and

Accessories Technical Manual: Installation, Maintenance,

Repackaging and Illustrated Parts Breakdown, Naval Air Systems

Command 1993

[2] Engineered Materials Handbook Vol 1 Composites. ASM

International Handbook Committee, Theodore J. Reinhart

Technical Chairman, ASM International 1987
The AMPTIAC Quarterly, Volume 7, Number 1 23

BACKGROUND

The phenomenon of superconductivity is having a tremendous

impact on the advancement of technology in many fields

including medicine and electronics. It is expected to have more

impact in the future of electric motors, power production and

transmission, transportation and communication systems.

Accordingly, the call to develop superconducting materials is

strong and will remain so as the technology improves and

becomes less expensive.

Discovering or developing a material which becomes superconducting at room temperature is the ultimate challenge in

superconductivity. But with the uncertainty of this ever being

achieved, the current focus of much of the research, development and commercialization of superconductors, is on

YBa2Cu3O7-δ (often abbreviated YBCO or Y123 and where

0≤δ≤1; see also Figure 1). The reason so much effort has been

put forth on researching and applying YBCO superconductors

rather than alternative high-temperature superconductors

(HTS) is because it has some of the best superconducting properties and offers the potential for lower cost products.

Upon the discovery of superconducting properties in the

YBCO ceramic at an exceptionally high critical temperature

(Tc

) of about 93 K in 1987, there was a flurry of research and

development activity. This relatively high temperature, which is

above the temperature at which nitrogen liquifies (77K),

opened up the possibility for numerous advancements in electronic, magnetic, and related technologies. Prior to YBCO, all

superconductors required costly liquid helium for cooling.

HTS are a potentially revolutionary technology, especially for

power generation, transmission, distribution, and storage. The

potential energy savings are significant, as the reduction of

energy losses over power transmission systems would result in a

smaller amount of power needing to be generated to maintain

equivalent levels of usage. This also results in a higher capacity

available from existing generating plants, and an overall

improved system reliability. Cleaner generating technologies

such as wind and solar power would be made accessible to a

wider population.

YBCO has quickly become the most studied superconducting material, and through the evolution of its processing technology, it has also become one of the most frequently applied

and commercialized as well. Although the application areas for

superconductors are broad and range from microelectronics to

transportation, only a small percentage of the potential applications have reached the commercialization stage. Even many

of those are niche technology areas such as Brookhaven

National Laboratory’s particle accelerator.

LEVITATION APPLICATIONS

The levitation of objects as small as a simple permanent 

magnet (PM, as seen in Figure 2) or as large as a passenger train

is possibly one of the most recognizable capabilities of superconductors. Superconductors produced in bulk form have a

greater levitating capability than do superconducting films.

They are usually placed in an array opposite an array of PMs,

so as to produce a maximum levitating force. (Please see the

accompanying sidebar “Magnetic Levitation Explained” for more

details.)

Bearing Systems

Superconducting bearing systems could potentially yield virtually frictionless systems that require no lubrication. However,

one of the biggest obstacles facing YBCO in this sort of levitation application is its low mechanical strength, which limits the

maximum speed that can be achieved by the bearing system,

since at high speeds the centrifugal force generated can be sufficient to cause severe mechanical failure.[1] Another obstacle

facing superconducting bearing applications is fabricating a

homogeneous superconducting material, where the levitating

properties do not vary across the plane of the superconductor.

Benjamin Craig and Richard Lane

AMPTIAC Technical Staff

Rome, NY
24 The AMPTIAC Quarterly, Volume 7, Number 1

A derivative application of these superconductor-levitated

bearing systems is an energy storage system using a flywheel.

These systems, when compared to conventional bearings, can

reduce power losses by a factor of 10, achieve diurnal storage

efficiencies up to 90%, and store over 2 kWh of energy.[2] 

Maglev Trains

Maglev trains have become one of the more admired applications in the levitation realm, primarily because of the concept

of virtually no friction, which could lead to a highly efficient

transportation system. Maglev trains have the ability to operate

at much higher speeds (>300 mph) than wheel-based trains,

while maintaining safety and reliability, and ultimately providing a much-needed alternative to air travel.

Although there are a number of maglev projects underway

around the United States, the technology remains mostly in

the development and testing stage. The first maglev train in

the US has recently been placed on its tracks at Old Dominion

University in Virginia. Even though the ODU train and several other current projects use copper wound electromagnets

rather than superconductors for the levitation force, it is an

important step toward developing and implementing the levitation technology as well as gaining support and funding for

future projects. Many of these future projects will use the more

advantageous superconductor technology when it is fully

developed. The Japanese have been researching, developing

and testing maglev trains that employ low-temperature superconductors (LTS; with Tc

’s which are much lower than 77K)

for a number of years. (See Figure 3)

Superconducting maglev technology is also being used for

Many materials exhibit a traditional electrical resistance behavior above some 

critical temperature, and superconductivity below that temperature. For most

materials however, this critical temperature is very near absolute zero. As the 

material’s temperature approaches this critical value (Tc), the material becomes

less resistive, until it finally exhibits a complete disappearance of electrical resistance upon reaching Tc

. Materials in the superconductive state conduct electricity

perfectly, or without resistance.

SUPERCONDUCTOR PROPERTIES

There are three properties that are important to understand when discussing

superconductor materials. One is the critical temperature (Tc) below which a

superconductor reaches zero resistance, and above which the material is in a 

normally resistive state. (The current world record holder is an HgTlBaCaCuO

compound with a Tc of 138 K at ambient pressure.) The second property is 

the critical current density (Jc) which indicates the maximum current that a superconductor can carry without destroying its superconductive state. Finally, the 

critical magnetic field (Hc

) is the maximum magnetic field a superconducting

material can tolerate. Higher magnetic fields result in a reversion to the normal

conducting state.

Figure 2. Permanent Magnet Levitating Over a YBCO

Pellet. (From the Consortium de Recherches pour

L’Emergence de Technologies Avancées, Lab. de

Cristallographie, Centre National de la Recherche

Scientifique, France; Reprinted with Permission)

Superconductor 

Definition and Mechanism

Figure 1. Crystal Structure of YBCO.

YBCO

YBa2Cu3O7-δ

where 0≤δ≤1

Also abbreviated Y123

Oxygen

Copper

Yttrium

Barium

c = 11.68 Å

a = 3.885 Å

b = 3.818 Å

Temperature

Resistance

Tc
Superconductors are inherently perfect diamagnetic materials, which completely shield

applied magnetic fields from penetrating the

superconducting material. In the simplest case,

when a permanent magnet (PM) is placed over

a superconductor, the magnetic field produced

by the PM is repelled by an equal and opposite

field produced by the superconductor. This

causes the PM to levitate above the superconductor. In the same way, electromagnets can

be used to levitate superconducting magnets.

Superconducting maglev trains are based on this

concept of diamagnetism.

The AMPTIAC Quarterly, Volume 7, Number 1 25

national defense efforts in an upgrade to the High Speed Test

Track operated by the 846th Test Squadron at Holloman AFB.

It will employ a maglev system to achieve a Mach 9 ground test

capability, and will assist NASA in establishing the requirements

and understanding the potential for launch assist programs.

ELECTRIC POWER APPLICATIONS

Wires/Tapes

The first and most obvious use for the first HTS was distribution of electricity. Just replacing current copper cables with an

HTS will result in power savings of approximately 7%.[3]

While this may not sound like much, a 7% drop in power production implemented on a large scale easily results in billions of

dollars saved. Moreover, additional power to the consumer will

be immediately available, thus reducing the need to construct

new power plants to meet increasing demands. Replacing

wiring in motors, generators and transformers will increase the

savings to 8% or better.

To make this savings possible, however, fabrication of the

HTS cables would have to be the same cost as copper cables,

which has not been achieved. The goal set forth is to lower the

cost of HTS wires to $10/kA-m making them desirable for

widespread use (copper is about $4/kA-m).

YBCO offers the potential to operate in high magnetic 

fields at temperatures above 77 K and obtain the cost/performance goal if a low cost continuous fabrication method can be

developed. Current continuously-produced YBCO wires/tapes

are a maximum of about 1 meter long.[4] Cost/performance

projections suggest a continuous YBCO wire will run $30 to

$50/kA-m (depending on operating temperature) by 2005,

with at least a four fold decrease by 2010.[5]

Superconducting Magnetic Energy Storage (SMES)

SMES is a type of uninterruptible power source (UPS) which

provides energy backup to critical systems in case of a power

interruption, reduction or loss. A superconducting coil stores a

significant amount of energy that can be used when the main

power supply fails. SMES has a high storage capacity, can boost

power output, is very reliable, and can respond very quickly to

any sort of disturbance that requires its use. Several 1 MW

units are currently in use providing quality power control to

facilities around the world.

Electromotors

Melt-textured[6] YBCO is used for the rotor components

to create high power density electromotors.[1] Electromotors employing this superconducting technology can

generate a power density approximately eight times higher

than conventional motors. They also have many advantages

over conventional motors, including increased horsepower and

efficiency, as well as reduced size (shown in Figure 4), weight,

Magnetic Levitation

Explained

Figure 3. Japan’s Maglev Train. (Reprinted with Permission of

Central Japan Railway Company)

Superconducting State

Magnetic Flux is Indicated by Colored Lines

= Flux of PM

= Induced Flux in Superconductor

Permanent Magnet

Superconductor

Non-Superconducting State
noise, cost and pollution.[7] These motors are potentially

capable of providing a dramatic increase in efficiency over conventional motors used to operate industrial pumps, fans, belt

drives, and compressors.

The US Navy is interested in HTS motors for ship propulsion. Although the 20,000 hp and 35,000 hp motors required

for electric war-, cruise- and cargo-ships are not yet attainable,

there has been significant progress toward this level of power. A

5000-horsepower motor has already been built and tested, with

6500-hp AC synchronous motors in development for delivery

in the summer of 2003.[8] The HTS propulsion electromotors

are designed to significantly reduce the size and weight of 

conventional propulsion motors with the same power output,

thereby increasing fuel efficiency and creating more space for

cargo and equipment. The expected world market for motors

utilizing superconducting technology is approximately $400

million per year and is projected to grow to $2-4 billion per

year within ten years.

Fault Current Limiters

Superconductors have characteristics that make them inherently

good fault-current limiters, which protect against power surges.

That is, they can go from a superconducting state to a resistive

state by simply increasing the current beyond their critical 

current level (Jc), which is the point at which their superconductive behavior breaks down. For this particular application,

the superconductor can detect a surge, undergo a change in its

conductive state, absorb the surge of energy, and return to its

original state once the disturbance has been eliminated.

While costs are still high for superconductor-based fault

current limiters primarily due to material fabrication, the

potential improvements over conventional limiters motivate

their development. The advantages of superconducting fault

current limiters are numerous and they include improved

safety, reliability, power quality, flexibility, maintainability,

and operating capacity, as well as reduced fault current levels

and standby energy losses.[7] For instance, a typical transformer sees fault current levels up to 10-20 times the steady

state current, but a superconducting fault current limiter can

reduce this level to three-to-five-times steady state. Second

stage testing has been performed on 15 kV superconductor

fault current limiters.

Communications Filters

Wireless networks are rapidly growing throughout the world,

and their increased use will cause an increase in data traffic 

and thus significantly increase the amount of interference. A 

perfect filter would be able to completely screen out noise

without cutting any of the desired signal, and filters utilizing

YBCO superconducting technology can almost attain this.

Aside from improving the quality of the signal by reducing

the noise, the communications’ bandwidth can be increased by

30 to 80% and the transmit power needed for the signal can be

reduced. YBCO superconducting filters provide the further

advantage of increased sensitivity (the result of noise reduction)

which can expand the range over which the wireless technology

can be used. A practical advantage of superconducting filters

over conventional filters installed in base stations is that they

have a dramatically reduced size and weight.[9] It has been

reported that the market for superconducting filters is estimated to grow to $8 billion over the next five years.[10] 

Superconducting Quantum Interference Device

The superconducting quantum interference device, or SQUID,

is extremely sensitive to magnetic fields. These electronic

devices are based on the Josephson effect, which is the tunneling of electrons from one superconductor (S) layer, through a

26 The AMPTIAC Quarterly, Volume 7, Number 1

Figure 4. Conventional Motor (Left) and an HTS Electromotor (Middle). Internal View of an HTS

Electromotor (Right). (Reprinted with Permission of American Superconductor)

Figure 5. SQUID SNS Junction.

Contacts

Superconductor

N-layer

Insulator
negatively charged (N-type)-non-superconducting material, to

another superconductor layer. This creates an SNS junction as

shown in Figure 5.

The use of YBCO for SQUIDs instead of typical low 

temperature superconductors gives several advantages, including

a less complex apparatus, increased flexibility and mobility, 

and reduced cost. Magnetic sensing devices with tremendous

sensitivity can be used for various purposes, like geological and

astronomical observation. The United States military has

employed this technology to locate mines and submarines.

Having the greatest magnetic sensing capability of any device,

SQUIDs will have many other functions as well.

Magnetic Resonance Imaging/Nuclear Magnetic Resonance

Superconductors play a major role in magnetic resonance

technology, which has a huge market with magnetic resonance imaging (MRI) and nuclear magnetic resonance

(NMR) spectrometers. Magnetic resonance, which relies on

powerful magnets, originally utilized very expensive electromagnets or very large and heavy permanent magnets, thus

allowing only limited access to these systems. The development

of low-temperature superconductors led to a vast improvement

in machine size, weight, image quality and ultimately availability to a variety of medical facilities, but the cost of cooling the

superconducting magnets is still high. The development of

YBCO superconductors is a big step for this technology mainly

because they do not require the expensive liquid helium cooling

systems. With the development of HTS, magnetic resonance

systems can become more widely available at lower costs, while

providing great improvements in sensitivity, quality, and observational time compared to the conventional low-field copper

coil, heavy permanent magnet and LTS systems.[11]

NOVEL PROCESSING METHODS

The downfalls of YBCO are its inherent brittleness and the 

difficulties in producing the superconducting phase. YBCO is

a ceramic material and is therefore highly susceptible to cracking and fracture. The best method found thus far to improve

the mechanical properties of YBCO without significant degradation in its superconducting properties, is to add silver. Silver

does not react with YBCO and forms particulates primarily at

the grain boundaries, thus decreasing grain boundary resistivity and increasing the critical current density. The addition of

Ag however, adds another level of complexity to a technology

where reducing costs is a major driving force.

The second major hurdle has been the high processing 

temperature required to produce the superconducting phase,

hindering thin film fabrication. High temperatures cause diffusion between the YBCO layer and the substrate, degrading the

superconducting properties. Substrate materials must therefore

be selected which react very little if at all with YBCO. Grain

alignment is also very important in YBCO to produce the

highest Jc materials. This is achieved by depositing YBCO 

epitaxially onto lattice-matched substrates.

Substrate selection becomes even more critical as thermal

expansion characteristics must match closely to limit stresses,

and a low dielectric constant in high frequency applications is

also desirable. Materials identified that best fit these qualifications are, not surprisingly, ceramics similar to YBCO.

Therefore, in order to produce functional thin film devices, 

tailored ceramic substrates are used as buffer layer(s) between

the YBCO film and a primary substrate material.

In the past, problems associated with processing YBCO

superconductors have resulted in unique fabrication methods developed for both bulk materials and thin films.

Existing processing techniques were modified to increase the

oxygen content during YBCO growth and promote grain

alignment. Ex-situ processing methods are generally used for

bulk materials and thick film depositions. This approach

requires a post anneal at high temperatures to produce the

superconducting phase and results in materials with a low Jc.

The advantages of ex-situ processes are that they are low

cost, can be scaled up for commercialization, and can be

used to coat intricate shapes. In-situ deposition methods 

are used to fabricate high Jc thin films on lattice-matched

substrates eliminating the post anneal process. Pulsed laser

deposition (PLD) has become the preferred deposition

method, although there are several others capable of producing in-situ YBCO superconducting thin films. In-situ

processing techniques are generally high cost, with continuous large-scale fabrication a difficult task.

Melt Processing

Melt-texturing is a method to optimize grain alignment in

YBCO bulk materials. This technique can produce YBCO

disks with a Jc of 104 to 105 A/cm2 under a magnetic field of up

to 3 T.[12] Liquid-phase removal is a more specific melttexturing technique that can achieve a Jc of about 104 A/cm2,

and does not require seeding.[12] The advantages of this 

technique are that it is simple, a rapid growth rate is achieved,

and it is a good method for creating materials with high aspect

ratios. Seeded growth, on the other hand, is a process that uses

a seed crystal on which to grow a single-domain superconductor with a well-defined orientation.

Although melt texturing has provided some significant

advancements in bulk processing of YBCO superconductors,

there are some issues left to be addressed, including improving

superconducting and mechanical properties, and increasing the

growth rate of the grains for large-scale production.[12]

Ion Beam Assisted Deposition

Ion Beam Assisted Deposition (IBAD) is used to create textured substrate materials for the epitaxial deposition of YBCO.

To create Josephson junction devices, biaxially textured yttria

The AMPTIAC Quarterly, Volume 7, Number 1 27

Figure 6. Multilayer YBCO Wire Technology.

Silver Contact

YBCO

SmBCO

CeO2

IBAD YSZ

Nickel Alloy
stabilized zirconia (YSZ) is deposited on silicon

using IBAD, followed by epitaxial deposition of

CeO2 and YBCO by PLD. Conventional photolithography can then be used to pattern the layered material into an electronic device. 

IBAD is also under research at Los Alamos

National Laboratory for the development of

YBCO wire technologies. Like the Josephson junctions, YSZ is deposited via IBAD, but for wire

applications the primary substrate is a nickel alloy.

The nickel alloy is used for its ductility producing

a flexible wire. PLD is then used to produce the

subsequent layers of CeO2, SmBCO, and YBCO.

The multilayer approach, seen in Figure 6, helps to

maintain higher Jc levels with increasing wire thicknesses.

Inclined Substrate Deposition

A second method to create a biaxially textured

substrate for YBCO superconducting thin films

is referred to as the “inclined substrate deposition” (ISD) process. (See Figure 7.) A nickel alloy

substrate is mounted at a specific angle with

respect to the oxide vapor flux from an e-beam evaporator.

With the proper angle of inclination, a bi-axially textured

buffer layer oxide (such as MgO) may be deposited across the

nickel surface. YBCO is then deposited on the buffer oxide

using PLD or metalorganic chemical vapor deposition. The

process can produce deposition rates up to 100 Å/sec, making

it better suited for production. Research and development

efforts on YBCO wire technology using ISD are currently

underway at Argonne National Laboratory.

Rolling-assisted Biaxially Textured SubstratesTM

The “rolling-assisted biaxially textured substrates” (RABiTS)

technique was developed at Oak Ridge National Laboratory

and is a third method of producing a textured substrate for

YBCO. This method is specific to wire fabrication. A biaxially

textured nickel substrate is formed by cold rolling, followed by

a heat treatment causing recrystallization.[13] The buffer

layer(s) and the YBCO layer can then be deposited using PLD. 

CONCLUSION

Since its discovery in 1987, steady advancements have been

made in developing YBCO superconductor technology, but

difficulties with processing and fabricating YBCO parts are

inhibiting its widespread application and commercialization.

The continuing successes in material development and novel

processing techniques to overcome these difficulties (for

instance coated conductors and melt-texturing) suggest a

promising future for YBCO.

Many exciting and potentially revolutionary applications

that may be capable of changing our day-to-day lives dramatically have been envisioned. Many of these applications simply

await the maturation of superconductor technology (with

higher temperature performance and lower costs), while some

are already being commercialized and implemented in various

systems and locales around the world. Improved power service

and more reliable electrical systems, significant energy savings,

lower pollution, safe high-speed transportation, relatively 

inexpensive and widely available MRI, and more robust and

capable wireless communication systems are just some of the

advances made possible by superconducting materials. Until

room temperature superconductors are developed, or until

cheaper and more capable superconducting materials can be

made, YBCO will remain the material of choice for many 

current superconductor applications.

REFERENCES

[1] T. Habisreuther, M. Zeisberger, D. Litzkendorf, O.

Surzhenko, and W. Gawalek, “Developing Melt-Textured

YBCO”, JOM, The Minerals, Metals, & Materials Society, Vol.

52, No. 6, June 2000, pp. 26-29

[2] J.R. Hull, “Using High-Temperature Superconductors for

Levitation Applications”, JOM, The Minerals, Metals, &

Materials Society, Vol. 51, No. 7, July 1999, pp. 13-18

[3] O. Port, “Moving More Juice through the Wires: Superconductivity Could Shave Billions off Energy Bills”, Science

and Technology, February 2002

[4] T. G. Holesinger, S.R. Foltyn, P.N. Arendt, H. Kung, Q.X.

Jia, R.M. Dickerson, P.C. Dowden, R.F. DePaula, J.R. Groves,

and J.Y. Coulter, “The Microstructure of Continuously

Processed YBa2Cu3O7 Coated Conductors with Underlying

CeO2 and Ion-Beam Assisted Yttria-Stabilized Zirconia Buffer

Layers”, Journal of Materials Research, Vol. 15, No. 5, 2000, pp.

1110-1119

[5] “Accelerated Coated Conductor Initiative”, prepared by

Energetics, Inc. for the DOE, 2002. http://www.eren.doe.gov/

superconductivity/pdfs/acci_to_print.pdf 

[6] The organization of the crystallography in a material is

called “texture.” Texturing a material is the act of organizing its

crystallography in a desired fashion

[7] C. Cox and R. Hawsey, “The Potential of Super28 The AMPTIAC Quarterly, Volume 7, Number 1

Figure 7. Graphical Depiction of the Inclined Substrate Deposition

Process, where the Oxide Vapor Flux Encounters the Substrate 

at an Off-axis Angle α.

Oxide Vapor Flux

Substrate Normal

Nickel Substrate

Bi-axially Textured

Oxide Crystals

E-beam Evaporator

α
The AMPTIAC Quarterly, Volume 7, Number 1 29

conductivity”, Energy Magazine, Business Communications

Company, Inc., Winter 2000. Also available at

http://www.eren.doe.gov/superconductivity/pdfs/potential_of

_supercon.pdf

[8] “American Superconductor Announces US Navy Contract

to Create World’s First HTS Ship Propulsion Motor”,

American Superconductor Press Release, February 20, 2002,

http://www.amsuper.com/press/2002/AMSC_022002.pdf

[9] R. Simon, “Conductus Technology: An Enabling

Technology for Advanced Wireless Networks?”, http://www.

Conductus.com/pdf/whitepaper_Rsimon_10-12-00.pdf 

[10] J. Flanigan, “Superconducting Filter Firms Get Hot”, 

Los Angeles Times Syndicate, February 18, 2000. Available 

at http://www.chron.com/cs/CDA/story.hts/business/

flanigan/460836

[11] J.A. Schofield, “Super-Conductors Lower Design Costs”,

Design News, June 9, 1997

[12] W. Lo, “Recent Progress in Large-Grain REBCO Melt

Texturing”, JOM, The Minerals, Metals & Materials Society,

Vol. 52, No. 6, June 2000, pp. 18-21

[13] M. Paranthaman, C. Park, X. Cui, A. Goyal, D.F. Lee,

P.M. Martin, T.G. Chirayil, D.T. Verebelyi, D.P. Norton, D.K.

Christen, and D.M. Kroeger, “YBa2Cu3O7-y Coated Conductors with High Engineering Current Density”, Journal of

Materials Research, Vol. 15, No. 12, 2000, pp. 2647-2652

Mr. Royce Forman, Senior Scientist of the Structural

Engineering Division, NASA Johnson Space Center,

Houston, Texas, was presented the 2002 John W.

Lincoln Award. It was given in recognition of his 

outstanding work over many years in advancing the

technology associated with the concept of aircraft 

structural integrity. The Award was presented at the

2002 USAF Aircraft Structural Integrity Program

(ASIP) Conference in Savannah Georgia on 10

December 2002. 

PRESENTATION OF THE JOHN W. LINCOLN AWARD

The Award, which consists of a

gold medal and a certificate of

recognition, was named 

in honor of the late Dr. John

W. (Jack) Lincoln of the

Aeronautical Systems Center,

Wright-Patterson Air Force

Base, Ohio. Dr. Lincoln was a

pioneer and major contributor

to the development and 

application of durability and

damage tolerance design to

ensure the safety and longevity

of both military and commercial aircraft. The Award has

been presented previously to: 

Dr. Lincoln (1996) 

Mr. Charles Tiffany (1997)

Mr. Thomas Swift (1998)

Professor Jaap Schijve (1999)

Professor Alten F. Grandt, Jr. (2000)

Dr. James C. Newman, Jr. (2001) 

A plaque with the names of 

the recipients is on display at

Wright-Patterson Air Force

Base, Ohio.
30 The AMPTIAC Quarterly, Volume 7, Number 1

New! Textile Preforms 

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Computational Materials Science (CMS) – 

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AMPTIAC surveyed DOD, government, and academic efforts

currently studying materials science by computational methods

and from this research compiled this report. It provides an indepth examination of CMS and describes many of the programs, techniques, and methodologies being used and developed. The report was sponsored by Dr. Lewis Sloter, Staff

Specialist, Materials and Structures, in the Office of the Deputy

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BONUS MATERIAL: Dr. Sloter also hosted a workshop

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Special attention was paid to novel combinations of materials

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The AMPTIAC Quarterly, Volume 7, Number 1 31

AMPTIAC Directory

Government Personnel

TECHNICAL MANAGER/COTR

Dr. Lewis E. Sloter II

Staff Specialist, Materials & Structures

ODUSD(S&T)/Weapons Systems

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AMPTIAC
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QUARTERLY

Volume 7, Number 1–2003 

MaterialEASE:

Contamination of 

Hydraulic Fluids and 

Systems

Deployment Made Easier 

with Composite Airfield Matting

YBCO Blazes the Trail for Superconductors

...and more!

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