Keep ‘Em Flying

Laser Peening Keeps 

Aircraft Turbine Blades 

in Action

AMPTIAC is a DOD Information Analysis Center Administered by the 

Defense Information Systems Agency, Defense Technical Information Center 

and Operated by IIT Research Institute

Smart 

Materials 

That Sense 

and Respond
How many times in the past year have I heard the word “synergy”? And of those times, how many were at home with my

wife or out at a restaurant? I would guess that the ratio is

something like 10:0, because like so many other management clichés or buzzwords, “synergy” lives only at the office.

Things like “cooperation,” “give-and-take,” and “understanding” live at home.

Why does this matter? Honestly, it probably doesn’t, but

aren’t we all just a little overloaded with how many catchphrases come along? I recall having lunch with the CEO

from one of the nation’s largest manufacturers of industrial

carbon products a few years back. He said that there were

three kinds of organizations in business: there were those that

resist change, those that accept change, and those that seek

change. He wanted his company to be the latter. It is

assumed in there somewhere that CHANGE... is GOOD,

but I digress.

In the early 1900’s, the main use for oil in this country

was for lighting. This application however, was quickly being

supplanted by electrically energized lights, and things looked

pretty bleak for the oil industry in the US. But then, out of

the blue came a new application for oil and refined fuels: the

automobile. Right around the time one application was

dying, another came along and saved an industry. (The rise

of the automobile practically wiped out the saddle and horseshoe businesses of course, as every change has consequences.)

In our business, we see change all the time. Sometimes

it is legislative change, such as Acquisition Reform, other

times it is simply a shift in thinking or technology. Most

changes are for the better, like when we learned about ductile-to-brittle transition temperatures in steels for Liberty

Ships, or machining larger radius fillets in crankshafts to

reduce stress concentration. Like Helmut Panke (current

Chairman of BMW A.G.) has said, any organization that

does not adhere to the triple-A strategy of adaptivity, agility

and anticipation will not survive long in today’s climate.

Changes in technology, legislation, innovation, and even

thinking will always alter the landscape for materials and

their applications. As such, change is inherent in all we do,

because we are forever pushing our own boundaries with

innovative development of new materials or clever re-application of existing materials.

Materials engineers, by our very nature, are seeking

change every day. We seek to utilize natural and physical laws

of structure, chemistry, and mechanics to enhance the performance of materials around us. And we fight for every last

scrap of strength, ductility, thermal stability, conductance,

etc., out of every material we touch.

This brings me to another of Panke’s aphorisms: the four

Cs of continuity, consensus, cooperation, and cadre. Our discipline is one of continuously striving to make better materials to meet the challenges of tomorrow. We work separately

on our projects, but together in our mission. From these, we

develop strength and fraternity in this dynamic world.

Materials engineering truly is the building block of all other

engineering disciplines... and that is no cliché.

Wade Babcock

Editor in Chief

Materials Technology and 

Management Seminar Clichés

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About the Cover: 

An integrally bladed rotor is undergoing the laser shock peening process featured in our lead article. (Red laser beams are added graphics; the actual beams are

invisible.) This technology has increased readiness of B1 bombers significantly. On the back cover, one of the most promising commercial applications of 

magnetorheological fluids is pictured. Dampers utilizing these adjustable viscosity liquids have found their way into automobile shock absorbers and also 

vibration reducers for cable-stayed bridges. (Shock absorber image used with permission. Copyright 2003 Lord Corporation, all rights reserved.) 
The AMPTIAC Quarterly, Volume 7, Number 2 3

INTRODUCTION 

Laser peening is an innovative surface enhancement process

used to increase the resistance of aircraft gas turbine engine

compressor and fan blades to foreign object damage (FOD) and

improve high cycle fatigue (HCF) life. [1,2,3,4] The process creates residual compressive stresses deep into part surfaces – typically five to ten times deeper than conventional metal shot peening. These compressive surface stresses inhibit the initiation and

propagation of fatigue cracks. Laser peening has been particularly effective in aircraft engine titanium alloy fan and compressor blades, however the potential application of this process is

much broader, encompassing automotive parts, orthopedic

implants, tooling and dies, and more. Significant progress has

been made to lower the cost and increase the throughput of the

process, making it affordable for numerous applications from

gas turbine engines to aircraft structures, land vehicles, weapon

systems, as well as general industrial use. Laser peening may also

be referred to as laser shock processing (LSP), and various other

commercial trade names. This paper reviews the status of laser

peening technology, material property enhancements, and

potential applications.

How Laser Peening Works

Laser peening drives a high amplitude shock wave into a material surface using a high energy pulsed laser. The effect on the

material being processed is achieved through the mechanical

“cold working” effect produced by the shock wave, not a thermal effect from heating of the surface by the laser beam.

The laser system is a high-energy, pulsed neodymium-glass

laser system having a wavelength of 1.054 μm. The laser peening system produces very short laser pulses, selectable from 8 to

40 nanoseconds, with a pulse energy of up to 50 joules. The

laser spot is typically 5-6 mm in diameter. The laser peening

parameters are typically selected to achieve a power density or

laser irradiance of 5-10 GW/cm2. [5]

To prepare a part for laser peening, an overlay opaque to the

laser beam is applied to the material surface being treated. An

additional layer, transparent to the laser beam, is placed over

the opaque overlay. With the two overlays in place, the laser

pulse is directed through the transparent overlay and interacts

with the opaque overlay as shown in Figure 1. The interaction

consists of the laser energy being absorbed in the first few

micrometers of the opaque overlay surface, vaporizing the

material and forming a plasma. The plasma temperature rises

rapidly through further heating from the incoming laser beam,

but thermal expansion of the plasma is limited by the transparent overlay material. The pressure in the confined plasma

increases rapidly, causing a shock wave to travel into the material through the remainder of the opaque overlay, and outward

through the transparent overlay material.

The opaque overlay serves to protect the part’s surface from

direct thermal contact with the laser-induced plasma, and provides a consistent surface condition for interaction with the laser

beam, independent of the actual material being treated. Direct

contact of a metal surface with the plasma will, in most cases,

form a thin melt layer on the surface of the metal, ranging from

a surface discoloration to a surface melt layer up to 15 to 25 μm

thick, depending on the laser irradiation conditions and metal

properties. Opaque overlays can be of a variety of forms; dry or

wet paint, black tape, metal foils, and adhesive-backed metal

foils have all been used with varying, but nominally equivalent

results in terms of the pressure pulses generated.

The transparent overlay serves to confine the plasma generated at the surface of the opaque overlay against the surface

being treated and can be any material transparent to the laser

beam. The simplest and most cost-effective method is to flow

water over the surface from an appropriately placed nozzle. The

water is not used to cool the part but serves the key function of

confining the plasma generated when the laser beam interacts

with the opaque overlay surface. The confinement increases the

Richard D. Tenaglia

David F. Lahrman

LSP Technologies, Inc.

Figure 1. Schematic of the Laser Peening Process.

Transparent Overlay

(flowing water)

Laser Pulse

Confined Plasma

Shack Wave

Opaque Overlay

(paint or tape)

Component
pressure developed by the plasma on the surface up to 10 times

over the surface pressure developed if the plasma is unconfined

and allowed to accelerate away freely from the material surface.

In practice, the laser system is located next to a peening cell

in which the parts are robotically positioned during processing.

The size of the area to be treated depends on the part design

and service conditions. Sometimes, a part requires that only a

small area be treated and a single treated spot will suffice.

Examples might include around small bolt holes, or at the root

of a notch in the side of a thin section[6]. In other instances,

the areas requiring treatment will be larger, such as a patch on

a turbine blade, crankshaft fillet, or gear. In these cases, successive spots are overlapped until the desired region is completely

covered.

The shock wave traveling into the material being processed is

the means for enhancing material properties. If the peak pressure of the shock wave is above the dynamic yield strength of the

material, it will cause dynamic yielding as it travels into the

material. The yielding of the material introduces tensile plastic

strain in the plane of the surface, creating a residual compressive

stress. As the peak pressure of the shock wave decreases with distance into the material, the total plastic strain associated with

the shock wave decreases. This plastic strain gradient gives rise

to the compressive stress gradient below the surface. Because the

plastic strain produced by the shock wave extends much deeper

then that produced by conventional shot peening, the compressive residual stresses produced by laser shock peening also extend

deeper into the material. The deeper residual stresses, in general, provide much more substantial property benefits.

MATERIAL PROPERTY ENHANCEMENTS

Residual Stress

Laser peening produces a number of beneficial effects in metals

and alloys. Foremost among these is increasing the resistance of

materials to surface-related failures, such as fatigue, fretting

fatigue and stress corrosion cracking. Numerous metals and

alloys have been laser peened successfully, including titanium

alloys, steels, aluminum alloys, nickel-base superalloys, cast

irons, and a powder metallurgy iron alloy.

The material property enhancements are derived from the

deep compressive residual surface stresses imparted by laser

peening. Figure 2 shows an example of the deep compressive

stresses achieved in two titanium alloys versus the shallower

compressive stress profiles when conventional shot peening was

used. Stress profiles were determined by standard X-ray diffraction measurements. The compressive residual stresses produced

by laser peening extend in excess of 1.0 mm deep into the surface, whereas the compressive stresses for shot peened samples

are present to a depth of about 0.2 mm.

Thermal Stability of Residual Stresses

In service conditions involving elevated temperatures, the thermal stability of the residual stresses becomes an important

issue. To retain the benefits of the residual stresses at higher

service temperatures, they must be resistant to thermal recovery. A titanium alloy, Ti-8Al-1V-1Mo, was laser peened, then

held at elevated temperatures in the service temperature range

of interest, for four hours. Afterwards, the residual stress profiles were measured. The results shown in Figure 3 demonstrate

that after four hours at elevated temperature residual stress

recovery near the surface is minimal. [7]

Fatigue

The key benefits achieved in most applications with laser peening are significant increases in fatigue life and fatigue strength.

The most dramatic increases in fatigue strength are achievable

in thin sections for through-the-thickness cracks propagating

into the structure from a stress concentration associated with an

edge, be it a hole, notch, corner, inclusion or other feature.

Substantial increases in fatigue strength are also achieved in

thicker structures laser peened on a single surface in the area of

a stress riser or stress concentration. Figure 4 shows a comparison of fatigue properties for 7075-T7351 aluminum specimens

subjected to laser peening and shot peening. [8] The notched

fatigue specimens were tested in 3-point bending, using test

conditions of R=0.1 and Kt=1.68. The data illustrate the typical fatigue enhancement of laser peened parts, including a 30-

4 The AMPTIAC Quarterly, Volume 7, Number 2

Figure 2. Residual Stress Profiles for Laser Peened and Shot

Peened Titanium Alloys.

Figure 3. In-depth Residual Stress Profiles after Elevated

Temperature Exposure of Laser Peened Ti-8Al-1V-1Mo 

for 4 Hours.

Shot Peened Ti-6Al-4V

Laser Peened Ti-6Al-4V

Shot Peened Ti-6Al-2Sn-4Zr-2Mo

Laser Peened Ti-6Al-2Sn-4Zr-2Mo

0.000 0.010 0.020 0.030 0.040 0.050

Depth, inches

Residual Stress, ksi

20.0

0.0

-20.0

-40.0

-60.0

-80.0

-100.0

-120.0

-140.0

-160.0

0

-200

-400

-600

-800

-1000

Residual Stress, MPa

Depth, mm

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Ti-8Al-1V-1Mo

As Processed

450 °F, 4 Hr

750 °F, 4 Hr

0.000 0.010 0.020 0.030 0.040 0.050

Depth, inches

Residual Stress, ksi

40.0

20.0

0.0

-20.0

-40.0

-60.0

-80.0

-100.0

-120.0
The AMPTIAC Quarterly, Volume 7, Number 2 5

50 percent increase in notched fatigue strength and an increase

in fatigue life of about an order of magnitude.

The earliest investigation of the effect of laser peening on the

fatigue behavior of thin sections was performed on F101-GE102 aircraft gas turbine engine fan blades. [9] In this investigation, the effects of shot peening and laser peening surface treatments on increasing the resistance of the airfoils to foreign

object damage (FOD) were compared. The results of the

fatigue testing are shown in Figure 5. The baseline, undamaged

blades failed within 106 cycles at 70 ksi. The notched, untreated blades failed at 20 to 30 ksi. The estimated average failure

stress for the dual intensity [10] shot peened blades was 35 ksi,

and for the high intensity [11] peened blades, 45 ksi. By comparison, the failure stress of the laser shock peened notched

blades averaged about 100 ksi, well above the failure stress of

the undamaged blades. Even the laser peened blades with electro-discharge machined (EDM) notches averaged around 75-

80 ksi. These results indicated that laser shock peening would

enable a blade to continue to operate safely, even with FOD at

some level above that previously viewed as cause for removal

and repair of the blade.

Corrosion

In limited studies, some laser peened materials have shown

increased resistance to corrosion and stress corrosion cracking

(SCC). In 2024-T351 aluminum, for example, potentiodynamic tests showed anodic current density shifts after laser

peening, indicating enhancement of pitting resistance for both

initiation and propagation. There was also a reduction of the

passive current density on laser shock peened surfaces, indicating increased corrosion resistance. [12]

PRODUCTION APPLICATIONS

Beginning in 1991, the B-1B Lancer’s F101 engine began

experiencing failures of titanium turbine blades due to FOD

caused by ice and hard objects ingested into the engine.

Chunks of blades that broke loose, in some cases, did irreparable damage to the rest of the engine. To avoid grounding the

B-1 fleet, the Air Force required a manual inspection of all the

fan blades before each flight. The time-consuming leading

edge inspections involved rubbing the leading edge with cotton balls, cotton gloves and even dental floss. If a single snag

was detected, the blade was replaced prior to the next flight. In

1994, over one million man-hours at a cost of $10 million per

year were required to complete the engine inspections and

keep the B-1 flying. 

GE Aircraft Engines (GEAE) investigated laser peening as a

potential solution to increase the durability of titanium fan

blades and decrease their sensitivity to FOD. The improvement

to high cycle fatigue performance was remarkable. Damage to

an F101 blade can reduce the fatigue strength from about 75

ksi to less than 20 ksi, which is less than half of the design

requirement. However, when laser peened blades are comparably damaged, they retain a fatigue strength of 75-100 ksi. Thus,

laser peening restores the structural integrity of damaged fan

blades. Sensitivity to FOD defects up to 0.25 inch in F101

blades was virtually eliminated.

In 1995, the US Air Force authorized the production development of laser peening, bringing this technology out of the

lab and into a production environment. LSP Technologies, Inc.

(LSPT) was founded in 1995 to provide laser peening equipFigure 4. Comparison of Laser Peening and Shot Peening

Fatigue Properties for 7075-T7351 Aluminum. (Data points

with arrows indicate tests halted with no failure.)

Figure 5. Comparing Effects of Laser Peen

and Shot Peen Processing on the Leading

Edge of F101-GE-102 Fan Blades.

Baseline, Untreated

Laser Shock Peened

Shot Peened

10,000 100,000 1,000,000 10,000,000 100,000,000

Number of Cycles

Maximum Stress Amplitude, MPa

320

280

240

200

160

Specimens Heated 24 Hr at 400°F

before Testing at Room Temperature

Type and Depth No Chisel EDM Chisel EDM Chisel EDM Chisel EDM

of Notch: Damage 0.25” 0.125” 0.25” 0.125” 0.25” 0.125” 0.25” 0.125”

Surface Treatment None None Dual Intensity High Intensity Laser Shock

Shot Peened Shot Peened Peened

106 Cycles at Indicated Stress, Ksi

100

90

80

70

60

50

40

30

20

106 Cycles
6 The AMPTIAC Quarterly, Volume 7, Number 2

ment and services to industry and the US military. By 1997,

GEAE had proven the beneficial effects of laser peening and

began production application to F101 blades, using four laser

peening systems designed and built by LSPT.

Application of laser peening avoided over $59 million in

blade replacement costs, secondary damage engine repair

costs, and cost avoidance from airfoil failures. Avoiding catastrophic engine failures over the remaining life of the B1B/F101 program is estimated to save another $40 million.

Due to this success, laser peening was applied to solve similar

problems for the F110-GE-129 engine (used on the F-16

C/D Falcon), and the Air Force estimates cost savings similar

to the B-1B/F101 program. The process has also been implemented in the F110-GE-100 engine (used on the F-16 A/B

Falcon), and the F101-GE-102 engine (used on the B1-B

Lancer). In March 2003, production laser peening also commenced on an integrally bladed rotors (IBR) for Pratt &

Whitney’s F119-PW-100 engine, used on the F/A-22 Raptor.

The production use of laser peening has been a notable success story for these military engine applications. Overall, the

potential savings from laser peening are estimated to approach

$1 billion when calculating this impact over all engines in the

Air Force fleet.

Figure 6 shows the application of the LaserPeenTM (Trademark

of LSP Technologies, Inc.) process to an integrally bladed rotor

used in Pratt & Whitney’s F119-PW-100 engine for the F/A-22

Raptor. Note that the red laser beams were added schematically

to illustrate the process. The actual laser peening pulses are in the

infrared spectrum (not visible to the human eye).

EMERGING APPLICATIONS

Much progress has been made at decreasing the cost and

increasing the throughput of laser peening, making the process

affordable for many new applications. Further progress is

expected as production applications of laser peening expand.

Numerous applications are under development or are good

candidates for improvement using this technology.

In addition to engine components for the Air Force, numerous applications for airframe structures exist, including:

• Fatigue-critical components such as F-16 bulkheads, wing

attachments, flight control mechanisms, wheels, brakes,

landing gear,

• Welded titanium and aluminum components for improved

reliability,

• Welded aging aircraft parts for improved reliability,

• Fasteners and fastener holes to combat fatigue, fretting

fatigue and stress corrosion cracking,

• Cost-effective, high reliability castings to replace forgings,

and 

• Mobile laser peening for deployment at repair depots for

treatment of large structures and detection of exfoliation corrosion.

For the Army, numerous opportunities exist for laser peening

enhancement of fatigue prone helicopter parts such as transmission gears and other drive train components. Laser peening

will enable the development of lightweight drive trains capable

of higher horsepower loads than present generation helicopters

(Figure 7). Laser peening can also improve the performance

and reliability of rapid cycling firearms and artillery, as well as

toughen support systems and vehicle components in tanks and

armored vehicles.

The US Navy, US Marines, and the Royal Air Force (RAF)

have interest in laser peening for improving the reliability of the

Pegasus engine for the Harrier. Another potential application

includes stress relief of nuclear propulsion system parts such as

tube/sheet welded assemblies in nuclear submarine and surface

ship vessels for improved resistance to stress corrosion cracking

(SCC) and crevice corrosion. Other candidates include fatigue

prone catapult and tail-hook arrest mechanisms, ship drive

gears and bearings, and prevention of stress corrosion cracking

(SCC) in welded components found on vehicles such as

HUMVEES.

Applications for laser peening are not limited to military

parts. As the process has become affordable, numerous industrial applications are emerging. Opportunities exist to apply

laser peening for weight reduction, increased reliability, and

improved fuel economy in automotive and truck parts such as

transmission gears and axles, rotating engine parts, and

impellers. Medical applications include treatment of orthopedic implants to improve the fatigue performance of hip and

knee replacement joints and spinal fixation devices. Laser peening is also expected to find applications in power generation

equipment for land based and nuclear power systems.

THE FUTURE FOR LASER PEENING

The future of laser shock processing is one of continuing

advancement in new production applications and technology

development. The biggest barrier to wider application of laser

peening in manufacturing has been the relatively high cost, and

to a lesser extent, the slow throughput of the process. This situation has improved rapidly with the availability of robust, production-ready laser peening systems and advances in processing

technology such as LSP Technologies’ RapidCoaterTM system

for automating the application and removal of the process overlay coatings. Much of this recent manufacturing-oriented

development for increasing throughput and decreasing cost has

Figure 6. Laser Peening of an IBR for the F-119-PW-100 Engine.
been supported by the Air Force Research Laboratory’s

Materials and Manufacturing Technology Directorate. The

variety of applications being evaluated for potential production

applications continues to increase. From several production

applications at present, this number is expected to expand rapidly over the next five years.

REFERENCES/ENDNOTES

[1] A. Clauer and D. Lahrman, Laser Shock Processing as a

Surface Enhancement Process, Durable Surfaces, Proceedings of

the Durable Surfaces Symposium, International Mechanical

Engineering Congress & Exposition, vol. 197, Trans Tech

Publications, Ltd, Switzerland, pp. 121-144, (2000)

[2] D. See, D. Lahrman, and R. Tenaglia, Affordable Laser

Peening, Proceedings of the 8th National Turbine Engine High

Cycle Fatigue Conference, Monterey, CA, (April 2003)

[3] A. Clauer, Laser Shock Peening for Fatigue Resistance, Surface

Performance of Titanium, J. Gregory, H. Rack, and D. Eylon

(eds.), TMS, Warrendale, PA, pp. 217-230, (1996)

[4] A. Clauer and J. Koucky, Laser Shock Processing Increases the

Fatigue Life of Metal Parts, Materials & Processing, vol. 6 (6),

pp.3-5, (1991)

[5] Laser Shock Processing, Technical Bulletin #1, LSP

Technologies, Inc., Dublin, OH, (1999)

[6] A. Clauer, J. Dulaney, R. Rice, and J. Koucky, Laser Shock

Processing for Treating Fastener Holes in Aging Aircraft,

Durability of Metal Aircraft Structures, S. Atluri, C. Harris, A.

Hoggard, N. Miller, and S. Sampath (eds.), Atlanta Technology

Publications, Atlanta, pp. 350-361, (1992)

[7] C. Lykins, P. Prevey, and P. Mason, “Laser Shock Peened

Compressive Residual Profile After Exposure to Temperature.”

AF Report WL-TR-95-2108, Wright Patterson AFB, OH,

(September 1995)

[8] P. Peyre, P. Merrien, H. Lieurade, and R. Fabbro, Surface

Engineering, vol. 11, pp. 47-52, (1995)

[9] S. Thompson, D. See, C. Lykins, and P. Sampson, Surface

Performance of Titanium, Ed. J. Gregory, H. Rack and D.

Eylon, The Minerals, Metals & Materials Society, pp. 239-251,

(1997)

[10] Dual intensity peening processes involve peening a part at

one intensity level, then specifying an additional peening step

at a lower intensity level. The purpose of the first peening

intensity is to impart deep compressive residual stresses into the

part, and shot peening at the second lower peening intensity

smoothes the surface.

[11] High intensity peening involves peening a part at a very

high level of bead size, bead velocity, and/or peening duration

to achieve severe stress inducement. High intensity peening

may also severely damage the surface of a part.

[12] P. Peyre, X. Scherpereel, L. Berthe, C. Carboni, R. Fabbro,

G. Beranger and C. Lemaitre, Materials Science and

Engineering, A280, pp. 290-302, (2000)

The AMPTIAC Quarterly, Volume 7, Number 2 7

Figure 7. Comanche RAH-66 Helicopter and Helicopter Drive Train Gears.

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8

The Chief of Naval Research Cheapskate Prize for Affordability was presented to a team from the Naval

Surface Warfare Center-Indian Head Division on 12 March by the Chief of Naval Research, RADM Jay

Cohen. What do “cheapskates” and Indian Head’s MicroElectroMechanical Systems (MEMS) Technology

Team have in common? Saving money – which for Indian Head’s team and the Navy

translates into $10’s of millions – hence, the name of the award.

The Cheapskate Award for Affordability celebrates technological improvements that

have had the greatest impact on the future availability of affordable technologies for naval

forces. MEMS technology miniaturizes complex electro-mechanical devices by combining sensing and actuating capabilities on a single silicon chip. The devices are found commercially in the communications, automotive and biomedical fields.

Researchers at Indian Head have been developing MEMS-based safe and

arm (S&A) technology for future Navy undersea weapons since 1995. As

an enabling technology for small, multi-mission torpedoes, MEMS-based

fuze S&As are ten times smaller, more capable, more reliable and have a

lower life cycle cost as compared to conventional S&A components.

In accepting the award for the Indian Head MEMS team, Mr. Lawrence

Fan (Weapons Department, Fuze/Safe Arming Branch) spoke of the advantages realized by the Navy’s CCAT (Anti-Torpedo Torpedo) and Advanced

Technology Ordnance Surveillance (ATOS) programs. “The benefits are

clear that MEMS provides miniaturization and enhanced performance over

the legacy systems. But moreover, we have developed MEMS systems that

will reduce acquisition and total ownership cost for the Fleet.” Fan was

referring to the cost avoidance of $10K per unit for each MEMS exploder

S&A device used in the CCAT torpedo (saving $10-20M on procurement

for this program alone) and the devices’ long shelf life and greatly reduced

need for in-service maintenance, which are projected to save the Navy additional $10’s of millions. 

RADM Cohen presented the award to the Indian Head team, saying “This is the first example of a very

significant application (for MEMS technology.)” He discussed the technological accomplishments of the

program, and added the old saying, “good things come in small packages.” Outwardly excited about the

advances made by the team, RADM Cohen commented, “We are happy to award you with this

prize...MEMS is the future!” 

Indian Head’s research and development of MEMS has been sponsored by the Office of Naval Research

(ONR), the Office of the Secretary of Defense (OSD) and the Defense Advanced Research Projects

Agency (DARPA). Fan acknowledged their continued collaboration stating, “Their commitment and

support...has and continues to ensure that this crucial technology is sufficiently mature for transition into

the Fleet and for enhancing Warfighter capabilities.” Fan also acknowledged IHDIV employees Mr. Don

Garvick, Mr. Ed Johnson and Mr. Bob Kavetsky who formed the core of the program coordination and

management team. He said, “They garnered support and got the word out on the potential of MEMS to

the S&T, Acquisition and OSD communities. As a result, our technical team was empowered to innovate

and to execute technology development that is transitioning into both undersea weapons and other DOD

applications.” 

Twenty seven people comprise the MEMS Technology Team, including: Mr. Wade Babcock 

(AMPTIAC Staff Engineer), Mr. Ralph Balestrieri, Mr. John Barbera, Mr. Gregory Birk, Mr. Donald

Boone, Mr. Victor Carlson, Mr. Kevin Cochran, Mr. Michael Deeds, Mr. Lawrence Fan, Mr. Mark Gelak,

Mr. Thomas Griffin, Dr. Daniel Jean, Mr. Thomas Jerow, Mr. Kenneth Johnson, Mr. Bruce Kuester, 

Dr. Howard Last, Mr. Doug Lee, Mr. Kwok Lee, Mr. Stephen Lee, Mr. Edward Litcher, Mr. John Murray,

Mr. Thomas Rawcliffe, Mr. John Renzi, Mr. Gabriel Smith, Mr. Paul Smith, Mr. Robert Simons, and 

Ms. Carolyn Vaughn. 

For additional information about the IHDIV MEMS project and capabilities, 

contact Lawrence Fan, (301) 744-6157.

cheap·skate n. Slang A stingy person; a

miser; a miserly person [syn: tightwad]

Team from NSWC-Indian Head Wins ONR Cheapskate Award

The Indian Head Division

MEMS Development Team.

(Pictured Left to Right:

Gabriel Smith, Ralph

Balestrieri, Daniel Jean, Paul

Smith, Kevin Cochran,

Kenneth Johnson, Donald

Boone, John Barbera,

Thomas Rawcliffe, Don

Garvick, Michael Deeds, and

Lawrence Fan.

The AMPTIAC Quarterly, Volume 7, Number 2
The AMPTIAC Quarterly, Volume 7, Number 2 9

Material EASE

MATERIALS THAT SENSE AND RESPOND: 

AN INTRODUCTION TO SMART MATERIALS

Richard Lane

and

Benjamin Craig

AMPTIAC Technical Staff, Rome, NY

INTRODUCTION

Each of us reacts to the world around and within us by sensing and 

actuating. When our hand is in contact with a hot object, we sense the heat,

our brain sends a command, and our arm muscles actuate our hand away

from the object. Similarly, because of internal sensing, we will tend to favor

the burned hand until it has healed. As technology progresses, it becomes

reasonable to ask, “Can we design analogous mechanisms that can intelligently interact with their environment, and structures that assess their

own health?” Such smart structures could have a tremendous impact in

advancing many fields including medicine, microelectronics, and robotics,

among others.

Often, simple devices made from a single sensing or actuating material

are used in certain applications. However, systems that involve both sensing

and actuating materials can be used to build more sophisticated applications. Such systems are referred to as smart structures, which incorporate

sensors and actuators with processing/control units connecting them. To get

an idea of how smart structures can be implemented, it is necessary to

understand the fundamental components of these structures: sensor and

actuator materials.

For centuries, materials have been known to react to the surrounding

environment producing some form of response. For instance, in 1824,

Rochelle salt was discovered to become electrically polarized by the application of heat. That was the first discovery of the effect known as pyroelectricity. Since that time, numerous additional materials have been discovered

having the inherent capability to convert one form of energy into another.

Sensors are materials that respond to a physical stimulus, such as a change

in temperature, pressure, or illumination, and transmit a resulting signal

for monitoring or operating a control. Actuators are materials that respond

to a stimulus in the form of a mechanical property change such as a dimensional or a viscosity change. Table 1 lists the sensor/actuator material 

classes that will be discussed in this MaterialEASE along with their 

associated energy stimulus and response forms.

SMART MATERIAL TYPES

Pyroelectrics

Pyroelectrics, as previously mentioned, are materials that become electrically polarized upon an applied temperature change. Materials used as

pyroelectrics include barium strontium titanate (Ba1-xSrx

TiO3), lead 

zirconate titanate (PbZr1-x Tix

O3), barium strontium niobate 

(Ba1-xSrx

Nb2O6), triglycine sulfates (TGS), lithium tantalate (LiTaO3), 

22AMPTIAC

Sensors and actuators have become an increasingly important technology as more systems become automated, requiring less human input or operation.

This MaterialEASE characterizes the leading sensor and actuator materials currently in use along with some new materials under research. For more

information on this exciting topic, consider purchasing the more complete AMPTIAC Report: Materials for Sensors and Actuators.

Table 1. Sensor and Actuator Material Classes.

Material Class Stimulus Response

Pyroelectrics Temperature Change Electric Polarization

Piezoelectrics Mechanical Strain Electric Polarization

Electrostrictors Mechanical Strain Electric Polarization

Magnetostrictors Mechanical Strain Change in Magnetic Field

Electroactive Polymers Mechanical Strain Electric Polarization

Electroluminescent Materials Electric Field Light Emission

Photoluminescent Materials Incident Light Light Emission

Electrochromic Materials Electric Field Color Change

Piezoelectrics Electric Current Mechanical Strain

Electrostrictors Electric Current Mechanical Strain

Magnetostrictors Magnetic/Electric Field Mechanical Strain

Shape Memory Alloys Temperature Change Mechanical Strain

Electroactive Polymers Electric Field/pH change Mechanical Strain

Electrorheological Fluids Electric Field Viscosity Change

Magnetorheological Fluids Magnetic Field Viscosity Change

Actuators Sensors
MACROSCOPIC MAGNETOSTRICTION MECHANISM

Magnetic materials have internal areas

called domains, within which all magnetic

dipoles are oriented in the same direction.

Domains with different orientations are separated by domain walls or boundaries. With

the application of an external magnetic field,

the boundaries move and domains rotate

and align themselves in the same direction,

ultimately causing a slight length/shape

change in the bulk material. The magnetostriction effect is illustrated in the figure.

10 The AMPTIAC Quarterly, Volume 7, Number 2

Material EASE

and polyvinylidene fluoride (PVDF). Ceramics are widely used due to

their lower cost including availability and ease of processing, and good

stability. Their weakness comes from their inherent brittleness.

Polymers, PVDF and its copolymer with trifluoroethylene (PVDFTrFE), provide a non-brittle alternative but do not obtain the level of

performance of ceramics.

Pyroelectrics are widely used for infrared detection in surveillance

and targeting applications. A pyroelectric infrared detector generally

employs a thin film of pyroelectric material oriented with the electroded surfaces normal to its polarization direction. When infrared

radiation is absorbed by the detector, the temperature of the pyroelectric material rises. This change in temperature alters the material’s

polarization causing a change in surface charges across the material

which produces an electrical signal via the electrodes. The resulting

signal is proportional to the incoming radiation.

Piezoelectrics

Piezoelectrics are materials that exhibit an electrical polarization with

an applied mechanical stress (direct effect), or a dimensional change

with an applied electric field (converse effect). They are used for both

sensing and actuating devices. Lead zirconate titanate (PbZr1-xTix

O3)

is the premier piezoelectric material as it may be doped to produce an

n-type or p-type material with a range of dielectric constants to meet

the requirements of numerous applications. Other piezoelectric materials that may be used are barium titanate (BaTiO3

), lead titanate

(PbTiO3

), lead metaniobate (PbNb2O6), and PVDF. Polymers are generally favored for sensing applications while ceramics are favored for

actuating. Figure 1 depicts the piezoelectric effect observed in lead zirconate titanate upon the application of compressive forces relative to

the crystal structure.

Piezoelectrics is a mature technology with numerous applications

throughout the military and commercial sectors. Devices using piezoelectrics include: adaptive optics, hydrophones and sonobuoys, fuse

devices, depth sounders, thickness gauging, flaw detection, level indicators, alarm systems, strain gauges, airplane beacon locators, fetal

heart detectors, and tire pressure indicators among many others.

Electrostrictors

Electrostrictors, like piezoelectrics, exhibit a dimensional change upon

an applied electric field or an electric polarization upon an applied

mechanical stress. Electrostrictors however, exhibit a non-linear

response as opposed to the linear response of piezoelectrics. The advantages of electrostrictive materials over piezoelectrics are that they have

almost no hysteresis, a quick response time, and higher displacements

with good reproducibility. These properties are desired for microposiFigure 1. The Piezoelectric Effect 

Lead

Oxygen

Titanium or Zirconium

Force Force

Force

Force

Polarization Up Polarization Down

No External Magnetic Field

Apply External Magnetic Field

Arrows indicate magnetic dipole

in each domain External Magnetic Field Direction
THE BASIC ONE-WAY SHAPE MEMORY EFFECT

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY

The AMPTIAC Quarterly, Volume 7, Number 2 11

AMPTIAC

tioner and adaptive optic actuation applications. A disadvantage of available

electrostrictors is their higher cost compared with piezoelectrics. Ceramic

materials that are used in electrostrictive devices are in a class called “relaxor ferroelectrics.” The term “relaxor” refers to the significant decrease in

dielectric constant with increasing frequency. Lead magnesium niobate –

lead titanate (0.9PbMg1/3Nb2/3O3 – 0.1PbTiO3

) is the most popular electrostrictive material. Research on polymeric electrostrictors has taken place,

but none have been developed thus far for practical use.

Magnetostrictors

Magnetostrictive materials (used in actuators) exhibit a change in shape

(strain or elongation) when an external magnetic field is applied. The

reverse effect is called piezomagnetism (used in sensors), where a magnetic field is produced/altered upon application of a mechanical strain.

Although usually minimal, ferromagnetic materials (e.g. Fe, Ni, Co,

etc.) exhibit magnetostriction to some extent. Ferromagnetic elements,

such as cobalt, are often alloyed with iron. Rare earth elements have exhibited significantly higher magnetostriction but only at temperatures lower

than room temperature. Other common magnetostrictive materials include

nickel-based alloys and particulate composites containing magnetostrictive

particles. Magnetostrictive sensors and actuators are used for transducers,

transformers, MEMS, vibration and noise control, linear motors, adaptive

optics, ultrasonics, speakers, drills, pumps, and position and mechanical

torque sensors.

Terfenol-D is used almost exclusively as the choice material for magnetostrictive applications because of its exceptional magnetostrictive properties. Terfenol is an intermetallic compound, TbFe2 (TER – Terbium; FE –

Iron; NOL – Naval Ordnance Laboratory, now the Naval Surface Warfare

Center), and D denotes the presence of the rare earth metal dysprosium.

SMAs

Shape memory alloys (SMAs) are actuators that, upon proper thermal and

mechanical treatment, have the ability to remember up to two shapes which

they had previously occupied. When subjected to a mechanical load below

a certain temperature, these special materials can be plastically deformed

beyond their elastic limit, but then are capable of regaining their original

shape if they are then heated above a certain temperature.

Nickel-titanium is the most common SMA and has some of the best

shape memory properties, but has relatively low transformation temperatures. Although they cannot match the outstanding shape memory capabilities of Ni-Ti alloys, copper-based alloys are a less expensive alternative. The

most common ternary Cu-based systems are Cu-Zn-Al and Cu-Al-Ni which

can generally achieve a shape memory strain of 4 to 5% (compared to about

8% for Ni-Ti) and have a broader range of transformation temperatures.[1]

Other alloys, such as iron-based alloys (e.g. Fe-Mn, Fe-Mn-Si, Fe-Pt, Fe-Ni,

Fe-Ni-Co and Fe-Pd), exhibit shape memory but are not capable of regaining their shape to the same extent as nickel-titanium and copper-based

alloys. Other forms of SMAs include composites and ferromagnetic alloys.

Some of the current SMA applications include use in spacecraft, aircraft,

automobiles, electronics, medicine, process systems, robotics, and domestic

appliances.

Wet EAPs

Wet electroactive polymers (EAPs) (also known as ionic EAPs) are polymers immersed in an electrolytic fluid that upon the application of an

external stimulus (such as an electric field,) can exhibit a significant

change in dimension or geometry. EAPs can act as sensors and/or 

actuators and are typically of the following compositions.

Polymer gels can take on water and expand, or conversely expel water

The actual mechanism of the shape memory effect can be described simply as a

reversible, thermoelastic, phase transformation between a parent austenitic phase

and a martensitic phase. The phase transformation occurs when a material in the

austenitic phase is cooled below the martensite start temperature (Ms

), where the

two phases coexist. The material must then accommodate the two phases without

changing shape through a mechanism called twinning. This is where mirror-image

lattices form adjacent to the parent lattices. The phase transformation is completed

upon reaching the martensite finish temperature (Mf

). The material can then be

plastically deformed into another shape. During this deformation the twinned

martensite is converted to a deformed martensite. The material remains deformed

until it is heated to the austenite start temperature (As

), and at this point the

martensite begins to transform back into austenite. Heating above the austenite finish temperature (Af

) allows the material to regain its original shape. (The extent to

which the shape is regained usually depends on the type of SMA, amount of deformation, and the material’s thermomechanical history.) When cooled again the

material does not automatically revert to the deformed shape. This is called the oneway shape memory effect. The entire shape memory process can be repeated.

Austenite (a) Cooled to Form Twinned Martensite 

(b) without a Shape Change, then Deformed by Moving

Twin Boundaries (c). Heating State (b) or (c) will Return

the Original Austenitic Structure and Shape.[1]

(b) 

Twinned Martensite Deformation

Cooling

Heating

(a) Austenite (c) Deformed Martensite
THE ELECTRO- AND MAGNETO-RHEOLOGICAL EFFECTS

12 The AMPTIAC Quarterly, Volume 7, Number 2

Material EASE

and contract in response to a change in the surrounding chemical

environment. The movement of water can be induced by a change in

pH, electric field, temperature, light or other environmental conditions. Polyacrylonitrile (PAN) has been used in polymer gel systems,

as it is a polyelectrolyte.[2] Another polymer gel activated by a

change in pH includes a polyvinyl alcohol-polyacrylic acid (PVAPAA) component.

Ionic polymer metal composites (IPMCs) are made up of a perfluorinated membrane (meaning all of the hydrogen atoms attached

to carbon atoms are replaced with fluorine atoms) with noble metal

plating (typically gold or platinum) for electrodes.[3] The ionic polymers used are typically either Flemion® (a perfluorocarboxylate) or

Nafion® (a perfluorosulfonate) which swell in water due to their ionic

and hydrophilic nature. Anions are located on the polymer membrane, while cations are present and freely moving in the fluid. When

an electric field is applied to the IPMC, the cations diffuse toward the

negative electrode, which causes the composite to deform.

Conductive polymers (CP) experience a volume change when they

are subjected to an electrochemical oxidation or reduction process

called doping. Polyacetylene, polyaniline (PANi), nylon, polypyrrole

(PPy) and polythiophene (PT) are examples of conductive polymers.

For these to function, an electrolyte must be present in order to supply

the ions. The application of a small electric field will prompt the electrochemical reactions causing the polymer to become conductive or

insulative, thus causing the ions and solvent to migrate either into or

out from the polymer matrix resulting in the volume change.

Although carbon nanotubes are not polymers, they are considered

to be the most recent addition to this list of electroactive actuators.

[3, 4] Carbon nanotubes, known to exhibit sensing and actuating

capabilities, are sheets of graphite one atom thick that are rolled into

cylinders forming a structure that has a very small diameter (on the

order of a nanometer) but a length greater than a micrometer.

Applying a voltage to a carbon nanotube structure residing in an electrolyte will cause it to bend achieving strains up to 0.2%.[3] Ions from

the electrolyte build up around the carbon nanotube surface and the

charge injection causes the bond lengths between carbon atoms to

change, thus causing the dimensions of the nanotube to change. With

dimensional changes in individual nanotubes being coherent the

effect is seen macroscopically also.

Electrorheological and Magnetorheological Fluids

Electrorheological (ER) and magnetorheological (MR) fluids experience a nearly instantaneous change in their rheological properties

upon the application of an electric or magnetic field, respectively. (See

accompanying article in this issue.) This change is reversible and

occurs also nearly instantaneously upon the removal of the applied

field. The physical changes can be quite substantial, turning a low 

viscosity fluid into a much more viscous, almost-solid substance.

These special fluids typically consist of a dispersed, polarizable

particulate phase suspended in a carrier fluid. While ER and MR 

fluids can use the same type of carrier fluid (e.g. high electrical resistivity, low-viscosity substance such as a hydrocarbon or silicone oil),

The electrorheological effect occurs in an ER fluid when an

electric field is applied causing the uniformly dispersed

solid particles to become polarized. Once polarized, they

begin to interact with each other, and form chain-like

structures, parallel to the electric field direction, connecting

the two electrodes (see figure below). Upon further intensification of the electric field, the chains begin to form thicker columns. A dramatic change in the suspension’s rheological properties is associated with this change in its structure. The columnar particle structures give the fluid a

greater yield stress. Upon removing the electric field, the

particles lose their polarization and return to their freely

roaming state. The period of time over which these events

occur is on the order of milliseconds. The magnetorheological effect is similar to the ER effect, but obviously,

instead of an electric field, a magnetic field is applied to

polarize the particles.

(a) No Electric Field (b) Applied Electric Field

Field direction
the particulate phase is different. For ER fluids the dispersed particles are

commonly metal oxides, aluminosilicates, silica, organics, or polymers.[5]

MR fluids use ferromagnetic or paramagnetic solid particles. Activators, surfactants, and other additives are also commonly included in both types of

fluids to improve their properties.

ER and MR fluids are mostly considered for use in damping applications. Specific applications include exercise equipment, valve, braking and

clutch systems, as well as in vibration control and shock absorbing systems.

Electroluminescent and Photoluminescent Materials

Luminescence is the property of emitting energy in the form of light 

(having a wavelength in the visible spectrum). The process of luminescence

occurs when a material’s valence electrons are excited to higher energy 

levels by some stimulus, then fall back to lower energy levels giving off photons, or light. Luminescent properties can be classified by the type of input

energy used to excite electrons to higher energy levels. Thermoluminescent,

electroluminescent and photoluminescent materials’ electrons are excited

by heat, applied electric field, and incident photons, respectively.

Electroluminescence (EL), in basic terms, is the emission of light

induced by an applied electric current. It is not the same phenomenon as

incandescence used in standard light bulbs, which generates heat. EL,

rather, is a much more efficient process since it is the direct conversion of

energy from an electric current into light. Electroluminescent and photoluminescent (PL) materials include inorganic as well as organic materials. Often the inorganic materials are made up of a combination of elements from the II, III, V, and VI groups on the periodic table. Some of the

inorganic base materials that have been studied include GaAs, CdS, InP,

and GaN.

Electroluminescence in polymers has received much attention recently. They can be fabricated to emit red, yellow or blue light, with blue light

being the most difficult to achieve. Some examples of conjugated (also

known as conducting) electroluminescent polymers include poly(alkylfluorenes), polyparaphenylene (PPP), and poly(p-pyridine) (PPy).[6]

Other electroluminescent polymers include polythiophenes (PT), poly(pphenylene vinylene) (PPV), poly(p-phenylene), and polyfluorenes.[7]

Polythiophenes and PPVs can exhibit electroluminescence from blue to

the near-infrared depending on the side group. Copolymers with an electroactive segment of poly(p-phenylene benzobisthiazole) (PBZT), exhibited photoluminescence with wavelengths representing blue to red visible

light.[8, 9] In general, conjugated polyquinolines can be modified to emit

light having a wavelength anywhere in the visible spectrum.[7]

The most common application of an electroluminescent material is in

a light emitting diode/device (LED). LEDs consist of an electroluminescent

material sandwiched between two electrodes, one of which is transparent

allowing the transmittance of the emitted light.

Electrochromic

When an electric current is passed through an electrochromic material 

its optical properties change such that the material has a significantly 

different appearance. That is, the absorptive, reflective, or transmissive

properties are altered enough to cause a change in its color, reflectivity 

or transparency.[10]

The mechanism relies on electrochemical reactions (oxidation/reduction) involving a transfer of electrons and ions between electrodes and the

electrochromic material. When an electric current is applied and electrons

and ions are being exchanged from one electrode to the other, there is an

amount of incident energy, with wavelengths in the visible spectrum, which

can be absorbed, therefore causing the material to change color and in

effect become less transmissive. The degree to which the color is changed

depends on the extent of the reaction, which is basically controlled by the

applied electric field. Oxides of the following metals exhibit electrochromic

properties: tungsten, molybdenum, titanium, manganese, vanadium,

ruthenium, iridium, rhodium, and niobium.[11] 

WO3

, which turns from clear to blue, is the most studied electrochromic

material. [11] The reaction is rather slow, but the coloration remains for a

significant amount of time after the electric current is removed.[12] V2

O5

changes from favoring the red end of the spectrum to the blue end. Lithium

nickel oxide, Lix

Ni1-xO (x is typically 0.3-0.5), turns from being clear into a

neutral gray color.[13]

The electrochemical oxidation of polyaniline can change it from

being transparent to green, then blue, and then purple. Upon electrochemical reduction this color scheme is reversed, and thus it is an 

electrochromic material. Polydiphenylamine (PDPA) is another electrochromic polymer.[10]

Electrochromic materials can be used to create a smart windows capable of reducing their transmittance by at least 65% in less than a minute

when an electric field is applied . Once the electric field is removed the effect

remains, but it is reversible when the current is reversed.[14]

SUMMARY

Major sensor and actuator technologies as well as current state-of-the-art

materials for those technologies have been presented in this MaterialEASE.

The use of sensor and actuator materials is continuing to grow in an

increasing effort to optimize operating systems. Pertinent examples include:

• Pyroelectric sensors offer infrared detection capabilities used for night

vision and motion detectors.

• Piezoelectric materials offer both sensing and actuating applications for

pressure detection and micropositioning applications respectively.

• Electrostrictors and magnetostrictors offer non-linear micropositioning

capabilities.

• Shape memory alloys offer temperature sensing and a high strain

response (but with a slow response time.)

Smart structures built with these materials will allow for more flexibility

and greater functionality over conventional materials systems in various

applications. 

There are numerous unexplored avenues for the application of sensing

and actuating materials, but their development is still far from complete.

Continued research on the materials themselves will spawn new as-yetunknown applications, and will also provide improved performance in

existing applications.

Although these special materials will not simply replace conventional

hydraulic, pneumatic and electric motor actuators altogether, the new 

actuators may eventually be implemented more widely than their longestablished counterparts, as they have a high energy density, large bandThe AMPTIAC Quarterly, Volume 7, Number 2 13

AMPTIAC A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY
14

width, and simple packaging. Traditional actuators can be large and

complex systems, adding weight and various additional costs to the

application. Sensor and actuator materials can decrease manufacturing, operating and maintenance costs, reduce weight and improve system performance. Therefore, when designing new systems, these materials should be given proper consideration as they present a very legitimate alternative to conventional systems.

REFERENCES

[1] Metals Handbook, 10th Edition, Vol. 2: Properties and Selection:

Nonferrous Alloys and Special-Purpose Materials, ASM International,

1990; DTIC Doc. AD-D450 152

[2] W.W. Gibbs, “Artificial Muscles,” Scientific American, 1996.

Available at http://www.sciam.com/

[3] Electroactive Polymer [EAP] Actuators as Artificial Muscles:

Reality, Potential, and Challenges, edited by Y. Bar-Cohen, SPIE – The

International Society for Optical Engineering, The Society of PhotoOptical Instrumentation Engineers, 2001

[4] Y. Bar-Cohen, “Nanotechnology Using Electroactive Polymers as

Artificial Muscles”, MST news, International Newsletter on

Microsystems and MEMS, Vol. 3/01, 2001, pp. 45-46

[5] S. Ramamurthy, M.V. Gandhi, and B.S. Thompson, Smart

Materials for Army Structures, Quantum Consultants, Inc.,

Michigan 1992; DTIC Doc. AD-A300 215

[6] D.D. Gebler, Y.Z. Wang, J.W. Blatchford, S.W. Jessen, L. –B. Lin, T.L.

Gustafson, H.L. Wang, T.M. Swager, A.G. MacDiarmid, and A.J. Epstein,

“Blue Electroluminescent Devices Based on Soluble Poly(p-pyridine),” Journal of Applied Physics, The American Institute of Physics,

1995; DTIC Doc. AD-A297 041

[7] X. Zhang, A.S. Shetty, and S.A. Jenekhe, “Electroluminescence

and Photophysical Properties of Polyquinolines,” University of

Rochester, 1999; DTIC Doc. AD-A366 991

[8] X.L. Chen and S.A. Jenekhe, “Electroactive and Photoactive

Nanostructured Materials from Self-Assembling Coil-Rod-Coil

Triblock Copolymers,” Polymer Material Science and Engineering,

Vol. 73, 1995, pp. 304-305; DTIC Doc. AD-A314 776

[9] J.A. Osaheni, and S.A. Jenekhe, “Copolymers: Design, Synthesis,

and Supramolecular Regulation of Photophysical Properties,”

Journal of the American Chemical Society, 1995; DTIC Doc. ADA294 825

[10] L.H. Dao, M.T. Nguyen, J.W. Chevalier, T.N. Do, J.Y. Bergeron,

and R. Paynter, “Processible, Stable, Conducting Polymers for

Electrochromic Display and Window Applications,” ANTEC ‘91

Conf. Proc., Society of Plastics Engineers and Plastics Engineering,

1991, pp. 861-863

[11] C.G. Granqvist, “Electrochromic Materials: Metal Oxide

Nanocomposites with Variable Optical Properties,” Materials Science

and Engineering, A168, Elsevier Sequoia, 1993, pp. 209-215; DTIC

Doc. AD-D258 149

[12] P. Judeinstein and J. Livage, “Electrochromic Properties of SolGel Derived WO3 Coatings,” Sol-Gel Optics, Vol. 1328, SPIE, 1990; pp.

344-351

[13] S.J. Wen, K. von Rottkay, and M. Rubin, “Electrochromic Lithium

Nickel Oxide Film by Pulsed Laser Deposition,” Electrochemical

Society Meeting Symposium on Electrochromic Materials and Their

Application III, Lawrence Berkeley National Laboratory, 1996

[14] J.C.L. Tonazzi, B. Valla, M.A. Macedo, P. Baudry, and M.A.

Aegerter, “Characterization of an all Solid-State Electrochromic

Window,” Sol-Gel Optics, Vol. 1328, SPIE, 1990, pp. 375-390; DTIC

Doc. AD-P006 442

The AMPTIAC Quarterly, Volume 7, Number 2

Material EASE

smart materials

Visit

http://amptiac.alionscience.com/ProductsAndServices/products.html

or call Gina Nash at 315-339-7080

Want to know more?

AMPTIAC’s 

State of the Art Report

“Materials for Sensors and Actuators.”

(AMPT-28)
INTRODUCTION

Fluids capable of a rapid and dramatic change in their rheological properties (properties associated with the flow of matter) in the presence of an electric or magnetic field are finding

many new applications. They are classified as being electrorheological (ER) or magnetorheological (MR) fluids

accordingly. ER and MR fluids are actuators that have the

repetitive ability to react to an applied field. In their liquid-like

state, they exhibit fluid-like properties. In their activated,

solid-like state however, they can physically resist an applied

force much like a solid material (or extremely high viscosity

liquid) would. 

These special fluids have recently gathered greater attention

due to their commercial success in state-of-the-art automobiles. The 2003 Corvette Anniversary Edition and Cadillac

Seville STS feature a shock absorbing system that incorporates

MR fluids as the primary damping component. (See this

issue’s MaterialEASE for a brief description of the electro- and

magneto-rheological effects, as well as an introduction to other

sensor and actuator materials.)

Willis M. Winslow discovered the ER effect in 1942, and

since then there has been much struggle first to completely

understand the effect, and second to develop ER fluids with

properties that meet the design requirements for practical

applications. Some of the properties of ER fluids that have

hindered them from performing sufficiently for many applications are yield stress, temperature stability, and power 

consumption.[1]

In the late 1940’s the MR effect was first reported. The

amount of effort that was put forth to study MR fluids was not

nearly as significant as that for ER fluids mainly because they

require particles with much higher densities, which results in

sedimentation – a significant complication. Recently, however,

there has been a renewed interest in MR fluids primarily

because they exhibit some superior properties.

ELECTRORHEOLOGICAL FLUIDS

General Composition

ER fluids basically consist of particles that are held in suspension by a non-conducting liquid. The suspending liquid,

which should have a high electrical resistivity, is typically a

low-viscosity hydrocarbon or silicone oil. The particles 

dispersed in this liquid are commonly metal oxides, aluminosilicates, silica, organics, or polymers.[2] In particular, the

particles are very small (on the order of a micrometer) and at

a concentration low enough to allow the fluid to maintain a

relatively low viscosity when the electric field is absent (zerofield viscosity).

One of the more common problems associated with these

fluids is sedimentation. This occurs over time and can sometimes be difficult to reverse depending on the particles used.

Since the suspending liquid is of a relatively low density, the

dispersed particles should have a relatively low density also in

order to maintain the dispersion. This extends the time it takes

for sedimentation to become a significant factor on the properties of the fluid.

A third substance is sometimes used as an activator, and is

applied to the surface of the particles. Amines and organic

compounds that readily form hydrogen bonds are good activators.[3] Water is sometimes used to increase the ER effect,

but consequently increases conductivity, power consumption,

and corrosion, while limiting the operating temperature

range.[1]

Finally, surfactants are sometimes used in ER fluids in order

to maintain a uniform dispersion and prevent an agglomeration of the particles. Often they are used in ER fluids that have

a high concentration of particles. There are also proprietary

additives used in many fluids that impart specific properties

and characteristics.

Typical Properties

The voltage required to induce rheological changes through a

given thickness of ER fluid is relatively small: approximately 1

to 4 kV/mm.[2] Typically, the current densities of ER fluids

are between 10-6 and 10-3 amp/cm2.[4] (Current density measurements are used to predict the power consumption of a particular ERF). One of the most important properties of an ER

or MR fluid is its dynamic yield stress, which is the minimum

stress required to cause the fluid to flow under the applied

field. Usually, higher dynamic yield stresses are desired and in

current ER fluids they range from approximately 100 Pa to

over 3 kPa.[4]

It is very difficult, however, to compare various ER fluids

and their properties due to the lack of standard testing procedures and conditions, as well as the strong dependence of ER

properties on their composition. But in general, for an ER

fluid to be used in a practical application it should meet the

properties provided in Table 1.

Benjamin Craig

AMPTIAC Technical Staff

Rome, NY

The AMPTIAC Quarterly, Volume 7, Number 2 15
16 The AMPTIAC Quarterly, Volume 7, Number 2

Specific Composition

The properties of ER fluids can be modified by varying the

components and compositions of the particles and liquid. In

general, increasing the concentration of particles in the fluid or

increasing the intensity of the applied field will increase the

magnitude of the ER effect. The properties of these fluids also

depend on particle size and density, carrier fluid properties,

additives, and temperature. Figure 1 displays the dynamic

yield stress for a few sample compositions of ER fluids.

Silica gel has been one of the more common types of particles used for ER fluids, but despite having high shear stresses

and low minimum field strength (to induce the ER effect),

these fluids have some serious disadvantages. They have a 

relatively high conductivity, poor stability, are abrasive and not

very resistant to sedimentation.[1] Aluminosilicates are among

the particles providing the best ER effect, [1] and metal

hydroxides can be activated with water or a polar solvent to

exhibit a good ER effect.[1] Poly(lithium methacrylate) and

poly(sodium styrene sulfonate) are polyelectrolytes that are

commonly used as the particulate phase, but water is typically

added to the fluid in order to increase the ER effect.[1] An ER

fluid containing a non-aqueous, crosslinked polyurethane 

particle phase does exhibit good properties and is capable of

operating at higher temperatures mainly because of the

absence of water. These particular fluids also have low 

viscosities and low conductivities.

Silicone oils have some very desirable properties, which

often makes them the easy choice for the suspending liquid.

They have a high stability and low temperature coefficient 

of viscosity, as well as a reasonable shear stress performance

capability.[1]

Influence of Particle Concentration

The volume fraction of the dispersed particulate phase can

have a very significant effect on the properties of an ER fluid.

A higher concentration can give the fluid a much higher ER

effect, but at the same time can cause problems.

Sedimentation is a major factor, since higher concentrations of

solid particles increases the amount of settling that will occur.

The other potential problem associated with an increase in the

volume fraction of particles is an increase in the zero-field viscosity. The effect of the concentration of particles on the

dynamic yield stress is given in Figure 2 for cellulose particles

(6% water) in mineral oil as a function of electric field.

Influence of Temperature

Temperature has an affect on the properties exhibited by ER

and MR fluids. The most obvious property affected by temperature is viscosity, which decreases as temperature increases.

The dynamic yield strength also decreases with an increase in

temperature, but this effect is greater in ER fluids than in MR

fluids. The more extensive change in dynamic yield strength

for ER fluids is due primarily to changes in conductivity and

relative permittivity of the particle and oil components of the

fluid over the temperature range. For MR fluids, though, the

reason for the decrease in strength is that the yield stress is

Table 1. Minimum Properties Needed by an ER Material to be

Utilized in a Variety of Applications[4]

Property Description Suggested Value

Dynamic yield stress at 4.0 kV/mm < 3.0 kPa

Current density at 4.0 kV/mm (DC) < 10 μA/cm2

Zero-field viscosity 0.1 – 0.3 Pa⋅s (1 – 3 Poise)

Operating temperature range -40 to +200 °C

Dielectric breakdown strength > 5.0 kV/mm

Particle size ~10 μm

Stability Low sedimentation 

No dynamic separation 

No electrophoresis 

No chemical changes 

Low volatility

Miscellaneous properties Non-abrasive

Non-toxic

Non-corrosive

Non-Flammable

Figure 1. Comparison of Dynamic Yield Stress vs. Electric Field for Two Groups of ER Fluids[4]

34 wt. % Zeolite in

Silicone Oil

3.16 wt. % Silica in

Silicone Oil

35% Polyvinyl Alcohol in

Vaseline Oil

012 345

Electric Field, kV/mm

Dynamic Yield Stress,kPa

0.3

0.25

0.2

0.15

0.1

0.05

0

Polyelectrolyte Dispersed in an

Oil

100 Parts Lithium Hydrazinium

Sulfate in 59 Parts Silicone Oil

16g Sodium Aluminosilicate

(4A) in 20 mL RTEMP

Hydrocarbon Oil

50 wt. % Aliphatic Starch in

Silicone Oil

19.2 wt. % Semiconducting

Polymer, 6.5 wt. % Water in

Silicone Oil

01 2 3 4 5 6 7 8 9 10

Electric Field, kV/mm

Dynamic Yield Stress, kPa

5

4.06

3.12

2.18

1.24

0.3
The AMPTIAC Quarterly, Volume 7, Number 2 17

directly proportional to the volume fraction of particles in the

fluid, and since the carrier liquid volume expands with the

increase of temperature, the volume fraction of the particles

decreases.

Other properties affected by temperature include conductivity and current density. The overall conductivity of the fluid

increases with increasing temperature, as does current density.[1] Figure 3 shows the temperature dependence of the ER

response and the conductivity of a fluid having a polyurethane

dispersed particulate phase in a silicone oil.

ER fluids that contain water

have an ER effect that is strongly dependent on temperature.

These ER fluids experience a

significant change in their ER

effect above 100°C and below

0°C, which limits their use to

applications that have operating

temperatures within this range.

Thus, much effort has been

made to create ER fluids that

exhibit a strong ER effect without requiring water. These are

called anhydrous ER fluids; an

example of which is

poly(anthracene quinone radical) particles in silicone oil

(PAnQR/silicone).[1]

ER fluids that can operate at

very low temperatures are also of interest. Cryogenic ER fluids

have been investigated in the form of aluminum powders (20-

vol.%) in liquid nitrogen. Strong, solid particle, columnar

structures form when an AC field of 10.7 kV/cm is applied.[1]

MAGNETORHEOLOGICAL FLUIDS

The key difference between electrorheology and magnetorheology is in the application of the stimulating field.

Electrorheology uses low current, high voltage to generate an

electric field, whereas magnetorheology uses low voltage, high

current through a coil to generate a magnetic field.

The MR effect is also similar to the ER effect, but obviously, instead of an electric field, a magnetic field is applied to

polarize the particles. The polarized particles interact and form

chains and columnar structures, and the rheological properties

are changed dramatically. These events also take place over an

extremely short period of time: on the order of a millisecond.

Upon removing the magnetic field, the particles lose their

polarization and return to their freely roaming state.

MR fluids have a similar composition to ER fluids in that

they typically contain a dispersed, polarizable, particulate

phase suspended in a carrier fluid. Unlike the ER fluids

though, the MR fluids use ferromagnetic or paramagnetic

solid particles. These particles are usually within an order of

magnitude of a micrometer in diameter. It is common for

them also to contain surfactants and other additives. 

MR fluids usually have greater yield strengths than do ER

fluids. The yield stress of an ER fluid is typically around 10

kPa, while that of MR fluids is about 100 kPa.[5] The MR fluids are also much more efficient in that they require a low voltage, whereas the ER fluids require a high voltage. This power

consumption aspect translates into a lower cost for MR fluids

as well as a safer system. In addition, the MR fluids are much

less sensitive to contaminants, and can effectively operate over

a broad temperature range: -40 to 150°C.[5] One major disadvantage of MR fluids is the strong tendency of sedimentation, in that once a significant amount of the particles coagulate, it is difficult to redisperse them. A disadvantage in both

ER and MR fluids is that the

carrier fluid is usually organic.

Organic fluids have problems

with degradation, polymerization, flammability, bacterial

growth, and can also be incompatible with other components

in systems where they are

used.[6]

The yield strength of MR 

fluids can be increased by

increasing the concentration of

particles or by increasing the

intensity of the magnetic field.

The higher concentration of

particles, though, corresponds

to a higher viscosity when the

magnetic field is absent, which

is not usually a desired property.

A comparison of the typical properties of ER and MR fluids is

given in Table 2.

MR fluids are not ferrofluids, which also have a rheological

response to a magnetic field (although to a lesser extent than

MR fluids). Hence, ferrofluids are not considered actuators

but they are colloidal fluids that have particles much smaller

than in the non-colloidal MR fluids (approximately one to

three orders of magnitude smaller.) They also do not form

chain-like structures of the same magnitude as MR fluids in

the presence of a magnetic field. Moreover, ferrofluids do not

Figure 2. Effect of the Volume Fraction of Cellulose on the

Dynamic Yield Stress as a Function of Electric Field[1]

Figure 3. ER-Behavior of a Polyurethane Based ERF[1]

Cellulose/Mineral Oil

T=26°C

0 10 100

Volume Fraction, %

Dynamic Yield Stress, Pa

1000

100

10

5 kV/mm

4 kV/mm

3 kV/mm

2 kV/mm

1 kV/mm

-20 0 20 40 60 80

Temperature, °C

Shear Stress, Pa

2000

1500

1000

500

10

0

0 kV/mm

3 kV/mm

Conductivity

5

4

3

2

1

0

Conductivity(nS/cm)

DC Couette Viscometry @ 1000 s-1
18 The AMPTIAC Quarterly, Volume 7, Number 2

experience changes in their rheological properties as extensively as do MR fluids.

APPLICATIONS

ER and MR fluids have the very attractive ability to undergo a

dramatic change in their viscosity, and thus their physical and

mechanical properties, in less than a millisecond through the

application of an electric or magnetic field, respectively. This

combination of a fast response time with a significant alteration of properties translates into a great capability for damping and other applications.

These smart fluids can be used in exercise equipment, valve,

braking and clutch systems, as well as in vibration control and

shock absorbing systems. Such systems can be used for

absorbing shock and vibrations in buildings, and damping

out vibrations in rotorcraft. One of the main advantages of

using these smart fluid components is that typically few or no

mechanical parts are necessary, and therefore can reduce the

complexity of a system.

An application that has been the subject of considerable

study is smart beams, which are structural components incorporating smart fluids. Smart beams have the ability to dampen out inherent vibrations within the structure or vibrations

resulting from external activity such as natural seismic activity.

This can assist in eliminating vibrations that could potentially

damage the structure. Smart beams modify their natural frequencies with the application of an electric field and thus their

damping properties.

The fundamentals of conventional shock absorbers have not

changed significantly since they were first introduced to automobiles, but there is a new system employing MR fluids and

is a major advancement in this technology. MR fluid shock

absorbers, deployed on some 2003 GM model automobiles,

provide a more stable and smooth ride by continuously varying their dampening rate. The new system is about 5 times

faster responding to road bumps than conventional shock

absorbing systems.

The US Army’s Manufacturing Technology Program has

sponsored the development of a finishing technique utilizing

MR fluids to polish precision optics.[9] This technique uses a

MR fluid with polishing abrasives added to the composition

and is known as Magnetorheological Finishing. The fluid’s

shape and stiffness can be adjusted and controlled in real time

through the precise application of a magnetic field that is governed by computer algorithms. This allows for the formation

of a pressure spot, which polishes any optical surface shape

(including spheres, aspheres, and flats). This technique can

reduce the typical cost of processing spherical optics by up to

40%, and can reduce system weight by 30%.[10]

A number of other MR and ER fluid applications are

already being developed. Some of these applications include

automobile passenger protection systems, prosthetics, and

dampers for washing machines.

SUMMARY

Decades of research have gone into

developing ER and MR fluid compositions suitable for military and commercial applications. Great advances have

been made and these “smart” materials

offer some of the most promising and

intriguing properties when compared to

other sensor and actuator materials.

MR and ER fluids are currently being

commercialized in automobile shock

absorbers. This application will

undoubtedly transform this fledgling

technology into a viable competitor in

the global marketplace. Although MR

fluids have recently taken the lead over

ER fluids in commercial development,

both types provide significant potential

for future applications. With further commercialization, usage

experience, and development, the knowledge of how to make

better ER and MR fluids and how to use them can only grow.

REFERENCES

[1] Electrorheological Fluids: Mechanisms, Properties,

Technology, and Applications, edited by R. Tao and G.D. Roy,

World Scientific Publishing Co. Pte. Ltd., New Jersey, 1994

[2] S. Ramamurthy, M.V. Gandhi, and B.S. Thompson, Smart

Materials for Army Structures, Quantum Consultants, Inc.,

Michigan 1992; DTIC Doc. AD-A300 215

[3] E. V. Korobko, “Some Aspects of Electrorheology,”

Advances in Intelligent Material Systems and Structures, Vol. 2:

Advances in Electrorheological Fluids, edited by M.A Kohudic,

Technomic Publishing Company, Inc., Pennsylvania, 1994,

pp. 16-29

[4] K.D. Weiss, J.D. Carlson, and J.P. Coulter, “Material

Aspects of Electrorheological Systems”, Advances in Intelligent

Material Systems and Structures, Vol. 2: Advances in Electrorheological Fluids, edited by M.A. Kohudic, Technomic

Table 2. Comparison of the Typical Properties of ER and MR Fluids[7, 8]

Property ER fluids MR fluids

Density (g/cm3) 1 – 2 3 – 4

Operable temperature range ( ̊C) 10 – 90 -40 – 150 (limited by carrier fluid)

Response time ~milliseconds < milliseconds

Power supply (typical) 2000 – 5000 V @ 1–10 mA 2 – 25 V @ 1 – 2 A (2-50 watts)

Maximum field ~4 kV/mm ~250 kA/m

Maximum energy density (J/cm3) 0.001 0.1

Plastic viscosity, ηp (Pa·s) 0.1 – 1.0 0.1 – 10

Maximum yield strength, τ2

y (kPa) 2 – 5 50 – 100

ηp/τ2

y (s/Pa) 10-8 – 10-10 10-10 – 10-11

Contaminants Cannot tolerate impurities Unaffected by most impurities

Figure 4. Cutaway of MR

Fluid-based Automobile

Shock Absorber. (Used

with Permission. Copyright

2003 Lord Corporation. All

rights reserved.)
The AMPTIAC Quarterly, Volume 7, Number 2 19

Publishing Company, Inc., Pennsylvania, 1994, pp. 30-52

[5] J.M. Ginder, L.D. Elie, L.C. Davis, “Magnetic Fluid-Based

Magnetorheological Fluids,” US Patent #5,549,837, 1996

[6] D.J. Carlson, “Aqueous Magnetorheological Material,” US

Patent #6,132,633, 2000

[7] M.R. Jolly, “Properties and Applications of Magnetorheological Fluids,” Mat. Res. Soc. Symp. Proc.: Materials for

Smart Systems III, Vol. 604, Materials Research Society, 2000,

pp. 167-176; DTIC Doc. AD-A381 141

[8] G. Yang, “Large Magnetorheological Fluid Damper for

Vibration Mitigation: Modeling, Testing, and Control,”

Department of Civil Engineering and Geological Sciences,

Notre Dame, December 2001. Available at http://cee.uiuc.

edu/sstl/gyang2/Ch2.pdf

[9] “Finishing Precision Optics,” Army Research Office,

http://www.aro.army.mil/arowash/rt/sbir/01ph3/qed.htm

[10] “Defense Honors Manufacturing Technology Achievements,” US Department of Defense, November 29, 2000,

http://www.defenselink.mil/news/Nov2000/b11292000_

bt712-00.html

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