It was some years ago when I first heard that expression – I’ve long

since forgotten where or when I heard it, so my apologies to its originator. It’s not an intuitive axiom, but with time and experience, I

have come to see the wisdom of it. This may seem an alien concept

to some, particularly in this country, where we pride ourselves on

being success-driven and intolerant of failure. It’s not too hard to

find quotes on the topic from numerous famous Americans, such as

Benjamin Franklin, George S. Patton, or even Donald Trump. My

own favorite quote follows:

“Failure is not an option” – these are the now-immortal words of

Gene Kranz, the flight director of the Apollo 13 moon mission,

when faced with the seemingly impossible task of bringing home

alive three astronauts before their dying spacecraft had completely

run out of power and the life-giving oxygen needed to sustain them.

Through this declaration, Kranz had laid down a challenge to the

hundreds of ground personnel supporting the mission: find a way.

Kranz’s team rose to the task; exceeding the constraints of design

and surpassing the limits of their own imaginations. The mission

was called “A Successful Failure,” in that while the primary mission

objective (landing on the moon) was not met, the greater goal of

returning the crew safely to the earth was, in spite of the odds. It was

the specter of failure (and all that it represented) that drove NASA

professionals to transcend conventional wisdom and practices to

bring the Apollo 13 crew home. However, while the basic philosophy of the Kranz doctrine is noble, it is not an accurate portrayal of

failure – at least not in an engineering sense. In fact, the term failure has many different and even conflicting connotations, depending largely on one’s perspective. It is this concept of failure and its

role in engineering design that I wish to examine further.

When it comes to any material or manmade structure, not only 

is failure not an option, it is an inevitability! The universe’s predisposition towards entropy (as stated by the second law of thermodynamics) can be a pesky and unforgiving master. It dictates that

highly-ordered matter (such as any industrially fabricated material)

degrades to lower-energy, more-disordered states. This is why metal

rusts, radioactive elements decay, and paper disintegrates – they are

all degrading to more fundamental (and functionally useless) base

states. Whether that degradation takes place in a fraction of a second or over eons, its ultimate outcome is the same – all materials are

predestined to fail given sufficient time.

As luck would have it, all three articles in this issue of the 

AMPTIAC Quarterly deal with one aspect of material failure or

another, thus some commentary on the topic seemed timely. At

present, there are over forty recognized mechanisms of material failure, ranging from the ordinary, like simple buckling or yielding to

more exotic mechanisms like radiation damage or selective leaching.

While nature dictates that failure cannot ultimately be avoided, it

can be delayed, deferred, or altered by sound design and material

selection practices. Understanding a system’s likely service environment allows engineers to identify potential failure mechanisms during the design cycle; and thus make the strategic material and design

decisions to prevent premature component failures and out-of-cycle 

sustainment activities. In this way, failure is not the antithesis of success, but a guidepost on the path to it. It is only by being mindful

of the limitations imposed by failure mechanisms on our palette of

material choices that we can design and build robust systems that

will reward the DOD’s acquisition investments with high rates of

readiness and maximal service lives.

Lastly, this issue marks another transition in the evolution of 

the Quarterly, as it represents a changing of the guard. As my

responsibilities in AMPTIAC have evolved, it is now time to pass

the mantle of the editor’s post to another member of our staff, 

Mr. Benjamin Craig. Ben has been a contributor to the Quarterly

for several years and has become a staple of the operation. I am 

confident he will bring new blood and fresh ideas to one of

AMPTIAC’s most successful enterprises. I would encourage all of

you to give Ben the same support and encouragement that you have

afforded me over these past several years.

My sincerest thanks,

Chris Grethlein

Deputy Director, AMPTIAC

Editorial: 

Failure is an Integral Part of Success

The AMPTIAC Quarterly is published by the Advanced Materials and Processes Technology Information Analysis

Center (AMPTIAC). AMPTIAC is a DOD-sponsored Information Analysis Center, administratively managed by

the Defense Technical Information Center (DTIC). Policy oversight is provided by the Office of the Secretary of

Defense, Director of Defense Research and Engineering (DDR&E). The AMPTIAC Quarterly is distributed to

more than 15,000 materials professionals around the world.

Inquiries about AMPTIAC capabilities, products, and services may be addressed to 

David H. Rose

Director, AMPTIAC

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We welcome your input! To submit your related articles, photos, notices, or ideas for future issues, please contact:

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About the cover: Sulfate reducing bacteria (SRB) often contribute to microbiologically influenced corrosion of metals.This type of bacteria forms biofilms (blue regions in the

image), and in this case caused the production of sulfide ions that bonded to metallic zinc to form zinc sulfide particles (green areas), which then aggregated to form spherical clumps (yellow spheres). Image reprinted with permission from “Formation of Sphalerite (ZnS) Deposits in Natural Biofilms of Sulfate-Reducing Bacteria,” M. Labrenz et.al.,

Science, Vol. 290, No. 5497, Dec. 2000, pp.1744-1747. ©Copyright 2000, AAAS.

Acknowledgement: The cover image was provided courtesy of Professor Jill Banfield, University of California Berkeley, Department of Earth and Planetary Sciences and

Department of Environmental Science, Policy, and Management, Berkeley, CA 94720-4767.
Table 1. Systems with Persistent Microbiologically Influenced Corrosion Problems[2].

Application/System

Pipelines/storage tanks

(water, wastewater, gas, oil)

Cooling systems

Docks, piers, and other 

aquatic structures

Vehicle fuel tanks

Power generation plants

Fire sprinkler systems

The AMPTIAC Quarterly, Volume 9, Number 1 3

Richard A. Lane

AMPTIAC

Rome, NY

INTRODUCTION

A renewed interest in corrosion prevention and control has

resulted in a major push within the DOD to help bring down

the Department’s enormous maintenance costs attributed to corrosion. Much of these rising costs can be directly attributed to

extending the useful life of systems well beyond their original

specifications. However, one type of corrosion that can produce

unexpected problems, premature failures, and costly repairs is

microbiologically influenced corrosion (MIC). Microorganisms

have long been known to influence corrosion, causing throughwall corrosion of piping and heat exchanger tubes 10-1000 times

faster than normal.[1] Effective prevention and control of MIC

involves an underlying knowledge of the microorganisms

responsible for increased corrosion rates as well as methods that

can be implemented to detect and prevent microbial growth.

MIC is not a form of corrosion, but rather is a process that 

can influence and even initiate corrosion. It can accelerate most

forms of corrosion; including uniform corrosion, pitting corrosion, crevice corrosion, galvanic corrosion, intergranular 

corrosion, dealloying, and stress corrosion cracking. In fact, if

unfamiliar with MIC, some corrosion problems may be 

misdiagnosed as conventional chloride-induced corrosion. One

prominent indicator of MIC is a higher rate of attack than one

would normally expect. MIC can affect numerous systems, and

can be found virtually anyplace where aqueous environments

exist. It is not exclusive to water-based systems, as it occurs in

fuel and lubrication systems as well. Table 1 lists applications

where MIC has been found to be prominent while Figure 1

shows one such location.

TYPES OF MICROORGANISMS

The types of microorganisms with species attributable to MIC

include algae, fungi, and bacteria.[3] Algae can be found in most

any aquatic environment ranging from freshwater to concentrated salt water. They produce oxygen in the presence of light (photosynthesis) and consume oxygen in darkness. The availability of

oxygen has been found to be a major factor in corrosion of metals in saltwater environments. Algae flourish in temperatures of

32 - 104°F and pH levels of 5.5 - 9.0. Fungi consist of mycelium structures, which are an outgrowth of a single cell or spore.

Mycelia are immobile, and can grow to reach macroscopic

dimensions. Fungi are most often found in soils, although some

species are capable of living in water environments. They metabolize organic matter, producing organic acids. 

Problem Components/Areas

• Stagnant areas in the interior

• Exterior of buried pipelines and tanks, 

especially in wet clay environments

• Cooling towers

• Heat exchangers

• Storage tanks

• Splash zone

• Just below low tide

• Stagnant areas

• Heat exchangers

• Condensers

• Stagnant areas

Microorganisms

• Aerobic and anaerobic acid producers

• Sulfate reducing bacteria

• Iron/manganese oxidizing bacteria

• Sulfur oxidizing bacteria

• Aerobic and anaerobic bacteria

• Metal oxidizing bacteria

• Slime forming bacteria

• Algae

• Fungi

• Sulfate reducing bacteria

• Fungi

• Aerobic and anaerobic bacteria

• Sulfate reducing bacteria

• Metal oxidizing bacteria

• Anaerobic bacteria

• Sulfate reducing bacteria
4 The AMPTIAC Quarterly, Volume 9, Number 1

Bacteria are generally classified by

their affinity to oxygen. Aerobic species

require oxygen to carry out their metabolic functions, while anaerobic species

do not live or metabolize in the presence

of oxygen. Facultative bacteria can grow

in either environment, although they

prefer aerobic conditions. Microaerophilic bacteria require low concentrations of oxygen. Oddly enough, aerobic and anaerobic organisms have often

been found to co-exist in the same location. This is because aerobic species

deplete the immediate surroundings of

oxygen creating an ideal environment

for anaerobes. Bacteria are further classified by shape into spherical (bacillus), rod (coccus), comma (vibrio), and filamentous

(myces) species. Figure 2 is an example of rod-shaped bacteria

observed using transmission electron microscopy.

Microorganisms in the planktonic state refer to those organisms floating freely in the aqueous environment or in air. They

can resist harsh chemicals

including acids, alcohols,

and disinfectants, and can

withstand drying, freezing, and boiling conditions.[6] Some spores

have the ability to last

hundreds of years and

then germinate once

favorable conditions exist.

Microorganisms in the

sessile state are those that

have attached themselves

to a surface and have developed a protective membrane, collectively called a biofilm. Microorganisms have the ability to reproduce quickly; some doubling in as little as 18 minutes. When left

untreated, they can rapidly colonize in stagnant aqueous environments, potentially introducing a highly active corrosion cell.

MICROORGANISMS THAT ACCELERATE CORROSION

Once a microorganism forms a biofilm on a material’s surface, a

microenvironment is created that is dramatically different from

the bulk surroundings. Changes in pH, dissolved oxygen, and

organic and inorganic compounds in the microenvironment can

lead to electrochemical reactions which increase corrosion rates.

Microorganisms may also produce hydrogen, which can cause

damage in metals. Most microorganisms form an extracellular

membrane which protects the organism from toxic chemicals

and allows nutrients to filter through.[6] Biofilms are resistant to

many chemicals by virtue of their protective membrane and ability to breakdown numerous compounds. They are significantly

more resistant to biocides (chemicals used to kill microorganisms) than planktonic organisms. Some bacteria even metabolize

corrosion inhibitors, such as aliphatic amines and nitrites,

decreasing the inhibitor’s ability to control corrosion.

Microorganisms’ metabolic reactions attributable to metallic

corrosion involve sulfide production, acid production, ammonia

production, metal deposition, and metal oxidation and reduction. Several groups of microorganisms have been attributed to

MIC, and are described briefly below.[7] Following these recognized forms, Table 2 then lists some specific microorganisms

within these categories, along with their characteristics.

Sulfate Reducing Bacteria

Sulfate reducing bacteria (SRB) are

anaerobic microorganisms that have

been found to be involved with numerous MIC problems affecting a variety of

systems and alloys. They can survive in

an aerobic environment for a period of

time until finding a compatible environment. SRB (see Figure 3) chemically

reduce sulfates to sulfides, producing

compounds such as hydrogen sulfide

(H2S), or iron sulfide (Fe2S) in the case

of ferrous metals. The most common

strains exist in the temperature range of

25 - 35°C, although there are some that

can function at temperatures of 60°C.

They can be detected through the presence of black precipitates in the liquid

media or surface deposits, as well as a

characteristic hydrogen sulfide smell.

Sulfur/Sulfide Oxidizing Bacteria

Sulfide oxidizing bacteria (SOB) are an aerobic species which

oxidize sulfide or elemental sulfur into sulfates. Some species

oxidize sulfur into sulfuric acid (H2SO4) leading to a highly

acidic (pH ≤ 1) microenvironment. The high acidity has been

associated with the degradation of coating materials in a number

of applications. They are primarily found in mineral deposits

and are common in wastewater systems. SRB are often found in

conjunction with SOB.

Iron/Manganese Oxidizing Bacteria

Iron and manganese oxidizing bacteria have been found in 

conjunction with MIC, and are typically located in corrosion

pits on steels. Some species are known to accumulate iron or

manganese compounds

resulting from the oxidation process. High concentrations of manganese

in biofilms have been

attributed to the corrosion of ferrous alloys,

including pitting of stainless steels in treated water

systems. Iron tubercles

have also been observed to

form as a result of the oxidation process (Figure 4).

Slime Forming Bacteria

Slime forming bacteria are aerobic organisms which develop

polysaccharide “slime” on the exterior of their cells. The slime

Figure 1. Interior of a

Ballast Tank on 

a Navy Ship[4].

Figure 2. Rod-Shaped Pseudomonas

Bacteria[5].

Figure 3. Biofilms (Blue)

Produced by SRB Cause 

the Formation of ZnS

(Green) and ZnS

Aggregates (Yellow) 

from Metallic Zinc.[8]

©2000 AAS. Reprinted 

with Permission.

Figure 4. Tubercles as a Result of MIC

(Courtesy of Metallurgical Technologies,

Inc.) [9].
The AMPTIAC Quarterly, Volume 9, Number 1 5

controls permeation of nutrients to the cells and may breakdown

various substances, including biocides. Slime formers have been

responsible for the decreased performance of heat exchangers as

well as clogging of fuel lines and filters. They can prevent oxygen from reaching the underlying metal surface, creating an

environment suitable for anaerobic organisms.

Organic Acid Producing Bacteria

Some anaerobic organisms also produce organic acids. These

bacteria are more apt to be found in closed systems including gas

transmission lines and sometimes closed water systems. 

Acid Producing Fungi

Some fungi produce organic acids which attack iron and aluminum alloys. Similar to slime formers, they can create environments suitable for anaerobic species. The widespread corrosion

problems observed in aluminum fuel tanks in aircraft have been

attributed to these organisms.

MIC IN METALS

Since MIC is a mechanism that accelerates corrosion, it should

be expected to occur more often in metal alloys with susceptibilities to the various forms of corrosion, and in environments 

conducive to biological activity. Metals used in the applications

listed in Table 1 include mild steels, stainless steels, copper

alloys, nickel alloys and titanium alloys. In general, mild steels

can exhibit everything from uniform corrosion to environmentally-assisted cracking, while the remaining alloys usually only

show localized forms. Mild steels, stainless steels, aluminum,

copper, and nickel alloys have all been shown to be susceptible

to MIC, while titanium alloys have been found to be virtually

resistant to MIC under ambient conditions. 

Mild Steels

MIC problems have been widely documented in piping systems,

storage tanks, cooling towers, and aquatic structures. Mild steels 

are widely used in these applications due to their low cost, but 

are some of the most readily corroded metals. Mild steels are 

Table 2. Common Microorganisms Found in Conjunction with Microbiologically Influenced Corrosion[10].

Genus or Species pH Temperature (°F) Oxygen Requirement Metals Affected Metabolic Process

Desulfovibrio 4-8 50-105 Anaerobic

Iron and steel, Use hydrogen in reducing

stainless steels, SO4

2- to S2- and H2S; 

aluminum, zinc, promote formation of 

copper alloys sulfide films

Desulfotomaculum 6-8 50-105 Anaerobic Iron and steel, Reduce SO4

2- to S2-

(some at 115-165) stainless steels and H2S

Desulfomonas - 50-105 Anaerobic Iron and steel Reduce SO4

2- to S2-

and H2S.

Acidithiobacillus 0.5-8 50-105 Aerobic Iron and steel, Oxidizes sulfur and sulfides 

thiooxidans copper alloys, to form H2SO4; damages 

concrete protective coatings

Acidithiobacillus 1-7 50-105 Aerobic Iron and steel Oxidizes ferrous (Fe2+) ions

ferrooxidans to ferric (Fe3+) ions

Gallionella 7-10 70-105 Aerobic Iron and steel, 

Oxidizes ferrous to ferric ions

and manganous (Mn2+) to 

stainless steels manganic (Mn3+) ions; 

promotes tubercule formation

Siderocapsa - - Microaerophilic Iron and Oxidizes iron carbon steel

Oxidizes ferrous to ferric 

Leptothrix 6.5-9 50-95 Aerobic Iron and steel ions and manganous to 

manganic ions

Oxidizes ferrous to ferric ions

Sphaerotilus 7-10 70-105 Aerobic Iron and steel, and manganous to manganic 

stainless steels ions; promotes tubercule 

formation

Sphaerotilus - - - Aluminum alloys - natans

Pseudomonas 4-9 70-105 Aerobic Iron and steel, Some strains reduce 

stainless steels Fe3+ to Fe2+

Pseudomonas 4-8 70-105 Aerobic Aluminum alloys - aeruginosa

Cladosporium 50-115 Produces organic acids when

resinae 3-7 (best at 85-95) - Aluminum alloys metabolizing certain fuel 

constituents Fungi Bacteria
6 The AMPTIAC Quarterly, Volume 9, Number 1

normally coated for corrosion protection, while cathodic protection may also be used for select applications. Galvanization (zinc

coating) is commonly used to protect steel in atmospheric environments. Bituminous coal tar and asphalt dip coatings are often used

on the exterior of buried pipelines and tanks, while polymeric coatings are used for atmospheric and water environments. However,

biofilms tend to form at flaws in the coating surfaces. Furthermore,

acid producing microorganisms have been found to dissolve zinc

and some polymeric coatings.[11] Numerous cases have also been

documented where microorganisms caused debonding of coatings

from the underlying metal. Delamination of the coating, in turn,

creates an ideal environment for further microbial growth.

Poor quality water systems and components with areas that

accumulate stagnant water and debris are prone to MIC. In

some extreme cases, untreated water left stagnant within mild

steel piping has caused uniform corrosion throughout the low

lying areas. This has been seen to occur in underground pipes

that have been left unused for periods of time.[11] Many power

plant piping failures have been found to be the result of introducing untreated water into a system. SRB has been the primary

culprit in such cases. A change to a more corrosion resistant

material is not always the most appropriate answer when it

comes to solving MIC problems. For example, an upgrade from

carbon steel to stainless steel in a nuclear power plant caused a

change in MIC problems, that in some instances were even more

severe. SRB has also been found in conjunction with underdeposit corrosion occurring in cooling towers. Wet soils containing

clay have played a major role in the occurrence of underground

MIC problems. Under such conditions, the exterior of underground piping and storage tanks have experienced coating

delamination and corrosion as a result of biofilm growth.

Stainless Steels

Stainless steels have suffered MIC problems under the same sets of

conditions as mild steels - primarily in situations where water

accumulates. There are two notable problems that have surfaced

with MIC of stainless steel. First, stainless steels corrode at an

accelerated rate, primarily through pitting or crevice corrosion,

which occurs in low lying areas, joints, and at corner locations.

This has been found to occur in tanks and piping systems that

were hydrotested* using well water, and then put in storage before

service without using biocides or drying the system to prevent

microbial growth.[11] In one particular case, a 304 stainless steel

pipeline for freshwater service, failed 15 months after being

hydrotested.[12] The second MIC problem discovered with stainless steels is that corrosion occurs adjacent to weldments.

Microorganisms readily attack areas around welds due to the inhomogeneous nature of the metal. In one case, perforation occurred

adjacent to a welded seam in a 0.2 inch diameter 316L stainless

steel pipe after being in service for four months under intermittent

flow conditions.[13] Stainless steels containing 6% molybdenum

or greater, have been found to be virtually resistant to MIC.[11]

Aluminum Alloys

The major applications where MIC has attacked aluminum

alloys have been in fuel storage tanks and aircraft fuel tanks. [11]

MIC problems typically occur in the low-lying areas of the

tanks and at water-fuel interfaces. Contaminants in fuels, such

as surfactants and water soluble salts, have largely contributed

to the formation of biofilms in these systems. Fungi and bacteria have been found to be the main culprits. Corrosion of

aircraft fuel tanks has been widely attributed to Cladosporium

resinae, a fungus. Its presence decreases the pH to approximately 3-4, which can harm the protective coatings and

underlying metal. The pseudomonas aeruginosa species is also

known to be connected with MIC of aluminum fuel tanks.

Additionally, heavy fungal growth on interior surfaces of helicopters has occurred after undergoing depot maintenance.[14]

Fungal growth had been reported in passenger areas of the H-53

helicopter before being returned to field use and as a result it was

slated for cleaning. Fungi could be found on virtually all interior surfaces of the helicopter. The surfaces were cleaned with

100% isopropanol, treated with a biocide, and followed by

application of a corrosion preventive compound. The procedure

removed most of the microorganisms present and was effective

at killing spores. However, some biofilms remained, which rapidly reproduced before the aircraft was even returned to service. 

Copper Alloys

Copper alloys find use in seawater piping systems and heat

exchangers, which are susceptible to MIC. Microbial products

that can be harmful to copper alloys include carbon dioxide

(CO2), hydrogen sulfide (H2S), ammonia (NH3), organic and

inorganic acids, and other sulfides.[11] MIC observed in copper alloys includes pitting corrosion, dealloying and stress corrosion cracking. Higher alloying content in copper usually

results in a lower corrosion resistance. Although MIC has been

found in both, more problems have been documented with

70/30 than with 90/10 Cu/Ni alloys. MIC has also been documented in Admiralty brass (Cu-30Zn-1Sn), aluminum brass

(Cu-20Zn-2Al), and aluminum bronze (Cu-7Al-2.5Fe).

Ammonia and sulfides have gained considerable attention as

compounds that are corrosive to copper alloys. Admiralty brass

tubes have been found to suffer stress corrosion cracking in the

presence of ammonia. Seawater that is high in sulfide content,

has caused pitting and stress corrosion cracking in copper

alloys. SRB has also been known to attack copper alloys causing dealloying of nickel or zinc in some cases.

Nickel Alloys

Nickel alloys are often used for applications subject to high

velocity water environments, including evaporators, heat

exchangers, pumps, valves, and turbine blades, as they generally have a higher resistance to erosive wear than copper

alloys.[11] However, some nickel alloys are susceptible to pitting and crevice corrosion under stagnant water conditions, so

that downtime and static periods can lead to potential MIC

problems. Monel 400 (66.5Ni-31.5Cu-1.25Fe) has been found

to be susceptible to underdeposit MIC. Pitting corrosion, intergranular corrosion, and dealloying of nickel have all been

observed with this alloy in the presence of SRB. Ni-Cr alloys

have been found to be generally resistant to MIC.

MONITORING/DETECTION METHODS

Early detection of potential MIC is crucial to the prevention 

of equipment failure and extensive maintenance. The most 
The AMPTIAC Quarterly, Volume 9, Number 1 7

common detection methods involve sampling bulk liquids from

within the system and monitoring physical, chemical, and biological characteristics. The goal is to identify favorable conditions for biofilm formation and growth, so that the internal

environment may be adjusted appropriately. Visual inspections

of accessible areas should also be performed on a routine basis.

Additional methods that may be utilized include coupon monitoring, electrochemical sensor and biosensor techniques.

Monitoring equipment is available for

measuring a number

of properties of the

bulk system. A common practice has been

to directly monitor

temperature, pH, conductivity, and total

dissolved solids, while

taking samples to 

evaluate (by portable

or laboratory testing

methods) dissolved

gases and bacteria counts, and to identify bacteria.[2] Bacteria

counting, via cultured growth, may be helpful, but strict conditions must be set to produce meaningful results. The most

important factor in bacterial counts is observing changes in

trends rather than in actual numbers. Consistency is crucial

where deviations in sample location, temperature, growing

media, growth time, and even changes in technicians can affect

the results. A strict schedule must also be maintained. Changes

in bacteria counts are used to adjust biocide usage, and may

also be indicative of biofilm growth in the case of differences

in counts across a system. Bacteria cultures can also be used to

identify specific species present (Figure 5). Direct bacteria

counts can be performed using a microscope to inspect bacteria which have been placed onto a slide and may also be stained

for viewing, as shown in Figure 6. Visual inspections should be

performed on exposed surfaces where algae and fungal growth

can occur and on surfaces exposed during maintenance procedures. The presence of SRB can be detected by observing black

particles in the liquid media and/or deposited on surfaces (a

result of iron sulfide and/or copper sulfide formation), or by a

distinct hydrogen sulfide odor.[17] Fluorescent dyes can be

used to enhance visual detection, as biofilms absorb some of

the dye, whereby an ultraviolet light is then used to expose the

microorganisms.

Coupons have been found to be quite useful in detecting

MIC, especially when used in conjunction with additional monitoring techniques. Coupons are small metal samples placed

within the system and periodically extracted to measure corrosion rates by a weight loss method and possibly to collect

microorganisms from biofilms present on the coupon for identification. Proper placement of the coupons within the system

plays a key role in MIC monitoring and detection. Coupons

should be placed in locations where MIC is likely to occur.

Electrochemical sensing techniques, such as electrical impedance

spectroscopy and electrochemical noise, are other means of

detecting MIC. Electrochemical sensors detect characteristics of

corrosion reactions, such as changes in electrical conductivity. As

with coupons, strategic placement of the sensors in the systems

is crucial to detecting MIC.

One type of sensor designed specifically for biofilm detection

uses a probe that attracts microbial growth.[1] Utilizing knowledge of the electrochemical conditions under which biofilms

occur, probes have been developed that replicate these preferred

conditions. The sensor then alerts operators when biofilm activity is present. Sensors should ideally be placed in areas where

biofilm growth is more likely. Another method that may be used

specifically to detect microorganisms in water systems is the use

of fluorogenic bioreporters.[18] These are compounds (dyes)

that experience a change in their fluorescence upon interaction

with microorganisms. Activity is determined by the ratio of 

fluorescence of the reacted dye, extracted from the system or

measured in-service, to the unreacted dye. The ratio increases

with biological activity and can be used to effectively regulate the

use of biocides. This method however, does not distinguish

between planktonic and sessile organisms. Thus, problems could

be growing in the system without being detected.

MITIGATION METHODS

Clearly, the best way to prevent MIC is to prevent the growth

of biofilms altogether. Once a biofilm has formed, it is more

resistant to biocides, and can rapidly grow if not completely

removed. The emphasis is placed on cleanliness and incorporating established corrosion prevention and control techniques for

the various metals and forms of corrosion. Monitoring and

detection of microorganisms will effectively guide preventive

maintenance procedures.

Maintaining the cleanliness of systems involves monitoring

the quality of water, fuel, or lubricants present in the system.

This includes water content in fuel and lubrication systems.

Water content should be monitored and removed when it

becomes too high. All fluids should be monitored for solid 

particles and filtered to prevent particle contamination. Contaminants increase the likelihood of biofilms, as they can sometimes be used as nutrients. Bacterial counts and biosensing provide information that can help adjust the level of biocides

introduced to the system to an optimal concentration. Biocides

are widely used and are effective at killing planktonic microorganisms. The cost of biocides is significant however, and they

are also quite toxic. Effectively managing their use can reduce

costs and minimize the damaging effects on the environment.

Figure 6. Inspection of Bacteria on a Stained Microscope Slide[16].

Figure 5. Bacteria Culture[15].
8 The AMPTIAC Quarterly, Volume 9, Number 1

Preventive maintenance also includes scheduled cleaning of

exterior components where any debris accumulation has

occurred. Non-abrasive cleaning methods are preferred so as to

not damage coatings. Inspection/cleaning should also be performed on normally inaccessible components that are exposed

during maintenance and repair activities. Designing systems

that minimize MIC prone areas and providing accessibility for

maintenance helps to promote system cleanliness. This involves

eliminating stagnant and low-flow areas, minimizing crevices

and welds, incorporating filtration, drains, and access ports for

treatments, monitoring/sampling, and cleaning.

Established corrosion prevention and control methods that

are employed to protect metals from the various forms of corrosion will also help mitigate MIC. This includes designing systems to minimize stagnant water conditions, proper base material and coating selection, cathodic protection, sealing crevices

and around fasteners, using gaskets to minimize galvanic corrosion, proper heat treatments, and post weld treatments. For

underground structures, providing ample drainage by backfilling

with gravel or sand will help prevent MIC. In some cases, a

change to an alternate material such as PVC piping has greatly

reduced underground pipeline corrosion problems. Coatings can

be formulated with biocides, though such coatings are not generally used on the interior of systems. Smooth surface finishes

with minimized defects are preferred. Research into alternative

coatings that may deter MIC has shown polydimethylsiloxane

coated 4340 steel to have favorable results.[19] The silicone

compounds significantly reduced MIC of the steel in a 0.6M

NaCl solution over a two year period. 

SUMMARY

The prevention and control of MIC may seem like a daunting

task. However, with knowledge of how and where MIC occurs,

as well as the prevention and control methods that may be used,

a majority of problems can be prevented. Maintaining the

cleanliness of systems is the best method to prevent MIC. Once

biofilms have established themselves, it is difficult to get rid of

the bacteria entirely. There is a need to implement a better

means of destroying biofilms and also to develop environmentally friendly biocides. It is virtually impossible for

designers/maintainers to stay abreast of all the technologies and

methods used in corrosion prevention and control, so outside

professional assistance is usually required. To optimize MIC

prevention and control, subject matter experts should be consulted when designing new systems where MIC has traditionally been prominent, for setting up preventive maintenance procedures for new systems, and for other related problems as they

arise. Ideally, all problems should be thoroughly documented

and entered in an information system for effective use in

designing future systems.

NOTES & REFERENCES 

Picture on Article Title Page: NASA Astrobiology Academy,

Ames Research Center, (http://academy.arc.nasa.gov/2003/

mirpics.htm)

* Hydrotesting is used to check system integrity subsequent to

manufacture. A system is filled with water and pressurized to

check for leaks, especially around weldments.

[1] G.J. Licina and G. Nekoksa, An Innovative Method for Rapid

Detection of Microbiologically Influenced Corrosion, Tri-Service

Conference on Corrosion, 1994, pp. 217-228. DTIC Doc: ADA331161

[2] P.J.B. Scott, Part 1 Expert Consensus on MIC: Prevention and

Monitoring, Materials Performance, Vol. 43, No. 3, NACE

International, March 2003

[3] B.J. Little, P.A. Wagner, and F. Mansfield, Microbiologically

Influenced Corrosion, NACE International, 1997

[4] Carderock Division, Naval Surface Warfare Center Website,

(www.dt.navy.mil/.../fun-mat/pai-pro-bra/pre)

[5] R.K. Pope, T.L. Daulton, R.I. Ray, and B.J. Little,

Adaptation of Environmental Transmission Electron Microscopy

(ETEM) and Electron Energy Loss Spectrometry (EELS) for Studies

of Microbiologically Influenced Corrosion, Microscopy and

Microanalysis, August 2000, (http://www7430.nrlssc.navy.

mil/facilities/emf/abstr2000a.pdf)

[6] D.H. Pope, D.J. Duquette, A.H. Johannes, and P.C. Wayner,

Microbiologically Influenced Corrosion of Industrial Alloys,

Materials Performance, NACE International, Vol. 23, No. 4,

April 1984

[7] Corrosion Doctors Website (http://www.corrosion-doctors.

org/Microbial/Frames.htm)

[8] M. Labrenz et. al., Science, Vol. 290, No. 5497, Dec. 2000,

pp. 1744-1747, www.sciencemag.org

[9] Metallurgical Technologies, Inc. (http://www.met-tech.com/

corrosion.htm)

[10] S.C. Dexter, Microbiologically Influenced Corrosion,

Corrosion: Fundamentals, Testing, and Protection, ASM

International, Vol. 13A, 2003, pp. 398-416

[11] B. Little, P. Wagner, and F. Mansfield, Microbiologically

Influenced Corrosion of Metals and Alloys, International Materials

Reviews, The Institute of Metals and ASM International, Vol.

36, No. 6, 1991

[12] W. Shin and J.W. McEnerney, EPRI Workshop on MIC,

Structural Integrity Association, 1986

[13] Y. Chung, H.J. Mantle, and G.E. Lasko, International

Conference on Microbially Influenced Corrosion, NACE

International, 1995, pp. 13-1 – 13-13

[14] B.J. Little, R.I. Ray, and J.S. Lee, An Overview of Microbiologically Influenced Corrosion in Aircraft, Naval Research

Laboratory, 1997. DTIC Doc: AD-A413907

[15] Edgewood Chemical Biological Center Website,

(http://www.edgewood.army.mil/images/bl3_petri_dish.jpg) 

[16] U.S. Army, (www.dewitt.wramc.amedd.army.mil/depart

ments_n...), (http://www.dcss.cs.amedd.army.mil/field/FLIP

30/tut/Tutorial/Micr_tut/Micr_tut_pages/GPR/Morph_

choice.htm)

[17] J.M. Jones, and B. Little, USS Princeton (CG 59):

Microbiologically Influenced Corrosion and Macrofouling

Status of Seawater Piping Systems, Naval Surface Warfare

Center, June 1990. DTIC Doc: AD-A231 251

[18] M. Chattaraj, M.J. Fehr, S.R. Hatch, and E.J. Allain,

Online Measurement and Control of Microbiological Activity in

Industrial Water Systems, Materials Performance, NACE International, Vol. 41, No. 4, April 2002

[19] P.M Natishan, J. Jones-Meehan, G.I. Loeb, N. Gray, B.J

Little, R. Ray, and M. Beard, Inhibition of Microbiologically

Influenced Corrosion, Tri-Service Conference on Corrosion,

November, 1997. DTIC Doc: AD-A336906
The AMPTIAC Quarterly, Volume 9, Number 1 9

Material EASE

Material Failure Modes, Part I

A Brief Tutorial on Fracture, Ductile Failure, Elastic Deformation, Creep, and Fatigue

Benjamin D. Craig

AMPTIAC

Rome, NY

29AMPTIAC

What do design engineers and failure analysis experts have in

common? Answer: material failure. These two groups are the

bookends to a material’s life. While materials selection is sometimes left up to a bona fide materials engineer, designers are typically responsible for determining what environments and operating conditions a component will encounter during service. In

many cases designers are also responsible for performing the

task of materials selection. This combined role essentially determines the fate of a material and quite possibly the system.

Failure analysis specialists explore the questions of how and why

a particular system, and more precisely, a material failed. To

preclude failure the designer should consider the questions of

when and how the system, and more specifically, the material

will fail. The first step toward preventing failure is understanding how it might occur.

If a material were resistant to all failure modes in all environments, a system or component could theoretically have an

infinitely long life. Unfortunately, all materials are susceptible

to failure. Even the best engineered materials are prone to failure given a sufficiently harsh service environment, or if they are

poor choices for a specific application. Furthermore, there are a

number of mechanisms and combinations of mechanisms that

cause materials to fail. The goal of the design engineer is to

cost-effectively design a system that operates at its maximum

efficiency for the longest possible period of time without having

to be replaced or overhauled. To meet this goal it is important

for the designer to be aware and have a certain level of understanding about how materials can fail.

The intent of this article is to provide an educational reference for designers and other engineers on the common modes of

material failure. Understanding potential failure modes in the

early stages of system design can lead to a more appropriate

selection of materials, prevent premature system failure and possibly lengthen system life; ultimately resulting in increased safety in some cases and reduced cost of ownership.

INTRODUCTION TO FAILURE

The failure of a material is not restricted to fracture or total 

disintegration; it can also consist of a change in shape, loss of

material or the alteration of mechanical properties. When a

material becomes unable to execute the function that it was originally intended or designed to perform, it has failed.

Environmental conditions and operating loads are often the

primary causes leading to a material’s failure. Examples of harsh

environments that commonly induce failure include corrosive,

high temperature, and high energy environments. Stress, impact,

and frictional loading are examples of operating conditions that

frequently cause a material failure. Combinations of harsh environments and mechanical loads often lead to a more rapid material wearout and failure.

There are several failure prevention methods that can be

employed, but often the first critical step is to properly select the

material or material system that will be used to construct the

given system component. Further prevention measures (e.g. protective coatings, cold working, etc.) can be implemented depending on the application, the conditions found in the operational

environment, mechanical loading, and the failure modes that

the selected material is traditionally susceptible to in a given system configuration. The rest of this article is devoted to providing

a background on the most common material failure modes.

FAILURE MODES

There are more than twenty different recognizable ways a material can fail, including the most common forms: fracture,

fatigue, wear, and corrosion.[1] Each of these and other common

failure modes are described briefly in the following sections or

will be featured in the next two issues of MaterialEASE.

Brittle Fracture

Brittle fracture occurs when mechanical loads exceed a material’s ultimate tensile strength causing it to fracture into two or

This issue of MaterialEASE is Part One of a three part series on material failure modes. It introduces the concept of material 

failure and covers a number of failure modes, including brittle and ductile failure, elastic distortion, creep, and fatigue.

Future MaterialEASE articles will cover other important failure modes including impact, wear, thermal shock and corrosion.

This series will make a valuable desk reference for any professional making material selection and design decisions. - Editor
10 The AMPTIAC Quarterly, Volume 9, Number 1

Material EASE

more parts without undergoing any significant plastic deformation or strain failure. Material characteristics and defects such

as notches, voids, inclusions, cracks, and residual stresses are

the typical initiation points for the formation of a crack leading

to brittle fracture (Figure 1). Once the crack is initiated the

material will undergo catastrophic failure fairly quickly under a

sustained load. There is little energy absorbed (compared to ductile fracture) during the brittle fracture process. This failure

mode commonly occurs in brittle materials such as ceramics

and hard metals.

Eliminating or minimizing surface and internal material

defects is an important method in improving a material’s resistance to brittle fracture. Many of these defects originate during

material fabrication or processing steps. Therefore, it is important to give these early stages in the life cycle proper attention in

order to reduce the material’s susceptibility to brittle fracture.

Fabricating a part with a smooth surface is also important in preventing brittle fracture. For instance, sharp textures and notches

on the surface of the material can initiate brittle fracture. Careful

handling of the material after it’s produced will also help to prevent unnecessary mechanical damage such as scratches and

gouges, which can ultimately lead to brittle fracture. Finally, an

appropriate materials selection process to choose a suitable

material for the intended application is important in ensuring

that it will be capable of handling the applied mechanical loads.

Ductile Failure

Ductile materials that are subjected to a tensile or shear stress will

elastically or plastically strain to accommodate the load and

absorb the energy. Yielding occurs when the material’s yield

strength is exceeded and can no longer return to its original shape

and size. This is followed by ductile fracture which occurs when

the deformation processes can no longer sustain the applied load.

Both of these failure modes are described in more detail below.

Figure 1. Brittle

Fracture Surface of

a High-Strength

Chain. Fracture

Began in a Small

Crack Resulting

from a Heat

Treating Problem

(Photo Courtesy of

Sachs, Salvaterra

& Associates, Inc.).

Figure 2. Yielding

Failure of UH-1

Helicopter Engine

Shaft and Bearing

Components[2].

Figure 3. (a) Ductile Fracture of 2 1/2 Inch Hose Fitting (b) Close-up of the Deformed Region Where a Pin Joining the “Ears” Became

Free from the One on the Right Causing the Deformation and Fracture of the One on the Left (Photos Courtesy of Sachs, Salvaterra 

& Associates, Inc.).

a b
The AMPTIAC Quarterly, Volume 9, Number 1 11

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

Yielding

Yielding failure (also known as gross plastic deformation) occurs

when a material subject to mechanical loading exhibits sufficient

plastic deformation such that it can no longer perform its intended function. This mode of failure results in deflected, stretched, or

otherwise misshapen components, and is typical in ductile materials such as metals and polymers. Ceramics and very hard metals

are inherently brittle materials and therefore yielding is not a significant concern. An example of this type of failure is often

observed in ductile materials subjected to a tensile stress. These

malleable materials tend to absorb the applied load by undergoing plastic deformation, which causes an elongation of the material. Yield strength is a measurement of a material’s resistance to

yielding failure, and it denotes the stress at which the material

begins to exhibit a disproportionate increase in strain with

increasing stress. Figure 2 shows a picture of several misshapen

helicopter components that experienced yielding failure.

Ductile Fracture

A failure mode that is somewhat opposite in nature to brittle fracture is ductile fracture. Ductile fracture occurs when a material

experiences substantial plastic deformation or strain while being

stressed beyond its yield strength and is consequently torn in two

pieces. An extensive amount of energy is absorbed during the

deformation process. Similar to brittle fracture, however, cracks

are typically nucleated at material defects, such as voids and

inclusions. As ductile materials experience plastic deformation,

existing voids coalesce to form the crack tip. The actual crack

propagation process in ductile fracture is generally a slow process

with the crack growing at a very moderate rate as voids coalesce

at the fracture surface. An obvious but important consideration is

that this type of failure is common in ductile materials, typically

metals and polymers.

Failures attributed only to ductile fracture are not common,

but rather this mechanism is typically a contributing factor in

the overall material failure. When a material does fail due to

ductile fracture it is most likely because the stress exceeded the

material’s strength limits. This indicates that the material chosen during design did not meet the performance requirements,

the loads applied were more than what was predicted, the material was improperly or poorly fabricated, or defective raw materials

were used for component fabrication.[3] Figure 3 shows pictures

of a component that failed by ductile fracture.

The best method for preventing a part from failing due to

ductile fracture is to perform proper materials selection during

the design stages of a system. In addition, appropriate quality

control procedures should be in place for producing the materials in order to reduce the number of defects. An appropriate

materials selection process will ensure that the operating loads

imposed as stresses on the chosen material will not exceed its

mechanical limits. However, design errors such as inaccurately

predicting mechanical loads have been known to occur. Underestimating a load for instance, could lead to ductile fracture.

Buckling

Buckling occurs when a material subjected to compressive or torsional stresses can no longer support the load, and it consequently fails by bulging, bending, bowing or forming a kink or other

unnatural characteristic. Bars, tubes, and columns are shapes

that are commonly susceptible to failure by buckling. In addition, I-beams and other more complex geometries may experience buckling under compressive or torsional loads. Strength and

hardness properties do not indicate a material’s susceptibility to

buckling. Buckling is dependent on the shape and respective

dimensions of the material as well as the modulus of elasticity,

which is dependent on temperature. Therefore, buckling is more

likely to occur at higher temperatures where the modulus of elasticity is lower, since materials have a tendency to soften when

they are heated. Figure 4 (a) shows a picture of a cylindrical

metal component after buckling under compressive stress, and

(b) a picture of a cylindrical aircraft component that failed by

torsional buckling.

Elastic Distortion

A material can fail without being permanently changed when it

is elastically deformed to such an extent that it fails to perform

its intended function. Elastic deformation occurs when a material is subjected to a load that does not exceed its yield strength.

This non-permanent distortion can cause the material, for 

example, to obstruct another component in a system resulting in

failure. Elastic distortion can be induced by a load and affected

by a change in temperature. For example, a material’s elastic

modulus is temperature dependent, and if an unanticipated 

temperature change occurs the material may undergo elastic

deformation at a smaller load than it would at the normal operating temperature. Selection of a material with a sufficiently

high modulus to withstand loads without experiencing elastic

deformation can prevent this type of failure from occurring, 

Figure 4. (a) Compressive Buckling Failure of Metal Cylinder, 

(b) Torsional Buckling Failure of an F-18 Engine Shaft[2].

a b
12 The AMPTIAC Quarterly, Volume 9, Number 1

Material EASE

especially if there is an unanticipated temperature change.

Control over operating conditions so that the material does not

observe load or temperature changes that would compromise its

ability to withstand elastic deformation will also help prevent this

type of failure from occurring.

Creep

Creep is a time-dependent process where a material under an

applied stress exhibits a dimensional change. The process is also

temperature-dependent since the creep or dimensional change

that occurs under an applied stress increases considerably as

temperature increases. A material experiences creep failure when

the dimensional change renders the material useless in performing its intended function. Sufficient strain or creep can result in

fracture, known as stress rupture, which is discussed briefly in a

subsequent section. Figure 5 shows the time-dependent nature of

creep failure.

Creep occurs when vacancies in the material’s microstructure

migrate toward grain boundaries that are oriented normal to the

direction of the applied stress. As this happens atomic diffusion

occurs in the opposite direction to fill the voids, resulting in an

elongation of the grain in the direction parallel to the applied

stress. Other mechanisms of creep include those where vacancies

migrate along grain boundaries, dislocations move to accommodate the applied stress in the form of strain, and adjacent grains

slide along their common grain boundary also to accommodate

the applied stress.[5]

Materials experience thermally activated creep at different

temperatures. For example, some materials, such as nickel-based

superalloys, are susceptible to creep at relatively high temperatures (e.g. 1000 - 1200 ̊C), while others, such as polymers or 

tin-lead solder, can be susceptible to creep at much lower temperatures (e.g. 25 ̊C). Generally, creep should be a consideration

when a material is operating at a temperature that is greater

than 0.3Tm, where Tm is the material’s absolute melting temperature. At 0.5Tm creep is very much a concern.[5]

Creep can occur in ceramics at temperatures above 0.4 to

0.5Tm, although it is much more common in metals and polymers.[6] Ceramics have a very high resistance to deformation by

creep partly because of their characteristically high melting temperatures. However, at extremely high temperatures ceramics can

exhibit a considerable amount of creep.

To prevent failure due to creep deformation it is very important to know the operating conditions of the system when selecting materials for an application. Creep has been a particular

problem for turbine engine blades since they experience a sustained stress over time at a relatively high temperature. As a

result, materials with high melting temperatures are often selected for such an application. Furthermore, it is important to ensure

quality material fabrication and processing in order to reduce

material defects and voids.

Creep Buckling

Creep buckling is a failure mode that occurs when the creep

process renders a material unable to support loads it could otherwise handle, and as a result the material buckles.

Stress Rupture

Stress rupture, also known as creep fracture, is a mechanism that

is closely related to creep except that the material eventually

fractures under the applied load. As discussed in the previous section, creep is the time- and temperature-dependent elongation of

a material that is subjected to a stress. When this stress overcomes the material’s ability to strain, it will rupture. Cracking

that precedes the rupture of the material can be either transgranular or intergranular*.

Thermal Relaxation

Thermal relaxation is a process related to the temperaturedependent creep failure mode. Failure by thermal relaxation

commonly occurs in fastener materials or other materials that

are prestressed such that they could support a greater load than

their non-prestressed counterpart. As the material undergoes

creep at high temperatures their residual stresses are relieved

which may render the material unable to support the given

load.

Figure 5. Creep and Rupture Data for 4130 Steel at 1000 ̊F[4].

Applied

Strain

0.1 1 10 100 1000

50

45

40

35

30

25

20

15

Time (hours)

Stress (ksi)

1000°F

28% - Rupture

Occurs

0.5% 1%

2% 5%

0.5%

1%

2%

5%

28%
The AMPTIAC Quarterly, Volume 9, Number 1 13

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

Fatigue

Fatigue is an extremely common failure mode and deserves considerable attention because it can inflict damage on a material at

a stress level that is far less than the material’s design limit.

Fatigue has been attributed with playing a role in approximately

90% of all material structural failures.[6]

A material that fractures into two or more pieces after being

subjected to a cyclic stress (fluctuating load) over a period of

time is considered to have failed by fatigue. The maximum value

of the cyclic stress (stress amplitude) for fatigue failure is less

than the material’s ultimate tensile strength. It is often the case

that the maximum value of the cyclic stress is so low that if it

were applied at a constant level the material would be able to easily support the load without incurring any damage. Cyclic loads

cause the initiation and growth of a crack, and ultimately, when

the crack is significant enough such that the material can no

longer support the load, the material fractures.

The fatigue failure mechanism involves three stages: crack

initiation, crack propagation, and material rupture. Similar to

both ductile and brittle fracture, fatigue cracks are often initiated by material inhomogeneities, such as notches, grooves, surface discontinuities, flaws, and other material defects.[7] These

inhomogeneities or initiation points act as stress raisers where

the applied stress concentrates until it exceeds the local strength

of the material and produces a crack. The best way to prevent

fatigue failure is to keep fatigue cracks from initiating, which

can be accomplished by removing or minimizing crack initiators,

or by minimizing the stress amplitude. Once fatigue cracks have

been initiated they will seek out the easiest or weakest path to

propagate through the material. Therefore, minimizing the

number of internal material defects, such as voids and inclusions, will increase the time it takes a crack to propagate. Finally,

when the crack has weakened the material to a point such that it

can no longer support the applied load it will rupture, which can

occur by shear or by tension.[7]

Fatigue is not so much dependent on time as it is the number

of cycles. A cycle consists of an applied stress being increased

from a starting value (in some cases, zero or even negative) up to

a maximum positive value (material loaded in positive direction)

and then decreasing past the starting point down to a minimum

value (in some cases this is a maximum negative loading), and

finally back up to the starting value. This cycle is illustrated in

Figure 6, where there is positive and negative loading. However,

negative loading is not required for fatigue to occur; rather, it

can be a fluctuating positive load. Moreover, the stress cycles do

not need to be symmetric, but can be randomly changing. In

general, ferrous, or iron alloy, materials do have a fatigue

(endurance) limit (SL

), which is the stress level (amplitude)

under which no failure will occur regardless of the number of

Figure 6. Fatigue Loading Cycle. Figure 7. S/N Curves for Ferrous and Non-Ferrous Metals[8].

Figure 8. Torsional Low-Cycle Fatigue Fracture of a Shaft. (Photo

Courtesy of Sachs, Salvaterra & Associates, Inc.)

Stress Amplitude

Ferrous Metals

Non-Ferrous Metals

1 Cycle

Cycles to Failure (Nf

)

104 105 106 107 108

Stress

Stress Amplitude (S)

Time

(+)

(-)

SL
The AMPTIAC Quarterly, Volume 9, Number 1

cycles. On the other hand, by increasing the stress amplitude, the

fatigue failure will commence after a smaller number of cycles.

Non-ferrous alloys, such as aluminum and titanium, do not have

a fatigue limit. This concept is demonstrated in Figure 7.

Metals and polymers are typically susceptible to fatigue failure, while ceramics tend to be resistant. There are several different types of fatigue including high-cycle fatigue, low-cycle

fatigue, thermal fatigue, surface fatigue, impact fatigue, corrosion fatigue, and fretting fatigue. Each of these will be discussed

in some detail in the following sections.

High-Cycle Fatigue

High-cycle fatigue is defined as fatigue where the material is subjected to a relatively large number of cycles before failure occurs.

Generally, for the fatigue mechanism to be considered high-cycle

fatigue the number of cycles required to produce failure is greater

than 10,000. The deformation exhibited by a material subjected

to high-cycle fatigue is typically elastic.

Low-Cycle Fatigue

A fatigue failure that occurs after a relatively small number of

cycles is considered to be low-cycle fatigue. Typically, when a

material fails due to fatigue after less than 10,000 cycles, it is

considered to be low-cycle fatigue. The mechanisms of crack

growth for materials experiencing low-cycle fatigue are similar

to the crack growth of a material subjected to a constant stress.

The deformation exhibited by a material subjected to low-cycle

fatigue is typically plastic (Figure 8). Since the plastic strains in

low-cycle fatigue are usually greater than in high-cycle fatigue,

the surface defects of the material are not as important as the

bulk material properties.[9]

Thermal Fatigue

Simple temperature fluctuations or repeated heating and cooling

can impose stresses on a material leading to fatigue damage and

potentially failure. Materials generally exhibit a dimensional

change or strain to some extent in response to temperature

changes. This response can be significant in some materials,

especially metals, and can induce thermal stresses on the material if it is mechanically confined in some way. When a material is

exposed to conditions of fluctuating temperatures it can cause

cyclic fatigue loading, which can result in crack growth and possibly fracture. This process is referred to as thermal fatigue.

Mechanical loading is not required for thermal fatigue to occur,

and this failure mode is different from fatigue under 

fluctuating stress at high temperature. If there is a temperature

gradient within the material that is exposed to fluctuating temperatures, it may experience thermal fatigue since different 

Material EASE

14

Table 1. Methods for Reducing or Eliminating Fretting Fatigue[10].

Principle of Abatement or Mitigation Practical Method

Reduction in surface shear forces • Reduction in surface normal forces

• Reduction in coefficient of friction with coating or lubricant

Reduction/elimination of stress concentrations • Large radii

• Material removal (grooving)

• Compliant spacers

Introduction of surface compressive stress • Shot or bead blasting

• Interference fit

• Nitriding/heat treatment

Elimination of relative motion • Increase in surface normal load

• Increase in coefficient of friction

Separation of surfaces • Rigid spacers

• Coatings

• Compliant spacers

Elimination of fretting condition • Drive oscillatory bearing

• Remove material from fretting contact (pin joints)

• Separation of surfaces (compliant spacers)

Improved wear resistance • Surface hardening

• Ion implantation

• Soft coatings

• Slippery coatings

Reduction of corrosion • Anaerobic sealants

• Soft or anodic coatings
The AMPTIAC Quarterly, Volume 9, Number 1 15

sections of the material’s microstructure will respond unequally to

the temperature changes. Failure from thermal fatigue can occur

not only from fracture but also from a permanent change in shape.

Thermal fatigue is a significant concern in certain applications such as internal combustion engines, heat exchangers, and

turbine engine blades. Metals are especially susceptible to thermal fatigue because they often have a microstructure that is 

temperature dependent. Composites are susceptible to thermal

fatigue because they consist of multiple unique materials 

which respond differently to temperature changes. For example,

upon temperature fluctuations the reinforcing material can

exhibit significant strain while the matrix material experiences

minimal strain. This leads to a fatigue type loading on the

matrix material, which can result in the initiation of a crack.

The best way to mitigate thermal fatigue in composite materials

is to choose a reinforcement material and a matrix material 

that have similar thermal expansion coefficients.[5]

Surface Fatigue

The MaterialEASE in the next issue of the AMPTIAC Quarterly

will contain a brief description of this failure mode.

Impact Fatigue

Impact fatigue occurs when a material is subjected to repeated

impacts to a localized area causing the initiation and propagation of a fatigue crack. This repeated impact loading can ultimately result in fatigue fracture.

Corrosion Fatigue

For an in-depth discussion on corrosion fatigue and how it 

differs from stress corrosion cracking read the article in this 

issue of the AMPTIAC Quarterly entitled: EnvironmentallyAssisted Cracking.

Fretting Fatigue

Fretting damage† on the surface of a material can act as a

nucleating point for a crack. Under cyclic loading (typically

small amplitude loading) the nucleation of a crack at the location of fretting damage and the subsequent crack propagation

and fracture of the material constitutes fretting fatigue. Fretting

of a component under fatigue conditions will lead to a much

quicker nucleation of cracks than fatigue of a component not

subjected to fretting. Furthermore, cracks can be initiated by

fretting damage at a much lower stress than if the material is 

in a normal, undamaged condition. The fatigue strength‡ of a

material can be reduced by up to 70% under fretting conditions.[10] Fretting fatigue is a particularly problematic failure

mechanism because it can occur in hidden areas and result in

the sudden, catastrophic failure of a component. Joints, bearings, axles and shafts are typically very susceptible to fretting

fatigue.[10, 11] Methods for reducing damage by fretting fatigue

are briefly described in Table 1.

Creep-Fatigue Interaction

At elevated temperatures creep and fatigue can act simultaneously to produce a concerted, harmful effect on a material. A material operating in high temperature conditions can experience

both creep strains and cyclic strains that can seriously compromise the material’s expected lifetime. For example, if a material

experiences creep strains while undergoing fatigue cycling, its

fatigue life can be greatly reduced. Similarly, if a material experiences fatigue cycling while undergoing creep, its creep life can

be significantly reduced. The combined effect of creep and

fatigue can pose serious problems for those designing a system to

perform for a defined lifetime. There has been significant

research into predicting the combined effects of creep and fatigue

on materials in various operating conditions.[12]

FAILURE PREVENTION

In general, the most effective ways to prevent a material from

failing is proper and accurate design, routine and appropriate

maintenance, and frequent inspection of the material for defects

and abnormalities. Each of these general methods will be

described in further detail below.

Proper design of a system should include a thorough materials selection process in order to eliminate materials that could

potentially be incompatible with the operating environment and

to select the material that is most appropriate for the operating

and peak conditions of the system. If a material is selected based

only on its ability to meet mechanical property requirements, for

instance, it may fail due to incompatibility with the operating

environment. Therefore, all performance requirements, operating conditions, and potential failure modes must be considered

when selecting an appropriate material for the system.

Routine maintenance will lessen the possibility of a material

failure due to extreme operating environments. For example, a

material that is susceptible to corrosion in a marine environment

could be sustained longer if the salt is periodically washed off. It

is generally a good idea to develop a maintenance plan before the

system is in service.

Finally, routine inspections can sometimes help identify if a

material is at the beginning stages of failure. If inspections are

performed in a routine fashion then it is more likely to prevent a

component from failing while the system is in-service.

CONCLUSION

From a research standpoint, engineers must consider all 

plausible material failure modes when developing and maturing a

new material or when ‘evolving’ an old material. However, material failure can often be the result of inadequate material selection by

the design engineer or their incomplete understanding of the consequences for placing specific types of materials in certain environments. Education and understanding of the nature of materials and

how they fail are essential to preventing it from occurring. Simple

fracture or breaking into two pieces is not all-inclusive in terms of

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC
The AMPTIAC Quarterly, Volume 9, Number 1

Material EASE

failure, because materials also fail by being stretched, dented or

worn away. If potential failure modes are understood, then critical

systems can be designed with redundancy or with fail-safe features

to prevent a catastrophic failure. Furthermore, if appropriate effort

is given to understanding the environment and operating loads,

keeping in mind potential failure modes, then a system can be

designed to be better suited to resist failure.

MaterialEASE 30 will be published in AMPTIAC Quarterly,

Volume 9, Number 2, and will contain the next installment of

failure modes. These will include: Impact, Spalling, Wear,

Brinelling, Thermal Shock, and Radiation Damage.

ACKNOWLEDGEMENT

The author would like to thank Sachs, Salvaterra & Associates,

Inc. for their contribution of photos included in this article.

NOTES & REFERENCES

* Transgranular indicates that a crack proceeds through grain

boundaries and across the grain, whereas, intergranular indicates that a crack navigates around or between grain boundaries.

† Fretting wear is a damage mechanism whereby two surfaces

that are in intimate contact with each other and subjected to a

small amplitude relative motion (cyclic in nature) tend to incur

wear. The MaterialEASE in the next issue of the AMPTIAC

Quarterly will contain a brief description of this failure mode.

‡ Fatigue strength is the maximum stress that a material can

endure without failure for a given number of cycles.

[1] J.A. Collins and S.R. Daniewicz, Failure Modes: Performance and Service Requirements for Metals, M. Kutz (editor),

Handbook of Materials Selection, John Wiley and Sons, 2002, pp.

705-773

[2] Visual Examples of Various Structural Failure Modes,

Naval Postgraduate School, www.nps.navy.mil/avsafety/gouge/

structures/structures.ppt

[3] Ductile and Brittle Fractures, Metals Handbook, 9th

Edition, Vol. 11: Failure Analysis and Prevention, ASM

International, 1986, pp. 82-101

[4] J.M. Holt, H. Mindlin, and C.Y. Ho (editors), Structural Alloys

Handbook, Vol. 1, CINDAS/Purdue University, 1997, p. 74

[5] J. P. Shaffer, A. Saxena, S.D. Antolovich, T.H. Sanders, Jr., and

S.B. Warner, The Science and Design of Engineering Materials,

2nd Edition, McGraw-Hill, 1999

[6] R.E. Hummel, Understanding Materials Science: History –

Properties – Applications, Springer-Verlag, 1998

[7] Failure of Gears, Metals Handbook, 9th Edition, Vol. 11:

Failure Analysis and Prevention, ASM International, 1986, pp.

586-601

[8] H.E. Boyer (editor), Atlas of Fatigue Curves, ASM

International, 1986

[9] J. Schijve, Fatigue Crack Growth under VariableAmplitude Loading, ASM Handbook, Vol. 19: Fatigue and

Fracture, ASM International, 1996, pp. 110-133

[10] S.J. Shaffer and W.A. Glaeser, Fretting Fatigue, ASM

Handbook, Vol. 19: Fatigue and Fracture, ASM International,

1996, pp. 321-330

[11] Wear Failures, Metals Handbook, 9th Edition, Vol. 11:

Failure Analysis and Prevention, ASM International, 1986, pp.

145-162

[12] J.B. Conway, Creep-Fatigue Interaction, Metals Handbook,

9th Edition, Vol. 8: Mechanical Testing, ASM International, 1986,

pp. 346-360

16

... Don’t forget to look for 

Material Failure Modes Parts 2 & 3 

in upcoming issues of MaterialEASE!
The AMPTIAC Quarterly, Volume 9, Number 1 17

Benjamin D. Craig

Richard A. Lane

AMPTIAC

Rome, NY

INTRODUCTION

Cracking is possibly the most common material failure mode,

and may be the most dangerous, as complete fracture can occur

nearly instantaneously and without any advance warning. Harsh

environments can compound the cracking problem as they

often supplement the mechanisms that are tearing the material

apart, thereby accelerating the rate of failure. Environmentallyassisted cracking is a very broad and complex subject area in

terms of the various mechanisms through which it can occur. It

can generally be classified into three different forms: stress corrosion cracking (SCC), corrosion fatigue (CF) and hydrogenassisted cracking (HAC). It is important to distinguish between

these three forms, as they can appear to be very similar in nature

despite some fundamental differences. 

Each type of environmentally-assisted cracking is described in

the following sections, along with their typical mechanisms,

influencing factors, and mitigation and prevention strategies.

The last section provides a comparison of some of the key differences and similarities between the three phenomena.

Hydrogen-assisted cracking is described first since it commonly

plays a role in both SCC and CF.

HYDROGEN-ASSISTED CRACKING

The presence of hydrogen has the ability to influence the

mechanical integrity of a metal, thus making it more susceptible to cracking. If hydrogen is transported to a localized region,

such as a crack tip, it can accelerate the crack growth rate.

Hydrogen can be introduced to a metal through a number of

media, as it is present in water, air (gaseous hydrogen, water

vapor, pollution, etc.), and many other substances.

Hydrogen plays a role in a number of cracking mechanisms,

including stress corrosion cracking, corrosion fatigue, and fatigue

cracking. However, there are cracking phenomena that occur

under constant stress loads and in which hydrogen plays a significant part, but corrosion processes are absent. These are considered separate cracking mechanisms from SCC, CF, and general

fatigue. Furthermore, hydrogen can induce minor damage to a

material, which may not result in the fracture of that material. 

The phrase hydrogen-assisted cracking has been loosely defined

and encompasses a number of different mechanisms, and in

some cases is considered to be interchangeable with the phrases hydrogen-induced cracking, hydrogen embrittlement, and

hydrogen damage. For the purpose of this article, HAC is considered to be anything where hydrogen plays a major role in the

initiation or propagation of cracks. Some of the mechanisms

where hydrogen contributes to the failure of a material by stress

corrosion cracking or corrosion fatigue will be discussed in

their respective sections.

Cracks that have been propagated with the assistance of

hydrogen typically are not significantly branched and can be

either intergranular or transgranular. Materials that experience

HAC usually do not exhibit much plastic deformation, thus the

fracture that occurs in response to HAC mechanisms typically

is brittle fracture. The multiple hydrogen damage mechanisms

can act together or alone to initiate and propagate cracks.

Mechanisms of HAC are described in the following section.

Hydrogen-Assisted Cracking Mechanisms

One mechanism of HAC involves the diffusion and buildup of

gaseous hydrogen (H2) in a void region of the metal (e.g. crack

space, microstructural void). This process can easily occur if the

structure is exposed to a hydrogen-rich environment. This

gaseous hydrogen exerts a pressure against the walls of the

metal, thus assisting in propagating the crack, or initiating a

crack in the case where one doesn’t already exist (i.e. when gas

collects in a void). The latter process can occur when H2 gas is

“pushing” against the metal from the inside and augments the

stress load being applied to the material so that the total stress

exceeds that required to initiate a crack. This effectively creates

an area of stress concentration and a nucleating site for a crack.

The propagation of a crack is also assisted with the pressure of

the hydrogen gas pushing against the crack walls from the

inside, which again works in combination with the stress

applied to the metal.

A second general mechanism of HAC occurs with hydrogen

adsorbing to the metal surface, thereby reducing the surface

energy of the metal at that point. The reduction of surface energy can then facilitate the initiation of a crack, or can enhance

the propagation rate of the crack.

The third general mechanism of HAC involves atomic

hydrogen migrating into the microstructure of the metal. This

results in a reduction of the interatomic bond strength of the

metal, which provides a point of nucleation for a crack or accelerates the crack propagation process.

Forms of Hydrogen Damage

There are a number of different forms of hydrogen damage that

apply to metallic materials, resulting from the combined factors
18 The AMPTIAC Quarterly, Volume 9, Number 1

of hydrogen and residual or applied tensile stresses. Hydrogen

damage can result in cracking, embrittlement, loss of ductility,

blistering and flaking, and also microperforation. These and

other types of hydrogen damage are briefly described in the 

following sections. Table 1 provides lists of general types of

metals that are typically susceptible to the various types of

hydrogen attack.

Hydrogen-Induced Cracking

Hydrogen-induced cracking refers to the cracking of a ductile

alloy when under constant stress and where hydrogen gas is

present. Hydrogen is absorbed into areas of high triaxial stress

ultimately initiating the observed damage.

Hydrogen Embrittlement

Hydrogen embrittlement is the brittle cracking or fracture of a

ductile alloy during plastic deformation in a hydrogen gas containing environment.

Loss of Tensile Ductility

The loss of tensile ductility sometimes occurs in metals exposed

to hydrogen, resulting in a significant decline in elongation and

reduction in area properties. It is most often observed in low

strength alloys, but has also been observed in some steels, stainless steels, aluminum alloys, nickel alloys, and titanium alloys.

High Temperature Hydrogen Attack

High pressure hydrogen will attack carbon and low-alloy steels

at high temperatures. This occurs when hydrogen diffuses into

the metal and reacts with carbon, resulting in the formation of

methane. This in turn results in decarburization of the alloy

and possibly the formation of cracks.

Blistering

Blistering occurs primarily in low strength metals. It is a result

of atomic hydrogen diffusion into defect areas of the alloy. The

monotonic atoms combine into gas molecules in voids within

the metal. Then, the high pressure of H2 entrapped within the

metal causes the material to blister or rupture. This form of

attack has been observed in low strength steels exposed to

hydrogen sulfide (H2S) or when cleaned in pickling baths.

Shatter Cracks, Flaking, and Fish Eyes

These forms of hydrogen damage are similar to blistering and

are seen primarily during processing. Hydrogen is more soluble

at the melting temperatures of metals allowing it to enter defect

areas. The decreased solubility of hydrogen when cooled then

produces the damage features.

Microperforation

Microperforation has been observed in steels in a high pressure

hydrogen and room temperature environment. The hydrogen

produces fissures in steel alloys, such that gases and liquids can

permeate the material.

Degradation in Flow Properties

An increase in creep rate can occur in iron alloys and steels

under ambient conditions in hydrogen environments, and in

several other alloys at elevated temperatures.

Hydride Formation

The precipitation of metal hydride phases in magnesium, tantalum, niobium, vanadium, uranium, zirconium, titanium, and

their alloys, in the presence of hydrogen results in a degradation

of mechanical properties and cracking.

Managing Hydrogen Damage

Methods to protect against or mitigate hydrogen damage

include:

• Limit hydrogen introduced into the metal during processing.

• Limit hydrogen in the operating environment.

• Structural designs to reduce stresses (below threshold for

subcritical crack growth in a given environment).

• Use barrier coatings.

• Use low hydrogen welding rods.

• Select appropriate materials resistant to hydrogen damage.

STRESS CORROSION CRACKING

Stress corrosion cracking (SCC) is an environmentally-induced

phenomenon that occurs when a metal is subjected simultaneously to a tensile stress and a corrosive environment. This is not

to be confused with similar phenomena such as hydrogen

embrittlement, in which the metal is embrittled by hydrogen,

often resulting in the formation of cracks. Moreover, SCC is not

the cause of cracking that occurs when the surface of a metal is

corroded, resulting, in the creation of a nucleating point for a

crack. Rather, it is a synergistic effect of a corrosive agent and a

modest, static tensile stress. If either the corrosive media or the

tensile stress were absent, the effect would not be the same, and

might be absent completely. Another form of corrosion similar

Table 1. Metals’ Susceptibilities to Hydrogen Damage[1].

HydrogenInduced

Cracking

Hydrogen

Embrittlement

Loss in

Tensile

Ductility

High

Temperature

Hydrogen

Attack

Blistering Shatter

Cracks,

Flakes,

Fisheyes

MicroperforationDegradation

in Flow

Properties

Metal

Hydride

Formation

Steels

Nickel-alloys

Metastable

stainless steel

Titaniumalloys

Carbon and

low-alloy

steels

Steels

Nickel-alloys

Be-Cu 

Bronze

Aluminumalloys

Carbon and

low-alloy

steels

Steels

Copper

Aluminum

Steels 

(forgings and

castings)

Steels 

(compressors)

Iron

Steels

Nickel-alloys

V

Nb

Ta

Ti

Zr

U
The AMPTIAC Quarterly, Volume 9, Number 1 19

to SCC (although with a subtle difference) is corrosion fatigue,

which is discussed in the next section. The key difference is that

SCC occurs with a static stress, while corrosion fatigue requires

a cyclic stress. Figure 1 shows a micrograph of a cadmium-plated steel with SCC damage.

SCC is a process that takes place within the material,

where the cracks propagate through the internal structure,

usually leaving the outer surface unharmed. Furthermore,

there are two main types of SCC: intergranular and transgranular. For the intergranular form, the cracking progresses mostly along grain boundaries, whereas in transgranular SCC, the

cracking does not strictly adhere to the grain boundaries,

instead it can penetrate grains. Figure 2 illustrates the two

types of stress corrosion cracking. Stress corrosion crack propagation typically occurs in a stable or steady-state fashion.

However, as will be discussed in the section on SCC mechanisms, the crack propagation process can be discontinuous. Most cracks

tend to propagate in a

direction that is perpendicular to the direction of

applied stress. Aside from

an applied mechanical

stress, a residual, thermal,

or welding stress along

with the appropriate corrosive agent may also be

sufficient to promote

SCC. Pitting corrosion,

especially in notch-sensitive* metals, has been found to be

one cause for the initiation of SCC, but the crack initiation

mechanisms are often complicated. Other initiation sites

include fabrication defects, imperfections as a result of

machining (e.g. end grains), and material flaws.

SCC is a concern in alloys that produce a surface film in certain environments, such as an oxide film on aluminum, since

the film may protect the alloy from other forms of corrosion,

but not SCC. Moreover, SCC is a dangerous form of corrosion

because it can be difficult to detect, and it can occur at stress

levels well within the range that the metal is designed to handle. The stress corrosion cracking stress intensity factor, Kscc, is

typically much less than the critical stress intensity factor,

Kcrit.[4] This indicates that cracking can occur at much lower

stress intensity values with the simultaneous action of corrosion

than it can under conditions where corrosion is absent.

Additionally, the mechanism of SCC is not completely understood. There are a number of proposed mechanisms that

attempt to explain the phenomenon, but there is not one that

can describe each instance of SCC.

Stress Corrosion Cracking Mechanisms

There is no mechanism that completely describes all cases of

stress corrosion cracking, but there have been a number of proposed mechanisms for the phenomenon, which can be classified either as an anodic SCC mechanism or a mechanical fracture process. These mechanisms (described below) can act alone

or in conjunction with one another to produce SCC.

Anodic SCC involves the rupture of the protective oxide

layer (formed from corrosion of the base metal) at the crack tip,

anodic dissolution of the base metal, and crack growth under

constant stress. Crack growth can be either intergranular or

transgranular (shown in Figure 2).[5] There are a number of

SCC mechanisms classified under the mechanical fracture

process group. Descriptions of several of these follow.

Corrosion of the base metal can cause tunnels to form, originating from the crack tip. These tunnels degrade the strength

of the metal, and when the stress intensity becomes too great,

the crack propagates further. Then the process starts over again,

with corrosion causing the formation of more tunnels at the

same crack tip.[5]

Another mechanism involves exposure to aggressive species

from the surrounding environment, which can chemically

adsorb (form a chemical bond with the base metal) to the surface of the crack tip and aid in the propagation of the crack. The

adsorption of these species assist in the formation of dislocations

near the crack tip. These dislocations and the constant stress

applied to the metal cause plastic deformation of the metal near

the crack tip, resulting in further propagation of the crack.[5]

A similar mechanism has been suggested where a species

from the surrounding environment adsorbs to the surface of

the metal, reducing the bond strength between adjacent atoms

in the metal lattice structure. This results in an overall decrease

in material strength in which the stress required to cause brittle

fracture is reduced. This crack propagation mechanism is continuous and is controlled by the rate of mass diffusion of the

environmental species to the crack tip.[5]

A mechanism for discontinuous stress corrosion crack propagation involves the cyclic formation and rupture of a protective

film at the crack tip on a base metal. When a metal is exposed

to a corrosive environment, it will often form a protective film

at the surface. With an applied stress, the film, which is typically brittle, can rupture and consequently expose the surface of the

base metal and crack tip to the corrosive environment resulting

in further dissolution. This corrosion of the crack tip aids in the

propagation of the crack. The surface of the exposed metal in

collaboration with the corrosive environment eventually repairs

the protective film, and the process starts over again.[5]

A similar concept has been proposed where a film forms at the

surface of a metal, and brittle fracture is induced by dealloying

and/or vacancy injection. The crack proceeds through the film

Figure 1. Cadmium Plated Steel Rocket

Motor with SCC Damage[2].

(b) Transgranular

Figure 2. Pictures of Stress Corrosion Cracking. [3] (Courtesy of

Metallurgical Technologies, Inc.)

(a) Intergranular

Old Plating 4130 Steel (42 HRC)

Corrosion Product

(CI Rich)

SCC Damage
20 The AMPTIAC Quarterly, Volume 9, Number 1

and across the film/metal interface into the metal where it propagates under the stress of the applied load. Once the crack

stops, the process starts over with the formation of the film.[5]

The last mechanism worth mentioning is a combination of

hydrogen-assisted cracking (described earlier in this article) and

SCC. Corrosion reactions often result in the formation of

hydrogen gas. Hydrogen atoms (especially if the partial pressure

of the hydrogen is high) can diffuse or are absorbed into the lattice of the metal causing a deterioration of the metal’s properties. This, combined with the applied stress to the metal, can

result in crack propagation.[5]

Factors Affecting Stress Corrosion Cracking

There are a number of factors that contribute to the occurrence

and rate of SCC in metals. Increasing the temperature of a system, for example, often accelerates the rate of SCC. The presence of chlorides or oxygen in the environment can also significantly influence the occurrence and rate of SCC. These factors

can be categorized as materials, environmental, or mechanical

factors, some of which are listed in Table 2.

From Table 2 it is clear that stress corrosion cracking is

dependent on a number of factors. However, certain types of

alloys are more susceptible to SCC in particular environments,

while other alloys are more resistant to that same environment.

Some specific environments that can cause SCC of certain metals are listed in Table 3.

Managing Stress Corrosion Cracking

The composition of a metal has a significant affect on the

metal’s susceptibility to SCC. Therefore, material selection is

very important in preventing SCC from occuring in a system.

There are a few maintenance steps that can hinder further

growth of pre-existing damage within a material. Depending

on the geometry of the component, it may be feasible to use

corrosion preventive compounds or to reapply coatings in order

to protect the material from further corrosion and slow the

crack growth. There are several other methods that may be used

to minimize the risk of SCC. Some of these methods include:

• Choose a material that is resistant to SCC.

• Employ proper design features for the anticipated forms of

corrosion (e.g. avoid crevices or include drainage holes).

• Minimize stresses (including thermal stresses).

• Control or modify the environment (e.g. pH, oxygen content, etc.).

• Use surface treatments (shot peening, laser peening) which

increase the surface resistance to SCC.

• Barrier coatings will deter SCC as long as they remain intact.

• Reduce exposure of end grains, which can result from design

and/or manufacturing (i.e. end grains can act as initiation

sites for cracking because of preferential corrosion and/or a

local stress concentration).

CORROSION FATIGUE

Corrosion fatigue (CF) is the environmentally-assisted

mechanical degradation of a material due to the combined

effects of corrosion and fatigue (a direct result of cyclic stress

loading). It is often considered to be a component of stress corrosion cracking, but the fracture mechanics and methods of

prevention deviate enough from those of SCC that it warrants

a separate discussion. Furthermore, SCC occurs under static

stress while corrosion fatigue occurs under a cyclic stress (part

of which is tensile stress).

Corrosion fatigue is a potential cause for the failure of many

types of metals and alloys in various types of environments. To

provide protection against this phenomenon or to design

around it, it is important to first understand what corrosion

fatigue is and what the mechanisms are that govern it.

Table 2. Materials, Environmental and Mechanical Factors that

Influence Stress Corrosion Cracking.

Materials Factors Environmental Factors Mechanical Factors

Composition Temperature Stress

Microstructure pH Strain rate

Contaminants Electrochemical 

or impurities Potential 

Grain size Solute species

Grain orientation Solute concentration

Oxygen concentration

Table 3. Environments that May Cause Stress Corrosion

Cracking of Metals[6].

Material Environment

Aluminum alloys NaCl-H2O2 solutions

NaCl solutions

Seawater

Air, water vapor

Copper alloys Ammonia vapors and solutions

Amines

Water, water vapor

Gold alloys FeCl3 solutions

Acetic acid-salt solutions

Inconel Caustic soda solutions

Lead Lead acetate solutions

Magnesium alloys NaCl-K2CrO4 solutions

Rural and coastal atmospheres

Seawater

Distilled water

Monel Fused caustic soda

Hydrofluoric acid

Hydrofluorosilicic acid

Nickel Fused caustic soda

Ordinary steels NaOH solutions

NaOH-Na2SiO2 solutions

Calcium, ammonium, and sodium 

nitrate solutions

Mixed acids (H2SO4-HNO3)

HCN solutions

Acidic H2S solutions

Seawater

Molten Na-Pb alloys

Stainless steels Acid chloride solutions (e.g. MgCl2 and BaCl2)

NaCl-H2O2 solutions

Seawater

H2S

NaOH-H2S solutions

Condensing steam from chloride waters

Titanium alloys Red fuming nitric acid, seawater, 

N2O4, methanol-HCl
The AMPTIAC Quarterly, Volume 9, Number 1 21

Corrosion fatigue is essentially a decrease in fatigue strength

due to the effects of electrochemical degradation (corrosive

environment), as illustrated in Figure 3. The stress required for

both crack initiation and propagation is lower in corrosive environments. The crack growth rate can be much higher in a corrosive environment than it is in a non-corrosive environment.

Therefore, the fatigue life of a material is shortened if it is

simultaneously exposed to a corrosive environment and fatigue

conditions. Fatigue cracking is often characterized by “beach

marks” or striation patterns which are perpendicular to the

crack propagation direction, as shown in Figure 4.

Corrosion Fatigue Mechanisms

Corrosion fatigue is a complex process that no one mechanism

can describe completely for all cases. The general mechanism of

corrosion fatigue has been described as being hydrogeninduced, the result of anodic dissolution, or a combination of

the two. Corrosion fatigue cracks are often initiated at the surface. Subsurface cracks initiate at areas of stress concentration,

such as material defects near the surface. Corrosion fatigue

cracks are typically transgranular with little branching. The

final failure event of the material is simply a mechanical process

without any assistance from corrosion. Thus, at that final stage

the mechanism becomes exactly the same as fatigue.

Anodic Dissolution

Anodic dissolution is a very active mechanism for assisting with

fatigue cracking in metals, and typically occurs in aqueous environments or environments containing liquids. The mechanism

basically consists of three steps. In the first step, the protective

oxide film, which is generated through the corrosion reaction

between the corrosive environment and the base metal, is ruptured near the crack tip by the fatigue process. The exposed

base metal is then attacked by the corrosive media causing dissolution, and consequently sharpening or dulling of the crack

tip, depending on the rate of repassivation (the reformation of

protective film). During the anodic dissolution, the passive film

is repaired, and the corrosion process is stopped. The process

then begins all over again with the rupture of the protective

film by the fatigue process, thereby exposing the base metal to

the corrosive media. This process and the crack growth rate are

dependent on the rate of anodic dissolution, rate of repassivation, etc.[9] For example, if the rate of dissolution is much

faster than the rate of repassivation, then the crack tip would be

blunted.[9]

An effective method for hindering the anodic dissolution

mechanism responsible for corrosion fatigue crack propagation

is cathodic protection. Cathodic protection increases the rate at

which the protective film reforms, thereby reducing the time

available for corrosion of the crack tip following rupture of the

passive film.[9]

Hydrogen-Induced Mechanisms

The presence of hydrogen at the crack tip can cause damage to

the metal and can aid in the propagation of the crack under

cyclic loading. Thus, the crack growth rate is accelerated by

hydrogen damage. Within the mechanism of hydrogeninduced corrosion fatigue cracking are several different mechanisms by which this hydrogen damage and cracking can occur.

Gaseous hydrogen environments can aid in crack growth

through a pressure process in the void space of a crack or

Figure 3. Comparison of Fatigue (S/N)

Curves for a Material in an Inert

Environment and an Aggressive

Environment[7].

Figure 4. Characteristic Fatigue Striation Pattern (Note the

Crack Proceeds Perpendicular to the Striation Marks as

Indicated by the Blue Line)[8].

Inert Environment or High Frequency

Aggressive Environment

Log Nf (Number of Stress Cycles to Failure)

Stress (S)
Table 4. Factors Affecting Corrosion Fatigue[9].

22 The AMPTIAC Quarterly, Volume 9, Number 1

microcrack. The relatively high pressure from diatomic hydrogen gas acting as a localized force in the crack region can supplement the stress on the metal and consequently accelerate

the crack growth rate. This is considered corrosion fatigue

when cathodic reactions associated with the corrosion of a

metal release hydrogen atoms that combine to form gaseous

hydrogen (H2), which results in a pressure buildup in the

crack void space.[9]

Atomic hydrogen dissolved in a metal can also lead to an

increased fatigue crack growth rate. Hydrogen atoms within a

metallic crystalline structure can lower the bond strength

between the individual atoms. Moreover, hydrogen atoms generated during the corrosion process can diffuse through a

metallic structure under an applied stress, and collect near the

point of maximum stress. The consequence of dissolved hydrogen in a metal is that it can reduce the strength of the metal,

and if a crack exists, it will propagate with less resistance where

there is a concentration of hydrogen atoms.[9]

A similar mechanism has been observed when hydrogen is

adsorbed on the surface of the metal near the crack tip. The

adsorbed hydrogen lowers the surface energy of the metal,

which facilitates crack growth. Similarly, species other than

hydrogen can adsorb to the surface of the metal, resulting in a

decrease in the surface energy and an accelerated crack growth

rate.[9]

Metal hydride formation near a crack tip region may also contribute to fatigue crack propagation. Metal hydrides can precipitate near this region when certain metallic alloying elements

(e.g. Ti, Ni, Nb, V and Zr have tendencies to form metal

hydrides) are exposed to a hydrogen environment. The resulting

hydrides are brittle and reduce the strength of the metal at the

crack tip, leading to further propagation of the fatigue crack.[9]

Finally, it has been proposed that dissolved hydrogen enables

the movement of dislocations by reducing the stress required

for migration. This enhances the plastic flow of the metal,

which further enables crack propagation.[9]

Factors Affecting Corrosion Fatigue

There are a number of factors that affect the onset of corrosion

fatigue and the growth rate of cracks caused by this mechanism.

For example, corrosion, such as pitting, causes stress raisers in

the vicinity of the pit, much like notch effects. This can lead to

crack initiation at a stress below that for a material in a noncorrosive environment. The crack will then propagate at a faster

rate, as corrosive elements enter the crack. Temperature, metal

composition, strength and fracture toughness are other examples of environmental and material factors that affect the occurrence and rate of corrosion fatigue. These and other factors

influencing corrosion fatigue are provided in Table 4.

Managing Corrosion Fatigue

Similar to preventing stress corrosion cracking, material selection is very important in corrosion fatigue prevention.

Fracture toughness and strength are both important material

properties when considering how to protect against corrosion

fatigue. However, increased strength normally reduces fracture

toughness and vice versa. One method to enhance fracture

toughness while maintaining strength is to reduce the metal’s

grain size. Additionally, a smooth or highly polished surface is

more resistant to crack initiation. High temperatures also contribute to corrosion fatigue, thus maintaining operating temperatures at relatively low levels will help minimize its effects.

Components exhibiting long cyclic periods of stress typically

do not experience any environmental assistance with cracking.

Also similar to SCC, maintenance efforts such as using corrosion preventive compounds or reapplying protective coatings

to damaged areas may help inhibit corrosion and slow the

crack growth rate.

Methods to deter corrosion fatigue include the following:

• Employ designs which minimize stresses to the components.

• Choose heat treatments that reduce residual stresses.

• Use surface treatments that enhance corrosion fatigue resistance, such as shot peening or laser peening.

Metallurgical

Alloy composition

Microstructure and 

crystal structure

Heat treatment

Grain boundary structure

Grain shape and size

Surface texture

Distribution of alloy 

elements and impurities

Deformation mode 

(slip character, twinning, 

cleavage)

Mechanical properties 

(strength, toughness, etc.)

Environmental

Type of environments 

(gaseous or liquid)

Partial pressure of damaging 

species in aqueous or 

other liquid environments

Concentration of damaging 

species in aqueous or 

other liquid environments

Temperature 

pH

Electrochemical potential

Viscosity of the environment

Mechanical

Fatigue load frequency

Fatigue load ratio

Fatigue load waveform

Maximum stress-intensity 

factor and stress-intensityfactor range

Load interactions in variable 

amplitude loading (over/

under/spectrum load)

Residual stress

Geometrical

Crack size

Crack geometry

Specimen thickness

(plane strain versus 

plane stress) 
The AMPTIAC Quarterly, Volume 9, Number 1 23

• Use inhibitors and barrier coatings to block corrosive species

from the metal.

• Reduce hydrogen contamination during fabrication, heat

treatment or manufacturing.

• Select materials that are not sensitive to corrosion fatigue.

COMPARISON OF SCC, CF, AND HAC

Corrosion fatigue, stress corrosion cracking and hydrogenassisted cracking are similar phenomena in that they are all

environmentally-assisted cracking mechanisms. However, it is

important to recognize their

differences for the purpose of

employing the appropriate prevention techniques. The difference between stress corrosion

cracking and corrosion fatigue

is that SCC is a crack propagation process in a corrosive environment under a static or sustained tensile stress, whereas

CF is the failure of a material

through crack propagation by

the combined effects of a corrosive environment and cyclic

stress loading. At a very low

cycle frequency, CF can appear

to be nearly indistinguishable

from SCC. A visible difference

between SCC and CF is that stress corrosion cracks often have

many small branches, while corrosion fatigue cracks have little

or no branching. This is illustrated in Figure 5. Critical stress

intensity factors for CF are often lower than that for SCC. This

is because CF can more rapidly cause protective oxide films to

rupture, thus exposing the base metal to corrosive conditions,

ultimately resulting in the formation of a crack. Another

important difference between SCC and CF is that they are prevented using different methods (although some methods of

prevention are the same, e.g. stress reduction, coatings, surface

peening, etc.). Hydrogen-assisted cracking or hydrogen embrittlement can be part of these

two mechanisms, but in other

cases it can also be characterized as its own mechanism. 

For example, metals can be

damaged in the presence of

hydrogen resulting in enhanced

stress corrosion or fatigue crack

growth rates. Additionally,

metals may exhibit cracking

that is initiated and/or propagated in the presence of hydrogen without the existence of

corrosion mechanisms. This

can occur with or without the

assistance of a static stress load.

There are often complex relationships that exist between

corrosion fatigue, stress corrosion cracking and hydrogenassisted cracking. An illustration of the interrelationship

between these mechanisms is given in Figure 6. The textured

Figure 5. Branching Characteristics of SCC and CF[10].

Figure 6. Conceptual Interrelationship of Corrosion Fatigue,

Stress Corrosion Cracking and Hydrogen-Assisted Cracking[11].

Table 5. Characteristics of Environmentally-Assisted Cracking Mechanisms[12].

Factor SCC Corrosion Fatigue Hydrogen-Assisted Cracking

Stress Static tensile Cyclic + tensile Static tensile

Aqueous corrosive agent Specific to the alloy Any Any

Temperature increase Accelerates Accelerates < Ambient: increases

Pure metal Resistant Susceptible Susceptible

Crack morphology Transgranular, Intergranular, Transgranular, Unbranched, Transgranular, Intergranular,

Branched Blunt tip Unbranched, Sharp tip

Corrosion products in cracks Absent Present Absent

Crack surface appearance Cleavage-like Beach marks and/or striations Cleavage-like

Cathodic protection Suppresses Suppresses Accelerates

Near maximum strength Susceptible but minor Accelerates Accelerates

Corrosion Fatigue Cracks

have Little Branching Stress Corrosion Cracking

is Highly Branched

Corrosion Fatigue

Hydrogen Damage Stress Corrosion 

Cyclic

Stress

Static

Stress
24 The AMPTIAC Quarterly, Volume 9, Number 1

areas in the figure represent the combination of two failure

mechanisms. The darker area in the center represents the interaction of all three phenomena. The region between the dotted

lines indicates a transition from cyclic to static stress or vice

versa. For example, extremely low amplitude cyclic stress could

be considered to be nearly static. Table 5 provides some of the

characteristics of these three environmentally-assisted cracking

mechanisms for comparison.

CONCLUSION

There are other environmental conditions such as temperature,

radiation, and pH that can have deleterious effects on a material, absent of corrosion and hydrogen, that lead or contribute

to crack initiation and/or propagation. However, the most

common and often the most severe conditions typically involve

a corrosive environment and a static or dynamic load. Materials

subject to these conditions can undergo rapid and unanticipated failure because of undetected material defects. Stress corrosion cracking, corrosion fatigue and hydrogen-assisted cracking

are often the culprits in these types of failures, which can be catastrophic to certain systems. Understanding and differentiating

the three will ultimately lead to more effective strategies in

control and prevention, especially through more appropriate

material selection.

NOTES & REFERENCES

* Notch-sensitivity indicates a particular material’s susceptibility

to fracture that is initiated at a stress raiser, such as a notch, surface defect or scratch. Brittle materials tend to be notch-sensitive.

[1] Environmentally Induced Cracking, ASM Handbook, Vol.

13: Corrosion, 9th Edition, ASM International, 1987, pp.

145-189

[2] Naval Air Warfare Center Weapons Division, Materials

Engineering Laboratory, http://www.nawcwpns.navy.mil/r2/fs/

MatEngr.htm#

[3] Metallography/Microstructure Evaluation, Metallurgical

Technologies Inc., http://www.met-tech.com/metal.html

[4] Environmentally Induced Cracking, ASM Handbook, Vol.

13: Corrosion, ASM International, 1987, pp. 145-189

[5] G.H. Koch, Stress-Corrosion Cracking and Hydrogen

Embrittlement, ASM Handbook, Vol. 19: Fatigue and Fracture,

ASM International, 1996, pp. 485-506

[6] M.G. Fontana, Corrosion Engineering, 3rd edition,

McGraw-Hill, 1986

[7] W. Glaeser and I.G. Wright, Mechanically Assisted

Degradation, Metals Handbook, Vol. 13: Corrosion, 9th

Edition, ASM International, 1987, pp. 136-144

[8] Kennedy Space Center Corrosion Technology Testbed,

NASA Kennedy Space Center, http://corrosion.ksc.nasa.gov/

faticor.htm

[9] P.S. Pao, Mechanisms of Corrosion Fatigue, ASM Handbook,

Vol. 19: Fatigue and Fracture, ASM International, 1996, pp.

185-192

[10] J. Pearce, Metallic Corrosion – Stress Corrosion Cracking,

Azom.com, http://www.azom.com/details.asp?ArticleID=102

[11] Evaluating Corrosion Fatigue, ASM Handbook, Vol. 13A:

Corrosion: Fundamentals, Testing and Protection, ASM

International, 2003, pp. 625-638

[12] P.R. Roberge, Handbook of Corrosion Engineering,

McGraw-Hill, 2000

Research and Engineering (R&E) Portal Launched

Ft. Belvoir, VA – The Office of the Director, Defense Research & Engineering (DDR&E) and the Defense Technical Information

Center (DTIC) are pleased to announce that the R&E Portal is now available to Department of Defense (DoD) employees and

their contractors. The Portal provides one-stop access to current and historical R&E information, including DTIC technical data

resources.

Dr. Ronald M. Sega, Director of Defense Research and Engineering, and the sponsor of the Portal, wants the R&E community

to have easy access to comprehensive technical information. His vision is that DoD personnel will quickly locate answers, from their

workstations, to questions such as: What is DoD doing in R&E? When will the work be completed? Why is the work being done?

Who is the point of contact for more information? 

The Portal brings together Web applications that support DDR&E strategic planning and the congressional reporting process.

Consolidated information on R&D projects, provided by the services, can also be found in the Portal. A working research tool,

the R&E Portal includes an enhanced query capability that displays the results of text searches within the context of a selected

taxonomy. It also offers a customized search tool designed specifically for analysis. The new E-Gov database, created to consolidate and submit R&D data in support of the E-Government Act of 2002, provides a centralized view of federally funded R&D

projects. The R&E Portal can be found at https://rdte.osd.mil. Access is controlled by the DTIC registration process. Go to:

https://register.dtic.mil/DTIC for registration information. For more information about the R&E Portal, contact

rdte_help@dtic.mil. 

DDR&E’s mission is to ensure that the warfighters today and tomorrow have superior and affordable technology to support their

missions and to give them revolutionary war-winning capabilities. DTIC (www.dtic.mil) is the premier provider of defense scientific, research, and engineering information. A DoD Field Activity, DTIC reports to the DDR&E (http://www.dod.mil/ddre).
The AMPTIAC Quarterly, Volume 9, Number 1 25

2005 Device Research Conference

06/20/05 - 06/22/05

Santa Barbara, CA

Contact: TMS Meeting Services

184 Thorn Hill Rd

Warrendale, PA 15086 

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: www.tms.org/drc.html

Mega Rust 2005

06/20/05 - 06/24/05

Louisville, KY

Contact: R.I. Bentley

Naval Surface Warfare Center

Phone: 602.364.5052

2005 Electronic Materials Conference

06/22/05 - 06/24/05

Santa Barbara, CA

Contact: TMS Meeting Services

184 Thorn Hill Rd

Warrendale, PA 15086

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: www.tms.org/emc.html

17th University Conference on Glass

Science & 1st International Materials

Institute Workshop on New

Functionality in Glasses

06/26/05 - 06/30/05

State College, PA

Contact: Donna Lucas

Materials Research Institute - 

Penn State University

University Park, PA 16802 

Phone: 814.865.1656

Fax: 814.865.2326

Email: dzm@psu.edu

Web Link: www.mri.psu.edu/conferences

2005 National Space & Missile

Materials Symposium

06/27/05 - 07/01/05

Summerlin, NV

Contact: M. Kubal; Anteon Corporation

5100 Springfield St, Ste 509

Dayton, OH 45431 

Phone: 937.254.7950 ext 1168

Fax: 937.253.2296

Email: mkubal@anteon.com

Web Link: www.usasymposium.com

3rd International Conference on

Advanced Engineered Wood Composites

07/10/05 - 07/14/05

Bar Harbor, ME

Contact: Doreen Parent, The AEWC Center 

University of Maine, Orono, ME 04469 

Phone: 207.581.2123

Email: doreen.parent@umit.maine.edu

Web Link: www.aewc.umaine.edu/conference

2005 World Summit 

on Advanced Capacitors

07/11/05 - 07/13/05

San Diego, CA

Contact: Intertech Corporation

19 Northbrook Dr

Portland, ME 04105 

Phone: 207.781.9800

Fax: 207.781.2150

Web Link: www.intertechusa.com

2005 Advanced Gun Barrel Materials 

& Manufacturing Symposium

07/12/05 - 07/14/05

St. Michael, MD

Contact: Dr. William de Rosset, USMA

United States Military Academy

West Point, NY 10996

Email: aw2604@usma.edu

Web Link: www.dean/usma.edu/

departments/math/ARL-BENET

GUNSYMPOSIUM/

Interdisciplinary Transport Phenomena

in Microgravity & Space Sciences IV

08/07/05 - 08/12/05

Contact: Engineering Conferences

International

Six Metro Tech Center

Brooklyn, NY 11201 

Phone: 718.260.3743

Fax: 718.260.3754

Email: info@eci.poly.edu

Web Link: www.engconfitl.org/5aw.html

The Integrated Systems Health

Management (ISHM) Conference

08/08/05 - 08/11/05

Cincinnati, OH

Contact: Ms. Cathy Griffith; Anteon Corp.

5100 Springfield Pike, Ste 509

Dayton, OH 45431 

Phone: 937.254.7950

Email: cgriffith@anteon.com

Web Link: www.usasymposium.com/ishm

12th International Conference 

on Environmental Degradation 

of Materials in Nuclear 

Systems-Water Reactors

08/14/05 - 08/18/05

Salt Lake City, UT

Contact: TMS Meeting Services

184 Thorn Hill Rd

Warrendale, PA 15086 

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: www.tms.org/Meetings

6th Pacific Rim Conference on 

Ceramic & Glass Technology

09/11/05 - 09/16/05

Maui, HI

Contact: Dr. Sylvia M. Johnson, PacRim 6

Program Chair, NASA Ames Research Center;

NASA Ames Research

Moffet Field, CA 

Web Link: www.ceramics.org/meetings/ 

International Conference on Silicon

Carbide & Related Materials 2005

(ICSCRM 2005)

09/18/05 - 09/23/05

Pittsburgh, PA

Contact: TMS Customer Service

184 Thorn Hill Rd

Warrendale, PA 15086

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: www.tms.org/Meetings

MS&T ’05 (Materials Science &

Technology 2005)

9/25/05 – 9/28/05

Pittsburgh, PA

Contact: TMS Meeting Services

184 Thorn Hill Rd

Warrendale, PA 15086 

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: http://doc.tms.org

IMAPS 38th Annual Symposium 

on Microelectronics

09/29/05 - 10/01/05

Philadelphia, PA

Contact: IMAPS-Intl Microelectronics 

& Packaging Society

611 2nd St, NE

Washington, DC 20002 

Phone: 202.548.4001

Fax: 202.548.6115

Email: imaps@imaps.org

Web Link: www.imaps.org

International Symposium on

Superalloys 718, 625, 706 &

Derivatives

10/02/05 – 10/05/05

Pittsburgh, PA

Contact: TMS Meetings Services

184 Thorn Hill Rd

Warrendale, PA 15086

Phone: 724.776.9000 

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: http://doc.tms.org

Mark Your Calendar
26 The AMPTIAC Quarterly, Volume 9, Number 1

Army Research Laboratory Celebrates Recent Special Edition of the AMPTIAC Quarterly.

In recognition of the success of the Special Army

Materials Issue of the AMPTIAC Quarterly

(Volume 8, Number 4), many of its authors

assembled recently for a celebration at the Army

Research Laboratory’s (ARL) offices at Aberdeen

Proving Ground, Maryland. Brief welcoming and

congratulatory addresses were given by Dr. James

McCauley, ARL Fellow, article author, and key

coordinator for the issue; and Dr. Steven

McKnight, newly-appointed Materials Division

Chief, Weapons and Materials Research

Directorate (WMRD), and also a contributing

author. Also in attendance were other members

of the ARL staff, Mr. David Rose (AMPTIAC

Director), and Mr. Chris Grethlein (Editor of the

AMPTIAC Quarterly).

The highlight of the event was the presentation of the cake, which bore a remarkably sharp image of the issue’s cover! The contributors in attendance assembled for a group picture with the cake (in foreground).

A Correction...We at the AMPTIAC Quarterly wish to extend our sincerest thanks to our readership – both in print and on-line – for all of the positive reviews and feedback we have received in response to our recent special edition (Volume 8, Number 4), which highlighted materials research at the

Army Research Laboratory (ARL). Reprint requests and downloads off the website have been at record-setting paces. It is gratifying to see the collective

six-month effort of so many people, both at ARL and at AMPTIAC, be so well-received.

We take great pride in providing our readership with timely and informative articles which meet the highest standards of journalistic excellence and

technical accuracy. Even so, errors do (albeit infrequently) make it to print, despite our best efforts. One such error in our last issue (v8, n4) was recently brought to our attention; on page 24 of the issue in Table 1. This table lists many of the major manufacturers of ceramic armor materials, and which

material products they currently produce for armor applications. In the bottom third, the table fails (by omission) to list Cercom, Inc. as a manufacturer of hot-pressed Silicon Carbide (SiC). In fact, Cercom has been one of the world’s largest manufacturers of SiC for many years. We apologize for this

error and any misperceptions it may have caused among our readers. In response, we have corrected this omission in the on-line version of the Quarterly

(downloadable in PDF format via our website). For those who have a particular interest in ceramic materials or ceramic armor applications, we would

recommend that you consider downloading a new and correct version for your records.

Thank you for your continued support. - Editor

Pictured from left to right: 

William Nothwang, Ernest Chin, 

Jerry LaSalvia, Pauline Smith, 

Laszlo Keckskes, Sandra Young, 

Robert Dowding, Kes Chesonis, 

John LaScala, Joseph South, 

James Sands, William Drysdale, 

Steven McKnight, Robert Carter, 

Larry Burton (front), Chris Grethlein

(AMPTIAC, back), Robert Woodman,

James McCauley, David Rose 

(AMPTIAC).
The AMPTIAC Quarterly, Volume 9, Number 1 27

John W. Lincoln Award Presented

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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Arlington, VA 22209-2110

(703) 588-7418, Fax: (703) 588-7560

Email: lewis.sloter@osd.mil

ASSOCIATE COTR

ENVIRONMENTAL PROTECTION

& SPECIAL FUNCTION MATERIALS

Dr. James Murday

Naval Research Laboratory

4555 Overlook Ave, S.W. Code 6100

Washington, DC 20375-5320

(202) 767-3026, Fax: (202) 404-7139

Email: murday@nrl.navy.mil

DEFENSE TECHNICAL INFORMATION CENTER

(DTIC) POC

Melinda Rozga, DTIC-AI

8725 John J. Kingman Rd, Ste 0944

Ft. Belvoir, VA 22060-6218

(703) 767-9120, Fax: (703) 767-9119

Email: mrozga@dtic.mil

DIRECTOR, AMPTIAC

David Rose

201 Mill Street

Rome, NY 13440-6916

(315) 339-7023, Fax: (315) 339-7107

Email: drose@alionscience.com

DEPUTY DIRECTOR, AMPTIAC

Christian E. Grethlein, P.E.

201 Mill Street

Rome, NY 13440-6916

(315) 339-7009, Fax: (315) 339-7107

Email: cgrethlein@alionscience.com

TECHNICAL INQUIRY SERVICES MANAGER

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Alion Science and Technology Personnel

Mr. Robert P. Bell, who retired from Lockheed Martin Aeronautics Company in July

2003, was presented the 2004 John W. Lincoln Award. It was given in recognition of his

outstanding work during his 37 year career with Lockheed Martin in advancing technology associated with aircraft structural integrity. At the time of his retirement, he was the

group supervisor and technical lead for the C-141 Aircraft Structural Integrity (ASIP)

Group. He is credited with leading the work to successfully apply the concepts of risk

analysis as developed by Dr. Lincoln to a number of critical C-141 problems, which

enabled the aircraft to continue to fulfill its missions during periods of increased airlift

requirements caused by crises such as Desert Storm, which interrupted normal aircraft

maintenance and inspection. Since his retirement from Lockheed Martin, he consults in

the area of aircraft structural integrity with CACI International. The Award was presented at the 2004 USAF Aircraft Structural Integrity Program (ASIP) Conference in

Memphis, Tennessee on 30 November 2004. 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 insure the safety and longevity of both military and commercial aircraft. The Award has been presented previously to Dr. Lincoln (1996), to Mr.

Charles Tiffany (1997), to Mr. Thomas Swift (1998), to Professor Jaap Schijve (1999), to

Professor Alten Grandt, Jr. (2000), to Dr. James Newman (2001), to Mr. Royce Forman

(2002) and to Mr. Ward Rummel (2003). A plaque with the names of the recipients is on

display during the ASIP Conference and then at Wright-Patterson Air Force Base, Ohio.
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