The objective of this course is to provide a basic overview of failure analysis. It will include discussion of failure mechanisms, analytical techniques and case histories • To provide you with a clear understanding of terms used so that you can ask the right questions and interpret common observations with ease Types of failures Failure modes How to conduct failure analysis Analyze data Failure mechanism Prevention of Failures Failures examples

1. Failure Analysis
By - K.Sevugarajan
Contact details
Metz Lab Pvt.Ltd.
First floor, Thangavel Nagar
Walajabad Main Road,
Mannivakkam-600048
Cell: +91-8190810222
Mail: sevuarajan@metzlab.org
www.metzlab.org

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Outline
• Principles
• Types of failures
• Failure modes
• How to conduct failure analysis
• Analyze data
• Failure mechanism
• Prevention of Failures
• Failures examples

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Introduction
• The objective of this course is to provide a basic
overview of failure analysis. It will include discussion of
failure mechanisms, analytical techniques and case
histories
• To provide you with a clear understanding of terms
used so that you can ask the right questions and
interpret common observations with ease

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1. Principles
Examinations
♦Detection and characterization of damage
Materials
♦Identification of damage mechanisms, allowing
application of appropriate damage initiation/
propagation modelisation
Engineering Analysis
♦Identifications of damage development with
respect to specific manufacturing process
♦Basis for determining safe operating periods and
expected remaining life.

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Qualities Desired in an Analyst
• Ability to remain unbiased and reject conventional
wisdom.
• Ability to facilitate a group of people (if using a team)
towards a common objective.
• Trained in logic tree approaches to failure analysis.
• Affinity for listening and questioning for
understanding.
• Patience and perseverance.
1. Principles

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1. Principles
Failure Analysis Tasks
• Prioritize - Determine what is most important to
work on.
• Analyze - Analyze the failure event to determine root
causes.
• Recommend - Develop recommendations as
solutions to the causes are discovered.

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1. Principles
First Principle of Failure Analysis
Do Not Touch!!!!!!
Observe !!
Remember the phrase
“See but do not touch”
Visual Examination is everything
Macroscopic/Microscopic
Gut feel is very important
Understand the Operating conditions of the part

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2. Types of failures
• Ductile
• Brittle
• Fatigue
• High
Temperature
Excess deformation,elastic or plastic,
tearing or shear failure
Cleavage, sudden
Cycling load, strain, thermal, corrosion,
rolling contact, fretting
Creep, oxidation,
local melting, warping
• Static Delayed Embrittlement - Hydrogen, caustic,
• Stress Raisers
liquid metal, temper, environmental
Sharp fracture initiation points

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3. Failure modes
Failures can be classed in three broad categories: failures caused by the deformation
of parts, failures due to rupture and failures due to surface damage.
PERMANENT DISTORTION : The part can no longer be used because it is deformed.
FRACTURES : Various types of rupture may be distinguished, depending on the
appearance of the fracture surface and the forces applied.
Static sudden fracture under or static constant load, resulting from an impact
or from exceedence of the maximum allowable load.
Ductile and brittle fracture
Delayed breakage
Fracture due to hydrogen embrittlement
Stress corrosion fracture
Fatigue fracture Creep fracture
Stress corrosion fracture

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3. Failure modes
SURFACE DAMAGE : This category covers many different types of damage
affecting a wide variety of mechanisms.
The common characteristic of all these is that they cause deterioration of
the surface of the metal, which eventually leads to the destruction of the
part.
Surface fatigue (or “contact fatigue”)
Frosting or hairline cracks
Uniform spalling
Wear
Abrasive wear
Adhesive wear or scuffing Fretting-corrosion
wear Cavitation-Erosion
Thermal fatigue
CORROSION

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3. Failure modes
• Misuse or Abuse
• Assembly errors
• Manufacturing defects
• Improper maintenance
• Fastener failure
• Design errors
• Improper materials
• Improper heat treatments
• Unforeseen operating
conditions
• Inadequate quality assurance
• Inadequate environmental
protection/control
• Casting discontinuities
Causes of Failure

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3. Failure modes
Frequency of Causes of Failure in Some
Engineering Industry Investigations

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3. Failure modes
Frequency of Causes of Failure in Some
Engineering Industry Investigations

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4. How to conduct failure analysis
Practical Issues in Failure Analysis
• Visual Inspection - surface cleanliness
• Electrical tests for continuity.
• “Drop and suck” test - solvent placed in local
area, sucked and analyzed for contaminants.
• Cross sectioning to see thickness variations
during processing
• Scanning/Auger Spectroscopy or Rutherford Back
Scattering
• Delamination

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4. Steps in Failure Analysis
• Description of Failure Situation
• Visual Examination
• Design/Stress Analysis
• Chemical Analysis
• Fractography
• Metallographic Examination
• Properties- hardness or other mechanical
properties
• Failure Simulation

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4. Stages In a Failure Analysis
• Collect data
• Visually examine failure
• Non Destructive Testing
• Select samples
• Examine and analyze
• Determine failure mechanism
• Write report

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4. Sample Preparation
• Fracture surface is dirty and contaminated
- Rinse in alcohol or acetone using
ultrasonic cleaner - Dry
- Replicate using cellulose acetate tape
- Gold or carbon coat (200A) the surface
- Examine in microscope

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4. Collection of Data
• Collect information
• Review sequence of events leading to failure
• Get drawings and records, repair history
• Photograph the failure in several angles
before destruction for examination
• Get information on good samples for
comparison

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4. Visual Examination
• Examine before cleaning
• DO NOT TRY TO FIT THE BROKEN PIECES
BACK TOGETHER! YOU MAY DESTROY
THE REAL EVIDENCE- AVOID THE
TEMPTATION

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Acronym
es
Technique Information provided
EC Eddy current Detection of anomalies by differential
electrical current response
MRI Magnetic resonance imaging Identification of features and structure via
introduction of alternating magnetic fields
MT Magnetic particle examination Detection of surface and near surface flaws
in ferromagnetic materials by flux leakage
PT Penetrant testing Identification of flaws and cracks open to
the surface in many materials via liquid
retention
RT Radiographic examination Identification of material flaws and features
via density differences measured by
penetrating radiation
UT Ultrasonic examination Detection of anomalies by differential
reflection of ultrasonic pulses
4. Typical Non destructive testing

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4.Materials analysis
Chemical analysis: Chemical analysis is an integral part of an
investigation, because it indicates whether a component is made of the
specified material
Metallography : Examination of cross sections of materials involved in a
failure can provide important insights into the probable cause of the
incident.
Metallography can reveal such as :
• macrostructure,
• depth of surface hardening
• microstructure, such as grain size and the phases present
• non-metallic inclusions
• porosities…

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4.Materials analysis
Fractography and SEM examination : Fractography generally involves a
scanning electron microscope
SEM observations can reveal such as :
• fine microstructure, such as phases and precipitations
• cracks initiation and fatigue striations
• fracture modes (dimples, cleavage, intergranular fracture)
Microanalysis : Corrosion products, inclusions, metallurgical phases
can be also chemically identified via electron microscopy and energy
dispersive spectrometry.
Mechanical testing :In addition to the examination methods, hardness
measurements can be realized.

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4.Materials analysis
Surface aspect evaluation : Surface roughness can also be evaluated.
Special testing
This group of tests includes all those that do not easily fit into the
previous categories. The following are a few of the more important
techniques.
• Finite element analysis: Finite element analysis, or FEA, is an
advanced modeling technique that can help to predict the magnitude
of stresses on individual components within complex assemblies.
• Simulation: In some instances, sophisticated test apparatus can be
developed for approximating the service conditions involved in a
materials failure.

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5. Analyze data
The assembled results from the different analysis and tests must be
considered collectively, because the final hypothesis needs to be in
substantial agreement with all physical evidence and test results.

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Determine failure mechanism
A part or assembly is considered failed if one of the
following conditions occur:
• It becomes completely inoperable
• It’s operable but no longer functions
satisfactorily
• It’sdeteriorated to the point it is unsafe
or unreliable.

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Failure Mechanisms

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Failure Mechanisms
Characteristics of Ductile fracture
Ductile fracture has dimpled, cup and cone fracture appearance. The dimples can
become elongated by a lateral shearing force, or if the crack is in the opening
(tearing) mode.
Steel 22MnB5
GS52 cast iron
Steel 20MnCr5
with elongated manganese
sulphide
The size and shape of the dimples depends
on the inclusions

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Failure Mechanisms

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Failure Mechanisms
Brittle fracture displays either cleavage (transgranular) or
intergranular fracture. This depends upon whether the
grain boundaries are stronger or weaker than the
grains.

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Prevention of Failures
• Many failures can be avoided by:
• Correct design
• Selection of appropriate materials
• Correct processing
• Consideration of service environment
• Required: system engineering approach

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Prevention of Failures: Design
• Design for maximum stress
• Include safety margin
• Avoid and do not create stress raisers
• Do not break fiber reinforcements

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Prevention of Failures: Materials
• Temperature range of operation
• Do not cross polymorphic transformations
• Understand fatigue conditions
• Stress-rupture lifetime
• Quenched and tempered materials loose
strength at higher temperature
• Age-hardened materials lose strength at high
temperature

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Prevention of Failures: Processing
• Cast to required grain size
• Casting may create gas porosity and segregation
• Cold working and forging create cracks, flaws,
inclusions
• Welding creates gas porosity, cracks, recrystallization
affecting strength
• Heat treatment may create surface cracks upon
quenching, decarburize surface layers, create
agglomerations at grain boundaries

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Prevention of Failures: Service
• Thermal and chemical environment must be
understood
• Avoid overload
• Use tools for applications it was designed for
• Control wear
• Check parts by non-destructive testing methods
• Have rigorous maintenance program and quality
control
• Avoid bogus parts

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Failure Analysis Report
• Description of the failed component
• Service condition at the time of failure
• Prior service history
• Manufacturing and processing history of component
• Mechanical and metallurgical study of failure
• Metallurgical evaluation of quality
• Event Summary of failure causing mechanism
• Recommendations for prevention of similar failures

36. UH-1N Turbine: helical Shaft Failure F-18 Engine Shaft
Torsional Buckling
Torsion Failures
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Examples

37. Gross Plastic Deformation
UH-1N Engine
Shaft/Bearing
UH-1N Turbine
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38. Ductile & Brittle Failure in Tension
Brittle
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39. Brittle Failures from Rotor Systems
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Rivermarks & Chevrons
Arrows shows origin
of failure

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Fatigue Failures

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Bending Deformation & Failure
In-flight
failure

43. Buckling
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Damaged Rotor of Gas Turbine

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Heat Check Lines

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Feature of Stress Corrosion
Cracking - Crack Branching

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Microstructure of Weld Zone

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Cracks due to Thermal Stresses in
the Weld Zone

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Failure in Super heater Outlet
Header

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Chevron Notches in Fasteners

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Bolt Failure Due to Ductile
Overload

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Ductile and Brittle Fracture
• Ductile fracture -
Fracture accompanied by
plastic deformation and,
therefore, by energy
absorption - cup and cone
• Brittle Fracture -
No Energy absorption
Left Bolt Rc 57 Brittle
Right Bolt Rc 15 Ductile

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Failure of Bolts
Bending fatigue of the bolt

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Failure of Gears
Progressive pit of a pinion gear tooth due to surface
contact fatigue

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Distortion Failures
failures occurDistortion
when a structure or
component is deformed. It
fails because it can no
longer support the load it
was intended to carry.

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Wear Failures
Wear - undesired removal of material from rubbing
surfaces.
• Abrasive
• Adhesive

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Spring Failure
Spring failure by combination of bending, torsion and
fatigue.

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Cracking in Cup
Stress corrosion cracking of deep-drawn brass cup

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Cracking in Tube
Stress corrosion cracking of brass tube

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Horse Bit Failure
Fracture in horse bit

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Stirrup Failure
Horse racing stirrup failure

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Bicycle Hub Failure
Bicycle hub failure in rear wheel

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Bicycle Pedal Crank Failure
Fatigue crack in a crank

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Steel Bolt Failure
High tensile steel bolt fatigue failure

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Road Vehicle Stub Axle Failure
Bending fatigue of a steel stub axle

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Car Engine Failure
Combustion chamber Engine Failure

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Cylinder Split along Seam

68. Thank You !