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FAILURE ANALYSIS
Introduction
Definition
Failure Analysis and Prevention
Objectives of Failure AnalysisObjectives of Failure Analysis
Part one
The causes of fracture
I Tupes of fracture
Il Test methods
Part two
Some examples
Conclusions
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Failure causes
Failure causes %
Design 10
Material/Process 60
Use 30Use 30
carenze di progetto
utilizzo non adeguato
non conformit
materiale/processo
INTRODUCTION
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WHAT IS FAILURE ANALYSIS?
The FAILURE ANALYSIS is the critical method adopted toidentify the physical reasons that originate the fracture or thefunctional anomaly.functional anomaly.
The word FAILURE does not referred exclusively toBREACKAGE but to any phenomenon that induces aperception of a not regular operation of a mechanical part.
It is a technical instrument to improve the quality and thereliability of product.reliability of product.
It evidences the critical situations of a component (part orcomplex product) that lead to economic decline, object orpeople damages or accidents.
It s an instrument of continuous improvement of the product.
FAILURE ANALYSIS E PREVENZIONEQualit ed Utilizzo Atteso di un Prodotto
CUSTOMER SATISFACTIONIn the early 80s, by opening of markets, emerged
the need to improve
Product Quality
Greater attention to Product, resulted in
development of activities designed to:
Manufacture products immediately
MAJOR SAFETY
MAJO RELIABILITY
MORE PERFORMANCE
HIGHER EFFICIENCY
EASY MAINTENANCE
Product Quality
And orient business strategy to
Customer Satisfaction
comply
(do the right thing, right the first time)
This choice has generated quality products,able to satisfy greater expectations ofconsumers and users .
EASY MAINTENANCE
LOW OPERATING COSTS
LOW ENVIRONMENTAL IMPACT
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FAILURE ANALYSIS E PREVENZIONEProblem Solving, Qualit e Soddisfazione del Cliente
Objectives of quality improvement can be reached with the activity ofFailure Analysis, by applying the methods of :
PROBLEM SOLVINGPROBLEM SOLVING
analyzing and evaluating fully technically relevant properties of a product:
SHAPE ADAPTABILITY
CAPABILITIES SERVICE LIFE
When a functional problem arises its necessary pay great attention andavoid mistakes such as: :avoid mistakes such as: :
Do nothing and hope that the problem will go away
Deny the existence of the problem and minimize its importance
Considering the issue accidental
Follow false trails
FAILURE ANALYSIS E PREVENZIONEModel of Problem Solving
Identify
Standardization Determining the causes
Identify
Identify the problem
Collect data
Make assumptions
Test hypothesis
Validate and verify the corrective actions
Corrective actions
development
Test hypothesis
Develop conclusions
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FAILURE ANALYSIS AND PREVENTION
Definition of Failure
Failure:
Occurrence of an event or a situation undesired . Occurrence of an event or a situation undesired .
When a component does not carry out its function properly.
Levels of Rupture:
1. Loss of efficiency
2. Loss of efficacy
3. Loss of operation
FAILURE ANALYSIS AND PREVENTION : Design life
There is no mechanicalcomponent that can endure andwork forever.
Breaks can not be totally avoided .
Can be evaluated, anticipated andcontrolled .
The premature failure (InfantMortality) are often associatedwith problems of quality andworkmanship.
Breaks during the life cycle(Design Life) are less frequentand often random.and often random.
Breaks at the end of the life cycle(Wearout Failures) are due tonatural wear of the components.
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AIM OF FAILURE ANALYSIS
Its carried out to identify the causes of failure Its carried out to identify the causes of failure and prevent the phenomenon happen again.
It can, but does not necessarily, lead to the identification of the causes of fracture.
It is used to activate corrective actions for recovery or improvement.
FAILURE ANALYSIS: Levels of investigations
Three levels to identify:
Physical causes: emergingfrom the laboratory analyzes,
For example:
Rupture of a pressure vessel Physical causes: emergingfrom the laboratory analyzes,calculations, simulations andrelated materials.
Human causes: humanfactors, operating errors,improper use, etc..
Underlying causes:procedural errors,environmental problems, or
Rupture of a pressure vessel
Corrosion with thicknessreduction
Inadequate inspectioncontrols
Insufficient training ofinspection staff
environmental problems, orimponderable causes
Insufficient training ofinspection staff
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OBJECTIVES OF FAILURE ANALYSIS: Requirements
Failure Analysis requires an interdisciplinary approach for Failure Analysis requires an interdisciplinary approach for
an appropriate choice of corrective actions .
Many breaking involve factors crossing several disciplines,
such as metallurgy, mechanical engineering, quality control,
maintenance, human factors, etc..maintenance, human factors, etc..
Teamwork
PART ONE
Causes of RuptureCauses of Rupture
Failure ModesFailure Modes
Investigation methodsInvestigation methodsInvestigation methodsInvestigation methods
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CAUSES OF RUPTURE
PRIMARY CAUSES
Design deficiency
Material defects
Production and/or installation defects
Improper application state
Environment
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DESIGN
COMPROMISE PROJECT DEVELOPMENT
Idea
General arrangement
PRICE
QUALITY
PERFORMANCES
RISKS
General arrangement
Detail:
materials selection
production process
product objectivation
required performances
application conditionsRISKS
application conditions
constrains
criticalities and fracture
risks
CONSTRAINS
Structural computationStructural computation
Stress analysis
and
component sizing
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MATERIAL
SELECTION
Identification of the optimal
combination among:
SELECTION
Materials
Heat Treatments
Technologies
CONSTRAINS
Functional
SpecificationsSpecifications
Object Analysis and
MISSION Settlement
(performance,
duration,
operative cycles)
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CONSTRAINS
Product
specificationspecification
Quality standard,
definition of acceptability,
limits of defects,
dimensional and shape dimensional and shape
tolerances .
DESIGN DEFICIENCY
NOTCHESNOTCHES
VARIATIONS ON THE CHEAP
(ABATEMENT-cost reduction)
TAKE OFF WEIGHT VARIATIONS
CARRY OVER
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DESIGN DEFICIENCY
NOTCHES
To place notches in high stresses zone increases theoperational failure risk.operational failure risk.
(e.g. reduced junction radius in change of sections of ashaft undergone torsionals or bending stresses)
DESIGN DEFICIENCY
ABATEMENTS VARIATIONS and/or TAKE OFF WEIGHT
It is necessary to have a good evaluation of the ratioeconomical advantages / risk factor increases.economical advantages / risk factor increases.
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DESIGN DEFICIENCY
TECHNOLOGICAL TRANSFER or CARRY OVER:
Carefully consider the possible increase of theCarefully consider the possible increase of thestresses and the Mission of the new component
Material Defects
Forged and Moulded
components
Flashes
Extrudes and drawn
components
Flakes
Melting
Porosity, gas
Flashes
Burnt parts
Flakes
Segregations
Shrinkage pores
Band distributions
Inclusions
Flakes
Dechoesions
Signs
Burnt parts
Porosity, gas
Shrinkage pores
Segregations
Cold joints
Inclusions
Plates and sheets
Flakes
Peeling
Scales
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Material defects
They are generally described as Discontinuties which reduce the
performances of products
Despite the controls and continous improvement of productionDespite the controls and continous improvement of production
processes , defects are always present in materials.
It may be necessary to make strict and frequent controls,
depending on the criticality of the product.
Manufacturing
Technological process
aimed to the realization of
a product as described by
Manufacturing/Installation
a product as described by
technical documentation,
using raw materials.
InstallationInstallation
Construction process on site
(plants, structures,
buildings, ecc.)
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Manufacturing defects
Machining
Cracks
Vibrations
Microstructural damages due to worn tools
Re-melting due to electrostatic discharges
Intergranural - electrochemical attack
Residual stress
Grinding defects
Manufacturing defects
Plastic deformation (Molding)
Cracks, rips, failed filling Cracks, rips, failed filling
Thread folding (rolling)
Die tracks
Surface ripps
Residual stress
Stress corrosion cracking (lubricants) Stress corrosion cracking (lubricants)
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Manufacturing defects
Mechanical processing
Steel hub made of 42CrMo4.
Explosion during broaching due to folding of molding
Manufacturing defects
Mechanical processing
Molded water trap of brass OT58:
Tool contaminated by particles of Fe which oxidizes forming
blotches
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Heat treatment
Grain coarsening
Incomplete phase
Manufacturing defects
Incomplete phase
transformations
Quenching cracks
Decarburizing
Residual stresses
Manufacturing defects
Welding
Lack of melting
Cracks and brittlenes in HAZ
Residual stresses
Porosities
Slag inclusions
Craters
Hydrogen embrittlement
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Residual stresses
They are stresses present in the component after heattreatment, mechanical working and / or plastic strain.
They are caused by not uniform deformation for processes thatinduce high temperature or stress gradient in thecomponents.
Residual stresses can show a positive or negative effect:
Positive if compressive stresses (fatigue life)
Negative if tensile (cracks and deformation after mechanicalworking (cutting, turning, drilling, grinding).
Residual stresses releaving
Stress Relieving is carried out at temperature of about 75 Cabove the transformation temperature (A in Fe-C diagram).above the transformation temperature (A1 in Fe-C diagram).
In practice, the treatment is carried out at about 650 C for anhour or until the whole piece reachs the treatment temperature.
In this way about 90% of residual stresses are released .
Alloy steels are heat treated at higher temperatures.
At the end of the cycle, the components are removed from theAt the end of the cycle, the components are removed from thefurnace and cooled in still air.
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Installation defects
Assembly/Installation
Misalignment
Component lack
Wrong choice of component
Wrong positioning
Excessive/scarce tightening Excessive/scarce tightening
torque
Not suitable tools
Unauthorized modification
Unsuitable conditions of use / stress
Not always a priorexpected
They depend on theThey depend on themanner of usage.
No more allowable
Use in nonstandardconditions in respect toproducer specificationsproducer specifications
Working environment moreaggressive than expected
Insufficient maintenance
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Stresses
Main types of
stresses and
cracking mode:
overloaded
Environment
Not always evaluable in advance
(humidity, temperature,(humidity, temperature,
contamination, etc..).
Difficult to assess in retrospect,
downstream of the failure.
Often its synergistic with other
critical factors (i.e. pressure
variability, internal stress, etc..)
Triggers failure modes peculiar,
often unexpected
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Erosion
Seat pump for food mixture stainless steel AISI406
Cratering surface erosion by solid
METHOD OF RESEARCH
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There is an old saying of American carpenters that analysts haveadopted for Failure Analysis :
MEASURE TWICE BEFORE CUT
The failure analysis can be considered as a surveyinvestigation of an inanimate body.
Before start, well its necessary organized mentallyabout the procedure that have be adopted.
Its therefore essential working with: Its therefore essential working with:
METHOD
ORGANIZATION FOR FAILURE ANALYSIS
COLLECTING OF FUNDAMENTALINFORMATION
VISUAL INSPECTION
NOT-DESTRUCTIVE TESTING
RESIDUAL STRESS RELIEF
DESTRUCTIVE TESTING
ANALYSIS OF RESULTS
GUESSES AND REPORT OF ANALYSIS
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DATA COLLECTION: what information are to be collected?
Acquire all the information Acquire all the information relating to events that occurred before and at the time of rupture
Acquire all the information relating to the manufacturing procedures of the particular Brokenof the particular Broken
operational requirements
DATA COLLECTION: what information are to be collected?
operational requirements
Running time (hours, km,)
Temperature e pressure
Materials specifications
Static and dynamic loadingconditions
Environmental conditions(corrosion, erosion)
Vibrations and cyclic loads appliedVibrations and cyclic loads applied
Maintenance applied
Other data deemed useful to theinvestigation
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VISUAL ANALYSIS
It 's the first and mostimportant step in ruptureanalysis: from everythingthat it can be record, it willinfluence the correctinfluence the correctcontinuation of theinvestigation
Examining the scene,sketching, take measures,notes and photographs,whenever possible
Selecting parts to removeand analyze in the laboratoryand analyze in the laboratory
Carefully examine all the finds
VISUAL ANALYSIS
Carefully examine all the findswith the aid of a magnifying
Take pictures and micrography
Assess the presence ofabrasion, overheating, stressstates, corrosion.
Remove samples of corrosion orforeign material for necessaryanalysisanalysis
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When the size of the affected component is relevant, the choice of thesampling areas is decisive on the outcome.
VISUAL ANALYSIS
VISUAL ANALYSIS
Dimensionalmeasurements, if deemednecessaryAnalyze the fracture:triggers, appearance offracture at the starting, inpropagation and in the finalstages of breaking.stages of breaking.
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SAMPLES TAKING
VISUAL ANALYSIS
identify the sites of taking andphotograph it before cutting
take as much as possible in the area ofrupture
avoid damage of the zones of rupture
clean samples befora examine it
Do not use abrasives or acids forcleaningcleaning
... clean the samples before examine it without using anyabrasives or acids for cleaning (when its enough!).
VISUAL ANALYSIS
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NOT-DESTRUCTIVE TESTING
RADIOGRAPHY
CT (Computerized tomography)
MAGNETOSCOPY
PENETRATING LIQUIDS
ULTRASOUNDS
INDUCED CURRENTS
Modes of fracture
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Modes of fracture
STRAIN
FRACTURE
CORROSION
WEARWEAR
Instantaneous
Fracture can be:
Instantaneous Overcharge (ductile/brittle)
Progressive Fatigue Corrosion Wear Creep Creep
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Modes of fracture
Fracture
It is typically defined as separation of material.
It can ductile or brittle
Any mechanism of structural separation, which
progressively leads to rupture.
Modes of fracture
Plastic strain
It occurs when a geometric modification prevents the component to perform its
function.
Changes in the geometry result in changes involume (bulge, shrinkage) or shape (twisting,bending or crushing).
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Modes of fracture
Corrosion
Decaying of the material for environmentalcauses.
The most common type of corrosion metals isthe electrochemical corrosion.
Other forms comprise brittleness by immersionin liquid, molten salts, heat oxidation, etc..
Modes of fracture
abrasiveabrasive erosiveerosive
Wear
Removal or distribution ofsurface by contact and relativemotion with solid, liquid or gas.motion with solid, liquid or gas.Loss of material and load-bearingcapacity, phenomena ofadhesion, increased friction andformation of metal chips.
adhesiveadhesive
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Instantaneous fracture: Strain Ductility
Ductility
tendency of a material to deformsignificantly plastically before fracturing.
Brittlenes
Tendency of a material to fracture without exhibit before asignificant plastic deformation
Instantaneous fracture: Fracture brittleness
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Instantaneous fracture by overcharging: Ductility and brittleness
Ductile fracture Brittle fracture
Ductile fracture: DIMPLES (micro-ductility)
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Traction
Ductile fracture: DIMPLES orientation
Traction
Twisting
Brittle fracture: CLEAVAGE and INTERGRANULAR
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Brittle fracture: CLEAVAGE
Brittle fracture: INTERGRANULAR
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Ductile / Brittle Transition
Materials with body-centered cubic lattice
Damage produced by repeated stress through time
Fatigue: Progressive Fracture
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Main features of fatigue
It is essentially a surface phenomenon.It depends on the stress value, not onthe frequency.the frequency.
Also the propagation rate depends onthe amount of the stress value.
May synergistically appear with othersources of degradation of materials (eg,thermal fatigue, stress corrosion, etc.)..
The morphology of fracture ischaracteristic.
Fatigue: Morphology of fracture
Flession + traction Twisting
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At higher magnification ...
Flession + traction Twisting
At higher magnification ...
Flession + traction Twisting
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Waves of fatigue (beach marks)
Waves of fatigue (beach marks)
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PITTING CORROSION
Nozzle head shot blasting machine by water of C40 with nickel plating
Pitting:contamination of the grit with iron oxidePitting:contamination of the grit with iron oxide
Tube of stainless steel AISI 304
Pitting: perforating corrosion
Interstitial Corrosion: CREVICE
It occurs at the interstices, wherepassive film breaks (e.g., theconjunction of two metallic parts)conjunction of two metallic parts)
- generally its development is due todifferentiated aeration betweenexternal and internal surfaces
- its generally produced in neutralenvironments
- it affects bulk materials and coatings
- its also produced in metal-nonmetalcontacts (eg. seals), obviouslydamaging the metal part.
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CORROSION FATIGUE
Wheel rim of magnesium alloy: fatigue fracture enhanced by corrosion
The wheel rim is not varnished: corrosion starts from edge of thespokes and there nucleates fatigue fracture
WEAR: Abrasive wear
Al 6060 of the body of hydraulic pump:
Abrasion of inner wall: insufficient hydrostatic capacity of oil atlow rpm
Recommended