Failure Analysis 1 - Intro · 2017. 11. 2. · 3 Steps in Failure Analysis 1) Gathering background information and evidence 2) Visual examination (unaided eye/photography-macro and

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Course Materials

1. W.D. Callister, Jr., D.G. Rethwisch, “Materials Science and Engineering: An Introduction”, 8th Ed, John Wiley and Sons, 2010.

2. G.E. Dieter, “Mechanical Metallurgy” (SI Metric Edition), McGraw-Hill, 1988.3. W.F. Hosford, “Mechanical Behaviour of Materials”, Cambridge University Press,

2005.4. A.J. McEvily, J. Kasivitamnuay, “Metal Failures: Mechanisms, Analysis,

Prevention”, Wiley-Interscience, 2013.5. I. Milne, R.O. Ritchie, and B. Karihaloo (Eds.), “Comprehensive Structural

Integrity”, Elsevier, 2008.6. M.F. Ashby, D.R.H. Jones, “Engineering Materials I”, 3rd Ed, Butterworth-

Heinemann, 2005. 7. A.K. Das, “Metallurgy of Failure Analysis”, McGraw-Hill, 1997.8. W.T. Becker, R.J. Shipley (Eds.), ASM Handbook, Volume 11, “Failure Analysis

and Prevention”, ASM International, 2002.9. D. Hull, “Fractography: Observing, Measuring and Interpreting Fracture Surface

Topography”, Cambridge University Press, 1999.10. H.M. Tawancy, A. Ul-Hamid, N.M. Abbas, “Practical Engineering Failure

Analysis”, Marcel Dekker, New York, 2004.

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Steps in Failure Analysis

1) Gathering background information and evidence2) Visual examination (unaided eye/photography-macro

and micro)3) Obtaining specimens, marking and coding4) Chemical analysis5) NonDestructive Testing (NDT) (Dye penetrant,

Magnetic particle, Eddy current, Ultrasonic, Radiography)

6) Destructive Testing (Tension, Compression, Bending, Torsion, Impact, Fatigue, Fracture Toughness, Creep, Wear)

7) Specialized tests simulating the service environment8) Collecting all pertinent information&writing FA report

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Information Required In FA Report

1) Information regarding the failure event2) Service conditions regarding the failure3) Service records for the component4) Chemical composition and mechanical properties of

the component5) Mechanical and metallurgical test results6) Proposed cause and mechanism for failure7) Recommendations for failure prevention

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Schematic bathtub curve depicting failure rate as a function of service life

Bathtub Curve

(Source: A.K. Das, “Metallurgy of Failure Analysis”, McGraw-Hill, New York, 1997, p. 4)

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Fracture is the separation of a material into two or more pieces as a result of imposed stress.

BrittleGranularCleavage

DuctileStrain to fractureFibrousAppearance of fractureShearCrystallographic mode

Terms UsedBehavior

Fracture

Terms commonly used to describe fractures:

(Source: G.E. Dieter, “Mechanical Metallurgy”, McGraw-Hill, London, 1988, p. 242)

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{0002}{0001}HCPNone{111}FCC{001}{110}BCCCleavage planeSlip planeCrystal structure

On an atomic scale, fracture occurs by the formation of new crack surfaces through the breaking of interatomic bonds.

If fracture occurs by the breaking of atomic bonds perpendicular to specific crystallographic planes, this type of fracture is called cleavage. Slip on the other hand occurs by the breaking of atomic bonds duringthe gliding of specific crystallographic planes.

(Source: 1. W.F. Hosford, “Mechanical Behaviour of Materials”, Cambridge University Press, Cambridge, 2005, p. 121, p.218; 2. Pineau, A., Pardoen, T., Failure of metals, in “Comprehensive Structural Integrity”, Chapter 2.06, Elsevier, Oxford, 2008 p. 688.)

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In metals, two fracture modes are possible: ductile and brittle.

Ductile metals typically exhibit substantial plasticdeformation with high energy absorption before fracture.

Ductile Fracture

Brittle metals normally display little or no plastic deformation with low energy absorption during fracture.

Brittle Fracture

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Ductile and brittle are relative terms; whether a particular fracture is one mode or the other depends on the situation.

Ductility may be quantified in terms of percent elongation (%EL) and percent reduction in area (%RA).

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Macroscopic Fracture Profiles

Highly Ductile Moderately Brittle Brittle

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Ductile FractureCup-and-cone fractures are common in ductile metals.

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Ductile Fracture (cup-and-cone)

Microvoid coalescence process

FibrousShear

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Dimples are traces of the microvoids produced during fracture.

(Source: W.F. Hosford, “Mechanical Behaviour of Materials”, Cambridge University Press, Cambridge, 2005, pp. 212-213.)

Dimples