Conducting the Failure Analysis

George F. Vander Voort, Consultant

Principal EngineerP.O. Box 10

Wadsworth, IL 60083-0010

george@georgevandervoort.com

Catastrophic failures of all-

welded T-2 Tankers and

Liberty Ships in WW2 focused

attention on the field of failure

analysis and led to the

development of fractography

and fracture mechanics

Duplessis Bridge, Three Rivers,

Quebec, CanadaOhio River Bridge

Bridge failures have also

focused attention on

fractography, fracture

mechanics and failure analysis.Silver Bridge Between Ohio and

West Virginia

Despite Our Knowledge, Bridge Failures Still Occur!

Failure of bridge over the Tennessee River near Clifton, TN, reported in

newspapers on May 16, 1995.

Reasons for Conducting a Failure Analysis

• Determine the cause(s) of the failure

• Prevent similar problems with identical components

• Improve the performance of future parts

• Absolve your company of liability

• Pass the liability to others

Not all failures involve fracture

Non-Fracture Failures

• Ductile Deformation

• Creep

• Distortion

• Wear

• General Corrosion

• Leakage, e.g., Selective Leaching, Pitting, Crevice

Corrosion

Causes of Failure

• Poor Design

• Imperfections in Materials

• Imperfections in Manufacture/Fabrication

• Overloading/Service Abuse

• Improper Maintenance or Repair

• Environmental Effects

• Combinations of the above

Examination Steps

• Assemble Background Information

• Visual Examination of Failure

• Fractographic Examination

• Verify Materials Used

• Determine Mechanical Properties

• Metallographic Examination (Macro/Micro)

• Analyze Corrosion Deposits

Examination Steps

• Stress/Fatigue Life Calculations

• Perform Simulations

• Summarize and Analyze Data

• Write Report

• Follow-up on Recommendations

Information About the Failure

• Date and Time of Failure

• Temperature

• Environment

• Extent of Damage

• Sequence of Events

• Stage of Operation

• Drawings or Photographs

Information About the Failure

• Service Deviations/Abnormalities

• Information on Repairs

• Opinions of Operating Personnel

• Prior Observations

• Injuries

Information on the Failed Part

• Location, Name of Part

• Identifying Numbers, Owner, User

• Manufacturer, Fabricator

• Function of the Part

• Service Life at Time of Failure

• Rating of Part

• Load History

• Environment

Information on the Failed Part

• Manufacture/Fabrication Techniques Used

• Specifications and Codes

• Inspection Methods

• Stress: Orientation, Level, Nature

• Heat Treatment History

• Relevant Test Records

• Service Performance History of Like Parts

Be Objective!!!

Do Not Approach the Investigation

with Preconceived Notions!

The Failure Analyst Should –

Whenever Possible:

• Go Immediately To The Failure Site

• Get or Protect the Parts From Further

Damage Due to Repair Attempts, Improper

Handling, Corrosion, etc.

• Protect Parts from Damage During

Shipment to the Lab

• Get Someone Else to Do This If You

Cannot

For Most Failure Studies…

The origin(s) of the failure

must be determined, and

examined, if any conclusive

results are to be obtained

Failure Analysis Tools

• Human Eye and Brain

• Hand Lens

• Stereomicroscope

• Macro-Camera

• Light Optical Microscope

• Hardness Testers

• Replication Tape, etc.

Failure Analysis Tools

• SEM with EDS/WDS

• Electron Microprobe

• X-Ray Diffraction

• X-Ray Fluorescence

• Other Chemical Analytical Methods

• Mechanical Test Equipment

• PC and Modeling Software

Nondestructive Testing

• Magnetic Particles

• Dye Penetrant

• Fluorescent Penetrants

• Ultrasonic Inspection

• X-Ray Radiography

• Eddy Current

Look for Defects, Enhance their Visibility

Sequence for Examination of

Fractured Components

• Visually survey the entire component to obtain an overall

understanding of its operation

• Classify the fracture from a macroscopic standpoint as

ductile, brittle, fatigue, torsion, etc.

• Determine the origin(s) by tracing the fracture back to its

starting point(s)

• Determine the loading (tension, compression, etc), stress

level and orientation

• Use macrofractography to determine the fracture mode

and confirm the fracture mechanism

Do Not Remate Fracture Faces!!!!

Remating broken fracture pieces tells

you next to nothing and may destroy

much of the fine fracture details, thus

making microfractography difficult or

impossible

Before Cutting!!!!

Every possible piece of information

should be obtained before any

destructive work is started

Microfractography

• Certain failure modes or mechanisms cannot be

detected or proven by macroscopic examination

procedures.

• Microfractography can be used to obtain evidence

for certain mechanisms, such as stress-corrosion

cracking or fatigue.

Examining Fractures

Light Microscopy

Unaided Eye

Hand Lens

Stereomicroscope

Light Optical Microscope

• Direct Examination or Replicas

• Cross Sections – Fracture Profile

Examining Fractures

Electron Microscopy

Scanning Electron Microscope

Direct Examination or Replicas

Cross Sections – Fracture Profile

Transmission Electron Microscope

Replicas

Macroscopic Fracture Features

Necking or lack of necking

Flatness or curvature of fracture surface

Branching, or lack of crack branching

Crystalline or matte surface appearance

Microscopic Fracture Features

Cleavage facets and river marks

Dimples

Intergranular grain patterns

Striations

Splitting

Voids and tears

Metallographic Examination

Macroscopic Methods

Internal Quality

Surface Cases

Hard or Soft Spots

Flow Lines

Weldments or Coatings

Localized Heating/Grinding Scorch

Service Abuse

Microscopy Can Detect…

Grain Size

Inclusion Content

Matrix Phases or Constituents

Second Phases

Abnormal/Undesirable Phases

Surface Conditions

Degree of Homogeneity

Segregation/Banding

X-Ray Diffraction Is Used For…

Phase Identification

Amount of Phases (e.g., retained austenite)

Residual Stress

Texture

Chemical Analysis Techniques

X-Ray Fluorescence

ICP – Atomic Emission Spectrometry, Atomic

Absorption Spectroscopy

Flame AAS

Graphite Furnace AAS, Combustion Analysis

Inductive or Resistance Heated Fourier

Transform Infrared Spectrometry

“Wet” Techniques

Simulations

Evaluate the suitability of a materials in a

specific environment

Determine influence of temperature on

properties

Confirm that a specified heat treatment was

performed

Determine if a material was embrittled

Test various hypotheses

Typical Questions to Answer

What was the sequence of the failure?

What was the crack speed?

Where was the crack path?

Where there one or more initiation sites?

Did the failure start at, or below, the surface?

Was the failure located by a stress concentrator?

How long was the crack present?

Typical Questions to Answer

How high was the load?

Was the loading static, cyclic or intermittent?

How was the stress oriented?

What was the temperature?

If cyclic loading, how many cycles?

Was wear a factor?

Was corrosion a factor?

Typical Questions to Answer

If wear or corrosion were factors, what was the

mechanism?

Were the specified materials used?

Is a better material necessary?

Was the design adequate?

Are design changes needed?

Did the material meet specifications?

Were there any heat treatment irregularities?

Typical Questions to Answer

Any fabrication problems?

Was it properly assembled and aligned?

Was it repaired during service?

If repaired, was it done right?

Was it run-in properly?

Was it lubricated and maintained?

Was the failure due to abuse?

Typical Questions to Answer

Can the design be improved? How?

Are failures likely to occur in similar parts?

What can be done to prevent such failures?

The Report

The report should be written in a clear,

concise, logical manner, listing the most

probably cause(s) of the failure and other

legitimate possibilities, indicating any that

are conjectural

The Report Should Address

the Following:

Description of the failed item

Conditions at the time of failure

Relevant background information

Mechanical and metallurgical study

Evaluation of material quality

Evaluation of manufacturing process

Discussion of any anomalies

Description of failure mechanisms

Recommendations

The Report Should be Clearly Structured

with Sections such as:

Summary Recommendations

Introduction Background

Experimental Procedure Simulations

Results Discussion

References Appendices

Recommendations

Any recommendations regarding the

design, materials, fabrication methods,

etc., should be thoroughly reviewed that

they do eliminate the problem, but

without causing new ones.