Fractography is the interpretation of features observed on fracture surfaces and, although it is simple in many cases, it can prove to be fairly difficult in practice. This is particularly the case on high strength quenched and tempered steels, or in alloys (such as cast irons and pearlitic steels) where the microstructure affects the crack path. For metallic alloys, significant reference sources exist, often in the form of atlases of fractographs (see, for example, the references below). Once the fracture mechanism types have been identified at low magnification, the high magnification fractographs can be used for confirmation and to build up a 'reference library' of fractographs.

In general terms, there are three basic crack growth mechanisms possible in fast fracture - intergranular along grain boundaries (or interdendritic fracture), brittle fracture via cleavage along crystallographic planes (or through pearlite lamellae), and transgranular ductile fracture via microvoid coalescence. Fatigue, by definition, involves ductile fracture, which is usually transgranular (through the grains), although intergranular fatigue is possible under certain special circumstances. Although it may prove difficult to fractographically distinguish between fast fracture, fatigue or stress corrosion cracking under certain circumstances, overall consideration of the facts and circumstances of a particular case usually allow correct interpretations of the evidence.

Several internet sites exist to aid in identification of the fractographs shown, for instance, the various mechanisms of fracture (including fatigue) are outlined on a Virginia Tech page on fractography.  The scanning electron microscope (SEM) is an indispensable tool in the study of fracture surfaces, and a good introduction to the SEM is given on the webpages of the Iowa State University Materials Science & Engineering Department.

The fractography resource provides a general introduction to the science of fractography, together with images illustrating the various failure mechanisms. The images are presented as thumbnails and larger versions can be opened by clicking on these thumbnail images.

Fractography Resource Part 1 - Fatigue Macrofeatures

Fractography Resource Part 2 - Fatigue Microfeatures

Fractography Resource Part 3 - Fast Fracture - Macrofeatures

Fractography Resource Part 4 - Fast Fracture - Microfeatures (Cleavage, MVC)

Fractography Resource Part 5 - Fast Fracture - Microfeatures (IG)

Compendium of Fractographs - Steels, aluminium alloys, WC-Co, stainless steel and polycarbonate

References

1. Materials Handbook, 10th edition, Vol. 11 Failure Analysis, ASM International, Materials Park, Ohio
2. Materials Handbook, 10th edition, Vol. 12 Fractography, ASM International, Materials Park, Ohio
   
   Papers on the Methodology of Failure Analysis
   
   
3. GF Vander Voort, Conducting the failure examination, Metals Engineering Quarterly May 1975 p.31
4. BG Whalley, The analysis of service failures - part 1, The Metallurgist and Materials Technologist December 1982 p.569
5. BG Whalley, The analysis of service failures - part 2, The Metallurgist and Materials Technologist January 1983 p.21
6. BG Whalley, The analysis of service failures - part 3, The Metallurgist and Materials Technologist March 1983 p.137
7. BG Whalley, The analysis of service failures - part 4, The Metallurgist and Materials Technologist April 1983 p.193
8. BG Whalley, The analysis of service failures - part 5, The Metallurgist and Materials Technologist June 1983 p.273
   
   Papers on the Techniques Used in Failure Analysis
   
   
9. JA Nelson, Metallography’s role in failure analysis, Advanced Materials & Processes Vol. 11 1994 p.21
10. A Wedgwood, Measuring residual stress: the key to longevity, Materials World January 1994 p.5
11. AG Wojcik, Potential drop techniques for crack characterisation, Materials World August 1995 p.379
12. T Kobayashi and DA Shockey, FRASTA: a new way to analyze fracture surfaces, Advanced Materials & Processes Vol. 11 1991 p.28
13. T Kobayashi and DA Shockey, Fracture analysis via FRASTA, Advanced Materials & Processes Vol. 12 1991 p.24
    
    Fractography in Failure Analysis
    
    
14. MN James, Fractography during failure analysis - what it reveals, The South African Mechanical Engineer Vol. 37 January 1987 p.25
15. JB Ward, Analysis of glass fractures, Materials & Design Vol. 8 No. 2 March/April 1987 p.100
16. RD Zipp, Preservation and cleaning of fractures for fractography, Scanning Electron Microscopy, 1979 No. 1 p.355-362
17. EP Dahlberg and RD Zipp, Preservation and cleaning of fracture surfaces - update, Scanning Electron Microscopy, 1981 No. 1 p. 423-429
    
    Welds, Design, Inspection and Lessons From Failures
    
    
18. MN James, Design of weldments subject to dynamic loading, Mechanical Technology April 1996 p.31
19. MG Silk, Weld inspection methods, Metals and Materials April 1989 p.192
20. JD Harrison, Lessons from service failures, The Welding Institute Research Bulletin March 1980 p.68
    
    Forensic Engineering and Case Studies
    
    
21. MN James, The role of the fracture expert in failure analysis, Forensic Engineering 1991 Vol. 3 No. 1 p.7
22. MN James, Some potential pitfalls in failure analysis, International Journal of Fatigue 1995 Vol. 17 No. 7 p.457
23. AW Knott, Are you an expert? Forensic Engineering 1987 Vol. 1 p.7
24. R Ziernicki, Working with the manufacturer in product cases, Forensic Engineering 1991 Vol. 3 No. 4 p.171

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