Chapter 8

2. Chapter 8 Fractography and Failure Analysis Fractography • Fracture Surface Orientation • Fracture Surface Morphology • Failure Analysis • Destructive Examination • Failure Analysis Report

3. Fractographyis performed at macroscopic and microscopic levels of magnification.

4. Ductile metals loaded under tension will fracture at a 45° angle to the tensile stress. Brittle metals loaded under tension will fracture perpendicular to the tensile stress.

5. Necking is the reduction of the cross-sectional area of a test specimen. Shear lip is the 45° final fracture of a test specimen.

6. Ductile metals loaded under compression will bulge but do not usually fracture. Brittle metals loaded under compression will fracture along planes parallel to the compression stress but will not bulge.

7. Ductile metals loaded under torsion will fracture perpendicular to the axis of the metal (parallel to the torsional stress). Brittle metals loaded under torsion will fracture in a spiral at a 45° angle to the axis of the metal (parallel to the tensile stress).

8. Ductile dimples caused by microvoidcoalescence are characteristic of ductile fractures.

9. Brittle fractures occur by transgranular cleavage or intergranular separation.

10. Arrest lines are an indication of a progressive fracture.

11. Mechanical nicks or corrosion pits on the surface of a component can sometimes be used to locate the initiation points of a fatigue fracture.

12. At high magnification, fatigue crack propagation is revealed as striations.

13. Microcracksin the morphology are further evidence of fatigue.

14. The origin of a fracture is the point where the fracture is initiated.

15. Ratchet marks are an indication of a fracture with multiple origins.

16. The morphology of a fracture face changes as the force for the fracture changes.

17. A checklist may be used to review the stress, temperature, and operating conditions at the time of failure.

18. A checklist may be used to indicate material characteristics.

19. A failure overview can pinpoint areas that require more detailed investigation.

20. An ultrasonic cleaning bath of organic solvent is used to remove light amounts of grease, deposits, or residues.

21. Cathodiccleaning is used to remove adherent deposits from a metal surface.

22. A checklist may be used to determine which features to look for during macroscopic examination.

23. Photomacrographyis accomplished using a digital overhead camera.

24. Next to sunlight, flashlight is the best light source for color photography of fractured surfaces.

25. Proper selection and use of lighting methods permits key features on a fracture surface to be revealed.

26. The electron beam interaction with a specimen causes various types of emissions. Two types, backscattered electrons and secondary electrons, can be used to form an image of the surface.

27. EDXAidentifies and measures the concentration of chemical elements present in a specimen.

28. X rays are emitted from a teardrop-shaped volume of a specimen.

29. Electron probe microanalyzers use WDXA to analyze chemical elements present in micrometer-size areas of a specimen.

30. An X-ray map can be compared to an electron micrograph of the fracture surface to reveal the chemical elements in a specimen.

31. A minimum of two metallurgical mounts are produced from specimens removed from the bulk of the metal.

32. The specimen from the fracture face must be carefully cut, mounted, ground, and polished to reveal the fracture origin.

33. Failure analysis reports are documents that describe the cause(s) of a failure and offer recommendations about prevention of future failures.