1. Material failure analysis
Failure and Root Cause Analysis

2. Types of Analysis Two types of analysis: Failure analysis
how the material failed
Root cause analysis
how it could have been prevented

3. Failure Analysis Determining: How did the material fail?
Why did it fail?
Who or which party is responsible?

4. Root Cause Analysis Emphasizes managerial role in failures
How managerial techniques can be improved
Focus on prevention, not failure determination
Large plants
Construction sites
Manufacturing facilities

5. Steps in Failure Analysis
Assess the situation
Photography and sample handling
Determine product and material standards
Macroscopic examination
Microscopic inspection

6. Steps in Failure Analysis
Material characterization
Mechanical testing
Hardness testing
Crack testing
Bend testing
Strain testing
Determine how failure occurred from initial to final state
Vickers Hardness tester
Hardness tester
Public domain image from:

7. Baseball Madness
Suspect 1
Suspect 2
Suspect 3

8. Baseball Madness Principle: Fact: Conclusion:
Glass is brittle and will fracture if struck by a medium to high velocity projectile.
Fact:
A glass window was broken.
A baseball was found in the vicinity of the broken window.
Suspect 3 has a baseball bat.
Conclusion:
Suspect 3 hit a baseball that struck the window and caused the glass to fracture.
Using the Engineering Method and Investigation Pyramid

9. Failure Analysis
Just like pathologists determine cause of death, mechanical or materials engineers must determine cause of failure

10. Failure Analysis Components can fail because of: Material selection
Design
Produce usage
Method of production
Defect within product

11. Failure modes of a book shelf
Unloaded
Books in middle causing sag in wood
Shelf made of thermoplastic material
Support place close together
Manufactured crack in middle of shelf
Shelf infested with wood worms
To illustrate what is meant by failure, look at the failure modes of a bookshelf placed on two supports in the following conditions…
Here you can see that in each example, the product failed due to one of several reasons:
Material selection
Design
Produce usage
Method of production
Defect within product

12. Causes of Demise Congenital Disease Consequence of previous operation
Manufacturing defect that leads to failure of material
Disease
Corrosion, degradation, wear, etc. that leads to failure
Consequence of previous operation
Failure stemming from a previous repair or adjustment
Trauma
Sudden failure caused by gross mechanical overstress (e.g., collision)

13. Example
Car (black) pulls out of driveway and is side swiped by on coming car (white). A manufacturing fault in the white car’s brakes leads to progressive weakening of the clutch plate over a period of service.

14. Example
Disease:
Degradation of clutch brake due to surface defect in the in forging initiates a fatigue crack that runs to completion after many thousands or millions of stress cycles.
Clutch plate of a truck

15. Example Consequence of previous operation:
Failure stemming from an earlier repair to fix the clutch plate resulted in welding that altered the microstructure. This introduced residual stress and cracks in heat affected zones that lead to eventual failure by fatigue.
Clutch plate of a truck

16. Answering the three main questions
How did it fail?
Clutch plate failure
Why did it fail?
Old repair lead to crack formation leading to fatigue crack failure.
Who or which party was responsible?
Owner of the white car.

17. Failure Mechanisms
What caused the component to fail?

18. Mechanisms of Failure Manufacturing defects Material overload
Flaw introduced during manufacturing process
Material overload
Inappropriate consumer use of the material
Loading material beyond specifications
Normal wear through use
Fatigue, corrosion, creep, etc.

19. Manufacturing Defects
Congenital faults in a product
Result in (1) failure the first time it comes under load or (2) progressive weakening and eventual failure by fatigue

20. Material Overload Materials have limits
Products should be used according to material and engineering specifications
Materials cannot be used universally

21. Material Overload
The strength of a material is measured by laboratory tests
ASTM (American Society for Testing and Materials) and BSI (British Standards Institution) provide standards covering safety, performance, and reliability of products
Most common measurement is tensile strength; other strength data includes compression tests and shear tests

22. Sample of ASTM Standards
Example: Hardness testing

23. Example: ASTM E9
Old clutch plate
New clutch plate
Hardness tester
Start with old clutch plate and brand new clutch plate
Test hardness using ASTM standard protocol and hardness tester
Determine if hardness is same as regular clutch plate
Theorize why the hardness varies between failed plate and new plate

24. Material Overload
Types of materials exhibit different behaviors depending on the way their atoms and molecules are bonded and how they stack together to form crystal structures
copper
diamond

25. Material Overload
Tensile test curves for 3 different types of material:
Brittle (ceramics)
Ductile (most metals)
Thermoplastic polymers

26. Material Overload
Illustration showing the characteristic fracture paths in ductile (left) and brittle (right) materials that are being subjected to different modes of material overstress (overloading).
Looking at how these materials fracture with axial, shear, and bending forces.

27. Normal Wear Ultimately, products will fail with time
Wear, fatigue, corrosion, creep

28. Normal Wear Wear Fatigue Corrosion Creep
Damaged rendered through normal period of use
Fatigue
Repeated cycles of loading and unloading
Corrosion
Wasting away of metal surfaces due to chemical reactions among positively charged ions
Reduces material’s capacity to support loads
Creep
Gradual deformation under steady tensile load
Eventually causes creep rupture failure
Creep is when a material component gradually deforms under a steady tensile load. The atoms or molecules in the microstructure of the material have to continually adjust to accommodate the forces being applied. This causes damage to the crystal structure of the material, creating voids and cracks in the material that will eventually spread and lead to a creep rupture failure. This usually takes a good amount of time.
Ex: roof gutters will eventually split after a long period of steady loading, and after being exposed to extreme temperatures. Grocery bag handles stretching and breaking under constant stress of heavy groceries.

29. Summary Engineers determine to source of material failure
Deductive reasoning as well extensive laboratory techniques are utilized
Manufacturers often introduce source of failure into product
Materials will ultimately fail over period of use of the product from manufacturing flaws, material overload, or wear