L14 Failure Analysis Flashcards
What are the various ways to classify engineering failures?
- Design Errors
- Fabrication/manufacturing defects
- Assembly errors
- Misuse during operation
Design Errors
What aspects of a design determine a products overall reliability? What do these aspects ensure?
- Shape
- Size
- Configuration
- Material selection (for appropriate combination of properties, including treatments)
These are important to ensure that the product will:
1. perform the function intended
2. withstand any applied loads without deforming excessively
3. not fail as a result of unanticipated stress levels that result from presence of stress raisers – sharp corners, configurational discontinuities (cracks), etc
Fabrication/Manufacturing Defects
What are some common fabrication/manufacturing defects?
- welding defects (porosity, lack of penetration)
- improper heat trating
- machining/grinding defects (gouges, burns, tears, scratches, cracks)
- decarburization
- casting defects (porosity, shrinkage cavities)
Assembly Errors
Give reasons for assembly errors.
- Competitive industry leads to faster and cheaper assembly processes
- Increasingly complicated products
- Automated inspection techniques
True or False:
Misuse during operation is the least common type of failure.
False: Misuse during operation is one of the most common failure types, and should be one of the first suspects during investigation.
True or False:
Corrosion failures often result from maintenance neglect.
True: Corrosion failures often result from maintenance neglect, and can result in a premature failure of a component, structure, or machine.
The Failure analysis
To which questions must I find answers to, in the failure analysis?
- What exactly is the failure problem? (what event precipitated the malfunction of a component, machine, or process?)
- What is the root cause of the failure problem?
- What are possible solutions?
- Which of these is the best solution?
ROOT CAUSE
3 types of root cause:
- Physical - related to one of the failure types or mechanisms seen in class (like creep, fatigue failure, fracture due to overload, etc)
- Human - the actions of an individual is what led up to the failure, as a primary cause (e.g. poorly written set of maintenance instructions)
- Latent - relates to failure resulting from organizational policy
Name common failure analysis procedures (there are 12)
- Collection of background data ad sample selection for examination
- Preliminary visual examination of the failed part
- Nondestructive testing
- Mechanical testing (destructive – e.g. tensile, hardness, impact)
- Selection, identification, preservation, and/or cleaning of critical specimens
- Macroscopic examination and analysis of fracture surfaces, secondary cracks, and other important surface features
- Microscopic examination and analysis of fracture surfaces
- Selection, preparation, examination, and analysis of metallographic sections
- Determination of the actual stress state of the failed component
- Determination of the failure mode
- Chemical analyses (bulk, local, surface corrosion or coatings)
- Application of fracture mechanics
Determination of failure modes
Name possible failure modes, as discussed in classes (there are 10 at least)
- Ductile fracture
- Brittle fracture
- Fatigue (high-cycle, low-cycle, corrosion, thermal)
- Corrosion (uniform, galvanic, pitting, crevice)
- Stress-corrosion cracking
- Distortion (elastic and plastic)
- Creep and creep rupture
- Liquid-metal embrittlement
- Hydrogen embrittlement
- Radiation damage
