CRE Failure Analysis & Testing 2 — Questions and Answers
Question 1: Which failure analysis technique uses a scanning electron microscope (SEM) to examine fracture surfaces at high magnification?
- Fractography (Correct answer)
- Thermography
- Radiography
- Acoustic emission testing
Correct answer: Fractography
Fractography uses SEM and other microscopy tools to examine fracture surfaces and identify failure modes such as fatigue, overload, or corrosion.
Question 2: In accelerated life testing (ALT), the Arrhenius model is most commonly used to accelerate failures caused by:
- Mechanical vibration
- Temperature stress (Correct answer)
- Humidity cycling
- Electrical overstress
Correct answer: Temperature stress
The Arrhenius model relates the rate of chemical/thermal degradation to temperature, making it the standard model for temperature-accelerated life testing.
Question 3: A component shows beach marks on its fracture surface. This is most indicative of:
- Brittle overload fracture
- Fatigue crack propagation (Correct answer)
- Stress corrosion cracking
- Ductile tearing
Correct answer: Fatigue crack propagation
Beach marks (also called clamshell marks) are macroscopic striations on fracture surfaces that indicate cyclic loading and fatigue crack propagation.
Question 4: The primary purpose of HALT (Highly Accelerated Life Test) is to:
- Determine the MTBF of a product
- Precipitate and discover design weaknesses (Correct answer)
- Validate that a product meets its specification limits
- Measure warranty return rates
Correct answer: Precipitate and discover design weaknesses
HALT applies stresses beyond specification limits to rapidly discover design weaknesses and failure modes before production.
Question 5: In root cause analysis, the '5 Whys' technique is best suited for:
- Complex failures with many independent causes
- Simple to moderately complex failures with a single cause chain (Correct answer)
- Statistical determination of failure rates
- Identifying intermittent electronic failures
Correct answer: Simple to moderately complex failures with a single cause chain
The 5 Whys method iteratively asks 'why' to drill down through a cause-and-effect chain, working best when there is a single root cause pathway.
Question 6: Which non-destructive testing (NDT) method is most effective for detecting surface cracks in ferromagnetic materials?
- Ultrasonic testing
- Liquid penetrant testing
- Magnetic particle inspection (Correct answer)
- Eddy current testing
Correct answer: Magnetic particle inspection
Magnetic particle inspection (MPI) reveals surface and near-surface discontinuities in ferromagnetic materials by detecting leakage flux around defects.
Question 7: Environmental Stress Screening (ESS) differs from HALT primarily because ESS:
- Uses stresses beyond design limits to find failures
- Operates within or near product specifications to screen out latent defects (Correct answer)
- Is applied only to prototype units
- Tests for thermal fatigue exclusively
Correct answer: Operates within or near product specifications to screen out latent defects
ESS applies stresses within or near specification limits to precipitate latent defects in production units without damaging good product.
CRE Failure Analysis & Testing 2
Which failure analysis technique uses a scanning electron microscope (SEM) to examine fracture surfaces at high magnification?