V. Reliability Testing
C. Product testing
Describe the purpose, advantages, and limitations of degradation types of tests, and use common models to develop product test plans, evaluate risks, and interpret test results.
6. Degradation (wear–to–failure) testing (Evaluate)
This works for those failure mechanisms that permit a measure of the change to performance or some critical aspect of a product’s performance.
Additional References
Quick Quiz
1-3. Identify the kind of failure that would most likely result from high cycle fatigue.
(A) early failure
(B) wear-out failure
(C) mid-life failure
(D) constant failure
(B) wear-out failure
Key words here are cycle fatigue, or even just fatigue. One of characteristics of a wear out failure mechanism is it takes time for it to occur. The defect may build up, as with corrosion, or wear away, as with abrasion, or it may grow, as with crack propagation or tin whiskers. The chance of failure increases over time.
Cycle fatigue tends to alter the material properties involved thus degrading the ability of the system to function. The accumulated damage with each cycle erodes the materials ability to operate within design specifications.
The failures due to fatigue may occur at any time, thus may occur early or during mid-life, yet fatigue failure mechanism tend to exhibit an increasing failure rate over time and independent of when they occur would be considered a wear-out failure.
Since fatigue failures tend to have an increasing failure rate, they would not be classified as having a constant failure rate (or shorthand called a constant failure).
1-131. A qualification test can be used to determine whether a design and selected production method will give a specification-conforming product. An acceptance test can be used to determine whether the completed product conforms to design. What can a destructive test be used for?
(A) qualification only
(B) acceptance only
(C) qualification or acceptance
(D) neither qualification nor acceptance
(C) qualification or acceptance
There are too many terms describing quality and reliability testing. Some refer to the purpose of the testing, e.g., qualityfication or acceptance. Other terms, e.g. accelerated or degradation, refer to the testing approach or mechanics involved with the testing. Degradation testing monitor a performance parameter (most often) of the product as it undergoes some form of stress or use. The parameter deteriorates toward a failure condition, thus allowing us to ascertain the time to failure results or either a qualification or acceptance purpose.
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