V. Reliability Testing
A. Reliability test planning
1. Reliability test strategies (Create)
Create and apply the appropriate test strategies (e.g., truncation, test-to-failure, degradation) for various product development phases.
In this lesson the focus is on the various type of reliability related testing.
Additional References
SOR 070 Creating a Reliability Program Plan that optimizes usage of reliability testing and tools (podcast)
Mechanical Systems Reliability Testing (article
Reliability Testing Considerations (article)
Norris Landberg solder joint fatigue (article)
Quick Quiz
1-2. Identify the kind of failure that would most likely result from insufficient hardware debugging.
(A) early failure
(B) wear-out failure
(C) random failure
(D) catastrophic failure
(A) early failure
The key wording is “most likely” as all types of failure may occur. The best answer in this case corresponds to the type of failures that will most likely occur if the process to find faults or errors is not done well (insufficient hardware debugging).
Since debugging or any product testing typically find faults or errors that are quickly revealed as failure, the most likely issues left undiscovered will also occur soon after the hardware is placed into service, i.e. early failure.
It is possible to conduct insufficient hardware debugging which finds all types of failure except wear-out failure mechanisms. The question does not include information about the details of debugging conducted, just a generic insufficient. Don’t over think the question or potential answers.
Random or catastrophic failures may be detected in hardware testing, plus defects undiscovered may lead to these types of failures. The likelihood of random or catastrophic failures are also more difficult to discover via product testing then the failures that have a decreasing hazard rate (early failures).
1-88. Why must a vendor perform tests on parts?
(A) to estimate total costs
(B) to determine functional capability under specified environmental conditions
(C) to identify the material flow and manufacturing processes to use
(D) to optimize configuration and size
(B) to determine functional capability under specified environmental conditions
Testing is done for many reasons, and from the question there is little information on the nature or pupose of the testing. Yet one thing a vendor has to provide is component/part specificaitons. These are often based on component testing done by the vendor prior to listing performance and environmental conditions on a data sheet.
1-92. Various tests are performed on a new part as specified by a reliability engineer. Which of the following would not be a direct result of those tests?
(A) a disclosure of the part’s deficiencies
(B) data useful to estimate MTBF
(C) knowledge about whether the part meets requirements
(D) an improvement in reliability
(D) an improvement in reliability
Testing does not improve reliability, it only reflects the current state which is useful for the other three options. One could argue that screening out bad units improves field reliability, yet the actual reliability does not really change, we just find and remove failures before they reach customer (or try to as it is a very ineffective process and expensive in most cases)
1-133. A sample for 400 parts is split into two subgroups, each of 200 parts. Testing is performed on each subgroup and each test is stopped after the first failure in that subgroup. A plot is then made of the times to first failure the distribution parameters are estimated. How would you best describe this type of testing?
(A) censored testing
(B) sudden-death testing
(C) step-stress testing
(D) hazard-rate testing
(B) sudden-death testing
The description of the test approach fits the definition of sudden death testing. See the paper by Ryszard Motyka for a comparison of sudden death testing versus traditional censored life testing. http://matwbn.icm.edu.pl/ksiazki/cc/cc36/cc36111.pdf
1-138. In general, why is reliability testing performed?
I. to monitor reliability growth as a function of time
II. to meet or exceed customer expectations
III. to detect unanticipated failure modes
IV. to compare estimated and actual failure rates
(A) I and III only
(B) II and IV only
(C) I, II, and III only
(D) I, II, III, and IV
(D) I, II, III, and IV
All valid reasons for reliability testing. In general we conduct testing to learn something about the design of a product or system. We want to reveal problems or check progress toward a goal or to verify design changes are effective. Every reliability test should include a clear statement about the information the test results will provide. Ideally it will also include who needs to make a decision based on the results.
