V. Reliability Testing
A. Reliability test planning
2. Test environment (Evaluate)
Evaluate the environment in terms of system location and operational conditions to determine the most appropriate reliability test.
Understanding the where and how of product use permits adopting test conditions that reflect or accelerate use conditions correctly.
Additional References
The Environmental Test Manual (article)
SOR 062 Are Environmental Standards Useful? (podcast)
SOR 059 How to Set Environmental Specifications for Testing (podcast)
SOR 043 Environmental Testing and Reliability (podcast)
Is Environmental Testing Part of Product Reliability? (article)
Create a Meaningful Environmental Test Plan (recorded webinar)
Quick Quiz
1-139. A sample of 25 mechanical parts is subjected to a 5-week stress test in which each part is subjected to a load stress that increases 50% each week. The test results are listed in the table.
Week Number of failures
1 0
2 1
3 1
4 3
5 7
You need to determine whether the failures observed reflect actual use failures. What additional information do you need?
(A) the times of the failures
(B) the history of cumulative stress
(C) the geometry of the test setup
(D) the mechanisms of the failures
(D) the mechanisms of the failures
The time to failure and test design information do not provide details concerning the failure mechanisms. Understanding the failure mechanism involved for each failure permits the comparison of the failures to use condition potential failures.
If the testing results in two more failure mechanisms, it makes the analysis more complex, yet both may occur at use conditions just at different rates. Or, a failure mechanism may only occur at a specific or high stress level. For example over small displacements the metal in a solder join is elastic to some degree thus resilient to failure (although may accumulate damage leading to eventual failure.) On the other hand if the displacement is too large the solder will separate due to the high shear stress. If the normal use conditions does not include the application of sufficiently high displacement to shear solder joints, these specific failures are not likely to occur under use conditions.
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