IV. Reliability Modeling and Prediction
B. Reliability Predictions
2. Reliability prediction methods (Apply)
Use various reliability prediction methods for both repairable and non-repairable components and systems, incorporating test and field reliability data when available.
Carefully consider the set of assumption you make when using any prediction method.
Additional References
Reliability Paradigm Shift From Time to Stress Metrics (article)
Creating Meaningful Reliability Predictions (recorded webinar)
When to do a reliability prediction (article)
Consider Reliability Prediction Value (article)
Quick Quiz
1-48. Identify the process that entails defining the system, establishing the reliability model, assigning failure rates to the equipment involved, and computing the reliability for each function and for the system.
(A) defining the program plan
(B) demonstrating reliability
(C) reliability prediction
(D) design review
C) reliability prediction
This could be defining the program plan, if limited to just these activities. Or, it could be the process to create a reliability prediction, which it certainly describes a common approach for predictions.
The process described is not a demonstration as it did not describe any working units or test conditions. We also can rule out a design review, as the process does not include providing feedback on a specific design.
1-61. How would you best characterize reliability prediction?
(A) It is a one-time estimation process.
(B) Is it continuous process starting in the concept and planning stage.
(C) It is more important than reliability attained in the field.
(D) It is finalized with a prediction using a parts-count method.
(B) Is it continuous process starting in the concept and planning stage.
A reliability prediction is an estimate of the future reliability performance of a the system in question. During each stage of the product life-cycle there are estimates of reliability performance including:
- engineering based guesses,
- simulations,
- parts count,
- parts stress count,
- vendor data,
- life testing data,
- physics of failure modeling,
- field data analysis.
1-68. If the predicted reliability is higher than the long-term actual probability, what is the most likely cause?
(A) deterioration of manufacturing processes and procedures
(B) poor initial estimation of reliability
(C) lack of employee training
(D) accumulation of random process variations
(A) deterioration of manufacturing processes and procedures
I would say the most likely cause is the huge error associated with reliability predictions. We can rule out the ‘initial estimation’ as while it may be the resulting reliability prediction that is rarely the case for comparison to field performance. Lack of training or accumulation of process variation may increase the difference, yet in this case, given this set of options, the most likely cause is option (A).
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