Many people have heard of, or are familiar with various reliability prediction methods like MIL-HDBK-217, Telcordia SR332, etc. These standardized handbook methods have widespread use in industry. They are primarily applicable when making the assumption that the component failure rate is constant (at the bottom portion of the bathtub curve) and are thus generally applicable to most electronic components. However, caution should be taken when using these prediction methods because there may be components for which this assumption is not correct including some electronic parts like electrolytic capacitors. There are some handbooks that deal with mechanical parts but they also generally view the failure rates as constant for the time period of interest.
In working with a client recently, they had a reliability goal that they wanted to achieve and desired a reliability prediction to verify that the goal was achievable. As their component parts list was reviewed, it became obvious that they had numerous parts that were subject to mechanical wear like an LCD touch screen, cable connectors, etc. For the electronic parts, the goal could be achieved but the components subject to wear had to also be evaluated and integrated into the analysis.
It then becomes necessary to deal with such components that will experience wear individually and determine whether or not they are apt to wear out within the reliability goal period of interest (or product lifetime). If it can be shown that the wear out occurs beyond the expected life of the product, then there is no problem. This determination can be done through testing or other analysis methods. If the component is likely to wear out within the expected product life, then decisions must be made regarding a maintenance strategy and the potential impact to warranty.
What has been your experience in performing predictions when you have components that can wear out?