The Problem

Validation of technical systems aims at demonstration of reliability for warranty or even for product lifetime. These targets require a huge amount of testing to be performed over a long period. Multiple degradation modes must be represented by a proper set of durability test conditions. As product families are co-developed for various applications and markets a set of targets has to be achieved simultaneously.

The relevant questions are: what is the minimum set of tests, which sequence is the most efficient and how large is the total test volume necessary for target achievement?

The Challenge

A rising number of variants in product families drives the amount of testing for reliability demonstration to unrealistic orders of magnitude in terms of budget and time. Transfer of test results across variants is justified only under certain conditions for certain failure modes. Therefore it is possible to achieve a high quality of validation through proper consideration of parts commonality, and hence a targeted reduction in test volumes.

As a matter of fact the actual failure rate of products is much lower than it could be according to the demonstrated reliability. However, this general observation helps only if the actually required amount of demonstration can be derived in view of future customer operation.

The Solution

Uptime Engineering supports in establishing a reliability process to derive demonstration tasks from reliability targets. The methods used for this purpose are strictly quantitative to deliver a sound basis for planning and control of validation activities.

• Target evidence is the first process step. It is embedded into the Usage Space Analysis, providing customer duty cycles as references for product validation.
• Transparency on risks and damaging conditions is generated by the reliability Risk Assessment. It includes the effects of product variants.
• Physics of Failure based models are used for the assessment of test efficiency in view of future customer duty cycles via Damage Calculation.
• Test Design delivers the required types, duration and sequence of tests
• In Validation Programme Optimisation test ensembles are re-distributed in scenarios in order to achieve the maximum validation effect for the available budget, time and equipment. Test volumes are allocated to match the risk distribution among the product components.
• Achievement of the ultimate goal – not to exceed a failure rate limit during customer usage – requires another step, reliability prediction. The predicted reliability is evaluated as a risk-weighted extrapolation of the demonstrated reliability level. It grants that no more validation is done than necessary for the actual customer use cases.
• Reliability Growth Analysis is executed during the validation to keep the process on track by evaluation of problem-solving measures.

The Commercial Impact

A reliability process accompanying the product development delivers the minimum amount of tests for achievement of the necessary reliability demonstration. In particular for product families, this can be of huge economic advantage.

The strictly quantitative nature of the applied methods results in practical, comprehensive recommendations and leads to the best possible allocation of resources.

Uptime LOCATE™ is used as the software platform for the reliability process. Thus a single source of data and information is established. It provided a reference for reliability risks and methods. Models and results can be re-used, e.g. additional future usage cases or applications of a product are easily assessed.