Stefan Kemmler

Planning of reliability life tests within the accuracy, time and cost triangle

If the focus during product development is on estimating a failure distribution function or a lifetime-quantile, analysis of failure behavior or determination of optimal design alternatives, there is often no alternative to life tests until failure. Alongside the determination of sample size for a desired accuracy of the result, engineers are also faced with the challenge of selecting the most suitable life test type at limited cost, time and test rig capacities. In this paper, results of a comprehensive simulation study are presented. Sudden Death tests, type-I and type-II censored and non-censored life test types are compared for two-parameter Weibull distributed data with respect to accuracy, time, cost and the investigation target. Significant influencing factors and boundary conditions, such as the maximum number of test rigs available, are taken into account to assure the practical applicability of the procedure for planning life tests. The database generated provides recommendations for an appropriate test configuration within an accuracy, time and cost triangle, including optimal test parameters. Furthermore, it enables engineers to substantiate qualitatively known correlations with numbers. This information can be used to describe the influence of a shift in boundary conditions. Finally, the use of the simulation results as basis for planning life tests is illustrated in a case study.

Systematisches Toleranz Design unter Berücksichtigung von Funktions- und Kostenaspekten nach der robusten Zuverlässigkeitsmethode SMAR²T

In today’s efficient development of technical products the tendencies and challenges shift to simulative computer aided engineering. Therefore in the industrial development of complex technical products, methods are applied which provide realistic results and simultaneously economize the required resources. These results become purposefully optimized regarding the respective requirement with in concurrently consideration of robustness, technical feasibility as well as the cost by varying sets of tolerances. In this paper an approach for the design of robust and reliable products with simultaneous considering of functional and cost-related aspects, SMAR2T (Systematic Method for Axiomatic Robust Reliability-Testing Method), is discussed and visualized by the application example of an overload clutch.