ASTM E3291-21

4.1?Reliability demonstration testing is a methodology for qualifying or validating a products performance capability. Demonstration methods are useful for components, devices, assemblies, materials, processes, and systems. Many industries require demonstration testing either for new product development and product introduction, in validating a change to an existing product or as part of an audit. Test plans generally try to answer the questions, How long will a product last? or What is its reliability?, under stated conditions at some specific time. When time is being used as a life variable, it must be cast in some kind of time units. Typical time units are hours (or minutes), cycles of usage, calendar time or some variation of these. In certain cases, time can be accelerated in order to reduce a plans completion time. In the automotive industry mileage may be used as the time variable. Certain means of accelerating tests involve the use of increased power, voltage, mechanical load, humidity, vibration, or temperature (often in the form of thermal cycling).

4.2?Two fundamental objectives in reliability test planning are: 4.3?Often a life distribution model is specified such as the Weibull, the exponential, the lognormal or the normal distribution. In addition, for the specific distribution assumed, a parameter is typically assumed (or a range of values for a parameter). For example, in the Weibull case, the shape parameter, ?, is assumed; in the lognormal case the scale parameter, ?, is assumed and in the normal case the standard deviation, ?, is assumed. In other cases, a non-parametric analysis can be used. Non-parametric cases typically require a larger sample size than parametric cases. This standard will discuss conditions under which distributions and associated parameters can be assumed.

4.4?Generally, a life requirement is cast as a mission time and associated reliability, for example, to demonstrate a reliability of 99% at time t=1000 hours of usage. In another case the requirement might be cast as a B_p life requirement, such as the 4.4.1?When a requirement and a confidence value have been stated, a derived plan will determine a sample size, 4.5?The RC nomenclature for specifying a test requirement is often used, where 4.6?This guide considers, the Weibull, lognormal and normal parametric cases as well as the basic non-parametric case for attribute reliability. The common exponential case is a Weibull distribution with assumed shape parameter ? = 1, but is considered as a separate case, distinct from the Weibull.

1.1?This standard covers fundamental concepts, applications and mathematical relationships associated with the planning of reliability demonstration tests as applied to components and materials testing.

1.2?The system of units for this guide is not specified. Quantities and examples are presented only as illustrations of a method or a calculation. Any examples used are not binding on any particular product or industry.

1.3?This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4?This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.