Reliability Growth Enhancing Defense System Reliability (2015) / Chapter Skim
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6 Reliability Growth Through Testing
6 Reliability Growth Through Testing
Pages 85-92
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From page 85... ...
Given that, a large fraction of this chapter deals with accelerated testing and related ideas. Reliability testing is used to identify failure modes and to assess how close a system is to the required reliability level.
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From page 86... ...
By identifying systems that are unlikely to achieve their required reliability early in development, increased emphasis can be placed on finding an alternate system design, which might include using higher reliability parts or materials, or allocating additional reliability testing resources to identify additional sources of reliability failures. Because it is extremely inefficient to make substantial design changes in later stages of development or after deployment, it is important to identify any problems in design or, more generally, the likely inability for a system to meet its reliability requirements, during the design and early development stages.
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From page 87... ...
Some of them are useful for identifying undiscovered failure modes, and some of them are useful for estimating current reliability levels. In this section we discuss three of them: highly accelerated life testing; reliability demonstration or acceptance tests; and accelerated life testing and accelerated degradation testing.
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From page 88... ...
Reliability Demonstration or Production Reliability Acceptance Test When a milestone of a system in development is completed, in order to ascertain whether reliability growth of a component or subsystem is satisfactory, the contractor can carry out a reliability demonstration test. The basic idea is that, under normal operating conditions, a number of units are tested for a specified amount of time, and the resulting data are used to assess whether the observed reliability is reflective of a target value.
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From page 89... ...
Stress loadings, such as constant stress, ramp stress, or cyclic stress; the allocation of test units to stress levels; the number of stress levels; the appropriate test duration; and other experimental variables can improve the accuracy of the resulting reliability estimates. It may be that initial guesses at a model to link extreme to normal stresses may turn out to be invalid for many ALT situations.
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From page 90... ...
We refer to this as accelerated degradation testing, which requires a reliability prediction model to relate degradation results of a test under accelerated conditions to failures under normal operating conditions. Proper identification of the degradation indicator is critical for the analysis of degradation data and subsequent decisions about maintenance schedules and replacements.
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From page 91... ...
Given the important benefits from effective testing for reliability growth and for reliability assessment, the panel recommends that DoD take several steps to ensure that contractors use tests that are capable of measuring agreed-on metrics; that the designs of test plans and the validation of reliability models linking extreme to normal use and degradation to failures are examined by reliability engineers prior to application; and that contractors supply DoD with all test data relevant to reliability assessment (see Recommendation 12 in Chapter 10) .3 We also recommend creation of a database that includes the results not only from contractor testing, but also from DoD developmental and operational testing and from field use.
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