Reliability Issues for DOD Systems Report of a Workshop (2002) / Chapter Skim
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1. Introduction and Overview
1. Introduction and Overview
Pages 1-9
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While the examination of such a wide variety of topics was useful in helping DoD understand the breadth of problems for which statistical methods could be applied and providing direction as to how the methods currently used could be improved, there was, quite naturally, a lack of detail in each area. To address the need for further detail, two DoD agencies the Office of the Director of Operational Test and Evaluation and the Office of the Under Secretary of Defense for Acquisition, Technology, and Logistics asked the NRC's Committee on National Statistics to initiate a series of workshops on statistical issues relevant to defense acquisition.
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The Workshop on Reliability Issues for DoD Systems, held lune 9-10, 2000, had multiple goals, partly because some of the described techniques are mature, while others are still undergoing active research. In addition, the intended audience for the workshop and this report comprises defense reliability experts, higher-level administrators who could help change the processes used in system development, and defense employees charged with the day-to-day responsibility of assessing the reliability of defense systems.
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Prominent among these was educating academics about the problems and constraints facing the defense acquisition community, which are often considerably different from those involved in analogous industrial applications. EIGHT KEY IDEAS The following eight key ideas represent a useful summary of the workshop sessions: (1)
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Benefits of Methods for Reliability Growth Management A general issue noted by many workshop participants is that defense systems do not satisfy their operational suitability requirements sufficiently often, and as a result DoD is spending too much for system redesigns, spares management, and maintenance. Speakers stressed that a change in emphasis is needed to address this problem, including greater focus on test and evaluation for suitability, but more important, use of a number of techniques that can help identify design flaws and provide assessments of reliability performance much earlier in system development.
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Need for Updating the RAM Primer Given that the RAM Primer has been used to disseminate reliability methods throughout the defense test community for nearly 40 years and that its current version is substantially out of date with respect to a wide variety of currently accepted techniques, a number of speakers strongly suggested that it be updated, possibly in a substantially different format. One possibility mentioned was to have the RAM Primer be a web-based document with embedded software for carrying out the variety of calculations necessitated by modern methods.
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The treatment should include discussion of a broad array of parametric models and should also describe nonparametric approaches. Gains from the Use of Alternative Modeling Approaches Many speakers pointed out that the defense test community relies on particular models for specific purposes, the key examples being the power law process in reliability growth estimation and the exponential time-tofailure distribution for a wide variety of reliability questions.
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They can therefore can be used to examine the maturation that would result from a specific test design given various characteristics of the system under test, and they can provide an estimate of the reliability of the"matured" system. Potential Advantages of the Application of Methods for Combining Developmental and Operational Test Information Speakers described several new approaches based on the use of models for combining information from developmental and operational test when the failure modes in these separate environments of use are well understood (or otherwise satisfy the necessary assumptions underlying the models)
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Presentations during the session on fatigue modeling included both illustrations of the necessary statistics/physical science partnership and descriptions of a variety of models motivated by recent research in materials science. Speakers suggested that fatigue modeling could be one of the techniques included in a revised RAM Primer.
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This is followed by a chapter on important areas of current research in reliability modeling and inference. The final chapter presents a general discussion of reliability issues and examines the need, expressed on several occasions during the workshop, to disseminate well-understood, broadly applicable methods for reliability test and evaluation, possibly through a comprehensive overhaul of the RAM Primer and other DoD documents that focus on reliability.
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