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Reliability and Maintainability Symposium, 1995. Proceedings., Annual

Date 16-19 Jan. 1995

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  • Annual Reliability and Maintainability Symposium 1995 Proceedings

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  • The P.K. McElroy Award for Best Paper

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  • Author index

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  • Cumulatlive Indexes

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  • Comparative analysis of two architectural alternatives for the N-version programming (NVP) system

    Page(s): 275 - 282
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    This paper presents a quantitative analysis of two configurations of one architectural approach to the integration of hardware and software fault tolerance. The importance of this work is to determine if there is a clear-cut advantage to using one configuration of N-version programming (NVP) over the other. A previous preliminary sensitivity analysis on the individual parameter values showed that downloading a faulty software version had the most significant effect on the reliability and safety of the system. The other parameters that we varied had little or no effect on the systems' performances, or on the relationship between the two systems. This fact demonstrates that our results are relatively robust for the particular parameter values that were chosen. Of course a significantly different set of parameter values may yield different results. Closed form solutions proved difficult to manage. We investigate the well-known anomaly for hardware fault tolerant TMR systems to see if the anomaly still holds when software faults are considered. The anomaly considered is that, for a TMR hardware fault tolerant system, discarding an operational component upon the first failure (and continuing in simplex mode) actually improves reliability. When software faults are considered in a more comprehensive analysis, the anomaly no longer holds View full abstract»

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  • A method to determine equivalent fault classes for permanent and transient faults

    Page(s): 418 - 424
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    The expanding size and complexity of dependable computing systems has significantly increased their cost while complicating the estimation of system dependability attributes such as fault coverage and latency. The increasing requirements of safety and reliability for a dependable system, however, have made the evaluation of dependability attributes a crucial task. One approach to performing such an evaluation is through fault injection. The development of a method which enumerates the equivalent faults associated with a given fault injection experiment would significantly reduce the amount of effort required to measure dependability parameters to the desired degree of accuracy and confidence. This research has developed a new method for determining the set of equivalent faults for either a permanent or transient fault injection experiment. The primary objective of the research effort was to expand the data obtained from a single fault injection experiment into a set of data associated with the equivalent fault set. The end result is an automated method for determining equivalent faults from a set of fault injection experiments. The expanded equivalent data sets are then evaluated to determine dependability parameter estimates for fault coverage and error latency View full abstract»

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  • Vibration fatigue of surface mount technology (SMT) solder joints

    Page(s): 18 - 26
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    Recent trends in reliability analysis of electronics has involved developing structural integrity models for predicting the failure free operating lifetime under vibratory and thermal environmental exposure. This paper describes a test program which was performed to obtain structural fatigue data for SMT solder joints exposed to a random vibration environment. A total of eight printed circuit board specimens with nine surface mounted components were fabricated and tested. Vibration time to failure data for individual solder joints of the SMT components were recorded. These data became the basis for understanding the physics of “why and how” SMT solder joints fail under vibration loading. Using procedures similar to those developed for aerospace structures, a fatigue model was developed that is based on the physics of the problem View full abstract»

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  • Optimal preventive-replacement intervals for the Weibull life distribution: solutions and applications

    Page(s): 370 - 377
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    Using a well-known single-unit replacement model with Weibull failure distribution assumption, normalization is used to reduce the model input parameters such that standard optimal preventive replacement solutions can be generated. Characteristics of the model solutions are discussed. The standard solutions are organized in charts and tables for ease of use. Procedures are developed and examples are given for applying the standard solutions for engineering problems with different system parameters. It is believed that the generated standard solutions and the developed procedures will be helpful for maintenance practitioners to apply theoretical research results in industrial practice View full abstract»

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  • Consideration of component failure mechanisms in the reliability assessment of electronic equipment-addressing the constant failure rate assumption

    Page(s): 54 - 59
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    The assumption of the constant failure rate can lead to excessive costs and nonoptimum design decisions. As this paper shows, simply summing constant failure rates can produce results which are highly inaccurate. Highly inaccurate results can introduce significant error in decisions made in everything from product design to logistics support requirements such as spares and maintainers. The authors argue that if a shift is made from reliability accounting tasks to reliability engineering analysis, the ability to address hazard rates versus time based on root-cause failure mechanisms will become cost-effective and can become an integral part of the concurrent engineering approach to product development. The notion of the constant failure rate should no longer be accepted as a rule. Instead, statistical distributions and assumptions must be shown to be appropriate every time they are used. Simplicity alone is not a sufficient reason to use any given methodology or approach View full abstract»

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  • A fault-list generation algorithm for the evaluation of system coverage

    Page(s): 425 - 432
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    The expanding size and complexity of dependable computing systems has increased their cost and at the same time complicated the process of estimating dependability attributes such as fault coverage and detection latency. One approach to estimating such parameters is to employ fault injection, however algorithms are needed to generate a list of faults to inject. Unlike randomly selected faults, a fault list is needed which guarantees to cause either system failure or the activation of mechanisms which cover the injected fault. This research effort has developed an automated technique for selecting faults to use during fault injection experiments. The technique is general in nature and can be applied to any computing platform. The primary objective of this research effort was the development and implementation of the algorithms to generate a fault set which exercises the fault detection and fault processing aspects of the system. The end result is a completely automated method for evaluating complex dependable computing systems by estimating fault coverage and fault detection latency View full abstract»

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  • Simultaneous development and qualification in the fast-changing 3.5" hard-disk-drive technology

    Page(s): 27 - 32
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    This paper presents an enhanced approach to utilizing test as an aid to maturing the 3.5" hard-disk drive (HDD) to improve time to market. It focuses on designing tests that provide maximum feedback to the design function on the designs “goodness or maturity” and the strategy focuses on consolidating different tests done by different groups (including selective customer testing) to maximize useful information flowing back to the design team. To improve design weakness identification, the paper offers an alternative to performing design verification testing (DVT) that focuses on problem discovery rather than specification compliance. This paper also covers conformance testing as testimony to the successful approach taken on DVT testing. Although not all elements of the consolidated test strategy have been fully implemented, results so far are very encouraging View full abstract»

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  • A modified bathtub curve with latent failures

    Page(s): 217 - 222
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    Burn-in and stress screening are becoming increasingly popular in the commercial electronics industry as customers become increasingly sensitive to failures occurring in the useful life of a product or system. For example, thermal stress screening (TSS) is an assembly-level electronics manufacturing process that evolved from the burn-in processes used in NASA and DoD programs. While burn-in subjects the product to expected field extremes to expose infant mortalities (latent failures), TSS briefly exposes a product to fast temperature rate-of-change and out-of-spec temperatures to trigger failures that would otherwise occur during the useful life of the product. In support of this known failure behavior, the classical bathtub curve should be modified to aid in the economic modeling of various screen types. We have conducted extensive modeling efforts that have resulted in a systematic approach to explicitly modeling the latent failures in the bathtub curve. In this paper, we describe the efforts that have been dedicated to model the latent failures known to exist in many products and systems. The resulting failure distribution is a truncated, mixed Weibull distribution. This model is proving to be an effective and relatively simple means to model the complex nature of failures of a system. With this increased flexibility, we can measure the impact of stress screens in varying conditions and ultimately design optimal screens View full abstract»

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  • Standardizing the FMECA format: a guideline for Air Force contractors

    Page(s): 66 - 73
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    Each reliability requirement extracted from a military standard (MIL-STD-1543, MIL-STD-785, MIL-STD-1629, etc.) must now be justified before a program office can approve its inclusion in a statement of work (SOW). Justification can be based on the criticality of high reliability to achieving program objectives or the lack of substitute commercial standards. With or without standards, the purpose of the reliability program is to assure that reliability engineering is a major contributor to the contractor's systems engineering process. In the case of failure mode and effects criticality analysis (FMECA), an ancillary purpose is to provide proof to the customer (the Air Force in the case of most US Space and launch vehicles) that reliability engineering was in fact included in the systems engineering process. This paper describes guidelines for building a comprehensive reliability engineering database using the failure mode, effects, and criticality analysis record (FMECAR) format View full abstract»

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  • Rationalizing scheduled-maintenance requirements using reliability centered maintenance-a Canadian Air Force perspective

    Page(s): 11 - 17
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    Failure modes and effects analysis (FMEA) and reliability centered maintenance (RCM)/maintenance steering group (MSG) decision logic have been successfully used by military and commercial aviation manufacturers for over three decades to develop preventive maintenance programs for new aircraft fleets. However, once a fleet is in place, there is a requirement to periodically validate or rationalize the applicability and effectiveness of individual tasks in the program, and to adjust task frequencies. Experience has shown that it is inefficient to re-apply FMEA/RCM decision logic to every aircraft item on a fixed frequency basis. This paper identifies how the Canadian Air Force (CAF) proposes to make more efficient and effective use of the in-service data it collects to identify those items for which the preventive maintenance requirement is ineffective or inapplicable. Moreover, it discusses how the same data source can be used in follow-up investigation to determine the actual failure mode history of an item as a basis for comparison with the FMEA-the basis upon which the requirement for the existing tasks is developed View full abstract»

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  • An approach to quantifying reliability-growth effectiveness

    Page(s): 166 - 173
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    This paper presents an approach for quantifying reliability growth effectiveness through the development of a performance parameter and the application of that parameter to an existing reliability growth model, the tracking, growth and prediction (TGP) model. The basis for this performance parameter is presented from two perspectives; based either on previous experience in other reliability growth tests when data are available, or by subjective assessment of a given corporate culture when data are not available. Quantification of this parametric variable with data is presented by normalizing past performance with the reliability growth program goals. Development of the parametric variable without data is accomplished through the characterization of attributes that are indicative of the corporate culture. Five case studies were used to develop the performance parameter based on test data and by subjective assessment of capability. Although the results of these estimates of the performance parameter varied, they were reasonably close. Based on results of uncertainty propagation analyses, it is reasonable to conclude that a modified TGP model provides a conservative estimate of the risk involved in achieving reliability growth goals. This conclusion is based on the model's durability in sustaining the introduction of uncertainty into the existing failure rate parameters as well as into the performance parameter View full abstract»

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  • A graphical model-based reliability estimation tool and failure mode and effects simulator

    Page(s): 74 - 81
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    A new graphical reliability estimation tool, Reliability Performance Module (RPM), is described. RPM combines the features of a powerful reliability tool, Reliability Estimation System Testbed (REST), developed at NASA Langley, with the convenient graphical modelling and simulation capabilities of an off-the-shelf commercial software package, Block Oriented Network Simulator (BONeS), from the Alta Group of Cadence Design Systems. In order to estimate the reliability of a system, the built-in BONeS graphics capabilities are used to describe the system, and the embedded REST execution engine produces a reliability analysis automatically. An additional benefit of this approach is that a detailed failure modes and effects analysis can be derived by using the simulation capabilities of the tool. The usage of and output from RPM is demonstrated with an example system. As compared to our current design process, RPM promises to reduce overall modelling and analysis time, provide better documentation, make trade studies easier, create reusable modelling components and subsystems, and provide the integration of reliability and timing analysis necessary to guarantee the safety of critical real-time systems. Future work will concentrate on producing a more seamless integration of the reliability and timing analyses. Additional planned enhancements include a distributed (parallel) processing mode, and availability and phased-mission analysis capabilities View full abstract»

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  • Exploratory research on nonthermal damage to electronics from fires and fire-suppression agents

    Page(s): 1 - 6
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    Electronic equipment is expected to operate reliably under normal conditions as well as under foreseeable abnormal conditions, particularly in life-critical and environmentally sensitive applications. One foreseeable abnormal condition to which electronic equipment may be subjected at least once during its life-cycle is a fire environment. Such an environment may include the thermal and corrosive effects in the immediate vicinity of the fire and the nonthermal effects associated with smoke contamination, humidity and corrosion in remote locations. Direct thermal effects are generally so severe that reasonable remedial actions may not be feasible. Fortunately, such effects are frequently restricted to a fairly small zone, often through the use of automatic fire detection and suppression systems. On the other hand, the thermal decomposition products of smoke and fire suppression agents resulting from even a small fire may permeate a building and cause nonthermal damage to electronic equipment in locations remote from the actual fire. With ever-increasing reliance being placed on electronic equipment in all types of applications and the consequent increase in value concentrations, nonthermal damage from fires and fire suppression agents is a topic of growing interest. The purpose of this exploratory research is to characterize nonthermal damage mechanisms, consequences, and potential preventive and remedial actions using a physics-of-failure approach View full abstract»

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  • Pacemaker reliability: design to explant

    Page(s): 460 - 464
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    Pacemaker reliability can be thought of as a measure of the change in quality during lifetime or mean time to replace (MTTR). Quality has been defined as the totality of all the features designed and built into a pacemaker, or any product. If these features are to function as intended for the designed MTTR, a formal quality system which covers design, qualification manufacturing, distribution and market monitoring must be in place. Some important elements of the quality system are shown. Managerial discipline is one of the most critical features of the quality system. No system will be effective if it is compromised or abandoned in a crisis. These different elements can be thought of as tools which are used by management, engineers, scientists and mathematicians. When used in accordance with procedures these tools shape the product into usable form which will meet customer expectations View full abstract»

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  • Innovations in military spares analysis

    Page(s): 397 - 401
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    The US Defense Secretary hopes to reap savings in the order of $30 billion with procurement reform. He admits that one of his toughest challenges will be to nurture and sustain America's technological edge, which he sees as a necessity in a period of declining force levels, during a time of declining budgets. With these thoughts in mind Science Applications International Corporation (SAIC) took the initiative to pursue alternative cost effective methods to raise spare parts utilization. SAIC's approach is to include repaired printed wiring assemblies (PWAs) in lieu of purchasing additional spare PWAs in the spares analysis calculation. This also negates the additional costs of inventory and storage of the logistically required spare PWAs View full abstract»

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  • Software-quality improvement using reliability-growth models

    Page(s): 182 - 187
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    In the traditional software development model, the system test phase is the last stage where the reliability, capability, performance and other important dimensions of the quality of a system can be evaluated. During this stage, a point is eventually reached where a decision must be made to either continue or stop testing. This is a crucial task that requires an objective assessment of the benefits and costs associated with each alternative. This paper outlines a methodology that improves the effectiveness of management decisions by providing estimates of the total number of errors to be found through testing, the number of remaining errors, the additional testing time needed to achieve reliability goals and the impact of these parameters on product quality, project cost and project duration View full abstract»

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  • A simple method for predicting the cumulative failures of consumer products during the warranty period

    Page(s): 384 - 390
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    In the design and manufacturing of both consumer and commercial products, an important design criteria is the length of the warranty period measured in calendar time. It is very important to know the expected number of failures during the warranty period. This paper provides an engineering tool that will predict the cumulative failures over the warranty period based on laboratory life data and the usage rate data for the products that are operated for only a limited fraction of the total available time. This method uses a joint distribution of the usage rate distribution and the laboratory life distribution to translate usage time to calendar time and not the mean usage since the product use in the field also follows a broad statistical distribution. The proposed technique permits an accurate calculation of the cumulative field failure over prospective warranty periods and thus is useful as an engineers' tool in design optimization as well as in decisions on product release View full abstract»

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  • Equipment life: can we afford to extend it?

    Page(s): 529 - 535
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    Almost without exception, military equipments remain in service beyond their original planned lives. This paper shows how the ability to extend life is greatly influenced by early project decisions. It describes how the identification and management of life-related risks provides a realistic framework on which to plan an equipment's future. It demonstrates how different procurement strategies deliver equipments with different life qualities. It asserts that a robust product will result when life, itself, and related issues, such as reliability and maintainability (R&M), are afforded sufficient priority in the specification and contract, linking payment milestones to achievement. Justification is given for the need to specify modular construction methods and to address growth and mid-life improvement (MLI) at the outset. Focus on maintenance, aided by integrated logistic support (ILS) principles, during design and in service is shown to assist in prolonging life. Ultimately, the paper affirms that we can afford to extend the life of military equipment, provided that the armed forces can continue to perform effectively in the modern battlefield View full abstract»

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  • On reliability growth testing

    Page(s): 162 - 165
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    Reliability development growth testing (RDGT) is the most common method used to improve equipment reliability. The author had an opportunity to perform an analysis of hardware that experienced environmental stress screening (ESS), environmental qualification testing (EQT), RDGT and field usage. The failure mode and corrective action data were used to qualitatively assess the effectiveness of RDGT testing. The results of this analysis yield the following conclusions: (1) RDGT is not a very good precipitator of field related failure modes, therefore RDGT alone does not appear to be a strong driver of reliability growth; (2) RDGT, EQT, ESS, and EQT tests precipitate a high percentage of failure modes that occur only in “chamber-type” environments, and are not related to field use; (3) of the three “chamber-type” tests (ESS, RDGT, and EQT) evaluated as precipitators of field related failure modes, ESS appears to be the most effective; and (4) “chamber-type” tests are more efficient in developing corrective actions than field operation View full abstract»

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  • The assurance of R&M in acquisition programs of the Royal Australian Air Force

    Page(s): 118 - 124
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    This paper addresses the techniques used to assure system reliability and maintainability (R&M) within the acquisition process of the Royal Australian Air Force (RAAF). The RAAF recognizes that R&M are principal determinants of the level of operational availability that will be achieved by weapon systems and key factors of life cycle cost. R&M are therefore important performance parameters relevant in the acquisition process. To ensure clarity, the RAAF acquisition process is explained and contrasted with the US process. R&M is assured in RAAF weapon system acquisition programs in the following manner: (1) the R&M requirements are developed in a logical manner from operational preparedness objectives for the weapon system; (2) R&M requirements are quantitatively specified; (3) competing tenderers for the weapon system development propose and submit self devised R&M program plans to achieve the R&M performance requirements; (4) prospective contractor proposals are reviewed and compared using the Reliability Guide; (5) the successful tenderer assumes the commercial risk of achieving all of the system performance requirements including R&M; and (6) monitoring of the contractor during system development is “hands-off” but “eyes open”. This approach to R&M in acquisition was chosen after consideration of the acquisition process in a number of countries, especially the US and UK. The approach is similar to that used by the UK and has been in use in Australia now for about two years View full abstract»

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  • Enhancing supportability through life-cycle definitions

    Page(s): 402 - 409
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    Design specifications for functional systems are typically derived from the extreme environmental conditions expected during their operational use. This practice can result in a system which is extremely over designed, and therefore excessively heavy, expensive and complex. A prime example is the military's requirement for cold temperature operations of -55 C, a temperature that has not been reached in twenty years. Equally likely, a system design based on operational environments may be inadequately designed since nonoperational environments, such as handling, transportation, storage, and maintenance may have been ignored. If these nonoperational environments prove to drive the durability of the system, failures will occur and the system's reliability will suffer, resulting in increased life cycle costs and reduced operational readiness. The United States Air Force has recognized this shortcoming in the design process and requires newly developed systems to be designed to endure the environments imposed by the entire life cycle profile-from manufacturing through deployment, operational usage and maintenance. Unfortunately, the procedures and data used to develop these life cycle profiles are not consistent from one development to the next. The Mission Environmental Requirements Integration Technology Program (MERIT) was created to provide a solution to this problem. This technology will result in decreased environmental definition costs, an optimum design for a given application, reduced cycle times and decreased life cycle warranty and maintenance costs View full abstract»

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