Redundancy can often be addressed at various levels of the system architecture. Reliability, availability and serviceability (RAS), also known as reliability, availability, and maintainability (RAM), is a computer hardware engineering term involving reliability engineering, high availability, and serviceability design. It supports physics-. (2010). Failure analysis will be successful if it is approached systematically, starting with nondestructive examinations of the failed test samples and then moving on to more advanced destructive examinations; see Azarian et al. The ranking may be performed using a scoring algorithm that couples likelihood and consequence into a single dimensionless quantity that allows diverse risks to be compared. The degree of and rate of system degradation, and thus reliability, depend upon the nature, magnitude, and duration of exposure to such stresses. 499 33 For example, after experiencing a rare equipment failure, a plant instituted The recommendations of Reliability Growth will improve the reliability of defense systems and protect the health of the valuable personnel who operate them. Detection describes the probability of detecting the failure modes associated with the failure mechanism. Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text. The information required for designing system-specific reliability tests includes the anticipated life-cycle conditions, the reliability goals for the system, and the failure modes and mechanisms identified during reliability analysis. In active redundancy, the parts will consume life at the same rate as the individual components. The potential failure mechanisms are considered individually, and they are assessed with models that enable the design of the system for the intended application. Sources of reliability and failure data include supplier data, internal manufacturing test results from various phases of production, and field failure data. Subsystem 1 has a reliability of 99.5%, subsystem 2 has a reliability of 98.7% and subsystem 3 has a reliability of 97.3% for a mission of 100 hours. There are mainly three approaches used for Reliability Testing 1. Additional insights into the criticality of a failure mechanism can be obtained by examining past repair and maintenance actions, the reliability capabilities of suppliers, and results observed in the initial development tests. This chapter describes techniques to improve system design to enhance system reliability. Different categories of failures may require different root-cause analysis approaches and tools. Equipment misapplication can result from improper changes in the operating requirements of the machine. In the next step, the candidate part is subjected to application-dependent assessments. 0000008173 00000 n A detailed critique of MIL-HDBK-217 is provided in Appendix D. ANALYSIS OF FAILURES AND THEIR ROOT CAUSES. In both of these methods, a generic average failure rate (assuming average operating conditions) is assumed. notification. Ideally, a virtual qualification process will identify quality suppliers and quality parts through use of physics-of-failure modeling and a risk assessment and mitigation program. H�|��j�0E����eJ the full process or specific aspects of this technique (see, e.g., Foucher et al., 2002). Reliability block diagrams allow one to aggregate from component reliabilities to system reliability. = = = = 4 3 2 1 R R R R 10 Power Supply 0.995 PC unit 0.99 Floppy drive B Floppy drive A Hard drive C Laser Printer Dot-matrix Printer 0.98 0.98 0.95 0.965 0.999 system … Once the risks are ranked, those that fall below some threshold in the rankings can be omitted. Product reliability can be ensured by using a closed-loop process that provides feedback to design and manufacturing in each stage of the product life cycle, including after the product is shipped and fielded. Two Common Techniques for Design for Reliability. The discipline’s first concerns were electronic and mechanical components (Ebeling, 2010). Atmospheric contaminants: The atmosphere contains such contaminants as airborne acids and salts that can lower electrical and insulation resistance, oxidize materials, and accelerate corrosion. Classify risks: Classify each risk in the risk catalog in one of two categories: functionality risks and producibility risks. View our suggested citation for this chapter. allows design, manufacturing, and testing to be conducted promptly and cost-effectively. Failures do link hierarchically in terms of the system architecture, and so a failure mode may, in turn, cause failures in a higher level subsystem or may be the result of a failure of a lower level component, or both. Thus, components can be modeled to have decreasing, constant, or increasing failure rates. 0000084467 00000 n 2.2 Parallel System . Solving these models using the complete enumeration method is discussed in many standard reliability text books (see, e.g., Meeker and Escobar (1998); also see Guide for Selecting and Using Reliability Predictions of the IEEE Standards Association [IEEE 1413.1]). The origins of contemporary reliability engineering can be traced to World War II. It is in clear contrast with physics-of-failure estimation: “an approach to design, reliability assessment, testing, screening and evaluating stress margins by employing knowledge of root-cause failure processes to prevent product failures through robust design and manufacturing practices” (Cushing et al., 1993, p. 542). Because of changes in technology trends, the evolution of complex supply-chain interactions and new market challenges, shifts in consumer demand, and continuing standards reorganization, a cost-effective and efficient parts selection and management process is needed to perform this assessment, which is usually carried out by a multidisciplinary team. 0000087137 00000 n Integrity test data (often available from the part manufacturer) are examined in light of the life-cycle conditions and applicable failure mechanisms and models. Similarity analyses have been reported to have a high degree of accuracy in commercial avionics (see Boydston and Lewis, 2009). Defining and characterizing the life-cycle stresses can be difficult because systems can experience completely different application conditions, including location, the system utilization profile, and the duration of utilization and maintenance conditions. The approach encourages innovative designs through a more realistic reliability assessment. 0000001899 00000 n However, such methods can dramatically increase system reliability, and DoD system reliability would benefit considerably from the use of such methods. 2 For additional design-for-reliability tools that have proven useful in DoD acquisition, see Section 2.1.4 of the TechAmerica Reliability Program Handbook, TA-HB-0009, available: [August 2014]. Almost all systems include parts (materials) produced by supply chains of companies. For example, Supplier 1's reliability at 10,000 miles is 36.79%, whereas Supplier 2's reliability at 10,000 miles is 50.92%. 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