Defining and Characterizing Life-Cycle Loads. For the wear-out failure mechanisms, the ratings are assigned on the basis of benchmarking the individual time to failure for a given wear-out mechanism with overall time to failure, expected product life, past experience, and engineering judgment. 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. In this example, we use the Discrete Event Simulation tool in the Reliability Analytics Toolkit to simulate system availability for a problem presented in MIL-HDBK-338, Reliability Design Handbook (page 10-42), as shown below. Redundancy can often be addressed at various levels of the system architecture. A = .001, B = .002, mission time (t) = 50 hours . Sign up for email notifications and we'll let you know about new publications in your areas of interest when they're released. Do you enjoy reading reports from the Academies online for free? The phases in a system’s life cycle include manufacturing and assembly, testing, rework, storage, transportation and handling, operation, and repair and maintenance (for an example of the impact on reliability of electronic components as a result of shock and random vibration life-cycle loads, see Mathew et al., 2007). faces; increase friction between surfaces, contaminate lubricants, clog orifices, and wear materials. 0000003574 00000 n All of these indices can be used to evaluate the reliability of an existing distribution system and to provide useful planning information regarding improvements to existing systems and the design of new distribution systems. In cold standby, the secondary part(s) is completely shut down until needed. (2006) for an example. A specific approach to design for reliability was described during the panel’s workshop by Guangbin Yang of Ford Motor Company. The origins of contemporary reliability engineering can be traced to World War II. Many testing environments may need to be considered, including high temperature, low temperature, temperature cycle and thermal shock, humidity, mechanical shock, variable frequency vibration, atmospheric contaminants, electromagnetic radiation, nuclear/cosmic radiation, sand and dust, and low pressure: Reliability test data analysis can be used to provide a basis for design changes prior to mass production, to help select appropriate failure models and estimate model parameters, and for modification of reliability predictions for a product. If the likelihood or consequences of occurrence are low, then the risk may not need to be addressed. Redundancy exists when one or more of the parts of a system can fail and the system can still function with the parts that remain operational. 0000003450 00000 n In many cases, MIL-HDBK-217 methods would not be able to distinguish between separate failure mechanisms. Different categories of failures may require different root-cause analysis approaches and tools. %PDF-1.3 %���� In this method, each limit-state function is linearized using Taylor expansion at the most likelihood point (MLP), then the multivariate saddle-point approximation is used for all linearized functions to compute system … ��J� ��EIm ��Ρ �DL 2��1�� f�9�` �HS �T�@Ǝ ;4��W�� ��� �anj� �.uT�"��@��]�wS�T� զ ��� }�������fj.��#�-�Ic����"6u�S�]�0 �;�] Severity describes the seriousness of the effect of the failure caused by a mechanism. Such a database can help save considerable funds in fault isolation and rework associated with future problems. Maintainability are the relative costs of fixing, updating, extending, operating and servicing an entity over its lifetime. Low temperature: In mechanical and electromechanical systems, low temperatures can cause plastics and rubber to lose flexibility and become brittle, cause ice to form, increase viscosity of lubricants and gels, and cause structural damage due to physical contraction. Collectively, they affect both the utility and the life-cycle costs of a product or system. For example, a specific multilayer ceramic capacitor without modification may become part of your laptop computer or family vehicle. Simply put, reliability is the absence of unplanned downtime. In active redundancy, the parts will consume life at the same rate as the individual components. Health monitoring is the method of measuring and recording a product’s health in its life-cycle environment. An entity with relatively low costs in these areas is considered maintainable whereas an entity with high costs may be considered unmaintainable or "high maintenance." In standby redundancy, some parts are not energized during the operation of the system; they get switched on only when there are failures in the active parts. The indices EENS, ECOST, and IEAR can be those specifically for each load point or for the overall system. They identify the potential failure modes, failure sites, and failure mechanisms. Test-Retest Reliability 2. Consider a computer system with three components: a processor, a hard drive and a CD drive in series as shown next. For a series system: The system works if A works and B works and C works and D works. Nuclear/cosmic radiation: Nuclear/cosmic radiation can cause heating and thermal aging; alter the chemical, physical, and electrical properties of materials; produce gasses and secondary radiation; oxidize and discolor surfaces; and damage electronic components and circuits. This process combines the strengths of the physics-of-failure approach with live monitoring of the environment and operational loading conditions. Register for a free account to start saving and receiving special member only perks. (2012) and Sun et al. x�bb�f`b``Ń3� ���ţ�1�c� 6A� The information collected needs to include the failure point (quality testing, reliability testing, or field), the failure site, and the failure mode and mechanism. 501 0 obj<>stream Start with a risk pool, which is the list of all known risks, along with knowledge of how those risks are quantified (if applicable) and possibly mitigated. Jump up to the previous page or down to the next one. In hot standby, the secondary part(s) forms an active parallel system. That number is the product of the probability of detection, occurrence, and severity of each mechanism. Characterize the risk catalog: Generate application-specific details about the likelihood of occurrence, consequences of occurrence, and acceptable mitigation approaches for each of the risks in the risk catalog. For example, if In terms of time, Suppose that Observe that for the constant failure rate (exponential) model, a Weibull distribution can be used: but this is much more difficult. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website. During this correct operation, no repair is required or performed, and the system adequately follows the defined performance specifications. Equipment misapplication can result from improper changes in the operating requirements of the machine. Mechanical shock: Some systems must be able to withstand a sudden change in mechanical stress typically due to abrupt changes in motion from handling, transportation, or actual use. For example, a motorcycle cannot go if any of the following parts cannot serve: engine, tank with fuel, chain, frame, front or rear wheel, etc., and, of course, the driver. _PU�b�5�I|�$��2Ua�����#+3�xm�Ϊ���8��i �J�:@\.�f(V�ޔ� �p�`�Ri؂�'�.�=�����J*.`�hhZ�� r8����1����Q0�`hhhZT����($���dA�@�%@���\��l���,��ET��3N`|��͠ɪ�ϸ�)�Q����#;�C� L�K'�����`���4��PN�!���h&�~��dN0�Cv��hg�bmv�m@� �D�qg��n�|``d�a`8а�@� "� Those systems are not only less likely to successfully carry out their intended missions, but they also could endanger the lives of the operators. Determine risk-mitigating factors: Factors may exist that modify the applicable mitigation approach for a particular part, product, or system. 0000113266 00000 n By having such a classification system, it may be easier for engineers to identify and share information on vulnerable areas in the design, manufacture, assembly, storage, transportation, and operation of the system. The life of the hot standby part(s) is consumed at the same rate as active parts. Howeve… Motors, power supplies, buttons, etc are examples of components found in cell phones, medical devices, industrial equipment, and vehicles.