Failure analysis techniques include nondestructive and destructive techniques. 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. In this process, every aspect of the product design, the design process, the manufacturing process, corporate management philosophy, and quality processes and environment can be a basis for comparison of differences. Furthermore, one user may keep the computer by a sunny window, while another person may keep the computer nearby an air conditioner, so the temperature profile experienced by each system, and hence its degradation due to thermal loads, would be different. To learn, in detail, how to bring DfR into the development process, watch the webinar: Implementing Reliability Physics into the Design Process: What Every Manager and Engineer Needs to Know. Prognostics is the prediction of the future state of health of a system on the basis of current and historical health conditions as well as historical operating and environmental conditions. The tests may be conducted according to industry standards or to required customer specifications. However, such methods can dramatically increase system reliability, and DoD system reliability would benefit considerably from the use of such methods. Lynn Ledwith Engineers often talk about the importance of design for reliability (DfR) and the impact it has on a product’s overall efficiencies and success. To this end, handbooks, guidances, and formal memoranda were revised or newly issued to reduce the frequency of reliability deficiencies for defense systems in operational testing and the effects of those deficiencies. Traditional military reliability prediction methods, including those detailed in Military Handbook: Reliability Prediction of Electronic Equipment (MIL-HDBK-217) (U.S. Department of Defense, 1991), rely on the collection of failure data and generally assume that the components of the system have failure rates (most often assumed to be constant over time) that can be modified by independent “modifiers” to account for various quality, operating, and environmental conditions. 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. By Field trial records provide estimates of the environmental profiles experienced by the system. Furthermore, reliability failures discovered after deployment can result in costly and strategic delays and the need for expensive redesign, which often limits the tactical situations in which the system can be used. Electromagnetic radiation: Electromagnetic radiation can cause spurious and erroneous signals from electronic components and circuitry. January 3, 2009. If the integrity test data are insufficient to validate part reliability in the application, then virtual qualification should be considered. It uses application conditions and the duration of the application with understanding of the likely stresses and potential failure mechanisms. After these preliminaries, once design work is initiated, the goal is to determine a design for the system that will enable it to have high initial reliability prior to any formal testing. The life-cycle environment of a system consists of assembly, storage, handling, and usage conditions of the system. These methods can also accommodate time-phased missions. W How do we assess reliability? 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. Sometimes, the damage due to the individual loading conditions may be analyzed separately, and the failure assessment results may be combined in a cumulative manner. Keep dimensions loose at this stage. This takes substantial effort, but there is valuable return in: Determining average and realistic worst-case scenarios. The techniques that comprise design for reliability include (1) failure modes and effects analysis, (2) robust parameter design, (3) block diagrams and fault tree analyses, (4) physics-of-failure methods, (5) simulation methods, and (6) root-cause analysis. Failures categorized as system damage can be further categorized according to the failure mode and mechanism. Mixed flowing gas tests are often used to assess the reliability of parts that will be subjected to these environments. 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 life of the hot standby part(s) is consumed at the same rate as active parts. (2010). Modeling 2. All rights reserved. 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. (2010a, 2010b). Reliability. Fault trees can clarify the dependence of a design on a given component, thereby prioritizing the need for added redundancy or some other design modification of various components, if system reliability is deficient. This has forced design teams to re-architect their designs, adding newer functionality and adopting aggressive scaling through technology migration to keep up with the market demands. The potential failure mechanisms are considered individually, and they are assessed with models that enable the design of the system for the intended application. To improve PTV reliability through design requires either reducing the PTV height, increasing the diameter, or a combination of both. A standby system consists of an active unit or subsystem and one or more inactive units, which become active in the event of a failure of the functioning unit. To address this need, ReliaSoft offers a three-day training seminar on Design for Reliability … The information collected needs to include the failure point (quality testing, reliability testing, or field), the failure site, and the failure mode and mechanism. Functionality risks impair the system’s ability to operate to the customer’s specification. There are two ways to produce a reliable system. Many developers of defense systems depend on reliability growth methods applied after the initial design stage to achieve their required levels of reliability. MyNAP members SAVE 10% off online. But it is important to remember that the accuracy of the results using virtual qualification depends on the accuracy of the inputs to the process, that is, the system geometry and material properties, the life-cycle loads, the failure models used, the analysis domain, and the degree of discreteness used in the models (both spatial and temporal). This transient stress can cause faster consumption of life during switching. In particular, physics of failure is a key approach used by manufacturers of commercial products for reliability enhancement. Finally, systems that fail to meet their reliability requirements are much more likely to need additional scheduled and unscheduled maintenance and to need more spare parts and possibly replacement systems, all of which can substantially increase the life-cycle costs of a system. In cold standby, the secondary part(s) is completely shut down until needed. At the design stage, these reliabilities can either come from the reliabilities of similar components for related systems, from supplier data, or from expert judgment. However, there are often a minimum and a maximum limit beyond which the part will not function properly or at which the increased complexity required to address the stress with high probability will not offer an advantage in cost-effectiveness. Hence, to obtain a reliable prediction, the variability in the inputs needs to be specified using distribution functions, and the validity of the failure models needs to be tested by conducting accelerated tests (see Chapter 6 for discussion). Test data can also be used to create guidelines for manufacturing tests including screens, and to create test requirements for materials, parts, and sub-assemblies obtained from suppliers. 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). Failure models of overstress mechanisms use stress analysis to estimate the likelihood of a failure as a result of a single exposure to a defined stress condition. This section discusses two explicit models and similarity analyses for developing reliability predictions. If the likelihood or consequences of occurrence are low, then the risk may not need to be addressed. Reliability Basics: Design of Reliability Tests. Set reliability goals based on survivability. ANSYS Sherlock automated design analysis software augments DfR by providing reliability insights as early in the product development process as possible. Design of Experiments (DOE) has been widely used to quickly identify important factors and to determine the best values of them in order to optimize the performance of a product or process. Also, you can type in a page number and press Enter to go directly to that page in the book. A failure cause is defined as the circumstances during design, manufacture, storage, transportation, or use that lead to a failure. This approach is inaccurate for predicting actual field failures and provides highly misleading predictions, which can result in poor designs and logistics decisions. They use failure data at the component level to assign rates or probabilities of failure. Ready to take your reading offline? Otherwise, design changes or alternative parts must be considered. (2012) and Sotiris et al. Reliability Growth Through Testing. The construction concludes with the assignment of reliabilities to the functioning of the components and subcomponents. Yang said that at Ford they start with the design for a new system, which is expressed using a system boundary diagram along with an interface analysis. 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]). Because this is a relatively new technique for prediction, however, there is no universally accepted procedure. High temperature: High-temperature tests assess failure mechanisms that are thermally activated. Determine risk-mitigating factors: Factors may exist that modify the applicable mitigation approach for a particular part, product, or system. The outputs for this key practice are a failure summary report arranged in groups of similar functional failures, actual times to failure of components based on time of specific part returns, and a documented summary of corrective actions implemented and their effectiveness. Click here to buy this book in print or download it as a free PDF, if available. Reliability Testing can be categorized into three segments, 1. The data need to be collected over a sufficiently long period to provide an estimate of the loads and their variation over time. Failure modes, mechanisms, and effects analysis is a systematic approach to identify the failure mechanisms and models for all potential failure modes, and to set priorities among them. The root cause is the most basic causal factor or factors that, if corrected or removed, will prevent the recurrence of the failure. Determine the impact of unmanaged risk: Combine the likelihood of risk occurrence with the consequences of occurrence to predict the resources associated with risks that the product development team chooses not to manage proactively. Similarity analyses have been reported to have a high degree of accuracy in commercial avionics (see Boydston and Lewis, 2009). Once the components and external events are understood, a system model is developed. An extension to the FMECA is the optimal selection of maintenance tasks that will reduce safety, environmental and operational risks while optimizing costs, using Reliability Centered Maintenance (RCM) decision making logic. General methodologies for risk assessment (both quantitative and qualitative) have been developed and are widely available. 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. In other words, there is no precise description of the operating environment for any system.1 Consider the example of a computer, which is typically designed for a home or office environment. High-priority failure mechanisms determine the operational stresses and the environmental and operational parameters that need to be accounted or controlled for in the design. o. DfR: A process for ensuring the reliability of a product or system during the design stage . If the two products are very similar, then the new design is believed to have reliability similar to the predecessor design. A manufacturer’s ability to produce parts with consistent quality is evaluated; the distributor assessment evaluates the distributor’s ability to provide parts without affecting the initial quality and reliability; and the parts selection and management team defines the minimum acceptability criteria based on a system’s requirements. However, changes between the older and newer product do occur, and can involve. Temperature cycle and thermal shock: Temperature cycle and thermal shock testing are most often used to assess the effects of thermal expansion mismatch among the different elements within a system, which can result in materials’ overstressing and cracking, crazing, and delamination. Rank and down-select: Not all functionality risks require mitigation. In this article, we will give an example using DOE++ to improve product reliability, and at the same time make sure the product meets its functional requirement. In general, there are no distinct boundaries for such stressors as mechanical load, current, or temperature above which immediate failure will occur and below which a part will operate indefinitely. Beginning in 2008, DOD undertook a concerted effort to raise the priority of reliability through greater use of design for reliability techniques, reliability growth testing, and formal reliability growth modeling, by both the contractors and DOD units. For example, misapplication of a component could arise from its use outside the operating conditions specified by the vendor (e.g., current, voltage, or temperature). Ideally, such data should be obtained and processed during actual application. John Graham Feature extraction is used to analyze the measurements and extract the health indicators that characterize the system degradation trend. This in turn requires Data obtained from maintenance, inspection, testing, and usage monitoring can be used to perform timely maintenance for sustaining the product and for preventing failures. Information on life-cycle conditions can be used for eliminating failure modes that may not occur under the given application conditions. This process combines the strengths of the physics-of-failure approach with live monitoring of the environment and operational loading conditions. If this is a page you have "bookmarked" or added to your "favorites", please be sure to update the link accordingly. If the magnitude and duration of the life-cycle conditions are less severe than those of the integrity tests, and if the test sample size and results are acceptable, then the part reliability is acceptable. Stay in the know. Get involved early in the concept phase of the design to ensure reliability; maintainability and safety are being addressed. Virtual qualification uses computer-aided simulation to identify and rank the dominant failure mechanisms associated with a part under life-cycle loads, determine the acceleration factor for a given set of accelerated test parameters, and determine the expected time to failure for the identified failure mechanisms (for an example, see George et al., 2009). Prognostics and health management techniques combine sensing, recording, and interpretation of environmental, operational, and performance-related parameters to indicate a system’s health. operation of a system. To search the entire text of this book, type in your search term here and press Enter. A detailed critique of MIL-HDBK-217 is provided in Appendix D. ANALYSIS OF FAILURES AND THEIR ROOT CAUSES. Detection describes the probability of detecting the failure modes associated with the failure mechanism. Fault trees can also assist with root-cause analyses. These practices, collectively referred to as design for reliability, improve reliability through design in several ways: Reviewing in-house procedures (e.g., design, manufacturing process, storage and handling, quality control, maintenance) against corresponding standards can help identify factors that could cause failures. The data are a function of the lengths and conditions of the trials and can be extrapolated to estimate actual user conditions. Producibility risks determine the probability of successfully manufacturing the product, which in turn refers to meeting some combination of economics, schedule, manufacturing yield, and quantity targets. It should contain information and data to the level of detail necessary to identify design or process deficiencies that should be eliminated. The basic elements of a fault tree diagram are events that correspond to improper functioning of components and subcomponents, and gates that represent and/or conditions. The complexities of today’s technologies make DfR more significant — and valuable — than ever before. Very slight changes to the design of a component can cause profound changes in reliability, which is why it is important to specify product reliability and maintainability targets before any design work is undertaken. 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. In-situ monitoring provides the most accurate account of load histories and is most valuable in design for reliability. Reliability is extremely design-sensitive. In the next step, the candidate part is subjected to application-dependent assessments. o …perform the specified function . Failure mechanisms are categorized as either overstress or wear-out mechanisms; an overstress failure involves a failure that arises as a result of a single load (stress) condition. It is necessary to select the parts (materials) that have sufficient quality and are capable of delivering the expected performance and reliability in the application. But, as you’ll soon find out, the use of DfR can, and should, be expanded. Failure susceptibility is evaluated using the previously identified failure models when they are available. Failures have to be analyzed to identify the root causes of manufacturing defects and to test or field failures. The approach encourages innovative designs through a more realistic reliability assessment. Improve reliability through managing risk. Subscribe to the Ansys Blog for email notifications. Diagnostics are used to isolate and identify the failing subsystems/components in a system, and prognostics carry out the estimation of remaining useful life of the systems, subsystems. They ensure that the supply-chain participants have the capability to produce the parts (materials) and services necessary to meet the final reliability objectives and that those participants are following through. Equipment misapplication can result from improper changes in the operating requirements of the machine. High-priority mechanisms are those that may cause the product to fail relatively early in a product’s intended life. Service records provide information on the maintenance, replacement, or servicing performed. Avoid mean time to failure (MTTF) and mean time between failures (MTBF) because they do not measure reliability. Such a database can help save considerable funds in fault isolation and rework associated with future problems. 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. Product Reliability Through Design Process The purpose of this report is to highlight the importance of product reliability within the product development process which includes design and manufacturing validation and continuous improvement initiatives. The value of the product that may be scrapped during the verification testing should be included in the impact. Sensing, feature extraction, diagnostics, and prognostics are key elements. Show this book's table of contents, where you can jump to any chapter by name. However, this common practice comes too late in the development process. The importance that engineering design plays in the reduction of maintenance costs is well known. Atmospheric contaminants: The atmosphere contains such contaminants as airborne acids and salts that can lower electrical and insulation resistance, oxidize materials, and accelerate corrosion. It’s important to consider reliability and validity when you are creating your research design, planning your methods, and writing up your results, especially in quantitative research. This optimizes product reliability, development time and cost savings. physical prototype . On Reliability testing procedures may be general, or the tests may be specifically designed for a given system. 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. These practices can substantially increase reliability through better system design (e.g., built-in redundancy) and through the selection of better parts and materials. Relying on testing-in reliability is inefficient and ineffective because when failure modes are discovered late in system development, corrective actions can lead to delays in fielding and cost over-runs in order to modify the system architecture and make any related changes. 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. An overly pessimistic prediction can result in unnecessary additional design and test expenses to resolve the perceived low reliability. The physics-of-failure approach proactively incorporates reliability into the design process by establishing a scientific basis for evaluating new materials, structures and electronics technologies. 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. Reliability block diagrams model the functioning of a complex system through use of a series of “blocks,” in which each block represents the working of a system component or subsystem. For overstress mechanisms, failure susceptibility is evaluated by conducting a stress analysis under the given environmental and operating conditions. These best practices also guide the process along. Improvement The following formula is for calculating the probability of failure. (For a description of this process for an electronic system, see Sandborn et al., 2008.) May 18, 2018, Industrial Equipment & Rotating Machinery, 10x Faster Transient Electromagnetic Field Simulation, ANSYS Discovery Release Powers Up 3D Design, Implementing Reliability Physics into the Design Process: What Every Manager and Engineer Needs to Know, Introduction to Reliability Physics Analysis. In-situ monitoring (for a good example, see Das, 2012) can track usage conditions experienced by the system over a system’s life cycle. Measurement 3. On-demand The goal of failure analysis is to identify the root causes of failures. Essentially, DfR is a process that ensures a product, or system, performs a specified function within a given environment over the expected lifetime. Reliability block diagrams allow one to aggregate from component reliabilities to system reliability. Unfortunately, there may be so many ways to fail a system that an explicit model (one which identifies all the failure possibilities) can be intractable. It defines the basic concepts of reliability growth and illustrates how these concepts can be most effectively applied using a variety of design and test methods. Keep in mind, it’s less expensive to design for reliability than to test for reliability. We will have an officer / volunteer meeting at about 7:15 PM for those who wish to join in. They design to the quality level that can be controlled in manufacturing and assembly, considering the potential failure modes, failure sites, and failure mechanisms, obtained from the physics-of-failure analysis, and the life-cycle profile. Topics covered include reliability growth management, reliability Sources of reliability and failure data include supplier data, internal manufacturing test results from various phases of production, and field failure data. Employ physics of failure (PoF) to acquire a deep understanding of how the desired lifetime and environment affect the design. A high percentage of defense systems fail to meet their reliability requirements. Learn More. Integrity test data (often available from the part manufacturer) are examined in light of the life-cycle conditions and applicable failure mechanisms and models. Fault tree analysis is a systematic method for defining and analyzing system failures as a function of the failures of various combinations of components and subsystems. Reliability Growth evaluates these recent changes and, more generally, assesses how current DOD principles and practices could be modified to increase the likelihood that defense systems will satisfy their reliability requirements. The acceptable combination of mitigation approaches becomes the required verification approach. Different categories of failures may require different root-cause analysis approaches and tools. Producibility risks are risks for which the consequences of occurrence are financial (reduction in profitability). Or register for the webinar: Introduction to Reliability Physics Analysis. Physics of failure uses knowledge of a system’s life-cycle loading and failure mechanisms to perform reliability modeling, design, and assessment. This article will discuss PCB reliability through vias, the potential concerns that are introduced into your board through their implementation, and how to minimize those concerns to acceptable levels. Performance assessment seeks to evaluate a part’s ability to meet the performance requirements (e.g., functional, mechanical, and electrical) of the system. That number is the product of the probability of detection, occurrence, and severity of each mechanism. As is the case for reliability block diagrams, fault trees are initially built at a relatively coarse level and then expanded as needed to provide greater detail. © 2020 National Academy of Sciences. Register for a free account to start saving and receiving special member only perks. A classification system of failures, failure symptoms, and apparent causes can be a significant aid in the documentation of failures and their root causes and can help identify suitable preventive methods. Ideally all failure mechanisms and their interactions are considered for system design and analysis. There are three methods used to estimate system life-cycle loads relevant to defense systems: similarity analysis, field trial and service records, and in-situ monitoring: 1 This is one of the limitations of prediction that is diminishing over time, given that many systems are being outfitted with sensors and communications technology that provide comprehensive information about the factors that will affect reliability. In electromechanical and mechanical systems, high temperatures may soften insulation, jam moving parts because of thermal expansion, blister finishes, oxidize materials, reduce viscosity of fluids, evaporate lubricants, and cause structural overloads due to physical expansions. This report examines changes to the reliability requirements for proposed systems; defines modern design and testing for reliability; discusses the contractor's role in reliability testing; and summarizes the current state of formal reliability growth modeling. Physics of failure encourages innovative, cost-effective design through the use of realistic reliability assessment. The page you have attempted to reach is no longer available. 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. REDUNDANCY, RISK ASSESSMENT, AND PROGNOSTICS. Marius Rosu For unmanaged producibility risks, the resources predicted in the impact analysis are translated into costs. “Risk” is defined as a measure of the priority assessed for the occurrence of an unfavorable event. It is important for FRACAS to be applied throughout developmental and operational testing and post-deployment. For wear-out mechanisms, failure susceptibility is evaluated by determining the time to failure under the given environmental and operating conditions. 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: http://www.techstreet.com/products/1855520 [August 2014]. The reliability potential is estimated through use of various forms of simulation and component-level testing, which include integrity tests, virtual qualification, and reliability testing. As the extent and degree of difference increases, the reliability differences will also increase. It supports physics-. In hot standby, the secondary part(s) forms an active parallel system. Preserving profits: Products get to market earlier, preventing erosion of sales and market share. Almost all systems include parts (materials) produced by supply chains of companies. The failures of active units are signaled by a sensing subsystem, and the standby unit is brought to action by a switching subsystem. In addition, fixes incorporated late in development often cause problems in interfaces, because of a failure to identify all the effects of a design change, with the result that the fielded system requires greater amounts of maintenance and repair. Design-out Maintenance is a dichotomy. However, the operational profile of each computer may be completely different depending on user behavior. Subsequently, DoD allowed contractors to rely primarily on “testing reliability in” toward the end of development. faces; increase friction between surfaces, contaminate lubricants, clog orifices, and wear materials. Reliability Block Diagrams. The higher the risk priority number, the higher a failure mechanism is ranked. The data to be collected to monitor a system’s health are used to determine the sensor type and location in a monitored system, as well as the methods of collecting and storing the measurements. If the part is not found to be acceptable after this assessment, then the assessment team must decide whether an acceptable alternative is available. Before using data on similar systems for proposed designs, the characteristic differences in design and application for the comparison systems need to be reviewed. The effects of manufacturing variability can be assessed by simulation as part of the virtual qualification process. Design for reliability is a collection of techniques that are used to modify the initial design of a system to improve its reliability. These factors include the type or technology of the part under consideration, the quantity and type of manufacturer’s data available for the part, the quality and reliability monitors employed by the part manufacturer, and the comprehensiveness of production screening at the assembly level. Design-out is a maintenance root cause elimination category where the solution is to design for reliability and intentionally create high reliability equipment through an engineering design change to its components, i.e. Reliability is about the consistency of a measure, and validity is about the accuracy of a measure. As a consequence, erroneous reliability predictions can result in serious problems during development and after a system is fielded. This pattern points to the need for better design practices and better system engineering (see also Trapnell, 1984; Ellner and Trapnell, 1990). The discipline’s first concerns were electronic and mechanical components (Ebeling, 2010). The process for assessing the risks associated with accepting a part for use in a specific application involves a multistep process: A product’s health is the extent of degradation or deviation from its “normal” operating state. Determine an application-specific risk catalog: Using the specific application’s properties, select risks from the risk pool to form an application-specific risk catalog. During the design phase, to maximize reliability, the feedback principle was practiced through formal data collection techniques, which is very useful in improving inherent reliability. Redundancy can often be addressed at various levels of the system architecture. Reliability in Research Design. The FRACAS accumulates failure, analysis and corrective action information to assess progress in eliminating hardware, software and process-related failure modes and mechanisms. The main idea in this approach is that all the analysts agree to draw as much relevant information as possible from tests and field data. Defining and Characterizing Life-Cycle Loads. Rigor is simply defined as the quality or state of being very exact, careful, or with strict precision8 or the quality of being thorough and accurate.9 The term qualitative rigor itself is an oxymoron, considering that qualitative research is a journey of explanation and discovery tha… In active redundancy, all of a system’s parts are energized during the. Featured Solutions to Design for Reliability. 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. The article describes the design separation feature in Altera software that seeks to address these as well as today’s conflicting needs for low power, small size and high functionality while maintaining high reliability and […] Therefore, DfR is most effective in the concept feasibility stage. On The prognostics and health management process does not predict reliability but rather provides a reliability assessment based on in-situ monitoring of certain environmental or performance parameters. ActiveCampaign. Damage models are used to determine fault generation and propagation. Wear-out failure involves a failure that arises as a result of cumulative load (stress) conditions. throughout the life of the product with low overall life-cycle costs. Load distributions can be developed from data obtained by monitoring systems that are used by different users. Historically, MTBF has been calculated using the empirical prediction handbooks, which assume a constant failure rate that is not always correct. A failure mode is the manner in which a failure (at the component, subsystem, or system level) is observed to occur, or alternatively, as the specific way in which a failure is manifested, such as the breaking of a truck axle. The answer is that they conduct research using the measure to confirm that the scores make sense based on their understanding of th… Mechanical shock can lead to overstressing of mechanical structures causing weakening, collapse, or mechanical malfunction. On Determine the resources required to manage the risk: Create a management plan and estimate the resources needed to perform a prescribed regimen of monitoring the part’s field performance, the vendor, and assembly/manufacturability as applicable. Reducing the PTV height is achieved by changing the PCB thickness. 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). From 1980 until the mid-1990s, the goal of DoD reliability policies was to achieve high initial reliability by focusing on reliability fundamentals during design and manufacturing. 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. 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. It is critical to understand rigor in research. The use of design-for-reliability techniques can help to identify the components that need modification early in the design stage when it is much more cost-effective to institute such changes. ...or use these buttons to go back to the previous chapter or skip to the next one. Knowledge of the likely failure mechanisms is essential for developing designs for reliable systems. Several techniques for design for reliability are discussed in the rest of this section: defining and characterizing life-cycle loads to improve design parameters; proper selection of parts and materials; and analysis of failure modes, mechanisms, and effects. Design for reliability (or RBDO) includes two distinct categories of analysis, namely (1) design for variability (or variability-based design optimization), which focuses on the variations at a given moment in time in the product life; From: Diesel Engine System Design, 2013. Decide whether the risk is acceptable: If the impact fits within the overall product’s risk threshold and budget, then the part selection can be made with the chosen verification activity (if any). Design for Reliability (DfR) Defined . Failure data was manipulated and calculated to get the failure rate. For complex systems, the apportionment calculation may become more complex, yet the concept still applies. The failure data form the basis of reliability research. They identify the potential failure modes, failure sites, and failure mechanisms. View our suggested citation for this chapter. Variable frequency vibration: Some systems must be able to withstand deterioration due to vibration. Low pressure: Low pressure can cause overstress of structures such as containers and tanks that can explode or fracture; cause seals to leak; cause air bubbles in materials, which may explode; lead to internal heating due to lack of cooling medium; cause arcing breakdowns in insulations; lead to the formation of ozone; and make outgassing more likely. So, let’s take a look at DfR fundamentals and how companies employ it to their best advantage. According to the Reliability Analysis Center: A failure reporting, analysis and corrective action system (FRACAS) is defined, and should be implemented, as a closed-loop process for identifying and tracking root failure causes, and subsequently determining, implementing and verifying an effective corrective action to eliminate their reoccurrence. These mechanisms occur during the normal operational and environmental conditions of the product’s application. Wear-out mechanisms are analyzed using both stress and damage analysis to calculate the time required to induce failure as a result of a defined stress life-cycle profile. DfR often occurs at the design stage — before physical prototyping — and is often part of an overall design for excellence (DfX) strategy. Some users may shut down the computer every time they log off; others may shut down only once at the end of the day; still others may keep their computers on all the time. Although the data obtained from virtual qualification cannot fully replace the data obtained from physical tests, they can increase the efficiency of physical tests by indicating the potential failure modes and mechanisms that can be expected. Design for Reliability is a very hot topic these days, and it can be a challenge to find a good starting point that will give you the foundation you need to start sifting through and exploring all of the available options. Do you want to take a quick tour of the OpenBook's features? (2012). Issue 24, February 2003. The National Academies of Sciences, Engineering, and Medicine, Reliability Growth: Enhancing Defense System Reliability, http://www.techstreet.com/products/1855520, 2 Defense and Commercial System Development: A Comparison, Appendix A: Recommendations of Previous Relevant Reports of the Committee on National Statistics, Appendix C: Recent DoD Efforts to Enhance System Reliability in Development, Appendix D: Critique of MIL-HDBK-217--Anto Peter, Diganta Das, and Michael Pecht, Appendix E: Biographical Sketches of Panel Members and Staff. Once the risks are ranked, those that fall below some threshold in the rankings can be omitted. Failure Modes, Mechanisms, and Effects Analysis. Such an analysis compares two designs: a recent vintage product with proven reliability and a new design with unknown reliability. The probability that a PC in a store is up and running for eight hours without crashing is 99%; this is referred as reliability. A large number of hardware mistakes are driven by arbitrary size constraints. Once these detailed reliabilities are generated, the fault tree diagram provides a method for assessing the probabilities that higher aggregates fail, which in turn can be used to assess failure probabilities for the full system. Share a link to this book page on your preferred social network or via email. Instead, concurrent engineering hinges on contributions from all essential project team members. The topics include: 1) Reliability Engineering Major Areas and interfaces; 2) Design Reliability; 3) Process Reliability; and 4) Reliability Applications. (2006) for an example. Each failure model is made up of a stress analysis model and a damage assessment model. In addition, at this point in the development process, there would also be substantial benefits of an assessment of the reliability of high-cost and safety critical subsystems for both the evaluation of the current system reliability and the reliability of future systems with similar subsystems. There are probably a variety of reasons for this omission, including the additional cost and time of development needed. With a good feature, one can determine whether the system is deviating from its nominal condition: for examples, see Kumar et al. Reliability engineering is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. The opposite is true for elements in parallel. They demonstrate that all manufacturing and assembly processes are capable of producing the system within the statistical process window required by the design. 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. A specific approach to design for reliability was described during the panel’s workshop by Guangbin Yang of Ford Motor Company. If no overstress failures are precipitated, then the lowest occurrence rating, “extremely unlikely,” is assigned. The simplest formulation for an overstress model is the comparison of an induced stress with the strength of the material that must sustain that stress. Health monitoring is the method of measuring and recording a product’s health in its life-cycle environment. Jump up to the previous page or down to the next one. An overly optimistic prediction, estimating too few failures, can result in selection of the wrong design, budgeting for too few spare parts, expensive rework, and poor field performance. Collectively, they affect both the utility and the life-cycle costs of a product or system. If no failure models are available, then the evaluation is based on past experience, manufacturer data, or handbooks. Similarity analysis estimates environmental stresses when sufficient field histories for similar systems are available. It appears to the panel that U.S. Department of Defense (DoD) contractors do not fully exploit these techniques. If no alternative is available, then the team may choose to pursue techniques that mitigate the possible risks associated with using an unacceptable part. With the goal of simultaneous design optimization, the typical engineering silos are counterproductive. Reliability predictions are an important part of product design. Virtual qualification can be used to optimize the product design in such a way that the minimum time to failure of any part of the product is greater than its desired life. Failure tracking activities are used to collect test- and field-failed components and related failure information. RAM Analysis. The output is a ranking of different failure mechanisms, based on the time to failure. Tan Guan Hong Senior Director, Smart Nation Systems and Solutions Government Technology Agency of Singapore High System Reliability through Design Innovation 18th IEEE High Assurance Systems Engineering 2. For managed producibility risks, the resources required are used to estimate the impact. 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 degree of and rate of system degradation, and thus reliability, depend upon the nature, magnitude, and duration of exposure to such stresses. Assessment of reliability as a result of design choices is often accomplished through the use of probabilistic design for reliability, which compares a component’s strength against the stresses it will face in various environments. One estimate of reliability is test-retest reliability. June 10, 2020, By In both of these methods, a generic average failure rate (assuming average operating conditions) is assumed. Failure models use appropriate stress and damage analysis methods to evaluate susceptibility of failure. The ratings of the part manufacturer or the user’s procurement ratings are generally used to determine these limiting values. ... “In traditional ball valves, there are certain areas of cavities that tend not to get a lot of flow through them and, therefore, collect fine and abrasive grit, which creates problems. But how do researchers know that the scores actually represent the characteristic, especially when it is a construct like intelligence, self-esteem, depression, or working memory capacity? Product differentiation: As electronic technologies reach maturity, there are fewer opportunities to set products apart from the competition through traditional metrics — like price and performance. Broad failure classifications include system damage or failure, loss in operating performance, loss in economic performance, and reduction in safety. Do you enjoy reading reports from the Academies online for free? This chapter describes techniques to improve system design to enhance system reliability. o …at the customer (with their use environment) o …over the desired lifetime Because variability in material properties and manufacturing processes will affect a system’s reliability, characteristics of the process must be identified, measured, and monitored. Failure susceptibility is evaluated by assessing the time to failure or likelihood of a failure for a given geometry, material construction, or environmental and operational condition. 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. Split-half reliability. Assessment of the reliability potential of a system design is the determination of the reliability of a system consistent with good practice and conditional on a use profile. They are risks for which the consequences of occurrence are loss of equipment, mission, or life. The recommendations of Reliability Growth will improve the reliability of defense systems and protect the health of the valuable personnel who operate them. There has been some research on similarity analyses, describing either. Details on performing similarity analyses can be found in the Guide for Selecting and Using Reliability Predictions of the IEEE Standards Association (IEEE 1413.1). These data are often collected using sensors. We emphasize throughout this report the need for assessment of full-system reliability. In the case of wear-out failures, damage is accumulated over a period until the item is no longer able to withstand the applied load. You're looking at OpenBook, NAP.edu's online reading room since 1999. Failure modes, mechanisms, and effects analysis is used as input in the determination of the relationships between system requirements and the physical characteristics of the product (and their variation in the production process), the interactions of system materials with loads, and their influences on the system’s susceptibility to failure with respect to the use conditions. Cost control: 70% of a project’s budget is allocated to design. As the “new” product is produced and used in the field, these data are used to update the prediction for future production of the same product (for details, see Pecht, 2009). While an invaluable and essential part of board design, vias introduce weaknesses and affect solderability. It is typical for very complex systems to initiate such diagrams at a relatively high level, providing more detail for subsystems and components as needed. As a result, those that need to be included in DfR include: Here are some DfR best practices that can apply to the development of nearly any project. This change was noted in the 2011 Annual Report to Congress of the Director of Operational Test and Evaluation (U.S. Department of Defense, 2011b, p. v): [I]ndustry continues to follow the 785B methodology, which unfortunately takes a more reactive than proactive approach to achieving reliability goals. These practices can substantially increase reliability through better system design (e.g., built-in redundancy) and through the selection of better parts and materials. Or register for the webinar: Introduction to Reliability Physics Analysis. written from the perspective that good design is a pre-requisite to the development of cost-effective products, this wor Chapter 5 discussed designing reliable systems; this chapter describes improving system reliability through testing. High System Reliability through Design Innovation 1. In a system with standby redundancy, ideally the parts will last longer than the parts in a system with active redundancy. or components: for examples of diagnostics and prognostics, see Vasan et al. The shortcoming of this approach is that it uses only the field data, without understanding the root cause of failure (for details, see Pecht and Kang, 1988; Wong, 1990; Pecht et al., 1992). While traditional reliability assessment techniques heavily penalize systems making use of new materials, structures, and technologies because of a lack of sufficient field failure data, the physics-of-failure approach is based on generic failure models that are as effective for new materials and structures as they are for existing designs. Furthermore, maintainability and reliability are recognized as being highly significant factors in the economic success of engineering systems and products. Related terms: Reliability Analysis; Power Device 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. The two methods discussed above are “bottom-up” predictions. This process merges the design-for-reliability approach with material knowledge. In a series system, the probability of failure for each element is lower than that for the overall system. The different types of reliability tests that can be conducted include tests for design marginality, determination of destruct limits, design verification testing before mass production, on-going reliability testing, and accelerated testing (for examples, see Keimasi et al., 2006; Mathew et al., 2007; Osterman 2011; Alam et al., 2012; and Menon et al., 2013). Develop a maintenance plan for the asset using FMEA/RCM to mitigate failure modes which cannot be eliminated through design. o. Life-cycle profiles include environmental conditions such as temperature, humidity, pressure, vibration or shock, chemical environments, radiation, contaminants, and loads due to operating conditions, such as current, voltage, and power. System designs have traditionally achieved reliability through redundancy, even though this inevitably increases component count, logic size, system power and cost. They are used for a number of different purposes: (1) contractual agreements, (2) feasibility evaluations, (3) comparisons of alternative designs, (4) identification of potential reliability problems, (5) maintenance and logistics support planning, and (6) cost analyses. Reliability is the extent to which an instrument would give the same results if the measurement were to be taken again under the same conditions: its consistency. Abstract: Avoiding failure modes is the ultimate goal of reliability engineering. Failure analysis is used to identify the locations at which failures occur and the fundamental mechanisms by which they occurred. A reliability block diagram can be used to optimize the allocation of reliability to system components by considering the possible improvement of reliability and the associated costs due to various design modifications. 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. ... Certain players have a knack for coming through in key situations no matter how late in the season or how worn down they are. When you are implementing reliability considerations in the concept feasibility stage, you are making all your decisions down the line with reliability in mind. 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