Therefore, the DfR process ensures that pursuit of reliability is an enterprise-wide activity. Practical Reliability Engineering, Fifth Edition. Patrick D. T. O'Connor. View Table of Contents for Practical Reliability Engineering Patrick D. T. O' Connor · Andre Kleyner This fifth edition retains the unique balanced mixture of reliability theory and . PDF · Request permissions · xml. Practical reliability engineering / Patrick D. T. O'Connor, Andre Kleyner. .. A solutions manual is available to teachers, free of charge, by writing to John Wiley .
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Practical. Reliability. Engineering. Third Edition Revised. PATRICK D. T. O' CONNOR. British Aerospace plc, UK with 1 Introduction to Reliability Engineering l . Practical Aspects. .. The Reliability Manual. Click link bellow and free register to download ebook: Guides Practical Reliability Engineering By Patrick O'Connor, Andre Kleyner, from easy to challenging. Practical Reliability Engineering, Fifth Edition | 𝗥𝗲𝗾𝘂𝗲𝘀𝘁 𝗣𝗗𝗙 on The two samples Kolmogorov Smirnof test (O'Connor and Kleyner ) ran on both.
About this book With emphasis on practical aspects of engineering, this bestseller has gained worldwide recognition through progressive editions as the essential reliability textbook. This fifth edition retains the unique balanced mixture of reliability theory and applications, thoroughly updated with the latest industry best practices. Notable additions include: New chapters on applications of Monte Carlo simulation methods and reliability demonstration methods.
Software applications of statistical methods, including probability plotting and a wider use of common software tools. More detailed descriptions of reliability prediction methods. Comprehensive treatment of accelerated test data analysis and warranty data analysis.
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Practical Reliability Engineering, 5th Edition
Returning user. Request Username Can't sign in? Forgot your username? Like other conceptual analysis methods, there is no single standard approach, and users should be encouraged to develop formats and methods appropriate to their products and problems.
QFD software is available. The method is described in more detail in Akao and many other printed and web sources.
Therefore the following questions should be answered: The higher is the risk the more attention should be paid to reliability and therefore more DfR activities should be included in the programme. Therefore, a more detailed design picture begins to emerge. Also load protection and non-material failure modes should be considered as part of FMECA process or as separate activities. CAE provides enormous improvements in engineering productivity.
Properly used, it can lead to the creation of more reliable designs.
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The effects of parameter changes or failure modes can be quickly evaluated, and dynamic as well as static operating conditions can be tested. Specialist CAE software is also available for design and analysis of systems and products incorporating other technologies, such as hydraulics, magnetics and microwave electronics. Multi-technology capability is now also available, so that mixed technology designs can be modelled and analysed.
CAE provides the capability for rapid assessment of different design options, and for analysing the effects of tolerances, variation and failure modes. Therefore, if used in a systematic, disciplined way, with adequate documentation of the options studied and assessments performed, designs can be optimized for costs, producibility and reliability.
However, there are important limitations inherent in most CAE tools. The software models can never be totally accurate representations of all aspects of the design and of its operating environment. For example, electronic circuit simulation programs generally ignore the effects of electromagnetic interference between components, and drafting systems will ignore distortion due to stress or temperature.
Therefore it is essential that engineers using CAE are aware of the limitations, and how these could affect their designs. The principle of FMECA is to consider each mode of failure of every component of a system and to ascertain the effects on system operation of each failure mode in turn.
Failure effects may be considered at more than one level, for example, at subsystem and at overall system level.
In the hardware approach actual hardware failure modes are considered e. In this approach function failures are considered e. Note that a functional failure mode can become a hardware failure effect in a hardware-approach FMECA.
Design The RPN procedure includes the following steps: Rating scales usually range from 1 to 10, with the higher number representing the higher severity or risk. For example, 10 points for severity indicates the worst possible consequence of the failure.
RPN is calculated as the product of the three ratings: This method includes consideration of failure rate or probability, failure mode ratio and a quantitative assessment of criticality, in order to provide a quantitative criticality rating for the component or function. The item criticality number is the sum of the failure mode criticality numbers for the item.
FMECA is widely used in many industries, particularly in those for which failures can have serious consequences, such as military, aerospace, automotive, medical equipment, and so on.
This team can be augmented by specialists from other functional areas, such as downloading, tech support, testing, facilities, marketing, and so on. For a criticality analysis, the reliability prediction information must also be available or it might be generated simultaneously.
A system functional block diagram and reliability block diagram Chapter 6 should be prepared, if not already available, as these form the basis for preparing the FMECA and for understanding the completed analysis. Design If the system operates in more than one phase in which different functional relationships or item operating modes exist, these must be considered in the analysis. The effects of redundancy must also be considered by evaluating the effects of failure modes assuming that the redundant subsystem is or is not available.
An FMECA can be performed from different viewpoints, such as safety, mission success, availability, repair cost, failure mode or effect detectability, and so on. It is necessary to decide, and to state, the viewpoint or viewpoints being considered in the analysis.
For example, a safety-related FMECA might give a low criticality number to an item whose reliability seriously affects availability, but which is not safety critical. The FMECA is then prepared, using the appropriate worksheet, and working to the item or subassembly level considered appropriate, bearing in mind the design data available and the objectives of the analysis.
For a new design, particularly when the effects of failures are serious high warranty costs, reliability reputation, safety, etc. However, it might be appropriate to consider functional failure modes of subassemblies when these are based upon existing designs, for example, modular power supplies in electronic systems, particularly if the design details are not known.
Design options should be analysed separately, so that reliability implications can be considered in deciding on which option to choose. Test results should be used to update the analysis. FMECA is not a trivial task, and can involve many hours or weeks of work.
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Even with aids such as these, FMECA can be an inappropriate method for some designs, such as digital electronic systems in which low-level failures e. These include: The FMECA provides a convenient listing of the failure modes which produce particular failure effects or symptoms, and their relative likelihoods of occurrence.
The effects and likelihood of failures can be consid- ered in relation to the need for scheduled inspection, servicing or replacement. See Chapter The failure detectability viewpoint is an important one in FMECA of systems which include these features. It is important to coordinate these activities, so that the most effective use can be made of the FMECAs in all of them, and to ensure that FMECAs are available at the right time and to the right people.
Using software instead of FMECA worksheets allows FMECAs to be produced more quickly and accurately, and greatly increases the ease of editing and updating to take account of design changes, design options, different viewpoints, and different input assumptions.
Like any other computer-aided design technique, computerized FMECA frees engineers to concentrate on engineering, rather than on tedious compilation, so that for the same total effort designs can be more thoroughly investigated, or less effort can be expended for the same depth of analysis. Failure effects can be ranked in criticality order, at different system levels, in different phases of system operation and from differ- ent viewpoints. Report preparation can be partly automated and sensitivity analyses quickly performed.
This method has the advantage that the format and type of analysis can be designed to suit the particular design and methods of analysis. Design 7. However, it is very important to appreciate the large amount of uncertainty inherent in reliability prediction, particularly at the level of individual failure events see Chapter 6.
Alternatively, and preferably unless credible quantitative data are available, a value scale such as 0—1 should be used, with prearranged assignment e. Generally, the more critical the failure mode the more pessimistic should be the worst-case reliability assumptions. Load-Strength analysis may begin at the early stages of the DESIGN phase and continue through most of the DfR process as more data about system characteristics become available.
The LSA should include the following: Table 7. The example shows approaches that can be used for different aspects of the analysis.
Event probabilities can be expressed as full distributions, or as the likelihood of a particular limiting case being exceeded.
The former is more appropriate when the load s can cause degradation, or if a more detailed reliability assessment is required. Both examples show typical, though rather simple, cases where the effects of combined loads might have been overlooked but for the analysis. The mechanical example is less easy to analyse and testing is likely to be the best way of providing assurance, if the assembly is critical enough to warrant it. Where the load—strength analysis indicates possible problems, further analysis should be undertaken, for example, use of probabilistic methods as described in Chapters 4 and 5, and CAE methods.
It is used in the development of systems such as petrochemical plants, railway systems, and so on and usually is part of the mandatory safety approval process. The usual guidewords are: HAZOP is also commonly used in risk assessments for industrial and environmental health and safety applications. The reliability and quality assurance QA staff must ensure that this faith is well-founded. New parts, materials and processes must therefore be assessed or tested before being applied, so that adequate training for production people can be planned, quality control safeguards set up and alternative sources located.
New parts, materials and processes must be formally approved for production and added to the approved lists.
Materials and processes must be assessed in relation to reliability. The main reliability considerations include: Whenever loading is cyclical, including frequent impact loads, fatigue must be considered. The environmental conditions of storage and operation must be considered in relation to factors such as corrosion and extreme temperature effects. The wear properties of materials must be considered for all moving parts in contact. There is such a wide variation of material properties, even amongst categories such as steels, aluminium alloys, plastics and rubbers, that it is not practicable to generalize about how these should be considered in relation to reliability.
Material selection will be based upon several factors; the design review procedure should ensure that the reliability implications receive the attention appropriate to the application. Chapter 8 covers mechanical design for reliability in more detail. However, there is a large class of failure modes which are not related to this type of material failure, but which can have consequences which are just as serious. Examples of these are: Main power fail System failure 1 Provide standby System design 2.
Connector power? Hydraulic supply Main AND 1. All of these modes can lead to perceived failures. Failure reporting systems always include a proportion of such failures. However, there is usually more scope for subjective interpretation and for variability due to factors such as skill levels, personal attitudes and maintenance procedures, especially for complex equipment.
Non-material failures can be harder to assess at the design stage, and often do not show up during a test programme. Design reliability assessments should address these types of failure, even though it may be impracticable to attempt to predict the frequency of occurrence in some cases, particularly for personnel- induced failures.
Its purpose is to highlight these items and summarize the action being taken to reduce the risks. The initial list will be based upon the design analyses, but updates will take account of test results, design changes and service data as the project develops.
Therefore, it should not usually include more than ten items and these should be ranked in order of criticality, so that management attention can be focused upon the few most important problems.
In many cases the maximum load can be pre-determined, and no special protection is necessary. However, in many other loading situations extreme external loads can occur and can be protected against. Standard products are available to provide protection against, for example, overpressure in hydraulic or pneumatic systems, impact loads or electrical overload.
When overload protection is provided, the reliability analysis is performed on the basis of the maximum load which can be anticipated, bearing in mind the tolerances of the protection system. In appropriate cases, loads which can occur when the protection system fails must also be considered. The probability of such loads occurring must be determined for a full reliability analysis to be performed. Where credible data are not available, the worst design load case must be estimated.
A common cause of failure is the use of safety factors related to average load conditions, without adequate consideration having been given to the extreme conditions which can occur during use of the product.
However, other weakening mechanisms are often more complex. Combined stresses may accelerate damage or reduce the fatigue limit. If complete protection is not possible, the designer must specify maintenance procedures for inspection, lubrication or scheduled replacement. Reliability analysis of designs with complex weakening processes is often impracticable. Tests should then be designed to provide the required data by generating failures under known loading conditions.
Chapter 8 covers these aspects in more detail.
Practical Reliability Engineering
To be effective, they must be performed by the people who understand the design. This does not necessarily mean the designers, for two reasons. First, the analyses are an audit of their work and therefore an independent assessment is generally more likely to highlight aspects requiring further work than would be the case if the designers were reviewing their own work.
Second, the analyses are not original work in the same sense as is the design. The designers are paid to be creative and time spent on reassessing this effort is non-productive in this sense. On the other hand, the creative talent may not be the best at patiently performing the rather tedious review methods. In this way, designers and the reviewers work as a team, and problem areas are highlighted as early as possible. The organization of reliability engineering staff to provide this service is covered in Chapter The reviewer should ideally be a reliability engineer who can be respected by the designer as a competent member of a team whose joint objective is the excellence of the design.
Since the reliability engineer is unlikely to spend as much time on one design as the designer, one reliability engineer can usually cover the work of several designers.
The ratio obviously depends upon the reliability effort considered necessary on the project and on the design disciplines involved. By working as a team, the design and reliability staff can resolve many problems before the formal analysis reports are produced, and agreement can be reached on recommendations, such as the tests to be performed.
Since the reliability engineer should plan and supervise the tests, the link is maintained. Design review techniques then lose credibility, as do reliability staff. The main victim is the design itself, since the protagonists usually prosper within their separate organizations. To be of continuing value, the design analyses must be updated continually as design and development proceed. Each formal review must be based upon analyses of the design as it stands and supported by test data, parts assessments, and so on.
The analyses should be scheduled as part of the design programme, with design reviews scheduled at suitable intervals. The reviews should be planned well in advance, and the designers must be fully aware of the procedure.
All people attending must also be briefed in advance, so they do not waste review time by trying to understand basic features. To this end, all attendees must be provided with a copy of all formal analysis reports reliability prediction, load—strength analysis, PMP review, maintainability analysis, critical items list, FMECA, FTA and a description of the item, with appropriate design data such as drawings.
The designer should give a short presentation of the design and clear up any general queries. Each analysis report should then form a separate agenda item, with the queries and recommendations as the subjects for discussion and decision. If experience has generated a checklist appropriate to the design, this could also be run through, but see the comments that follow.
With this procedure, nearly all aspects requiring further study or decision will have been discussed before, during the continuous, informal process of the team approach to preparing the analyses. The formal review then becomes a decision-making forum, and it is not bogged down with discussion of trivial points.
This contrasts markedly with the type of design review meeting which is based largely upon the use of checklists, with little preparatory work. Such reviews become a stolid march through the checklist, many of whose questions might be irrelevant to the design.
They can become a substitute for thinking. Three golden rules for the use of checklists should be: The design review team should consist of staff from sales, production, QA and specialists in key design areas. The people on the spot are the designers and the reliability engineering team member who may belong to the QA department.
The chairman should be the project manager or another person who can make decisions affecting the design, for example, the chief designer.
Sometimes design reviews are chaired by the procuring agency, or it may require the option of attending. A design review which is advisory and has no authority is unlikely to be effective, and therefore all those attending must be concerned with the project apart from specialists called in as advisers.
Three formal reviews are typical, based upon initial designs, completion of development testing and production standard drawings. Each review authorizes transition to the next phase, with such provisos deemed to be necessary, for example, design changes, additional tests.
This tool was originally developed by Toyota engineers on the premise that reliability problems occur when changes are made to existing designs that have already been proven successful. DRBFM encourages design teams to discuss the potential design problems or weaknesses from a cross functional multi-perspective approach, and to develop corrective actions. In these circumstances people are fallible, and can cause component or system failure in many ways. Human reliability must be considered in any design in which human fallibility might affect reliability or safety.
Also, where human operation is involved, product design should be made in full consideration of physiological and psychological factors in order to minimize the probability of human error in system operation. Attempts have been made to quantify various human error probabilities, but such data should be treated with caution, as human performance is too variable to be credibly forecast from past records.
Human error probability can be minimized by training, supervision and motivation, so these must be considered in the analysis. More on human factors in engineering can be found in Wickens et al. When a mock up, proof of concept, or engineering development unit is built it will make it easier to verify the results of the analysis and improve on the design.
FEA can be utilized to calculate the stresses caused by thermal expansion, vibration, accidental drop, and other environments. It can also be used to estimate fatigue life for products subjected to thermal cycling or vibration. More on fatigue is covered in Chapter 8. As shown in Figure 7. The new product development process needs to be attuned to the engineering analysis of returned parts to prevent old problems from recurring in new products.
Depending on the complexity of the returned parts, the engineering analysis tasks can be accom- plished by failure analysis or structured problem solving, or by using a combination of existing continuous improvement tools. Engineering analysis, for example, can determine that a failure occurred due to an assembly problem, end-user abuse, software malfunction, electronic or mechanical component failure, corrosion, overheating or vibration.Second, the analyses are not original work in the same sense as is the design.
Implementing DfR practices and tools is sometimes considered tedious and expensive. Examples of these are: Chapter 8 covers mechanical design for reliability in more detail. CAE provides enormous improvements in engineering productivity.
However, we often cannot assume that, because a measured value appears to be, say, normally distributed, that this distribution necessarily is a good model for the extremes. Technology Aspects.