and discuss the terminology and the main models used in system reliability studies.2 To present the main analytical methods used in reliability engineering and management.
3 To present and discuss basic theory of maintenance and preventive maintenance modeling and illustrate how these can be applied.
4 To present the main theory and a selection of methods for reliability data analysis, which is also called survival analysis.
5 To give an introduction to Bayesian probability and Bayesian data analysis.
The book does not specifically deal with how to engineer and manage a reliable system. The main topics of the book are connected to how to define and quantify reliability metrics and to predict the reliability of a system. Our aim is that the book will be a valuable source as follows:
1 A textbook for system reliability courses at university level.
2 A handbook for reliability engineers in industry and consulting companies.
3 A reference book for scientists and engineers in related disciplines.
The following delimitations apply:
The study object is built of hardware parts based on mechanical, electrical, or electronic technology, and may or may not have embedded software and communication to/from the outside. In most cases, the study object has a human/operator interface. Operators and third‐party personnel are outside the scope of the book. This means that human reliability, as such, is not covered. The prime focus of the book is on hardware items.
The reliability of purely software items is outside the scope of this book.
Structural reliability issues are not covered in this book.
The focus of the book is on components and rather simple systems. The theory and methods presented may also be useful for analyzing complex systems, but we have to realize that they may not be sufficient.
Failures caused by deliberate hostile actions is covered rather rudimentarily.
In the main part of the book, we assume that each item can have only two states, functioning or failed. Multistate reliability is not covered properly.
A general introduction to maintenance is not provided. The presentation is delimited to aspects of maintenance that are directly relevant for system reliability.
The book provides a thorough introduction to system reliability analysis, but does not cover reliability engineering and reliability management in a sufficient way.
1.8 Trends and Challenges
System reliability has been around since the 1940s. The relevance of reliability has increased steadily and we clearly see trends and challenges that will increase the relevance in the years to come. In this section, we briefly mention some of these trends and challenges. An overall trend is that customers expect new items to be BETTER, FASTER, and CHEAPER than the items they replace. More specific challenges include
1 Items get more and more complicated with a lot of embedded software. Hardware functions are replaced with software‐based functions. Because the software‐based functions are relatively cheap, many items are loaded with “nice‐to‐have” function that may also fail.
2 Most producers meet fierce international competition. To survive, this requires reduced development costs, shorter time to market, and less time spent on analyses and testing. New items have to be sufficiently reliable in the first concept version.
3 Customers require more and more of the items they purchase, related to functions, quality, and reliability. The requirements are often changing rapidly. Factors influencing item requirements are shown in Figure 1.9.
4 There is an increasing focus on safety and environmental friendliness and an increasing risk of item call‐back if the items should have safety‐related defects.
5 New items are increasingly made up of elements from a variety of subcontractors from many different countries, making it difficult for the main producer to verify the item reliability.
6 For some items, high‐speed operation reduces the tolerance of deviations and increases the consequences of failures, should they happen.
7 There is an increasing focus on warranty. Companies have disappeared because of excessive warranty costs.
8 An increasing number of items are now connected to a cybernetwork and are vulnerable to cyberattacks. Current challenges are related to the rapid developments of smart homes, smart cities, smart transport systems, the Internet of Things (IoT), cyber‐physical systems, systems of systems, and Industry 4.0. Within few years, we expect to see many more new initiatives of similar nature. This will make reliability analyses even more challenging.
Figure 1.9 Factors that influence item requirements.
1.9 Standards and Guidelines
A range of standards and guidelines stating requirements to reliability and safety have been issued. Any reliability engineer needs to be familiar with the standards and guidelines that are applicable within her subject areas.
1.10 History of System Reliability
This section highlights some achievements in the history of system reliability starting from the 1930s. We realize that our presentation is biased because we put too much focus on activities in Europe and in the United States. In addition, we have included mainly events and books that have influenced our own learning and understanding of system reliability. The development of reliability theory has been strongly influenced by a series of accidents and catastrophic failures. Some of these are mentioned, but you may find that we have missed many important accidents.
Some of the achievements mentioned in this section may be difficult to comprehend fully at this stage, and it may therefore be wise to postpone the reading of this section until you have delved deeper into the subject.
1930s
At the beginning of the 1930s, Walter Shewhart, Harold F. Dodge, and Harry G. Romig laid down the theoretical basis for utilizing statistical methods in quality control of industrial products, but such methods were not used to any great extent until the beginning of World War II. Products that were composed of a large number of parts often failed, despite the fact that they were made of individual high‐quality components.
An important achievement was made in the 1930s by the Swedish professor Waloddi Weibull (1887–1979) during his studies of the strength of materials. In Weibull (1939), he laid the basis for one of the most important probability distributions in reliability theory, the Weibull distribution (Weibull 1951).
1940s
It
