(i.e. not accessible for students and general readers of the book).
The two sites contain a number of PDF files. These files have version numbers and will be updated when required.
In addition to these two sites hosted by Wiley, we will maintain a GitHub site for the book.
Open Site
The open site contains:
1 A supplement to the book with comments to chapters, suggestions for further reading, and general information about the subject area.
2 Slides to the various chapters (made with LaTeX/Beamer).
3 Control questions to each chapter.
4 Errata (list of misprints and minor errors – a more frequently updated errata list may be found on the book's GitHub site).
Instructor Site
The instructor site contains:
1 Solutions to end of chapter problems.
2 Suggested lecturing plans (what to cover, which problems to use, etc.).
3 Additional problems with solutions.
4 FAQ list.
GitHub Site
The GitHub site is open to all users – and should have a clear link from the Wiley sites. The GitHub site will contain:
1 A brief description of the book.
2 Detailed R-scripts related to the book.
3 Detailed Python-scripts related to the book.
4 Errata list (see above under Open site).
5 FAQ related to the book – with our answers/comments.
The URL of the GitHub site is https://github.com/RausandBarros/ReliabilityBookScripts
Contact Person
The contact person for the book companion site and the GitHub site is Anne Barros ([email protected])
1 Introduction
1.1 What is Reliability?
Nowadays, nearly all of us depend on a wide range of technical products and services in our everyday life. We expect our electrical appliances, cars, computers, mobile phones, and so on, to function when we need them, and to be reliable for a rather long time. We expect services, such as electricity, computer networks, and transport, to be supplied without disruptions or delays. When a product, machinery, or service fails, the consequences may sometimes be catastrophic. More often, product flaws and service outages lead to customer dissatisfaction and expenses for the supplier through warranty costs and product recalls. For many suppliers, reliability has become a matter of survival.
There is no generally accepted definition of the reliability of a technical product. The definition and interpretation of the term vary from industry to industry and from user to user. For the purpose of this book, we choose a rather wide definition of the reliability of a technical item.
The ability of an item to perform as required in a stated operating context and for a stated period of time.
The term item is used to designate any technical system, subsystem, or component. The items studied in this book are built of hardware parts, and to an increasing degree, of software. When relevant, the user interface is part of the item, but operators and other humans are not part of the items studied here.
The reliability concept is illustrated in Figure 1.1. The required performance is determined by laws and regulations, standards, customer requirements and expectations, and supplier requirements, and is usually stated in a specification document, where delimitations of the operating context are stated. As long as the predicted performance at least fulfills the required performance, the item is reliable – when it is used in the same operating context and for the period of time stated in the required performance.
Figure 1.1 The reliability concept.
By operating context, we mean the environmental conditions the item is used in, the usage patterns, and the loads it is subjected to, and how the item is serviced and maintained.
Definition 1.1 is not new and is not created by us. Several authors and organizations have used this, or a very similar definition of reliability, at least since the 1980s. A more thorough discussion of reliability and related concepts is given in Section 1.3.
1.1.1 Service Reliability
A service is provided by a person, an organization, or a technical item to a person or a technical item. The entity providing the service is called a service provider, and the entity receiving the service is called a customer. Services can be provided on a (i) continuous basis (e.g. electric power, computer networks), (ii) according to a timetable (e.g. bus, rail, and air transport), or (iii) on demand (e.g. payment by debit cards).
Many services are provided by a single service provider to a high number of customers. A customer considers the service to be reliable when she receives the service (e.g. electric power) with sufficient quality without outages. We define service reliability as follows:
Definition 1.2 (Service reliability)
The ability of the service to meet its supply function with the required quality under stated conditions for a specified period of time.
Several quantitative service reliability metrics have been defined, but they vary between the different types of services.
1.1.2 Past and Future Reliability
In our daily language, the term “reliability” is used to describe both past and future behavior. We may, for example, say that (i) “my previous car was very reliable” and (ii) “I believe that my new car will be very reliable.” These two statements are quite different. The first statement is based on experience with the car over a certain period, whereas the second statement is a prediction of what will happen in the future. We distinguish them by using two different terms.
Reliability (single
