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Reliability Engineering

Massimo Lazzaroni, Loredana Cristaldi, Lorenzo Peretto, Paola Rinaldi, and Marcantonio Catelani

Reliability EngineeringBasic Concepts and Applications in ICT

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AuthorsProf. Dr. PhD. Massimo Lazzaroni Universit degli Studi di Milano Dipartimento di Tecnologie dellInformazione Via Bramante 65 I-26013 Crema Italy Email: massimo.lazzaroni@unimi.it Prof. Dr. PhD. Loredana Cristaldi Dipartimento di Elettrotecnica Politecnico di Milano Piazza Leonardo da Vinci, 32 I - 20133 Milano Italy Prof. Dr. PhD. Lorenzo Peretto Alma Mater Studiorum - Universit di Bologna Dipartimento di Ingegneria Elettrica Viale Risorgimento, 2 I - 40136 Bologna Italy Dr. PhD. Paola Rinaldi Alma Mater Studiorum - Universit di Bologna Dipartimento di Elettronica, Informatica e Sistemistica Viale Risorgimento, 2 I - 40136 Bologna Italy Prof. Dr. Marcantonio Catelani Dipartimento di Elettronica e Telecomunicazioni Universit degli Studi di Firenze via S. Marta, 3 I - 50139 Firenze Italy

ISBN 978-3-642-20982-6 DOI 10.1007/978-3-642-20983-3

e-ISBN 978-3-642-20983-3

Library of Congress Control Number: 2011928069 c 2011 Springer-Verlag Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microlm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specic statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typeset & Cover Design: Scientic Publishing Services Pvt. Ltd., Chennai, India. Printed on acid-free paper 987654321 springer.com

Preface

Nowadays, in many fields of application, it is fundamental to define and fulfil Dependability performances. For a complex equipment in avionics, automotive, transportation only considering some examples we have to take into account the functional requirements of the system and, in addition, its requirements in terms of Reliability, Maintainability, Availability and Safety. In other words, it is fundamental to evaluate as the functional requirements of the equipment under consideration are maintained in the time, in specified conditions of use. For these reasons it is fundamental, as starting point, to focus the attention on the correct use of the terminology in this field. To this aim, in Chapter 1, an overview of the most important terms correlated with Dependability is proposed. Referring to the International Standard, we can assume Dependability as the collective term used to describe the availability performance and its influencing factors: reliability, maintainability and maintenance support performance. On the basis of this concept, it is evident that dependability gives a general description of the item - a component, an equipment, a system, and so on- in non-quantitative terms. To express its performance in quantitative terms and thus to describe, measure, improve, guarantee and certify such an item, it is necessary to establish the characteristics of reliability, availability, maintainability, maintenance support performance and safety. Assuming the reliability of an item as the probability that such an item will adequately perform the specified function for a well-defined time interval in specified environmental conditions, it is well clear the importance of the probability and statistics sciences in both reliability definition and evaluation. So, Chapter 2, is devoted to introduce some important probability and statistics basic concepts that are necessary for the reliability evaluation. In particular, the statistical point of view is developed and discussed as a first approach to dependability feature of a system under consideration. A brief overview on probability and statistics is given in the first part and the reliability function is then derived. Furthermore, both the concept and model of the failure rate are also proposed. In Chapter 3 the techniques used for describe the performance of devices in a system are considered. To this aim the system is assumed as a combination of elementary devices subsystems and elements - that follow a well-defined functional structure. The reliability evaluation of series, parallel and mixed structures will be shown and discussed in details. To this aim, the concept of Reliability Block Diagram is defined as a mandatory tool. The theory is developed using many practical examples. Parallel configuration is further developed in order to discuss the different type of redundancy for reliability growth: active, warm and stand-by.

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Preface

At the end of this chapter, two different types of redundancy approaches are compared: system redundancy and component redundancy. The results so obtained are fundamental during the design phase of a system when reliability aspects have to be taken into account. Considering that the component reliability is often affected by different external and internal influencing factors stress, environment, quality, technology, and so on - the operating profile of a component must be taken into account for good reliability predictions. Chapter 4 focuses the attention on such aspects. It is interesting to remember that, in many situations, the operating profile changes according to the type of operation of the component. So, we can assume continuous operation or non-continuous operation, such as also sporadic operation. Moreover, storage conditions may have deep impact on reliability of the component when operating. Obviously, environmental factors need to be taken into account as well. The environment contributes to both aging and failures during the life of devices or systems. To this aim, both duration and intensity of environmental stresses must be included in the system operational model. In this chapter, after a brief introduction, the stress factors will be analyzed and some aspects concerning the component degradation are presented. Some concepts regarding the analysis of failure modes and laboratory test are also presented. The evaluation of the failure rate for an item represents, often, a very difficult task. In order to implement this evaluation for an electronic or an electromechanical equipment, it is possible to use ad hoc HandBooks (HDBKs) reliability prediction handbooks. In the first part of Chapter 5, a brief historical overview of such HandBooks is given, introducing first generation as well as second and third generation HDBKs. As practical application of reliability prediction in electronic field the USA military HDBK (MIL) and Farada HDBK is presented. In Chapter 6 the concept of Availability is explained and discussed. Availability is defined by the international standards as the aptitude of an element to perform its required function in given conditions up to a given point in time or during a given time interval, assuming that any eventual external measured are assured. So, the Availability is a concept that refers to reparable systems, that is systems where the operating life cycles can be often described by a sequence of up (operating) and down (not operating) states. In this case, the important variables to be determined are both the time to failure and the time to repair and or restore. For a more detailed and exhaustive description of the dependability performance a set of well known techniques are present in literature. Such techniques, normally classified into quantitative and qualitative, are methods of analysis to evaluate the dependability parameters and the failure modes in which a realistically complex system is, or, could be subjected. In Chapter 7 a simplified version of the Markov model is proposed. Other techniques able to allow the knowledge of the mechanism of the system failures and to identify all the potential weakness of the system under evaluation are presented in Chapter 8. In particular, we refer to the Failure Modes and Effects Analysis (FMEA) and the Failure Modes, Effects

Preface

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and Criticality Analysis (FMECA). These methods are able to highlight the failure modes leading to a negative final effect, also in terms of criticality on the system, operator and/or environment. A third method here presented is the Fault Tree Analysis (FTA), a deductive method for the analysis of a top event represented by a failure condition of the system as a function of failures of subsystems and components. Massimo Lazzaroni Loredana Cristaldi Lorenzo Peretto Paola Rinaldi Marcantonio Catelani

Contents

1 The Concept of Measurable Quality ...............................................................1 1.1 Introduction ................................................................................................1 1.2 Is Conformity Synonymous with Reliability? Some Definitions................2 1.3 Failures, Faults and Their Classification ....................................................4 References ...............................................................................................................6 2 The Concept of Statistical Reliability..........................................................7 2.1 Introduction ................................................................................................7 2.2 Definition of Probability.............................................................................8 2.2.1 Axioms of Probability ...