《可靠性工程理论与实践》第五版：提升产品质量与系统稳定性

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《可靠性工程：理论与实践》第五版是由Alessandro Birolini教授所著的一本专著，该书专注于提供系统、组件和设备的可靠性、可维护性、可用性和安全性的评估与设计方法。作者以其丰富的经验和深厚的专业背景，对这一领域进行了深入探讨，书中包含140幅图表、60个表格、120个实例以及50个问题，旨在帮助读者理解和应用可靠性工程的基本原理和实际操作。可靠性工程是现代工业制造和信息技术中的核心领域，它旨在确保产品在长时间内稳定运行，减少故障发生的可能性，从而节省成本并提高用户满意度。书中涵盖了可靠性工程的理论基础，包括故障模式和效应分析（FMEA）、可靠性增长模型、可靠性预测和寿命测试等核心概念。此外，还讨论了如何将可靠性融入到项目生命周期的各个环节，如早期设计阶段、生产过程控制以及后期的维护策略中，以实现并行工程和质量保证目标。通过阅读本书，读者可以学习到如何通过统计方法和技术工具来量化产品的可靠性，如何进行可靠性试验和数据分析，以及如何制定有效的故障预防和管理措施。对于从事制造业、航空航天、电子设备等行业的人来说，这是一本实用的参考书，能够提升他们产品的可靠性和竞争力。值得注意的是，本书的前两版曾以《技术系统的技术质量和可靠性》为名出版，表明作者对这一主题的持续关注和不断更新。版权信息显示，所有内容受到法律保护，未经许可不得复制或在其他媒体上使用，确保了知识的完整性和知识产权的尊重。《2007_Book_ReliabilityEngineering.pdf》是一本深度研究可靠性工程实践的权威指南，无论是作为专业人员的学习资料，还是作为企业内部培训教材，都能为读者提供丰富的知识和实践经验。通过阅读这本书，读者将能提升自己在保证产品质量、降低成本和提高系统稳定性方面的专业能力。

Basic Concepts, Quality and Reliability

Assurance of Complex Equipment and

Systems

The purpose of reliability erzgineerirzg is to develop methods and tools to evaluate

und demonstrate reliability, maintainability, availability, and safety of components,

equipment, and systems, as well as to support development and production

engineers

building in these characteristics.

order to be cost and time effective,

reliability engineering must be integrated in project activities, and support quality

assurance and concurrent engineering efforts. This chapter introduces basic

con-

cepts, shows their relationships, and discusses the tasks necessary to assure quality

and reliability of complex equipment and systems with high quality und reliability

requirements. A comprehensive list of definitions is given in Appendix Al.

Standards for quality assurance (management) systems are discussed in Appendix

A2.

Refinements of management aspects are given in Appendices A3

A5 for the

cases in which tailoring is not mandatory.

1.1

Introduction

Until the nineteen-sixties, quality targets were deemed to have been reached when

the item considered was found to be free of defects or systematic failures at the time

it left the manufacturer. The growing complexity of equipment and systems, as well

as the rapidly increasing cost incurred by loss of operation as a consequence of

failures, have brought to the forefront the aspects of reliability, maintainability,

availability, and safety. The expectation today is that complex equipment and

systems are not only free

from defects und systematic failures at time t

(when they are put into operation), but also perform the required function failure

free for a stated time interval and have a fail-safe behavior in the case of critical or

catastrophic failures. However, the question of whether a given item will operate

without failures

during a stated period of time cannot be simply answered by yes

or no, on the basis of

compliance test. Experience shows that only aprobability

for this occurrence can be given. This probability is a measure of the item's

Basic Concepts, Quality and Reliability Assurance of Complex Equipment and Systems

reliability

and can be

interpreted

as follows:

n statistically identical items are put into operation at time t

pegorm a given mission und

n of them accomplish it successfully, then

the ratio

n is a random variable which converges for increasing n to the

true value of the reliability (Appendix A6.11).

Performance Parameters as well as

reliability, maintainability, availability,

and

safety

have to be

built in

during design

development and retained during production and

operation of an item. After the introduction of some important concepts in Section

1.2, Section

1.3

gives basic tasks and rules for quality and reliability assurance of

complex equipment und Systems with high quality und reliability requirements

(see Appendix Al for a comprehensive list of definitions and Appendices A2

for a refinement of management aspects).

1.2

Basic

Concepts

This section introduces important concepts used in reliability engineering and

shows their relationships (see Appendix Al for a more complete list).

1.2.1

Reliability

is a

characteristic

of an item, expressed by the

probability

that the item

will perform its

required function

under

given conditions

for a

stated time interval.

It is generally designated by

From a qualitative point of view, reliability can be

defined as the

ability of the item to remain functional.

Quantitatively, reliability

specifies the

probabili~ that no operational interruptions

will occur during

stated

time interval. This does not mean that

redundant

parts may not fail, such parts can

fail and be repaired (without operational interruption at item (system) level). The

concept of reliability thus applies to

nonrepairable

as well as to

repairable

items

(Chapters 2 and

respectively). To make sense,

numerical Statement of reliability

(e.g.,

0.9)

must be accompanied by the definition of the

required function,

the

operating conditions,

and the

mission duration.

In general, it is also important to

know whether or not the item can be considered new when the mission Starts.

item

is a functional or structural

unit

of arbitrary complexity (e.g. component,

assembly, equipment, subsystem, system) that can be considered as an

entity

for

investigations. It may consist of hardware, software, or both and may also include

human resources. Often,

ideal

human aspects and logistic Support are assumed,

even if (for simplicity) the term

System

is used instead of

technical system.

1.2

Basic

Concepts

The

required function

specifies the item's task.

For example, for given

inputs, the item outputs have to be constrained within specified

tolerance bands

(performance Parameters should still be given with tolerances and not merely as

fixed values). The definition of the required function is the starting point for

any

reliabili9 analysis,

as it defines

failures.

Operating conditions

have an important influence upon reliability, and must

therefore be specified with care. Experience shows e.g., that the failure rate of

semiconductor devices will double for operating temperature increase of

20°C .

The required function andl or operating conditions can be

time dependent.

In these cases, a

mission profile

has to be defined and all reliability figures will be

related to it.

representative mission profile and the corresponding reliability

targets should be given in the

item's specification

Often the mission duration is considered as a Parameter

the

reliabilityfunction

is then defined by

R(t). R(t)

is the probability that no failure at item level will

occur in the interval

(0,

t].

The item's condition at

(new or not) influences

final results. To consider this, reliability figures at system level will have indices

(e.g.

Rs,(t)),

where

stands for system and

is the state entered at

(Table 6.2).

distinction between

predicted

and

estimated

assessed

reliability is

important. The first one is calculated on the basis of the item's reliability structure

and the failure rate of its components (Sections

2.2

2.3), the second is obtained

from a statistical evaluation of reliability tests (Section

7.2)

or from field data by

known environmental and operating conditions.

The concept of reliability can be extended to processes and services as well,

although

human aspects

can lead to modeling difficulties (see e.g. Section 1.2.7).

1.2.2

Failure

failure

occurs when the item stops performing its required function. As simple as

this definition is, it can become difficult to apply it to complex items. The

failure-

free time

(hereafter used as a synonym for

failure-free operating time)

is generally a

random variable.

It is often reasonably long, but it can be very short, for instance

because of a failure caused by a transient event at turn-on.

general assumption in

investigating failure-free times is that at

the item is free of

defects

and

systematic failures.

Besides their

frequency,

failures should be classified (as far as

possible) according to the mode, cause, effect, and mechanism:

Mode:

The mode of a failure is the

Symptom

(local effect) by which a failure

is observed; e.g., Opens, shorts, or drift for electronic components (Table

3.4);

brittle rupture, creep, cracking, seizure, fatigue for mechanical components.

Cause:

The cause of a failure can be

intrinsic,

due to weaknesses in the item

andlor wearout, or

extrinsic,

due to errors, misuse or mishandling during the

design, production, or use. Extrinsic causes often lead to

systematic failures,

Basic Concepts, Quality and Reliability Assurance of Complex Equipment and Systems

which are

deterministic

and should be considered like

defects

(dynamic

defects in software quality).

Defects are present at t

even if often they

can not be discovered at

Failures appear always in time,

even if the

time to failure is short as it can be with systematic or early failures.

Effect:

The effect (consequence) of a failure can be different if considered on

the item itself or at higher level. A usual classification is:

non relevant,

partial, complete,

and

critical failure.

Since a failure can also cause further

failures, distinction between

primaiy

and

secondaiy failure

is important.

Mechanism:

Failure mechanism is the physical, chemical, or other process

resulting in a failure (see Table 3.5 for some examples).

Failures can also be classified as

sudden

and

gradual.

In this case, sudden and

complete failures are termed

cataleptic failures,

gradual and partial failures are

termed

degradation failures.

As failure is not the only cause for an item being

down, the general term used to define the down state of an item (not caused by a

preventive maintenance, other planned actions, or lack of external resources) is

fault.

Fault is thus a state of an item and can be due to a

defect

or a

failure.

1.2.3

Failure

Rate

The

failure rate

plays an important role in reliability analysis. This Section intro-

duces it heuristically, see Appendix A6.5 for an analytical derivation.

Let us assume that

statistically identical

and independent items are put into

operation at time

under the same conditions, and at the time

a subset

V(t)

of these items have not yet failed.

Y(t)

is a right continuous decreasing step

function (Fig. 1.1).

tl,

...,

t„

measured from

are the

observed

failure-free

times (times to failure) of the

items considered. They are independent realizations

of a

random variable

(hereafter identified as a failure-free time) and must not

be confused with arbitrary points on the time axis

(

tl,

,...).

The quantity

is the

empirical mean

(empirical expected value) of

Empirical quantities are

statistical estimates, marked with

in this book. For

E[TI

converges to

the true value

[T]

MTTF

(given by Eq. (1 3)) of the mean failure-free time

(Eq. (A6. l47), see also Appendix A8.1.2). The function

is the

empirical reliability function.

As shown in Appendix A8.1.1,

k(t)

converges

to the reliability function

R(t)

for

n-t

For an arbitrary time interval

(t, t

6t1,

the

empirical failure rate

is defined as

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《可靠性工程理论与实践》第五版：提升产品质量与系统稳定性

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