Summary Reliability and Maintainability Engineering

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RELIABILITY AND MAINTAINABILITY ENGINEERING
EEE 571
2 UNITS

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COURSE OUTLINE
1.0 Reliability
1.1 The Importance of Reliability
1.2 Configuration and Functionality of Systems
1.2.1 Series System
1.2.2 Parallel System
1.2.3 Series-Parallel System
1.3 Reliability Prediction Model: Laws of Probability Relevant to Reliability
Prediction
1.3.1 Multiplication Rule
1.3.2 Addition rule
1.3.3 Binomial distribution
1.4 The Reliability of a Series System
1.5 The Reliability of a Parallel System
1.6 The Reliability of a Series-Parallel System
1.7 Reliability Measurement
1.7.1 Mean Time between Failures (MTBF)
1.7.1.1 MTBF of a series system
1.7.1.2 MTBF of a Parallel System
1.7.1.3 MTBF of a Series-Parallel System
1.7.2 Mean Time to Failure (MTTF)
1.8 Derivation of MTBF, MTTF and failure rate
1.9 Failures
1.9.1 Classification of Failures
1.9.2 Failure Rate
1.9.3 Reliability and Unreliability Equation and Curves
1.10 Failure Pattern (The Bath-tub Curve) of Equipment
1.10.1 Early Failure Period
1.10.2 Constant Failure Period
1.10.3 Wearout Failure Period
1.11 Some of the Failures Which the Designer/Manufacturer Will Not Be Held
Responsible
2.0 Maintainability
2.1 Factors That Affect Maintainability

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2.2 Terminologies Relating To Maintainability
2.3 Design and Methods for Improving Maintainability
3.0 Availability
3.1 Analysis of System Availablity
3.1.1 Steady- State Availability (Ass)
3.1.2 Intantanneous Availability
3.1.3 Mission Availability
3.2 Availability of Items in Series and Parallel Combinations
4.0 Test Characteristics of Electrical and Electronic Components
4.1 Prototype Testing
4.2 Pre-production Testing
4.3 Production Testing
4.4 Reliability Demonstration and Acceptance Testing
5.0 Faults Analysis
5.0 Fault Test in Electrical and Electronic Components
5.1 Fault Tree Analysis
5.2 Methods of fault Analysis
5.2.1 Cut-Set Method
5.2.2 Tie-Set Method

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LECTURE ONE

RELIABILITY

Definitions of reliability are as follows;
 Reliability is defined as the ‘probability that a specified item will perform a specified
function within a defined environment, for a specified length of time.
 It is the probability of an item to perform a required function under specified
conditions for a stated period of time.
 It is the probability that a componenet or a system will function without failure for a
prescribed period of time under specified condition.

It is worthy of note that other literature sources may define reliability by slightly different
statements, regardless of the approach, the three operative phrases “PERFORM A
REQUIRED FUNCTION”, “UNDER STATED CONDITION”, “FOR STATED
PERIOD OF TIME”, are always emphasized.

Probability is recognizd as a technical word implying “a measure of chance”.
Mathematically, reliability lies between 0 and 1

Reliability = 1.00 means the item will always work as intended (absolute certainity).
Reliability = 0.90 means 90 per cent likely to work as intended.
Reliability = 0.00 means absolutely certain it will not work as intended (Absolute
impossibility)


0 1
Absolute Absolute
Impossibility Certainty

Figure 1: The Probability Scale

1.1 The Importance of Reliability
Unreliability has a number of unfortunate consequences and therefore for many
products and services is a serious threat. Attainment of high reliability of items is important
to both the manufacturers and consumers because poor reliable items can have implications
on:
 Safety