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RELIABILITY ENGINEERING AND RISK
ANALYSIS A PRACTICAL GUIDE 3RD
EDITION MODARRES SOLUTIONS MANUAL
ACTUAL EXAM PAPER 2026 FULL
QUESTIONS AND CORRECT ANSWERS
⩥ Failure rate equation. Answer: lambda = (MTBF)^- 1 failure rate = (mean time between failure) ^- 1 ⩥ Non-repairable items. Answer: reliability is the survival probability over the item's expected life, or for a period during it's life, when only one failure can occur ⩥ hazard rate. Answer: items instantaneous probability of the first and only failure MTTF (Mean Time To Failure) ⩥ Repairable items equations. Answer: MTBF (Mean Time Between Failure) availability = MTBF/(MTBF + MTTR) ⩥ reliability principals. Answer: - design for reliability from the initial concept of the idea
- use proven components that have been used on previous products
- use fundamental design techniques
- design it to be rugged and robust
- reduce stress and critical components
- design for manufacturing and assembly
- allow for parameter variation (tolerances, etc) ⩥ statistic. Answer: a structured piece of data, carrying meaningful information ⩥ probability. Answer: the quantitative description of the likely occurrence of a particular event
- a numerical measure of the likelihood of an even relative to a set of alternative events ⩥ Probability equation. Answer: P(E)= (number of outcomes corresponding to event E)/(total number of outcomes) ⩥ Descriptive statistics. Answer: - describe a set of data
- analyse the characteristics of a sample and assess the parameters of a population ⩥ Inferential statistics. Answer: involves hypothesis testing using a sample to test differences in a population
⩥ Reliability (occurrence). Answer: how confident we are that a given finding can be reproduced - that it can be replicated that it is not a chance result, a 'freak occurrence' ⩥ Data variable samples and populations. Answer: - univariate (one variable)
- bivariate (two variables)
- multivariate (two or more variables) ⩥ Qualitative or categorical Quantitative
- discrete
- continuous. Answer: Types of Variables ⩥ Graphs for univariate data distributions. Answer: qualitative
- pie charts
- bar charts ⩥ Quantitative data. Answer: - scatter plot
- stem and leaf plots
- relative frequency histograms
⩥ data distributions. Answer: - shapes - symmetric, skewed left, skewed right, unimodal, bimodal
- proportion of measurements in certain intervals
- outliers ⩥ Issues Coding: Choosing Categories. Answer: Exhaustively - all cases are covered by the options Exclusivity - each case has only one possible option Relevance - item must pertain to the domain of concern Adequate domain coverage Specificity definition of each category must be precise - consistent coding (inter-rater reliability) ⩥ Nominal (categorical) [Data]. Answer: allocates into categories ex child won sack race or child did not win ⩥ Original [Data]. Answer: value is ranked relative to others ex Ben finished in 3rd place, Tom in 2nd, Jerry 1st ⩥ Interval [Data]. Answer: continuous numerical scale with the equal intervals ex Tom came second, 2.3 seconds after Jerry ⩥ Ratio [Data]. Answer: as interval but with an absolute zero ex Jerry came 1st (35 seconds), Tom 2nd (37.3 seconds)
⩥ Normal Distribution. Answer: a bell curve, a reflection of naturally occurring values where the mean, the median and the mode are the same ⩥ Variation. Answer: you want to understand how the response is dependent on variation in the explanatory variables, but you are also interested in lack of dependence ⩥ Hypothesis testing. Answer: you have an idea you want to test ⩥ control experiment. Answer: one where you don't apply the treatment or don't enable the part of your experiment that is supposed to produce the different outcome ⩥ Replication. Answer: - must be independent
- not part of a time series
- not grouped together in space
- of an appropriate spatial scale
- covers the normal variation in initial conditions ⩥ Strong inference. Answer: - a clear hypothesis
- an acceptable test ⩥ weak inference. Answer: natural experiments
⩥ mechanisms cause mode. Answer: 3 key classifications of mechanical failure ⩥ Availability. Answer: the probability that an item is in an operable state at any time and is based on a combination of MTBF and MTTR A(i) = MTBF/(MTBF+MTTR) ⩥ Operational Availability (Ao). Answer: the probability that the product will be ready for use when the customer wants to use it A(o)=uptime/operating cycle ⩥ Quality (again). Answer: total features and characteristics of a product or service that bear on its ability to satisfy stated or implied needs ⩥ Reliability (book). Answer: can also be expressed as the number of failures over a period ⩥ Durability. Answer: is a particular aspect of reliability, related to the ability of an item to withstand the effects of time dependent mechanisms such as fatigue, wear, corrosion or electrical parameter change. minimum time before wearout occurs
⩥ Brittle Fracture. Answer: an overstress failure mechanism that occurs rapidly with little or no warning when the induced stressed in the component exceeds the fraction strength of the material ⩥ creep. Answer: a time-dependent deformation process under load, thermally activated process ⩥ delamination. Answer: the debonding or the separation of adjacent material layers which were bonded before ⩥ plastic deformation. Answer: when the applied mechanical stress exceeds the elastic limit or yield point of a material, is permanent ⩥ electrically induced failures. Answer: failures caused as a result of electrical over stress three types electrostatic discharge gate oxide breakdown electromigration ⩥ Chemically induced failures. Answer: chemical process such as electrochemical reactions that can result in cracking of vias, traces, or interconnects leading to electrical failures two types
corrosion intermetallic diffusion ⩥ intermetallic diffusion. Answer: during wirebonding and solder reflow the joining process generates intermetallic layers which are byproducts of the joining process ⩥ 1. Identify
- Design
- analyze
- verify
- validate
- control. Answer: Design for Reliability (DFR) ⩥ Inherent Availability. Answer: the steady state availability which considers only corrective maintenance ⩥ Operational Availability. Answer: a measure of the 'real' average availability over a period of time in an actual operational environment ⩥
