Chapter 1 & 2 Flashcards
(51 cards)
What is reliability
This is the probability that a component/system will perform its prescribed duty without failure for a given time when operated correctly in a specified environment. Assurance that a product/system/component will start to operate safely and efficiently and also make forecasted ROI.
What are the key terms to note while defining reliability
Probability, system, prescribed duty, failure, given time, operated correctly, specified environment.
How does Competition among manufacturers necessitate the need for Reliability
This helps consumers to determine the product that will serve them well.
Why do we need reliability
Growing size of electrical systems, systems are to perform more complex functions, competition amongst manufacturers, critical systems that require higher reliability, systems being used in hostile environments.
What does the Bathtub Hazard rate concept represent
Failure rate behaviour of engineering systems as a function of time.
What’s the difference between lamda and lamda of t
Lambda is a constant failure rate while lambda of t is a time dependent failure rate.
What are the three regions that are involved in the bathtub hazard rate concept
Burn in/Break in region/Debugging region/Infant Mortality region, Useful life period, Wear out period.
What’s the characteristics of the infant mortality rate region
Hazard rate decreases.
What are some reasons for failure in Region I
Poor manufacturing methods, poor quality control, poor debugging, poor processes, human error, substandard material and workmanship.
What’s the characteristics of the useful life period
Hazard rate remains constant.
What are some reasons for failure in Region II
Low safety factors, undetectable defects, human errors, abuse, higher random stress, natural failures.
What’s the characteristics of the Wear out period
Hazard rate increases.
What are some reasons for failure in Region III
Wear caused by friction, poor maintenance, incorrect overhaul practices, corrosion and creep, short designed life, wear caused by aging.
What’s the mathematical representation for the Bathtub Hazard rate
What are alpha and theta usually called in the bathtub hazard rate mathematical representation
Scale parameters.
What are beta and b usually called in the bathtub hazard rate mathematical representation
Shape parameters.
What are the General reliability analysis formulas
Failure density function, hazard rate function, general reliability function, MTTF.
What is the mathematical expression for the failure density function
F(t) = lambda * e^{-lambda*t}
What’s the formula for reliability of an item based on the failure density function
e^{-lambda*t}
What’s the hazard rate function formula
-1/R(t) * dR(t)/dt
What does the general reliability function give us
The reliability of an item when its time to failure follows any time-continuous probability distribution.
What’s the formula for reliability of an item whose time to failure follows any continuous probability distribution
What are the three formulas for MTTF
Prove that all three formulas of the MTTF yield the same value
Substitute the formula for reliability into all three. e^{-lamda*t}
