Q2-Reliability
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Virginia Tech *
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Industrial Engineering
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Apr 3, 2024
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docx
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Uploaded by DrAntelope1810
Quality of Design -- Reliability
Quality of Conformance
vs. Quality of Design
Reliability
The probability that a product will perform its
intended function for a specified length of time
A producer must be able to estimate the Reliability of a product (or system) to make appropriate design decisions for quality, accurately forecast costs, and establish policies.
Light Bulb Example
The BrighterWorld company is producing a new light bulb with an expected life of 850 hours. A random sample of 1000 bulbs is selected from a preliminary production run and tested for 850 hours. After 850 hours of use:
R(t) + Q(t) = 1 Components in series
Copyright 2023 LL Clark Referenced Material
:
Operations & Supply Chain Management, 10
th
Ed. by Russell & Taylor
p. 1
R(t)
= # surviving to time t
# products total
Q(t)
=
# that have failed before time t
# products total
950 bulbs still work
50 bulbs have failed
Reliability =
Probability
of Failure
=
R
system
= R
A
R
B
Glen’s Prototype Example
Glen is building a new prototype for a product. The prototype will only function correctly if all 3 of the required components function correctly. Based on information
provided by suppliers, the reliabilities of the 3 components vary as follows: 0.9752, 0.9522, and 0.9641. What is the reliability of the prototype? Set of Tires Example
Gary purchases a new set of tires for his car. Each of the 4 tires has a 3-year warranty. The probability that a tire will last for 3 years is 0.9900. What is the probability that the company will have to pay for at least one warranty claim from Gary?
Copyright 2023 LL Clark Referenced Material
:
Operations & Supply Chain Management, 10
th
Ed. by Russell & Taylor
p. 2
0.85
0.90
B
A
all components must function for the system (product) to function
Event A: component A survives to time t
Event B: component B survives to time t
Components in parallel
only one of the components in parallel must be functioning for the system (product) to function
Multi-level Parallel Component Example Copyright 2023 LL Clark Referenced Material
:
Operations & Supply Chain Management, 10
th
Ed. by Russell & Taylor
p. 3
0.95
0.85
0.60
0.95
0.85
A
B
R
system
= R
A
+ (1 – R
A
)R
B
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