Md. Imrul Kaes - Reliability 2013-5-13
-
Upload
imrul-kaes-likhon -
Category
Documents
-
view
215 -
download
0
Transcript of Md. Imrul Kaes - Reliability 2013-5-13
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
1/13
RELIABILITY
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
2/13
DEFINITION
The ability of an item to perform a required
function under stated condition for a period of
time or the probability that an item will continue
to perform its intended function without failure
for a specified period of time under statedconditions.
5/12/2013
2
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
3/13
MAJOR IMPORTANCEOF RELIABILITY:
Reputation: a companys reputation is closelyrelated to the reliability of the product. The morereliable a product is, the more likely thecompany is to have a favorable reputation.
Customer satisfaction: while a reliable productmay not dramatically affect customersatisfaction in a positive manner, an unreliableproduct will negatively affect customersatisfaction.
Warranty Cost: if a product fails to perform itsfunction within the warranty period, thereplacement and the repair costs will negativelyaffect profits.
5/12/2013
3
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
4/13
GOAL:
The goal of reliability engineering is to evaluate
the inherent reliability of a product and pinpoint
the potential areas for reliability improvement.
5
/12/2013
4
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
5/13
RELIABILITY REDEFINED
High quality does not mean high reliability
Components can pass all quality control
checks, but when they are assembled, theinteraction effect may decrease the long term
operational capability of the assembly. Similarly,
when too many technically sophisticated
components are assembled, it may lose
reliability up to a certain degree.
5
/12/2013
5
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
6/13
System: Input Transformation Process -
Output
Series System: where all components are
assembled functionally in series.
Parallel System: where all components are
placed functionally in parallel.
Combination System: a combination of series
and parallel systems.
5
/12/2013
6
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
7/13
SERIES SYSTEM
Here the system will work if all the componentswork simultaneously.
Rs = 0.99 x 0.98 x 0.96 = 0.93 = 93%
System reliability is lower than the lowestreliability of individual component.
5
/12/2013
7
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
8/13
PARALLEL SYSTEM
Reliability of a system can be increased by placing
components in parallel. Thus, a system consisting
of n components in parallel will fail only if all
components fail simultaneously.
5
/12/2013
8
B1
B2A
B3
C
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
9/13
If A, B, C, D are in parallel connection and their failure
probability is F(A), F(B), F(C), F(D) correspondingly.
So The failure probability of the system
F = F(A) x F(B) x F(C) x F(D)
So, the reliability of the system R = 1-F
5
/12/2013
9
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
10/13
WHENRELIABILITYCHANGESWITHTIME5
/12/2013
10
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
11/13
Failure Rare (): On an average how many
components fail per hour.
MTBF (1/ ): On an average how many hours taken
by a component to be failed.
5
/12/2013
11
F(t) = 1- R(t)
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
12/13
Failure rate () of a system which has a series of components:
= 1+ 2+..+ n
MTBF (1/ ) of a system which has parallel - connectedcomponents:
5
/12/2013
12
-
7/30/2019 Md. Imrul Kaes - Reliability 2013-5-13
13/13
Reliability of the components are B1 = B2 = B3 =
0.75 and A = C = 0.97. These reliabilities are given
for 100 hours. Find out MTBF of the system per
10,000 hours.
5
/12/2013
13
B1
B2A
B3
C