Weibulls model and system reliability

8/9/2019 Weibulls model and system reliability

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GROUP 7

Weibulls model andSystem Reliability


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The Weibull distribution is word wide used to model Life Data.

The distribution can handle increasing, decreasing or constant

failure-rates and can be created for data with and without

suspensions (non-failures).

It is flexible and fits to a wide range of data, including ormal

distributed data.

The Weibull distribution is one of the most commonl! used

distributions in "eliabilit!

It gains in popularit! for reliabilit! wor#, particularl! in the area of

mechanical engineering because of the man! shapes it attains for

$arious $alues of reliabilit!, due to its inherent $ersatilit!.

Weibull model


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Weibull analysis includes:

% &lotting the data and interpreting the plot

% 'ailure forecasting and prediction

% $aluating correcti$e action plans

% Test substantiation for new designs with

minimum cost

% aintenance planning and cost effecti$e replacement strategies


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% *pare parts forecasting

% Warrant! anal!sis and support cost predictions

% +ontrolling production processes

% +alibration of complex design s!stems, i.e., +D+, finite

anal!sis, etc.

% "ecommendations to management in response to ser$ice

problems


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Weibulls formulae:


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Data Requirements Plotting Procedures

Life data that is relevant tothe failure mode iscritical

Order data from lowest tohighest failure time

Individual Data Estimate ercentagefailing before each failuretime !median ran"s#

$otal Units %raw best line &t through

data oints lotted onWeibull aer

'umber of observedfailures

Estimate weibullarameters

(tem $ime to )ailure

Grouped Data

$otal Units

'umber of grous


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Failure types include:

% De$elopment, production and ser$ice

% echanical, electronic, materials, and human failures

% ature lightning stri#es, foreign ob/ect damage, human error,

woodpec#er holes in power poles

% 0ualit! control, design deficiencies, defecti$e material

% Warrant! claims


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Advantages

The primar! ad$antage of Weibull anal!sis is the abilit! to pro$ide

reasonabl! accurate failure anal!sis and failure forecasts with

extremel! small samples

nother ad$antage of Weibull anal!sis is that it pro$ides a simple and

useful graphical plot of the failure data.

The data plot is extremel! important to the engineer and to the

manager


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*+stem reliabilit+

s products become more complex (ha$e morecomponents), the chance that the! will not function

increases.

The method of arranging the components affects the

reliabilit! of the entire s!stem.

+omponents can be arranged in series, parallel, or a

combination.


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R* , R-R./// Rn

- . n

)or a series s+stems0 the reliabilit+ isthe roduct of the individual

comonents/

1s comonents are added to the series0the s+stem reliabilit+ decreases/

*eries *+stem


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Rs , - 2 !- 2 R-# !- 2 R.#/// !- 2 Rn#

-

.

n

When a comonent does not function0 the

roduct continues to function0 using anothercomonent0 until all arallel comonents do

not function/

Parallel s+stem


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*eries2Parallel *+stem

3onvert to e4uivalent series s+stem

1 5

3

3

%

R1 R5 R3R%

R3

1 5 36 %R1 R5 R%

R36, - !-2R3#!-2R3#


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% Reliabilit+ can be achieved b+overdesign/

% $he use of large factors of safet+ can

increase the reliabilit+ of a roduct/

% When an unreliable roduct can lead

to a fatalit+ or substantial &nancial

loss0 a fail2safe t+e of device should

be used/

% $he maintenance of the s+stem is an

%esign


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% $he second most imortant asect of

reliabilit+ is the roduction rocess/

% Emhasis should be laced on thosecomonents which are least reliable/

Production


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% $he third most imortant asect of reliabilit+

is the transortation/

1 Pac"aging

1 *himent

% Performance of the roduct b+ the customer is

the &nal evaluation/

% Good ac"aging techni4ues and shiment

evaluation are essential/%

$ransortation


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$81'9 OU

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Weibulls model and system reliability