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AE4736 Experimental Techniques in Structural Analysis

AE4736 Experimental Techniquesin Structural AnalysisLecture 1 Philosophy of easurement

!r "o#er $ro%es

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&

'n this Lecture

'ntro(uctions )utline of the *ourse

easurement Systems

"e%ie+ of Physical ,nits

!efinitions

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*ourse Lecturers

!r "o#er $ro%es-L".

!r/ir/ aarten0aer -*iT$.

3

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"o#er $ro%es2 ea( ofAerospace !T La5oratory

easurement Technolo#y Al#orithmsfor2

Experimental echanics !T in Pro(uction Assem5ly

!T in aintenance

Structural ealth onitorin#

4

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Experimental echanics 3! )ptical Tomo#raphy of crac #ro+th

in in( Tur5ine 0la(e $8"P

9olume optical elasto#raphy for $8"P

3! strain measurement usin#shearo#raphy

*rac #ro+th an( (eformation of+oo(en structures (ue to temp/ "

:

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Pro(uction Assem5ly Selection of !T;S Technolo#y

*

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aintenance >ey topics for !T assessment2

8laps= lea(in# e(#es of +in#s= 5ir( strie=car#o (oors

ulti

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Structural ealth onitorin#

'nte#ration +ith !T aintenance9i5ration monitorin# of +in( tur5ines

Lam5 +a%e ultrasonic -P@T 8)S.

8i5re optic sensors for #as pipeline repair

!emonstrator ri#s2

in#5ox rotatin# ri#

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hich aster Trac are youstu(yin#B

C

!onDt no+

Aerospace aterials an(

anufacturin#

Aerospace Structures an(Aircraft !esi#n

)ther

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@oome( in

1

Aerospace aterials an( anufacturin#

Aerospace Structures an( Aircraft !esi#n)ther

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Typical Ans+ers to Sur%ey < 1 o+ (o you rate your no+le(#e of

measurement principlesB ee(s'mpro%ement

o+ (o you rate your no+le(#e ofelectronicsB ee(s 'mpro%ement

o+ (o you rate your no+le(#e of optospecs?

-static. !efinition of resolution

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::

-static. !efinition of resolution

V trans(ucer

%$ =".!S: .esolution is the smallest chan'e ininput that still results in a quanti(iablechan'e at the output

W

The resolution o( a system can be:

G !iscrete: ire

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:6

*ontinuous resolutionB

The resolution o( the ideal continuous system is in(initesimal

Ioever) in reality the noise puts a limit to it There(ore)the resolution o( a continuous system is also discrete

ideal continuous response noisy continuous response

smallestdetectable

chan'e inresponse

Examples of (iscrete resolution

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:7

Examples of (iscrete resolution

"ee( s+itch

ma#nets

.esolution 8 magnets2N

electric current

rotatin' heel

'

.esolution 8 windD

N 1

V

V

,out

9olt 1 9olt

,out

+ire

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:

Trans(ucer specifications

Sensiti%ity

"esolution*ross tal

ysteresis

*reep an( "elaxationEqui%alent noise= S" (ynamic

ran#e

'naccuracy

=orin' ran'e 8 validity limits (or 'iven speci(ications

The ma#or>specs?

!efinition of cross tal

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:C

!efinition of cross

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6


Sensiti%ity

"esolution*ross tal

ysteresis


ran#e

'naccuracy


The ma#or>specs?

!efinition of hysteresis -memory effect.

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!efinition of hysteresis -memory effect.

Iysteresis is the property that a transducer responds di((erentlyto increasin' and decreasin' inputs The transducer there(ore

seems to JrememberK the ma'nitude o( the precedin' input value

input

o

utput

Typical transducer hysteresis

maximum hysteresis

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6&

maximum hysteresis

Iysteresis disadvanta'e: !efines a non

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Sensiti%ity

"esolution*ross tal

ysteresis


ran#e

'naccuracy


The ma#or>specs?

*reep an( "elaxation

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6:

*reep an( "elaxation

reep: "esponse W chan#es +hile input V is constant

.elaxation: "esponse W is chan#in# +hile input V is alrea(y Oero

=orse yet: creep is time*rate /(requency1 dependent N

V WS

Time

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0

strain

"KY

L

A

0

p

creep

*

*

strain

time

0 *

! EA

A

plate

#au#e

plate loadin'

Erelax

ation

E

'au'e response

!

!


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Sensiti%ity

"esolution*ross tal

ysteresis


ran#e

'naccuracy


The ma#or>specs?

Equi%alent noiseK9; K9

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6

8 X error W X noise),TSX error X noise

K9; K9

K9

"esultin# noise -error. is not easy to compare +ith input quantity/hat (oes it mean2 1 m9 output noise if you +ant to measure 1 B

K

X noise),TW

K

8 X noise),T;S S

This mo(el is simpler an( equi%alent in the accuracy analysis/Equi%alent noise M noise),T;S K

K9

oise in time si#nal

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6C

#

time

noise part

V W X noiseS

K9

oise in time si#nal2

pea

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7

time

noise part

V W X noiseSK9

oise po+er spectral (ensity M2

n(f)

oise spectral (ensity M n(f)

K9&;O

V/ Hz

2n(f ) df

frequency

noise

oise ener#y M

88T-n.

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orin# ran#es

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7&

S

&ay apply to input or output: speci(y throu'h unit or /pre(erably1 explicitlyN

V Z V Z V1 W Z W Z W1S

ElectricalHmechanical orin' ran'es

S

S W M 7/: 9 X;< si#nal

Bias in output

9olt

1: 9olt

-8ull

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p

Sensiti%ity

"esolution*ross tal

ysteresis


ran#e

'naccuracy


The ma#or>specs?

'naccuracy is H

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1/ 'naccuracy M measurement < cali5rate( %alue-cali5ration is a measurement +ith much hi#her accuracy.

&/ 'naccuracy M measurement < a no+n %alue -intuiti%eB.

3/ 'naccuracy M measurement < stan(ar( %alue -or reference.

4/ The inaccuracy in a #i%en point of a measurement chain is theaccumulation or stochastic mean of all the errors an( noise accompanyin#the si#nal up to that point -assumin# no fee(5ac loops in%ol%e(.

Precision -an( other possi5le

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7:

specifications.B

precise an( accurate not precise an( not accurate precise 5ut not accurate

precision 8 repeatability0

ase 3 su''est a systematic error

M measurement M reference

*omments ?uestions

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AE4736-L1 2013 -FINAL

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