SHM Composite Dec2010

8/13/2019 SHM Composite Dec2010

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Simple Method for Delamination Detection in Composite

Israr Ullah, Jyoti K. Sinha

School of MACE, The University of Manchester, Sackville Street, Manchester M13 9PL, UK

E-ail! "srar#Ullah$%ost&ra'#anchester#ac#(k, )yoti#Sinha$anchester#ac#(k

Abstract

*elaination 'etection in the co%osite str(ct(re +ase' on the vi+ration res%onses

hen ecite' at the loer o'es has +een s(&&este' here# "t has +een o+serve' that

the nonlinear interaction +eteen the 'elainate' layers %ro'(ce hi&her haronics ofthe ecitin& fre.(ency# These hi&her haronics have o+serve' to +e (sef(l for the

'etection an' location of the 'elaination itho(t co%arin& the vi+ration 'ata fro

the healthy state of the co%osite str(ct(re# The %a%er %resents the o+servation +ase'

on the finite eleent analysis of a co%osite %late ith an' itho(t 'elaination an'

then on the e%erients on the co%osite %lates ith an' itho(t 'elaination#

Key words: Co%osite str(ct(res, /inite Eleent Mo'ellin&, *elaination,

0onlinear interaction, i+ration res%onse#
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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.! Introd"ction

*elaination 'etection in the co%osite str(ct(res is one of the active research areas

since 'eca'es# 0(+er of research has +een carrie' o(t to eet this o+2ective# The

ost coonly (se' etho' in the literat(re is +ase' on the vi+ration analysis 1-

435# These vi+ration +ase' st('ies incl('e 6a7 chan&e in o'al %araeters 6nat(ralfre.(encies an' o'e sha%es7 1-85 or the vi+ration res%onses +y co%arin& the 'ata

ith the healthy state con'ition 1, 4, 5, 6+7 a%%in& the 'eflection sha%e of the

s(rface of the co%osite str(ct(re either thro(&h the e+e''e' sensors 19-4:5 or

scannin& the co%lete s(rface +y the laser vi+roeter 1;-1= 1?5 hich is also not a

%ractical a%%roach (sin& the noral %ie=o-electrical shakers &enerally (se' in the

vi+ration testin

Consi'erin& these liitations, a si%le etho' hich ay +e relatively easy to

i%leent in %ractice an' not re.(irin& 'ata fro the healthy state con'ition is

nee'e' to eet the o+2ective# >ence it is ass(e' that the ecitation at a fe loer

o'es +y the conventional shaker is alays %ossi+le an' then scannin& the co%lete

co%osite s(rface thro(&h the laser vi+roeter ay not i%ose any %ractical

liitations# @ith this ass(%tion, the ecitation of a co%osite %late ith an' itho(t

a 'elaination at a fe loer o'es an' then the velocity res%onses eas(reents at

n(+er of %oints has +een consi'ere' in the %resent st('y# "nitially, the finite eleent

6/E7 o'el of a co%osite %late ith an' itho(t 'elaination has +een 'evelo%e' to

si(late this e%erient# The %late as then ecite' at a fe loer o'es so that the

a%lifie' stea'y state res%onses can +e o+serve'# The nonlinear interaction +eteen

the 'elainate' layers for the %late ith 'elaination as also consi'ere' '(rin& the

vi+ration res%onse estiation# The +reathin& 6o%enin& an' closin&7 of a crack in a

str(ct(re '(rin& vi+ration alays %ro'(ce the hi&her haronics of the ecitin&

fre.(ency 485, hence the siilar res%onses are e%ecte' for the 'elainate'

co%osite str(ct(re# "n fact, it has +een o+serve' that the nonlinear interaction

+eteen the 'elainate' layers %ro'(ce hi&her haronics of the ecitin& fre.(ency#

These hi&her haronics are then o+serve' to +e (sef(l for the 'etection an' location

of the 'elaination itho(t co%arin& the vi+ration 'ata fro the healthy state of the

co%osite str(ct(re# The %a%er %resents the o+servation +ase' on the finite eleentanalysis of a co%osite %late ith an' itho(t 'elaination an' then e%eriental

vali'ation on the co%osite %lates ith an' itho(t 'elaination#

#.! Composite $lates

The e%eriental co%osite %late a'e of E-&lass fi+re an' e%oy resins has +een

consi'ere' for the %resent st('y# "t has a total of < layers of e.(al thickness hich are

arran&e' as :o 9:o:o9:o9:o:o 9:o:o5 as shon in /i&(re 1# The si=e of the test

%late is 8:: 8:: an' total thickness 3#?# Bne test sa%le of the

co%soite %late has the 'elaination of 8: 8: si=e +eteen 3 r' an' 8th

layers fro the to% s(rface an' its centre locate' at the coor'inate of 64;?,


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4;?7 fro the one corner of the %late# These test %lates are shon in /i&(re 4# The

aterial %ro%erties of the %late are the 'ensity, 11


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/i&(re 3 6a7 An /E o'el of the E-&lass fi+re %late 6also shoin& 'elaination re&ion7, 6+7

Meas(reent locations 6arke' as 7 in /E si(lation

Ta+le 1 Calc(late' nat(ral fre.(encies

Mo'es >ealthy Plate *elainate' Plate

1 ?:#:3 >= 89#9 >=

4 1:1#84 >= 1::#9; >=

3 138#1 >= 138#41 >=8 183#?? >= 183#4 >=

? 1#= 1#=

4?#= 4?#?? >=

+.! esponse 'stimation

The velocity res%onses have +een estiate' (sin& the e%licitly 'ynaics analysis in

the ADAUS #1: /E co'e for +oth healthy an' 'elainate' %lates hen ecite' at

fe loer o'es# The non-linear interaction +eteen the 'elainate' layers has also

+een si(late' '(rin& the res%onse estiation for the 'elainate' %lates# Ty%ical

velocity a%lit('e s%ectra hen ecite' at Mo'e 3 an' 8 are shon in /i&(re 8# "t has

+een o+serve' that the o'es other than the ecite' o'e are also %resent in the

s%ectra for +oth the healthy an' 'elainate' %lates, %ro+a+ly '(e to anisotro%ic

aterial %ro%erties of the co%osite aterial# "n a''ition, the %roinent hi&her

haronics of the ecitin& fre.(ency has also +een o+serve' as e%ecte' '(e to the

nonlinear interaction +eteen the 'elainate' layers for the 'elainate' %late

co%are' to the healthy %late# The ecitin& fre.(ency 61F7 an' its hi&her haronics

64F, 3F, G7 are arke' as H-I in /i&(re 8#

x

y


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4:: 8:: 9:: 60S>7# The co%onent 1F hich is the a%lit('e

of the ecitin& o'e has not +een incl('e' in the e.(ation 617 +eca(se the o%eration

'eflection sha%e 6B*S7 at 1F &enerally re%resents the o'e sha%e of the ecitin&


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o'e# >oever, the a%lit('e of thehi&her haronics 'efinitely relate' to the si=e

an' location of the 'elaination# /inally the contri+(tion fro fe loer o'es has

+een 'efine' as JC((lative 0S> 6C0S>7 at each eas(re' location hich has

+een co%(te' as

==

q

iijj NSHCNSH 1 (2)

here q is the n(+er of o'es (se' for this co%(tation# >ere the first ? o'es

have +een (se'# The %lots of the C0S> of the %late ith an' itho(t 'elaination are

shon in /i&(re ? hich %rovi'es ecellent in'ication for the location of the

'elaination#

:

4::

8::

:

4::

8::

:

:#4

:#8

:#9

:#ealthy Plate *elainate' Plate

1 ?= ?;#8 >=

4 94#


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/i&(re ; Meas(reent locations 64? %oints in ? ? e.(i'istant &ri's7 on the %late

i+ration e%erients have also +een con'(cte' on the healthy an' 'elainate'

co%osite %lates shon in /i&(re # Co%osite %lates ere ecite' thro(&h the

shaker at the first < o'es# The stea'y state acceleration res%onses ere then

collecte' fro 4? locations on the %lates (sin& the n(+er of acceleroeters in

a+sence of the laser vi+roeter# The 'ata ere collecte' to the co%(ter at the

sa%lin& fre.(ency of 4: k>= for the f(rther analysis# The acceleration si&nals ere

then analy=e' to co%(te the velocity a%lit('e s%ectra for +oth the 4 cases# /e

ty%ical acceleration s%ectra for the healthy %late an' the 'elainate' %late are shonin /i&(re < hen ecite' at o'e at locations 9 an' 4: 6arke' in /i&(re ;7# The

H1FI in the s%ectra in'icates the ecitin& fre.(ency an' the co%onents 4F, 3F, G

re%resent the hi&her haronics of the ecitin& fre.(ency in the s%ectra# Bnce a&ain, it

has +een o+serve' fro the s%ectra that '(e to anisotro%ic nat(re of the co%osite

%late, the o'es other than the ecitin& o'e also contri+(te to the overall res%onse#

"n a''ition to this effect, the nonlinear interactions +eteen the 'elainate' layers in

the %late ith 'elaination also intro'(ce the hi&her haronics of the ecitin&

fre.(ency# Altho(&h the %resence of s(ch hi&her haronics has also +een o+serve' in

the healthy co%osite %late, %ro+a+ly a&ain '(e to anisotro%ic %ro%erty of the

co%osite aterial, +(t the effect as not %roinent co%are' to the %late ith

'elaination# The %lots of the C0S> of the %late ith an' itho(t 'elaination for

the e%eriental cases are also shon in /i&(re 9 hich, once a&ain, %rovi'es

ecellent in'ication for the location of the 'elaination# >ence the e%eriental

o+servations are consistent ith the /E si(late' res(lts#

697

6197

67

637617

6437

6117

61;7

61?7

6417 64?7


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4:: 8:: 9::


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interaction between the delaminated layers when excited at a few lower modes produced the

prominent higher harmonics components of the exciting frequency. Then the normalised

contribution of higher harmonic components at each mode has been defined as the

Normalised Summation of Harmonics (NSH) and then its cumulative for a few lower

modes as CNSH. The delamination location has clearly been identified by the proposed

CNSH method for the simulated examples. The method has then further been validated by the

experiments conducted on the composite plates same as used in the FE simulations with and

without delamination. Hence the proposed CNSH can be deemed as a good indicator for the

delamination detection. Since the development of method uses the velocity responses at just

few lower modes so it is practically feasible for real structure using the conventional shaker

and the laser vibrometer for this purpose.

References

15 *ia= al'es S# >#, So(tis C# *elaination 'etection in co%osite lainates fro

variations of their o'al characteristics# )o(rnal of So(n' an' i+ration 1999N 44#, Ki K# Location of 'elaination in lainate'

co%osite %lates +y %(lse' laser holo&ra%hy# B%tics an' Lasers in En&ineerin& 4::9N

8; 6?7! ?


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185 Ar A# 0#, El-*akhakhni @# @# 0on-'estr(ctive eval(ation of lainate' co%osite

%lates (sin& 'ielectroetry sensors# Sart Materials an' Str(ct(res 4::9N 1

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