ellipticalmethodfordamageidentificationincarbonfibre...

Research ArticleElliptical Method for Damage Identification in Carbon FibreReinforced Polymer Laminates

Daerefa-a Mitsheal Amafabia 1 Diogo Montalvatildeo 2 Opukuro David-West1

and George Haritos3

1Division of Automotive Mechanical and Mechatronics Engineering School of Engineering and TechnologyUniversity of Hertfordshire Hatfield AL10 9AB UK2Department of Design and Engineering Faculty of Science and Technology Bournemouth University Poole HouseTalbot Campus Fern Barrow Poole BH12 5BB UK3School of Engineering and the Environment Kingston University London Kingston Upon-ames Penrhyn Road KT1 2EE UK

Correspondence should be addressed to Daerefa-a Mitsheal Amafabia damafabiahertsacuk

Received 2 April 2019 Accepted 7 August 2019 Published 29 September 2019

Guest Editor Alexander Balitskii

Copyright copy 2019 Daerefa-a Mitsheal Amafabia et al is is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited

Oftentimes researchers in the area of vibration-based structural health monitoring (SHM) and damage detection focused theirattention on the global properties of structures which are modal frequencies and modal damping factors However the effect onthe local properties for SHM that is modal constants has not been extremely explored In this paper the elliptical plane modalidentification method is proposed to be used as a damage identification method itself It is observed that when the receptance isplotted in the elliptical plane the area of the ellipse formed close to the resonant frequencies (which depends on the modalconstants) can be used to detect damage namely composite carbon fibre reinforced polymer (CFRP) rectangular plates Althougha mathematical correlation has not been established yet results show that the method is sensitive to the presence of damage in thetest plates as the area of the ellipse changes with damage

1 Introduction

e ever-developing world as continuously demanded anadvancement in every field of endeavour to meet up withthe increasing desire for a better society yet does not havea damaging effect on the environment In the field ofengineering a composite carbon fibre reinforced polymer(CFRP) is one of such materials that has shaped andchallenged several industries such as marine aerospacecivil infrastructural and automotive and sports equip-ment owing to their rare mechanical properties namelystrength and stiffness to weight ratios [1ndash5] Despite theunique mechanical properties of CFRP low-impactdamages have been its shortcomings Such damages maybe introduced for instance by a hailstone bird strikedebris stones or tools drop during manufacturingmaintenance [6] Medium-to-low energy impacts (ie1ndash10ms and 11ndash30ms respectively) on the surface may

result in BVID (barely visible impact damage) ie in amark other than a small indentation that is difficult toidentify through visual inspection However the impactmay have resulted in damage that propagates under dif-ferent mechanisms through the thickness of the laminatedown to the opposite side which is usually hidden iscould compromise the integrity of the structure reducethe remaining useful life (RUL) [7] and raise safety issuesHence it is pertinent to implement systems that canpromptly identify and locate damage in composites inorder to avert an unexpected breakdown of structures

Several nondestructive techniques (NDTs) such asacoustic emission ultrasound visual inspection X-ray oreddy currents among others [8] have been developed overthe years in an attempt to get a more efficient simple andeconomical solution for monitoring and detection ofdamage in composite structures However no single tech-nique has proven appropriate for all circumstances Each

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 5237129 8 pageshttpsdoiorg10115520195237129

technique has its uniqueness effectiveness and range ofapplications It would be beneficial to develop a method thatcould detect damage in a structure based on its globalproperties through vibration testing In that regard re-searchers have engaged in continuous studies in the area ofthe analysis of the vibration characteristics of structures toidentify damage without prior knowledge of the location ofthe damage

e method is hinged upon knowing the state of thehealthy characteristics of the structure and using it as abaseline to compare with the vibration characteristics of thestructure at a planned period or at its damaged state ecomparison would highlight any noticeable deviation in thecase of the presence of damage and might even reveal thedamage location and its severity

An extensive review on SHM and techniques fordamage detection has been presented in [9ndash11] Montalvatildeoet al [12] presented a review of vibration-based SHM withspecial emphasis on composite materials Among otherdamage identification methods modal analysis is themostly applied technique [13] is method utilises thedeviation in the modal parameters (modal frequenciesmodal damping and mode shape) of a structure edynamic behaviour of the structure is analysed based on themodal parameters extracted from the raw data collectede modal properties can be used to monitor vibration anddamages in a CFRP

It is difficult to analyse the interactions between all thefeatures of mechanical systems However the dynamicproperties of the mechanical system can be represented if thebasic properties are assumed to be a single-degree-of-free-dom (SDOF) system and considered separately [14] edynamic characteristics of structures can be described withspatial modal or frequency response model as stated byMaia and Silva [14] It is interesting to note that these modelscan be linked with each other [14 15] e spatial distri-bution of mass stiffness and damping properties are il-lustrated in terms of matrixes of mass [M] stiffness [K] anddamping [D] (for the hysterically dampedmodel) or [C] (forthe viscously damped model) [14 15]

Over the years researchers have always been focusing onthe global properties of structures for SHM with little in-terest in the local propertiesmdashthe modal constants iswork explores the plausibility of damage identification withthe modal constants is study focuses on understandingthe possible relationships between the deviation in the ellipsearea and damage e modal constants of the CFRP materialdetermine the area and shape of the ellipse

2 Materials and Methods

21 Materials Preparation In this investigation laminateswith dimensions as shown in Table 1 were manufactured andused to conduct the experimental modal analysis ecomposite consists of plain weave carbon fibres as the re-inforcement and epoxy as the matrix

It is a unidirectional (UD) prepreg FIBREDUX 6268-HTA (12K) carbonepoxy material HexPlyreg 6268 providesgood adhesion to honeycomb core and suitable for aircraft

structures All the test samples were manufactured usingthe hand layup and a bagging film (Nylon 66) that canwithstand high temperatures and pressures was usedduring the curing process e bagging process can be seenin Figure 1

To avoid sticking of the prepreg laminates to the alu-minium plate (forming tool) the prepreg laminates weresandwiched between two release films e vacuum bag wassealed with an inner yellow sealant tape the pressure gaugeand vacuum pipes were connected to the vacuum baggingthrough valves For the autoclave curing cycle start-up heatwas 20degC and heat up rate was 1degCmin until it reached121degC e laminates were cured at 106 kPa for 2 hours andthen naturally cooled

22 VibrationTesting e composite plates were suspendedvertically under a free-free simulated configuration with 2nylon strings as shown in Figure 2 A force transducer isattached at the corner of the specimen and connected to anelectromagnetic shaker through a pushrod (stinger)

e response of the samples due to the generation of amultisine [16] excitation signal for a frequency range of 0 to800Hz with a frequency resolution of 025Hz was measurede responses were measured at a specific location usingthree lightweight PCB teardrop accelerometers type352A24 that weighs 08 g each at the corner of the specimento acquire the Frequency Response Functions (FRFs) eexperiments were performed for both healthy and damage-induced samples of the same configuration

A number of experiments were conducted by assem-blingdisassembling and results were generally consistentalthough a statistical analysis was not formally conducted

23 Static Testing In order to introduce damage in thespecimen static testing (ST) was performed using a 25 kNTinius-Olsen universal testing machine is technique hasbeen followed by other authors in the absence of impacttesting machines such as [3 17] e experimental setup forthe ST is illustrated in Figure 3

An indenter made from carbon steel with a hemispherictip of 245mm in diameter was used e setup consists of a350mm2 rectangular fixture base plate with a cutout of250times150mm A total of six vertical toggle clamps hold thespecimen to the fixture base three spaced equally on eachside of the length of the fixture base e specimen isclamped to the base plate to avoid movement duringloading e STwas conducted at a loading speed of 10mmmin with the application of varying force After each roundof loading the energy dissipated on the test plates was withinthe range of 041 kJ to 18 kJ e study considered fivedifferent stacking sequences and they are labelled in al-phanumeric style that is plates A1 A2 B1 B2 C1 C2 D1and D2 as shown from Figures 4ndash6

Since the area and the shape of the ellipse depend on thereal and imaginary modal constants a possible deviation inthe area of the ellipse due to damage would suggest acorrelation e area of the ellipse from the test specimenswas identified using the elliptical method [18ndash20]e ellipse

2 Advances in Materials Science and Engineering

modal identification software can also be used to determinethe global properties of a structure that is the modal fre-quency and modal damping

3 Results and Discussion

e theoretical development of the elliptical method and itsproperties are presented in [18] e elliptical method de-pends on the modal constantsmdashthe real and imaginary partsof the modal constant e real part of the modal constantcan be determined by using the following equation

AR H2

ωωrη2rω4

r minus A2I

1113969 (1)

while the imaginary part of the modal constant is de-termined by using the following equation

AI

H2ωωr

η2rω4r

tan sinminus 1 θω≪≫ωr1113872 11138731113960 11139611113960 1113961

minus 2+ 1

11139741113972

(2)

where AR is the real part of the modal constant AI is theimaginary part of the constant H is the amplitude of thereceptance ω is the natural frequency ωr is the angularfrequency for mode r ηr is the hysterical damping factor formode r and θ is the phase angle between the force and thedisplacement response From the results it was observedthat the presence of damage in the CFRP reduces the area ofthe ellipse Some representative elliptical shapes are shownin Figures 7 and 8

e amplitudes of the healthy and damaged ellipse forplate A1 shown in Figure 7 are multiplied by 5 and 10000scale multipliers respectively Despite a large amount ofmultiplier the area of the ellipse for the damaged plate isrelatively smaller than that for the healthy plate is

To vacuum pump

Aluminium plate

Release film

Prepreg laminate

Vacuum bag

Two layers of breather

ValveTo pressure gauge

Sealant

Release film

Figure 1 Vacuum bagging process

Suspensionstring

Shaker

Stinger

DAQcard

Compositeplate

Poweramplifier

Figure 2 Experimental setup for vibration testing [6]

Table 1 Types of specimens and designations

Quantity Designation Material Stackingsequence

Laminatetype

Dimensions(mm)

Aspect ratio(ab)

2 Plate A1ndashA3 FibreDUX 6268C-HTA 12K [90plusmn450]s

Quasi-isotropic 310times 240times 2 129

2 Plate B1-B2 FibreDUX 6268C-HTA 12K [900plusmn45]s


2 Plate C1ndashC3 FibreDUX 6268C-HTA 12K [900]2s Cross-ply 310times 240times 2 1292 Plate D1 FibreDUX 6268C-HTA 12K [90203]s Cross-ply 310times 240times 2 1291 Plate E1 FibreDUX 6268C-HTA 12K [90303]s Cross-ply 300times 241times 3 124

Cross-head mass

Indenter

Composite plate

Figure 3 Static testing

Advances in Materials Science and Engineering 3

Area of ellipse (damaged plate)Area of ellipse (healthy plate)

2 4 6 8 10 120Mode number

02468

101214

Are

a of e

llips

e for

heal

thy

plat

e

00001000200030004000500060007

Are

a of e

llips

e for

dam

aged

pla

te

(a)



02468

101214161820

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te

(b)



02468

10121416

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035

Are

a of e

llips

e for

dam

aged

pla

te

(c)



05

10152025303540

Are

a of e

llips

e for

heal

thy

plat

e0000050001000150002000250003000350004

Are

a of e

llips

e for

dam

aged

pla

te

(d)

Figure 4 Variation in the area of the ellipse for plates (a) A1 (b) A2 (c) A3 and (d) B1


02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0

00005

0001

00015

0002

00025

Are

a of e

llips

e for

dam

aged

pla

te

Area of ellipse (healthy plate)Area of ellipse (damaged plate)

(a)


02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0000020000400006000080001000120001400016000180002

Are

a of e

llips

e for

dam

aged

pla

te


(b)

Figure 5 Continued


05

101520253035404550

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te



(c)


0

5

10

15

20

25

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035000400045

Are

a of e

llips

e for

dam

aged

pla

te


(d)

Figure 5 Variation in the area of the ellipse for plates (a) B2 (b) C1 (c) C2 and (d) C3


Are

a of e

llips

e for

dam

aged

pla

te

0

5

10

15

20

25

30

Are

a of e

llips

e for

heal

thy

plat

e

0000100020003000400050006000700080009


(a)


010203040506070

Are

a of

elli

pse

for

heal

thy

plat

e

000E + 00500E ndash 04100E ndash 03150E ndash 03200E ndash 03250E ndash 03300E ndash 03350E ndash 03

Are

a of

elli

pse

for

dam

aged

pla

te


(b)

Figure 6 Variation in the area of the ellipse for plates (a) D1 and (b) E1

Sin theta vs amplitude

Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a

ndash100 ndash80 ndash60 ndash40 ndash20 0 20 40 60 80 100 120ndash120Amplitude H times scale multiplier

(a)

Figure 7 Continued



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)

Figure 7 Ellipse area for plate A1 (a) healthy (b) damaged

Raw dataSlope

EllipseCorrel


ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 8 Continued


suggests the area of the ellipse changes with damage andthere might be a possible correlation

Again the ellipse area for the healthy plate B1 is largerthan that for the damaged plate as shown in Figure 8 Al-though the area of the ellipse for the damaged plate appearsto be larger pictorially in reality it is opposite e largerappearance was due to being multiplied by a scale multiplierof 10000 and that of the healthy ellipse being multiplied byjust 1 scale multiplier

Obviously from Figures 4ndash6 there is a variation in thearea of the ellipse after the damage was introduced in the testplates In plate A1 the area of ellipse decreased at all the 10modes considered

It is important to note that the amount of reduction inthe ellipse areas as shown from Figures 4ndash6 is within thesame range Apart from specimen C3 the reduction rateacross all the modes in other specimens is over 97 eresults indicate that the elliptical method is sensitive to thepresence of damage in the composite CFRP rectangularplate

4 Conclusion

A novel method for damage identification from FRF basedon the representation of the receptance on the ellipticalplane was presented It was shown that the area of theellipse which is related to the modal constants (local modalproperties) is sensitive to damage in a consistent mannerHence this paper offers new possibilities for other re-searchers who are concerned with damage diagnosis inlightly damped structures since the elliptical plane modalidentification method provides promising results for dam-age identification in CFRP rectangular plates Howevermore studies are still required in terms of experimental workto find what the mathematical correlation is (if any) betweendamage and the shape of the ellipse for example by taking

into account that damage in CFRPs has complex mor-phologies that may affect the plates and how the modalconstants are affected by the presence of damage

Data Availability

e Frequency Response Functions (FRFs) data used tosupport the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interest

Authorsrsquo Contributions

Daerefa-a Mitsheal Amafabia and Diogo Montalvatildeo con-ceived and designed the experiments Daerefa-a MitshealAmafabia Diogo Montalvatildeo and Opukuro David-Westconducted the experiments Daerefa-a Mitsheal Amafabiaconducted the formal analysis Opukuro David-West DiogoMontalvatildeo and George Haritos supervised the work

Acknowledgments

is research was funded by the Niger Delta DevelopmentCommission (NDDC) Nigeria (Grant number NDDCDEHSS2015PGFSRVS02530)

References

[1] S S Kessler S M Spearing M J Atalla C E S Cesnik andC Soutis ldquoDamage detection in composite materials usingfrequency response methodsrdquo Composites Part B Engineeringvol 33 no 1 pp 87ndash95 2002


Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)

Figure 8 Ellipse area for plate B1 (a) healthy (b) damaged


[2] L Ye Y Lu Z Su and G Meng ldquoFunctionalized compositestructures for new generation airframes a reviewrdquoCompositesScience and Technology vol 65 no 9 pp 1436ndash1446 2005

[3] D Montalvatildeo A M R Ribeiro and J A B Duarte-SilvaldquoExperimental assessment of a modal-based multi-parametermethod for locating damage in composite laminatesrdquo Ex-perimental Mechanics vol 51 no 9 pp 1473ndash1488 2011

[4] D Montalvatildeo D Karanatsis A M R Ribeiro J Arina andR Baxter ldquoAn experimental study on the evolution of modaldamping with damage in carbon fiber laminatesrdquo Journal ofComposite Materials vol 49 no 19 pp 2403ndash2413 2015

[5] L Huang A H Sheikh C-T Ng and M C Griffith ldquoAnefficient finite element model for buckling analysis of gridstiffened laminated composite platesrdquo Composite Structuresvol 122 pp 41ndash50 2015

[6] D M Amafabia O David-West D Montalvatildeo andG Haritos ldquoDamage detection in CFRP composite platebased on evolving modal parametersrdquo in Proceedings of theBSSM 12th International Conference on Advances in Experi-mental Mechanics University of Sheffield Sheffield UKAugust 2017

[7] S Abrate ldquoImpact on laminated composites recent ad-vancesrdquo Applied Mechanics Reviews vol 47 no 11 p 5171994

[8] N M M Maia R A B Almeida A P V Urgueira andR P C Sampaio ldquoDamage detection and quantification usingtransmissibilityrdquo Mechanical Systems and Signal Processingvol 25 no 7 pp 2475ndash2483 2011

[9] D M Amafabia D Montalvatildeo O David-West andG Haritos ldquoA review of structural health monitoring tech-niques as applied to composite structuresrdquo SDHM StructuralDurability and Health Monitoring vol 11 pp 91ndash147 2017

[10] S W Doebling C R Farrar M B Prime and D W ShevitzldquoDamage identification and health monitoring of structuraland mechanical systems from changes in their vibrationcharacteristics a literature reviewrdquo No LA--13070-MSpp 1ndash136 Los Alamos National Laboratory Los Alamos NMUSA 1996

[11] S W Doebling C R Farrar and M B Prime ldquoA summaryreview of vibration-based damage identification methodsrdquo-e Shock and Vibration Digest vol 30 no 2 pp 91ndash1051998

[12] D Montalvatildeo N MMMaia and AM R Ribeiro ldquoA reviewof vibration-based structural health monitoring with specialemphasis on composite materialsrdquo -e Shock and VibrationDigest vol 38 no 4 pp 295ndash324 2006

[13] J-J Sinou ldquoA review of damage detection and health mon-itoring of mechanical systems from changes in the mea-surement of linear and non-linear vibrationsrdquo in MechanicalVibrations Measurement Effects and Control pp 643ndash702Nova Science NewYork NY USA 2009

[14] N M M Maia and J M M Silva -eoretical and Experi-mental Modal Analysis Taunton Research Studies Press andJohn Wiley and Sons Somerset England 1997

[15] D Montalvatildeo Amodal-based contribution to damage locationin laminated composites plates PhD thesis Instituto SuperiorTecnico Universidade de Lisboa Lisbon Portugal 2010

[16] P Guillaume P Verboven and S P E Vanlanduit ldquoMul-tisine excitations-new developments and applications inmodal analysisrdquo in Proceedings of the 19th InternationalModal Analysis Conference (IMAC-XIX) vol 2 pp 1543ndash1549 Kissimmee FL USA February 2001

[17] N F Rilo L M S Ferreira and R A C P Leal ldquoLow-velocityimpact analysis of glassepoxy platesrdquo in Proceedings of the 5th

International Conference on Mechanics and Materials inDesign (M2D2006) vol 110 p 0092 Porto Portugal 2006

[18] D Montalvatildeo and D-a M Amafabia ldquoAn alternative rep-resentation of the receptance the ldquoelliptical planerdquo and itsmodal propertiesrdquo Mechanical Systems and Signal Processingvol 103 pp 236ndash249 2018

[19] D Montalvatildeo D M Amafabia and J M Silva ldquoAnd yetanother method for the identification of modal constants inexperimental modal analysisrdquo in Proceedings of the 7th In-ternational Operational Modal Analysis Conference(IOMACrsquo17) Ingolstadt Germany May 2017

[20] D Montalvatildeo M Dupac D M Amafabia O David-Westand G Haritos ldquoOn reducing uncertainty on the ellipticalplane modal identification methodrdquo MATEC Web of Con-ferences vol 211 Article ID 06001 2018


CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018


Journal of

Chemistry

Analytical ChemistryInternational Journal of


ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of



Advances in Condensed Matter Physics


International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of


High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in



ChemistryAdvances in


Advances inPhysical Chemistry


BioMed Research InternationalMaterials

Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

technique has its uniqueness effectiveness and range ofapplications It would be beneficial to develop a method thatcould detect damage in a structure based on its globalproperties through vibration testing In that regard re-searchers have engaged in continuous studies in the area ofthe analysis of the vibration characteristics of structures toidentify damage without prior knowledge of the location ofthe damage

e method is hinged upon knowing the state of thehealthy characteristics of the structure and using it as abaseline to compare with the vibration characteristics of thestructure at a planned period or at its damaged state ecomparison would highlight any noticeable deviation in thecase of the presence of damage and might even reveal thedamage location and its severity

An extensive review on SHM and techniques fordamage detection has been presented in [9ndash11] Montalvatildeoet al [12] presented a review of vibration-based SHM withspecial emphasis on composite materials Among otherdamage identification methods modal analysis is themostly applied technique [13] is method utilises thedeviation in the modal parameters (modal frequenciesmodal damping and mode shape) of a structure edynamic behaviour of the structure is analysed based on themodal parameters extracted from the raw data collectede modal properties can be used to monitor vibration anddamages in a CFRP

It is difficult to analyse the interactions between all thefeatures of mechanical systems However the dynamicproperties of the mechanical system can be represented if thebasic properties are assumed to be a single-degree-of-free-dom (SDOF) system and considered separately [14] edynamic characteristics of structures can be described withspatial modal or frequency response model as stated byMaia and Silva [14] It is interesting to note that these modelscan be linked with each other [14 15] e spatial distri-bution of mass stiffness and damping properties are il-lustrated in terms of matrixes of mass [M] stiffness [K] anddamping [D] (for the hysterically dampedmodel) or [C] (forthe viscously damped model) [14 15]

Over the years researchers have always been focusing onthe global properties of structures for SHM with little in-terest in the local propertiesmdashthe modal constants iswork explores the plausibility of damage identification withthe modal constants is study focuses on understandingthe possible relationships between the deviation in the ellipsearea and damage e modal constants of the CFRP materialdetermine the area and shape of the ellipse

2 Materials and Methods

21 Materials Preparation In this investigation laminateswith dimensions as shown in Table 1 were manufactured andused to conduct the experimental modal analysis ecomposite consists of plain weave carbon fibres as the re-inforcement and epoxy as the matrix

It is a unidirectional (UD) prepreg FIBREDUX 6268-HTA (12K) carbonepoxy material HexPlyreg 6268 providesgood adhesion to honeycomb core and suitable for aircraft

structures All the test samples were manufactured usingthe hand layup and a bagging film (Nylon 66) that canwithstand high temperatures and pressures was usedduring the curing process e bagging process can be seenin Figure 1

To avoid sticking of the prepreg laminates to the alu-minium plate (forming tool) the prepreg laminates weresandwiched between two release films e vacuum bag wassealed with an inner yellow sealant tape the pressure gaugeand vacuum pipes were connected to the vacuum baggingthrough valves For the autoclave curing cycle start-up heatwas 20degC and heat up rate was 1degCmin until it reached121degC e laminates were cured at 106 kPa for 2 hours andthen naturally cooled

22 VibrationTesting e composite plates were suspendedvertically under a free-free simulated configuration with 2nylon strings as shown in Figure 2 A force transducer isattached at the corner of the specimen and connected to anelectromagnetic shaker through a pushrod (stinger)

e response of the samples due to the generation of amultisine [16] excitation signal for a frequency range of 0 to800Hz with a frequency resolution of 025Hz was measurede responses were measured at a specific location usingthree lightweight PCB teardrop accelerometers type352A24 that weighs 08 g each at the corner of the specimento acquire the Frequency Response Functions (FRFs) eexperiments were performed for both healthy and damage-induced samples of the same configuration

A number of experiments were conducted by assem-blingdisassembling and results were generally consistentalthough a statistical analysis was not formally conducted

23 Static Testing In order to introduce damage in thespecimen static testing (ST) was performed using a 25 kNTinius-Olsen universal testing machine is technique hasbeen followed by other authors in the absence of impacttesting machines such as [3 17] e experimental setup forthe ST is illustrated in Figure 3

An indenter made from carbon steel with a hemispherictip of 245mm in diameter was used e setup consists of a350mm2 rectangular fixture base plate with a cutout of250times150mm A total of six vertical toggle clamps hold thespecimen to the fixture base three spaced equally on eachside of the length of the fixture base e specimen isclamped to the base plate to avoid movement duringloading e STwas conducted at a loading speed of 10mmmin with the application of varying force After each roundof loading the energy dissipated on the test plates was withinthe range of 041 kJ to 18 kJ e study considered fivedifferent stacking sequences and they are labelled in al-phanumeric style that is plates A1 A2 B1 B2 C1 C2 D1and D2 as shown from Figures 4ndash6

Since the area and the shape of the ellipse depend on thereal and imaginary modal constants a possible deviation inthe area of the ellipse due to damage would suggest acorrelation e area of the ellipse from the test specimenswas identified using the elliptical method [18ndash20]e ellipse





AR H2

ωωrη2rω4

r minus A2I

1113969 (1)


AI

H2ωωr

η2rω4r


minus 2+ 1

11139741113972

(2)



To vacuum pump

Aluminium plate

Release film

Prepreg laminate

Vacuum bag



Sealant

Release film


Suspensionstring

Shaker

Stinger

DAQcard

Compositeplate

Poweramplifier




Laminatetype

Dimensions(mm)

Aspect ratio(ab)






Cross-head mass

Indenter

Composite plate





02468

101214

Are

a of e

llips

e for

heal

thy

plat

e

00001000200030004000500060007

Are

a of e

llips

e for

dam

aged

pla

te

(a)



02468

101214161820

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te

(b)



02468

10121416

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035

Are

a of e

llips

e for

dam

aged

pla

te

(c)



05

10152025303540

Are

a of e

llips

e for

heal

thy

plat

e0000050001000150002000250003000350004

Are

a of e

llips

e for

dam

aged

pla

te

(d)



02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0

00005

0001

00015

0002

00025

Are

a of e

llips

e for

dam

aged

pla

te


(a)


02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0000020000400006000080001000120001400016000180002

Are

a of e

llips

e for

dam

aged

pla

te


(b)

Figure 5 Continued


05

101520253035404550

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te



(c)


0

5

10

15

20

25

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035000400045

Are

a of e

llips

e for

dam

aged

pla

te


(d)



Are

a of e

llips

e for

dam

aged

pla

te

0

5

10

15

20

25

30

Are

a of e

llips

e for

heal

thy

plat

e

0000100020003000400050006000700080009


(a)


010203040506070

Are

a of

elli

pse

for

heal

thy

plat

e


Are

a of

elli

pse

for

dam

aged

pla

te


(b)



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 7 Continued



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


Raw dataSlope

EllipseCorrel


ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 8 Continued






4 Conclusion



Data Availability






Acknowledgments


References



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







AR H2

ωωrη2rω4

r minus A2I

1113969 (1)


AI

H2ωωr

η2rω4r


minus 2+ 1

11139741113972

(2)



To vacuum pump

Aluminium plate

Release film

Prepreg laminate

Vacuum bag



Sealant

Release film


Suspensionstring

Shaker

Stinger

DAQcard

Compositeplate

Poweramplifier




Laminatetype

Dimensions(mm)

Aspect ratio(ab)






Cross-head mass

Indenter

Composite plate





02468

101214

Are

a of e

llips

e for

heal

thy

plat

e

00001000200030004000500060007

Are

a of e

llips

e for

dam

aged

pla

te

(a)



02468

101214161820

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te

(b)



02468

10121416

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035

Are

a of e

llips

e for

dam

aged

pla

te

(c)



05

10152025303540

Are

a of e

llips

e for

heal

thy

plat

e0000050001000150002000250003000350004

Are

a of e

llips

e for

dam

aged

pla

te

(d)



02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0

00005

0001

00015

0002

00025

Are

a of e

llips

e for

dam

aged

pla

te


(a)


02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0000020000400006000080001000120001400016000180002

Are

a of e

llips

e for

dam

aged

pla

te


(b)

Figure 5 Continued


05

101520253035404550

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te



(c)


0

5

10

15

20

25

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035000400045

Are

a of e

llips

e for

dam

aged

pla

te


(d)



Are

a of e

llips

e for

dam

aged

pla

te

0

5

10

15

20

25

30

Are

a of e

llips

e for

heal

thy

plat

e

0000100020003000400050006000700080009


(a)


010203040506070

Are

a of

elli

pse

for

heal

thy

plat

e


Are

a of

elli

pse

for

dam

aged

pla

te


(b)



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 7 Continued



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


Raw dataSlope

EllipseCorrel


ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 8 Continued






4 Conclusion



Data Availability






Acknowledgments


References



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






02468

101214

Are

a of e

llips

e for

heal

thy

plat

e

00001000200030004000500060007

Are

a of e

llips

e for

dam

aged

pla

te

(a)



02468

101214161820

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te

(b)



02468

10121416

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035

Are

a of e

llips

e for

dam

aged

pla

te

(c)



05

10152025303540

Are

a of e

llips

e for

heal

thy

plat

e0000050001000150002000250003000350004

Are

a of e

llips

e for

dam

aged

pla

te

(d)



02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0

00005

0001

00015

0002

00025

Are

a of e

llips

e for

dam

aged

pla

te


(a)


02468

1012141618

Are

a of e

llips

e for

heal

thy

plat

e

0000020000400006000080001000120001400016000180002

Are

a of e

llips

e for

dam

aged

pla

te


(b)

Figure 5 Continued


05

101520253035404550

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te



(c)


0

5

10

15

20

25

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035000400045

Are

a of e

llips

e for

dam

aged

pla

te


(d)



Are

a of e

llips

e for

dam

aged

pla

te

0

5

10

15

20

25

30

Are

a of e

llips

e for

heal

thy

plat

e

0000100020003000400050006000700080009


(a)


010203040506070

Are

a of

elli

pse

for

heal

thy

plat

e


Are

a of

elli

pse

for

dam

aged

pla

te


(b)



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 7 Continued



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


Raw dataSlope

EllipseCorrel


ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 8 Continued






4 Conclusion



Data Availability






Acknowledgments


References



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




05

101520253035404550

Are

a of e

llips

e for

heal

thy

plat

e

0

0001

0002

0003

0004

0005

0006

Are

a of e

llips

e for

dam

aged

pla

te



(c)


0

5

10

15

20

25

Are

a of e

llips

e for

heal

thy

plat

e

000005000100015000200025000300035000400045

Are

a of e

llips

e for

dam

aged

pla

te


(d)



Are

a of e

llips

e for

dam

aged

pla

te

0

5

10

15

20

25

30

Are

a of e

llips

e for

heal

thy

plat

e

0000100020003000400050006000700080009


(a)


010203040506070

Are

a of

elli

pse

for

heal

thy

plat

e


Are

a of

elli

pse

for

dam

aged

pla

te


(b)



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 7 Continued



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


Raw dataSlope

EllipseCorrel


ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 8 Continued






4 Conclusion



Data Availability






Acknowledgments


References



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


Raw dataSlope

EllipseCorrel


ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(a)

Figure 8 Continued






4 Conclusion



Data Availability






Acknowledgments


References



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








4 Conclusion



Data Availability






Acknowledgments


References



Raw dataSlope

EllipseCorrel

ndash1

ndash08

ndash06

ndash04

ndash02

0

02

04

06

08

1

Sin

thet

a


(b)


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls



























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




ellipticalmethodfordamageidentificationincarbonfibre...

Documents