A novel microbond bundle pull out technique to evaluate the interfacial properties of fibre...

05/03/2305/03/23 INCCOM-VSSC 13, NOV- 14 and 15, INCCOM-VSSC 13, NOV- 14 and 15, Trivandrum City.Trivandrum City.

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Prof. K. PadmanabhanProf. K. Padmanabhan

Centre for Excellence in NanocompositesCentre for Excellence in NanocompositesSchool of Mechanical and Building SciencesSchool of Mechanical and Building Sciences

VIT-University, VelloreVIT-University, VelloreEmail: [email protected]: [email protected]

A Novel Microbond Bundle Pullout A Novel Microbond Bundle Pullout Technique To Evaluate The Technique To Evaluate The

Interfacial Properties Of Fibre Interfacial Properties Of Fibre Reinforced Plastic CompositesReinforced Plastic Composites


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Eastern Bottom up andEastern Bottom up and

Western Top down Philosophy !


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ContentsContents

General Design Considerations for CompositesGeneral Design Considerations for Composites The Interface Tests in CompositesThe Interface Tests in Composites Microbond Tests-Single and Multiple Microbond Tests-Single and Multiple Concept, Conduct and Evaluation of Multiple Concept, Conduct and Evaluation of Multiple

Fibre Microbond Tests Fibre Microbond Tests Fractography and FeedbackFractography and Feedback Comparison with Existing MethodsComparison with Existing Methods Conclusions and SummaryConclusions and Summary


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Information is where Information is where design begins !design begins !

Design is defined as the complete information required to produce a product or render service - Anonymous


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General Design RequirementsGeneral Design Requirements Tensile, Compressive, Shear , Flexure and CreepTensile, Compressive, Shear , Flexure and Creep Load Control, Position Control and Strain Control.Load Control, Position Control and Strain Control. Ductility and Plastic StrainDuctility and Plastic Strain Buckling, Collapsibility and CrushingBuckling, Collapsibility and Crushing Modularity and FlexibilityModularity and Flexibility Crumple Zones and Crashworthiness Crumple Zones and Crashworthiness Static and Dynamic Fracture EnergyStatic and Dynamic Fracture Energy Impact Strength and ToughnessImpact Strength and Toughness Noise Vibrations and HarshnessNoise Vibrations and Harshness Fatigue , Hot Wet Fatigue, Acoustic Fatigue, Fatigue Fatigue , Hot Wet Fatigue, Acoustic Fatigue, Fatigue

after DBTafter DBT Statics and Dynamics of Structures and AssembliesStatics and Dynamics of Structures and Assemblies Failure Mode Interactions, Multiple Causes of FailureFailure Mode Interactions, Multiple Causes of Failure Multi FunctionalityMulti Functionality


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Interface TestsInterface Tests Single fibre pullout testSingle fibre pullout test Single fibre push out test, brittle materialsSingle fibre push out test, brittle materials Micro bond single fibre pullout testMicro bond single fibre pullout test Fibre Fragmentation testFibre Fragmentation test Multiple fibre pullout test and Micro bond Multiple fibre pullout test and Micro bond

multiple fibre pullout test, Statistically multiple fibre pullout test, Statistically averaged results, More precise, Less averaged results, More precise, Less difficult, Mesomechanical in nature. difficult, Mesomechanical in nature.

Interlaminar shear strength test, ILSS.Interlaminar shear strength test, ILSS.


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The Fibre-Resin Micro The Fibre-Resin Micro bondbond

A drop of the cured resin on the fibre surface showing adhesion

Fibre pullout test through a micro vise design fixture

Ref: Bernad Miller, Umesh Gaur and Douglas E. Hirt, Composites Sci. Tech., 42, pp 207-219, (1991). A classic !


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Micro bond Bundle Pull-out Micro bond Bundle Pull-out TestTest

Carbon Fibre/ Epoxy Drop


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Multiple Fibre PulloutMultiple Fibre Pullout

Ref: K. Padmanabhan , Toyobo Confidentiality Report, 2002.

Micro bond Matrix slab

Ref: C. Y. Yue and K. Padmanabhan , Composites B, 30(1999) p205. A Classic !


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Present Advantages and Present Advantages and LimitationsLimitations

It is easy to formulate and evaluate compared to any known It is easy to formulate and evaluate compared to any known interfacial test method.interfacial test method.

It requires no tooling or shaping. It is less cumbersome to perform It requires no tooling or shaping. It is less cumbersome to perform and evaluate than the single fibre microbond test or the bundle and evaluate than the single fibre microbond test or the bundle pullout test .pullout test .

It has more physical relevance as it is mesomechancial in nature, It has more physical relevance as it is mesomechancial in nature, well averaged in results due to a fibre bundle and more precise well averaged in results due to a fibre bundle and more precise than the microbond single fibre pullout test .than the microbond single fibre pullout test .

It addresses the issue of volume fraction similar to the bundle It addresses the issue of volume fraction similar to the bundle pullout test which the single fibre pullout tests cannot give. pullout test which the single fibre pullout tests cannot give.

It is limited only by a consistent drop size and wetting angle and It is limited only by a consistent drop size and wetting angle and may not be applicable to thicker fibre bundles that are used in high may not be applicable to thicker fibre bundles that are used in high GSM ( grams per square metre ) fabric materials.GSM ( grams per square metre ) fabric materials.

Pressure is never considered in this test but most of the laminates Pressure is never considered in this test but most of the laminates are fabricated with about 1-20 bars of pressure .are fabricated with about 1-20 bars of pressure .

The resin slab technique described elsewhere can use pressurized The resin slab technique described elsewhere can use pressurized conditions and the influence of external pressure on the interfacial conditions and the influence of external pressure on the interfacial shear properties of laminated composites can be evaluated.So, the shear properties of laminated composites can be evaluated.So, the estimates of the present technique are conservative as the positive estimates of the present technique are conservative as the positive influence of compacting pressure on the interfacial properties , is influence of compacting pressure on the interfacial properties , is never considered. never considered.


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Modelling and AnalysisModelling and Analysis Carbon Fibre /epoxy Matrix Carbon Fibre /epoxy Matrix

Microbond Embedded Composite Microbond Embedded Composite SystemSystem Cylindrical Assemblage

Matrix Microbond

Pull Out Through a Micro vise

• Micromechanics

le


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Non-linear Quasistatic Non-linear Quasistatic AnalysisAnalysis

Surface to surface Surface to surface contactcontact

CA is anisotropic and CA is anisotropic and matrix is isotropicmatrix is isotropic

Only failure and post Only failure and post failure conditions were failure conditions were considered due to considered due to relevance and precision relevance and precision

Model has dihedral Model has dihedral symmetrysymmetry

Solid 8 noded brick 185 element Hex swept volumes


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Contact Angle and Embedded Contact Angle and Embedded Length of ResinLength of Resin

Fig . Schematic of the microbonds of resin droplets on the fibre bundle showing the angles of the cured droplet

θ

θ

θθ


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The EDM Drilled MicroviseThe EDM Drilled Microvise

Figs. Optical micrographs of EDM drilled microvises

with approximate diameters of 0.5 and 1mm .


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TABLE I

Features Of The Test Specimens And Methods

Type of fibre: Carbon fibre industrial grade .Tensile strength= 2.36 GPa and modulus Ef= 120 GPaNo: of filaments in a bundle = 600Resin : High Perf. epoxy adhesiveElastic modulus of cured resin, Em = 2.2 GPaVf in the bundle section = 0.14Ave. bundle Ф in composite = 0.428 mmRadius of bundle, r = 0.214 mmMicrovise Ф = 465 +/- 5 μm and 1mmAverage diameter and length of the resin drop, variable


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Pull Out Force Pull Out Force vs.vs. DisplacementDisplacement

Displacement

Fig . A schematic pull out force vs displacement plot for a multiple fibre microbond pull out test.


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Microbond Bundle Pullout TestSpecimen

ID (mm)

Drop Length (l)

mm

Contact

Angle(θ, deg )

Maximum Force for Fibre Pull Out (Newtons)

1234.5.6.

2.254.423.172.972.9

2.84

24.2512.530.520.520.25

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22.9764.8575.6581.2559.8532.52

Average 3.09 mm 21.7 degrees 56.18 NThe evaluated intrinsic bond strength, τ, = 13.52 MPa at Vf = 0.14

The evaluated interfacial shear stress at failure, IFSS = 56.23 MPa.


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Interfacial ParametersInterfacial Parameters Intrinsic bond strength, Intrinsic bond strength, ττ Interfacial shear strength, Interfacial shear strength, ττss

Interfacial frictional stress, τInterfacial frictional stress, τff Fibre/matrix coefficient of friction, Fibre/matrix coefficient of friction,

µµ Matrix shrinkage pressure, PMatrix shrinkage pressure, Po= o= ττf/ f/ µµ


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Interfacial Property Interfacial Property EvaluationsEvaluations τ = F/ πФ l ---------------------- (1)

where F is the peak debonding force in newtons minus the initial frictional force, if any. In the present case the microvise was

optimally designed not to produce any frictional trace with the fibres or the

adhering resin. Ф is the average diameter of the fibre bundle in mm and l is the embedded

length of the resin droplet in the fibre bundle in mm. The interfacial intrinsic bond

strength is given by the peak debonding force divided by the available outer

interfacial area.


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Interfacial EvaluationsInterfacial Evaluations A drop profile is illustrated in Fig. The wetting contact angle A drop profile is illustrated in Fig. The wetting contact angle

produces a force that compresses the resin against the fibre end produces a force that compresses the resin against the fibre end acting against the shearing process. This force , Fc, should be equal acting against the shearing process. This force , Fc, should be equal to F cot θ, F being the simultaneous direct force that produces the to F cot θ, F being the simultaneous direct force that produces the compressive component. This can be debonding /adhesive, tack or compressive component. This can be debonding /adhesive, tack or frictional at any tentative location in the load deflection plot that frictional at any tentative location in the load deflection plot that has be understood with care and the component should not be has be understood with care and the component should not be considered as due to only the maximum force . It manifests on considered as due to only the maximum force . It manifests on frictional onset as a second component .Thus we can writefrictional onset as a second component .Thus we can write

F = Fad + μFc -------------------------------------- (2)F = Fad + μFc -------------------------------------- (2)

Where , Where ,

Fad = Fmax = τA . ---------------------------------- (3)Fad = Fmax = τA . ---------------------------------- (3) A being the considered interfacial cylindrical area. In this case the A being the considered interfacial cylindrical area. In this case the

maximum force is also the force required for debonding. However, maximum force is also the force required for debonding. However, the peak pullout force can occur after debonding due to build up of the peak pullout force can occur after debonding due to build up of frictional stress which can again be addressed by the equation 2. frictional stress which can again be addressed by the equation 2.


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Interfacial EvaluationsInterfacial Evaluations So, So,

F = τA + μFF = τA + μFff cot θ ----------------------------------- (4) cot θ ----------------------------------- (4)

Here, FHere, Ff f , is a variable force down the load deflection plot , is a variable force down the load deflection plot unlike the peak debonding force that is singular, θ is the angle unlike the peak debonding force that is singular, θ is the angle of wetting and contact of the fibre bundle with the resin of wetting and contact of the fibre bundle with the resin droplet and μ is the static coefficient of friction as the pull out droplet and μ is the static coefficient of friction as the pull out occurs at a rate of 1-5 mm/min. It is evident from the load occurs at a rate of 1-5 mm/min. It is evident from the load deflection plot ( see Figure) that the value of the coefficient of deflection plot ( see Figure) that the value of the coefficient of friction is likely to change from the onset of frictional sliding friction is likely to change from the onset of frictional sliding to a steady value, if the frictional sliding persists. The various to a steady value, if the frictional sliding persists. The various stages of the failure process are already discussed in the stages of the failure process are already discussed in the schematic sketch shown in Fig. The interfacial shear stress schematic sketch shown in Fig. The interfacial shear stress (IFSS) is generated by dividing the equation (4) with A that (IFSS) is generated by dividing the equation (4) with A that also gives us the frictional stress values. Hence,also gives us the frictional stress values. Hence,

F/A = IFSS= τ+ μτF/A = IFSS= τ+ μτf f cot θ -------------------------------- (5) cot θ -------------------------------- (5)


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Fig . Drop length vs. Pull out force


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Fig . IFSS vs. Volume fraction


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FractographyFractography

Fig. The fibre bundle after the shear pull out of the bond. b) SEM picture of the resin microbond droplet sheared out of the fibre bundle. Notice that the drop is still intact in this case.


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FractographyFractography

Fig. : SEM fractograph of the microbond sheared through the fibre bundle. Notice the micro vise mark on the resin droplet due to compressive stresses near the exit. b) A completely sheared out intact drop from the bundle of fibres due to pull out.


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Conclusions1. The interfacial properties of the Carbon fibre /epoxy

composite, like the interfacial frictional stress, τf , the static coefficient of friction, μ, the instantaneous interfacial shear stress, the intrinsic bond strength ,τ, and the maximum interfacial shear strength, τi, were predicted and evaluated with the aid of micromechanical theories and the newly developed microbond bundle pullout technique. 2. The methods involved provide us with the interfacial

properties evaluated that are consistent within the experimental allowables. The average interfacial shear strength is 56.23 MPa from the bundle microbond pullout test performed at a Vf of 0.14. Higher volume fraction predictions are also made as practical impossibilities of achieving higher volume fractions of fibre bundles exist in the microbond tests due to the lack of pressure in forming the resin drops.


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ConclusionsConclusions 3. An important finding of this investigation is that the

mesomechanical evaluation of the interfacial properties is more reliable than the micromechanical predictions or their single fibre experimental evaluations due to their comparable values with the laminate level properties, raising new hopes on the precision (but not accuracy) of the strength based small specimen testing approaches.

4. There is a mesomechanical domain which appears to be different from the micro or the macromechanical domain. This domain is significant as most of the macromechanical properties depend on mesomechanical fracture features like craze, crack tip plasticity, fibre bundle debonding from matrix and damage tolerance, to mention a few.

5. The fractographic investigations substantiate the results obtained thereby throwing more light on the associated fracture mechanisms and the tools to be adopted to improve the techniques after understanding the fracture and failure modes .


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AcknowledgementsAcknowledgements

The AR and DB, New Delhi, are The AR and DB, New Delhi, are thanked for the funded project thanked for the funded project bearing number 1650/2012. The bearing number 1650/2012. The author thanks the CAMPT-VIT, author thanks the CAMPT-VIT, University ,Vellore, a FIST-DST facility University ,Vellore, a FIST-DST facility for the Instron 8801 testing of the for the Instron 8801 testing of the carbon/epoxy specimens. He also carbon/epoxy specimens. He also thanks M. Ramya for the assistance.thanks M. Ramya for the assistance.


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ReferencesReferences1.Akio Shindo, R Fuji and M. Sengoku and Japanese Bureau

of Industrial Technics, Japanese Patent 4405/1962 ( 13.6.62) .

2. J.D.H. Hughes, The carbon fibre/epoxy interface- A review, Composites Science and Technology,Volume 41, Issue 1, Pages 13–45, 1991 .

3. K. Padmanabhan, Interfacial properties of Zylon AS/epoxy composites, Toyobo Confidentiality Agreement Report, ( Toyobo Co. Ltd, Japan), May, 2002.

4. K. Padmanabhan and CY Yue, Interfacial properties of Zylon AS/epoxy composites by the multiple fibre pull out

technique-A case study, Proc-ACUN-4, UNSW, Sydney, Australia- 21-25, pp238-245, 2002,

5. Bernad Miller, Umesh Gaur and Douglas E. Hirt, Composites Sci. Tech., 42, pp 207-219, (1991).

6. J.K. Kim and YW Mai, Engineered Interfaces in Fibre reinforced Composites, Elsevier, Amsterdam , 1998.

7. Ever J. Barbero, Chapter 4, Micromechancics, in Introduction to Composite Materials Design, CADEC, Taylor and Francis, PA, (1999).

http://www.sciencedirect.com/science/article/pii/026635389190050Y

http://www.sciencedirect.com/science/journal/02663538

http://www.sciencedirect.com/science/journal/02663538

http://www.sciencedirect.com/science/journal/02663538/41/1

http://www.sciencedirect.com/science/journal/02663538/41/1


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ReferencesReferences8. C.Y. Yue and Padmanabhan. K, Interfacial Studies on

Surface Modified Kevlar Fibre/Epoxy Matrix Composites, Composites:B, Vol : 30, pp 205-217, 1999.

9. K. Padmanabhan, The Singapore- MIT Alliance Report , Macrostructural property evaluation of fibre/polymer composites from the micromechanical behaviour through the mesomechanical route-Part , Innovation in Manufacturing Systems and Technology, NTU, Singapore, November 2003,

10. M.R. Piggott, Mesostructures and mesomechanics in fibre composites, Composites Science and Technology, Vol:5, Issue 2, pp 121-252, (1995).

Thank you !


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Hygrothermal BehaviourHygrothermal Behaviour Fibre reinforced plastics are known for Fibre reinforced plastics are known for

environmental attacks that reduce their environmental attacks that reduce their function.function.

Mechanical properties degrade over time !Mechanical properties degrade over time ! Moisture plays havoc at elevated Moisture plays havoc at elevated

temperatures, in the presence of voids, temperatures, in the presence of voids, defects and in low Tdefects and in low Tgg plastics . plastics .

Diffusion and osmotic pressure are the driving Diffusion and osmotic pressure are the driving mechanisms for hygrothermal attackmechanisms for hygrothermal attack

Evaluation methods and surface preservation Evaluation methods and surface preservation Important in marine, biomedical, aeronautical, Important in marine, biomedical, aeronautical,

electronic and automobile applications electronic and automobile applications


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Multi Scale Composites for Multi Scale Composites for DentistryDentistry

Bis GMA, UDMA, Methacrylic Esters Bis GMA, UDMA, Methacrylic Esters contain glassy particles that are mostly contain glassy particles that are mostly less than 1 micron in sizeless than 1 micron in size

Esters and acrylates/ceramic filler Esters and acrylates/ceramic filler (barium alumina silica glass, glassy (barium alumina silica glass, glassy microfillers, 0.1 to 10 microns size) microfillers, 0.1 to 10 microns size) restorative composites.restorative composites.

Multi scale composites are also useful Multi scale composites are also useful as luting cements, crown and bridge as luting cements, crown and bridge materials and cements and veneer materials and cements and veneer materialsmaterials..


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Composites in Composites in ProsthodonticsProsthodontics

Tooth is a functionally gradedcomposite material with enameland dentin. In the third maxillary molar the occlusal stress can be 2-3 MPa.

The masticatory heavy chewing stress will be around 193 MPa.A composite restorative must with stand this with an FOS and with constant hygrothermal attack.


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Composites in Composites in Microelectronic PackagingMicroelectronic Packaging

The BOM includes Copper lead frame,Gold wires for bonding, Silver –epoxy for die attach, Silicon die and Epoxy mould composite with Phenolics, Fusedsilica powder and Carbon black powderas the encapsulant materials.


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ASTM STP D 5229 M ASTM STP D 5229 M RuleRule

The MOT( Maximum Operating The MOT( Maximum Operating Temperature) of the material, Temperature) of the material, device/component should be at least 25 device/component should be at least 25 º º Celsius lower than the lowest Tg Celsius lower than the lowest Tg (normally wet) of the material attained (normally wet) of the material attained after hygrothermal equillibration. All the after hygrothermal equillibration. All the polymeric materials and their composites polymeric materials and their composites must satisfy this rule in order to qualify must satisfy this rule in order to qualify for certification for reliability and for certification for reliability and durability.durability.


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That one coming being,That one coming being,Was covered with void,Was covered with void,That arose through the That arose through the

power of heatpower of heat-The Rig Veda ( The Existence-10.129.03)-The Rig Veda ( The Existence-10.129.03)

A novel microbond bundle pull out technique to evaluate the interfacial properties of fibre...

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