analyzation of frp composite’s mechanical failure … · analyzation of frp composite’s...

467

Int. J. Mech. Eng. & Rob. Res. 2012 G Srinivasulu and T N Charyulu, 2012

ANALYZATION OF FRP COMPOSITE’SMECHANICAL FAILURE AND INTERPHASE

PROPERTIES THROUGH MECHANICALCHARACTERIZATION AND FEA TECHNIQUES

G Srinivasulu1* and T N Charyulu1

*Corresponding Author: G Srinivasulu,[email protected]

This paper is proposed to analyse the multi shaped reinforced elements like carbon fibre, glassfibre and highly dispersed nano sized alumina particles in the matrix of thermoset polymer’sinterphase properties. The thermoset epoxy resin was taken as the matrix materials.Fundamental tests like tensile, compressive and flexural were carried out for the differentloading condition. The similar test was simulated through the FEA technique using ANSYSand the argument was established to explain the deviation among the results. A third phasematerial was introduced to represent the inter phase region and the mechanical properties asa function of inter phase strength was reported. In our analysis the different shape and sizefiber inclusions were used, i.e., spherical, cylindrical, rectangular, cylindrical fibers withhemispherical ends. The volume fractions of fiber inclusions were varied from 0% to 40% andthe FEA analysis was carried out to understand the behavior of material at the different loadingconditions. The analysis also extended to calculate the behavior of the hybrid composite whichcontains glass fiber, carbon fiber and alumina particles in the matrix of epoxy. Detailed analysesof the enhancements of the mechanical properties due to the incorporation of the interphasematerial were studied.

Keywords: Interphase, ANSYS, Fiber, Epoxy

INTRODUCTIONRecent studies have indicated that mechanicalperformance of the short fiber-reinforcedcomposites not only depends on matrix type,fiber type, fiber volume fraction, fiber

ISSN 2278 – 0149 www.ijmerr.comVol. 1, No. 3, October 2012

© 2012 IJMERR. All Rights Reserved

Int. J. Mech. Eng. & Rob. Res. 2012

1 Nova College of Engineering and Technology, Vegavaram, Jangareddygudem, West Godavari, Andhra Pradesh, India.

orientation, etc., but fiber-matrix interface andgeometrical shape are also of paramountimportance. The strength of the compositematerial is enhanced by the incorporation offibers and nano fillers. This is mainly due to

Research Paper

468


increase of the surface areas of the nano fillermaterials and fiber-matrix interface region. Thestress is absorbed at the interface region thusproving a better material for the advancedengineering application particularly in theaerospace industries. Shiqiang et al. (1999)showed the most important physical aspectsis the geometry of reinforcing fibers, whichinfluences adhesion between fiber and matrix,stress transfer and local mechanisms of failure.In addition to chemical bonding, the fiber/matrix bond strength in shear is largelydependent on the roughness of the fibersurface and the fiber/matrix contact area. Thethree composite systems reinforced by glassfibers of different fiber cross-sectional aspectratios. As a result, there are many fibersoverlapped with each other with large contactareas where the matrix resin is too thin to playthe role for stress transfer. The large fiberscontact areas caused by fibers overlappingare weak places and can act as a path forcrack propagation, a process of cumulativedamage progression occurred duringlongitudinal tensile and flexural tests withincreased Strains-to-failure, compared to thatof the composites reinforced by theconventional round glass fibers. Xiao-Fenget al. (2007) showed the nanomechanicalproperties of CCNT reinforced epoxycomposites were of the hardness, elasticmodulus and tensile strength of the CCNT/epoxy composite increase with increasing theweight percentage of the CCNTs. Observingfrom the cleavage surface and etched surfaceof the composite, it can be easily seen thatthe CCNTs dispersed well and inter-lock tightlywith epoxy matrix, which governed theirenhancement of mechanical and thermalproperties. The macroscopic behavior of

composites depends not only on theproperties of their individual constituents butalso on the elastic-plastic interaction betweenthe erent phases and on the interfaceproperties. In other work Kies reported similarobservations that the brittleness of compositesin the transverse direction is due to a strainconcentration phenomenon in the polymermatrix. Indeed, it is well known that theembedded short borosilicate glass fibers usedin this and in related works are of course muchstiffer than the epoxy matrix. Therefore, it isunderstandable that local strain concentrationsin the thin polymer layers between theneighboring fibers may occur. De Kok et al.(1993) displayed with f inite elementcalculations that high local strains may occurin the matrix already at a low global strain levelin the bulk composite. The application of theVon mises criterion pointed out that localstrains are concentrated in thin bands near thefiber/matrix interface. The authors also showedthat a thin rubbery interface facilitates thetransfer of the plastic strain between the matrixand the fibers, hence facilitating the capabilityto increase the overall strain in the compositeto a higher level. The test specimen shallconform to the dimensions of ASTM D638-10The Type IV specimen is the preferredspecimen and shall be used for tensile test.Calculate the compressive strength by dividingthe maximum compressive load carried by thespecimen during the test by the originalminimum cross-sectional area of the specimenof ASTM D695-10. Componeschi, Hsiao,Daniel and Lee made an effort to develop asuitable compression test method for thickcomposites and investigated the effect ofspecimen thickness on the compressivestrength. It was found that the failure strength

469


decreases with increasing thickness of theunidirectional laminate, but most of the failuresoccurred near or at the specimen end wherethe load is introduced.

Johnson et al. (2012) made an effort tostudy the stress transfer behavior for analumina fiber in epoxy resin using FEA. It wasshown that the presence of a transverse cracksignificantly influenced the stress transfermechanism. It was also shown that the stresstransfer length increases with the length of thetransverse matrix crack, therefore reducing thereinforcing efficiency of the fibre. The length ofthe transverse crack also had a significantinfluuence on the magnitude of the shear stressin the matrix at the fibre/matrix interface. Thusthe matrix crack can delay or even preventshear yielding of the matrix near the interface.Yang and Chen introduced the technique forModeling and analytical methods to predicteffective longitudinal Young’s modulus ofcomposites containing misoriented short fiber.The results showed that the Young’s modulusof this kind of composites strongly dependson fiber volume fraction and the angle betweenfiber and load direction. The role of matrixvolume fraction on stress distribution alongfiber length was predicted using finite elementmethod.

OBJECTIVESThe objectives of the research study is:

• To study the influence of the reinforcingelements by neglecting the interfaceproperties of the composite material;

• To study the influence of the reinforcingelements by considering the interfaceproperties of the composite material;

• To study the influence of the geometricalshape of the fiber inclusion; and

• To study the influence of the volume fractionof the reinforcing elements.

FINITE ELEMENT ANALYSESAll simulations in this work were carried out bythe commercial finite element package ANSYS12.0. The material properties for eachconstituent have been specified directlyaccording to the supplier’s data sheet. Tensile,compressive and flexure test are performed toinvestigate the mechanical failure and influenceof interfacial properties of FRP composite.Tensile test is performed in compliance withstandard ASTM D638-10 type IV specimenCompressive test is performed using the ASTMD695-10 standard specimen, and Flexural testalso performed in compliance with standardASTM D790 specimen.

The properties of discontinuous fibercomposites mentioned in the Table 1.

Carbon Fiber[55] 242 0.33 1.81

Glass Fiber[53] 723 0.22 2.55

Alumina Fiber[56] 380 0.24 3.95

Epoxy Matrix[54] 3.35 0.35 1.2

CFRP/EpoxyInterphase 6.7 0.34 ~ 1.2

CFRP/EpoxyInterphase 6.7 0.28 ~ 1.2

Alumina/EpoxyInterphase 6.7 0.3 ~ 1.2

Table 1: Properties of Discontinuous FiberComposites

MaterialElastic

Modulus(GPa)

Poisson’sRatio

Density(gm/cm)

470


RESULTS AND DISCUSSIONTensile Test

When uniaxial tensile force is applied to a solid,the solid stretches in the direction of the appliedforce (axially), but it also contracts in bothdimensions are perpendicular to the appliedforce. The value of the major principal stress ofthe CFRP gradually decreases with the increaseof the addition of the fiber content for thecylindrical fiber, rectangular fiber and thecylindrical fibers with the hemispherical ends. Themodulus increases in proportion to the filler theincorporation of a third material as interphase.This enhancement of properties may be due tothe proper bonding property of the fiber andmatrix. After 20% volume fraction of the fiberinclusion in Figure 1, the graph becomes almostlinear and parallel to the horizontal axis.

The experimental result shows at 2 to 3%vol of CF has higher strength. And the CFincrease the strength is decreasing up to 15%of CF content. From the Figure 1 the

experimental values are near to the simulatedvalues with Considered Interphase. It showsInterphase playes a major role to load transferfrom fiber to matrix. As per ASTM D standardSpecimen the tensile test simulated. The mainaim of this work to ensure that the strength ofthe composite mainly depend on Strength ofthe Interphase. The below Figure 2 shows thestrength was increased by consideringInterphase then the Neglected Interphase. Thisis mainly because of the load was effectivelytransferred matrix to the fiber.

Tensile Modulus of Short CFRPComposite

The Tensile modulus of the pure epoxy as wellas of the composites containing the shortCarbon Fiber (CF) and short Glass Fiber (GF)was analyzed. The modulus of pure epoxy is3.38 GPa. The composite with 1.09% vol ofCF shows a 3.6 GPa and improvement intensile modulus is 4.47 GPa improved due tothe incorporation of interphase properties

Figure 1: Strength of the Composite Material Under Uni-Axial Tensile Test as a Functionof the CFRP Volume Fraction

471


Figure 3: Tensile Modulus of Short CFRP Composite

Figure 2: Tensile Stress of 2.18% GF with 1% Alumina, Where Stress is Neglected,Interphase and Considered Interphase

472


using the tensile modulus formula. The abovemodulus has been calculated and plotted(Figures 3 and 4). The composite fiber radiusof 0.25 mm with 1.09% to 6.54% vol of CFshows a 6.47% to 12.67% and GF fiber showsa 9% to 14.53% improvement in tensile

modulus compare to neat epoxy. Tensilemodulus of CF is 24.48%, 4.04%, 22.74%,1.44% and 15.96% has improvement due tothe incorporation of interphase properties.

The Tensile modulus of the pure epoxy aswell as of the composites containing the short

Figure 4: Tensile Modulus of Short GFRP Composite

Figure 5: The Major Principal Strength of the Composite Material Under Uni-AxialCompression as a Function of the CFRP Volume Fraction

473


carbon fibers like CF and GF was analyzedwith 97 to 291 no. of FRP with incorporationof 1% Alumina particle keeping constant.Tensile modulus of 1% vol of CF with 1% vol ofGF has calculated as 21.38% improvedcompare to Neat epoxy. Figure 5 shows theimprovement of tensile modulus with respecto the fiber content. Further improvement in thetensile modulus achieved due to theincorporation of interphase properties. Tensilemodulus of 1% vol of CF with 1% vol of GFand 1% Alumina particle has calculated as4.11GPa it means 21.38% improved compareto neat epoxy and further improvement in thetensile modulus achieved due to theincorporation of interphase properties.

COMPRESSION TESTThe compressive test for the compositematerial shows the improvement of the majorprincipal stress at 7% and 12% of fiberinclusion for spherical and cylindrical fibers withhemispherical ends. Early increase of the

major principal stress was observed for therectangular and cylindrical fibers. Beyond the15% of f iber inclusion, there was noimprovement was observed for all type of fiberinclusion.

The experimental result shows at 5 to 12%vol of CF has higher strength. And increasingthe CF the strength is decreasing up to 15%of CF content. From the graph the experimentalvalues are near to the simulated values withconsidered Interphase (Figure 6). It showsInterphase plays a major role to load transferfrom fiber to matrix. Due to the perfect bondbetween fibers to matrix the simulated testresult showing higher values. But in practicalmatrix unable to transfer the load to fiber dueto the fibers are not evenly distributed.

The compressive modulus of the pure epoxyas well as of the composites containing theshort Carbon Fiber (CF) and short Glass Fiber(GF) was analyzed. The modulus of pure epoxyis 2.21 GPa. The composite with 0.98% vol of

Figure 6: Tensile Modulus vs. Hybrid Composites

474


CF shows a 4.33 GPa and the modulus is 4.07GPa reduced due to the incorporation ofinterphase properties. Using the compressivemodulus formula (iv) the above modulus hasbeen calculated and plotted (Figure 8). Thecomposite fiber radius of 0.25 mm with mmfiber length are incorporated as 0.98%, 1.98%and 2.97% vol of CF shows a 95.73%,127.08% and 94.9% improvement incompressive modulus compare to Neat epoxy.Tensile modulus of CF is predicted as 86.78%,82.62%, and 88.39% due to the incorporationof interphase properties.

Figure 7: Stress Distribution of 1.98% Vol of CFRP with 1% Alumina Particle

(a) Neglected Interphase (b) Considered Interphase

(c) Full Model of the Considered Interphase (d) Quarter Model

The compressive modulus of the pure epoxyas well as of the composites containing theshort carbon fibers like CF and GF wasanalyzed with 54 to 162 no. of FRP withincorporation of 1% Alumina particle keepingconstant. Compressive modulus of 1% vol ofCF with 1% vol of GF has calculated as79.86% improved compare to Neat epoxy.Further improvement in the compressivemodulus achieved due to the incorporation ofinterphase properties. Compressive modulusof 1% vol of CF with 1% vol of GF and 1%Alumina particle has calculated as 3.96 6GPa

475


it means 79.43% improved compare to Neatepoxy and 3.91GPa in the compressivemodulus achieved due to the incorporation ofinterphase properties

FLEXURAL TESTA bar of rectangular cross section rests on twosupports and is loaded by means of a loadingnose midway between the supports A support

Figure 8: Compressive Modulus vs. Volume Content of Fiber

(a) CFRP Composite (b) GFRP Composite

Figure 9: Flexural Stress Distributions

(a and b) Flexural Stress Distributions of 9% CFRP/Epoxy Composite Neglecting and Consideringthe Interphase Properties

476


Figure 9 (Cont.)

(c and d) Flexural Stress Distribution of 9% CFRP Neglecting and Considering the Interphase (Stresses in Fiber)

Figure 10: Flexural Stress Distributions

(e and f) Flexural Stress Distribution of 4% GFRP with 1% Alumina Particles Neglecting and Consideringthe Inter Phase (Stresses in Fiber)

(g and h) Shows Flexural Stress Distributions of Matrix to Fiber on 9% CFRP/Epoxy Composite Neglectingand Considering the Interphase

477


span-to-depth ratio of 16:1 shall be usedunless there is reason to suspect that a largerspan-to-death ratio may be required.

CONCLUSIONThe present study has shown that the ultimatetensile and compressive strength of the shortcarbon fiber and glass fiber reinforcedcomposite was gradually decreases but themodulus increases with the increase of thefiller content. The flexural modulus of the neatepoxy was increased by the addition of carbonfiber, glass fiber and further improvement ofthe flexural modulus is possible by adding aconstant volume fraction of the Aluminaparticles in the epoxy matrix. In this study wehave reported that the interface region plays avital load not only to act for the mechanism ofload transfer but also the as means to improvethe mechanical properties of the material. Thefindings will help for the proper choice of thereinforcing material for the load bearingstructures for critical application.

REFERENCES1. ASTM D638-10 Type IV Standard Test

Method for Tensile Properties of Plastics,This Standard has Been Approved forUse by Agencies of the Department ofDefense.

2. ASTM D695-10 Standard Test Method forCompressive Properties of Rigid Plastics1, This Standard has Been Approved forUse by agencies of the Department ofDefense.

3. Campbell F C (2005), ManufacturingTechnology for Aerospace StructuralMaterials, 1st Edition, Elsevier Ltd.

4. Camponeschi E T (1991), “CompressionTesting of Thick Section CompositeMaterials Composite Materials: Fatigueand Fracture”, ASTM STP 1110, Vol. 3,pp. 439-456, American Society for Testingand Materials, Philadelphia.

5. Godara A and Raabe D (2007), “Influenceof Fiber Orientation on GlobalMechanical Behavior and MesoscaleStrain Localization in a ShortGlass-Fiber-Reinforced Epoxy PolymerComposite During Tensile DeformationInvestigated Using Digital ImageCorrelation”, Max-Planck-Str., Dusseldorf,Germany.

6. Hsiao H M, Daniel I M and Wooh S C(1995), “A New Compression Test Methodsfor Thick Composites”, J. Compos. Mater.,Vol. 29, No. 13, pp. 1789-1806.

7. Kies J A (1962), Maximum Strains in theResin of Fiber Glass Composites, USNaval Laboratory Research Report NRL,Vol. 5752.

8. De Kok J M M, Meijer H E H and Peijs AA J M (1993), “The Influence ofMatrixplasticity on the Failure Strain ofTransversely Loaded CompositeMaterials”, p. 242, Composites Behaviour(ICCM/9), Woodhead Publishing,Cambridge.

9. Peters S (1998), Handbook ofComposites, 2nd Edition, Chapman & HallThomson Science is a Division ofInternational Thomson Publishing,Mountain View, Calfornia, USA.

10. Shiqiang Deng, Lin Ye and Yiu-Wing Mai(1999), “Influence of Fiber Cross-

478


Sectional Aspect Ratio on MechanicalProperties of Glass Fibre/EpoxyComposites I, Tensile and FlexureBehavior”, Composites Science andTechnology, Vol. 59.

11. Xiao-Feng Li, Kin-Tak Lau and Yan-ShengYin (2008), “Mechanical Properties ofEpoxy-Based Composites Using CoiledCarbon Nanotubes”, CompositesScience and Technology, Vol. 68.

analyzation of frp composite’s mechanical failure … · analyzation of frp composite’s...

Documents