Your SlideShare is downloading. ×
Effect of alkali treatment on vibration characteristics and mechanical properties of natural fabric reinforced composites
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Introducing the official SlideShare app

Stunning, full-screen experience for iPhone and Android

Text the download link to your phone

Standard text messaging rates apply

Effect of alkali treatment on vibration characteristics and mechanical properties of natural fabric reinforced composites

993
views

Published on

In this article, the effect of alkali treatment (with 5 wt. % sodium hydroxide solution for 30 min) on the compressive, …

In this article, the effect of alkali treatment (with 5 wt. % sodium hydroxide solution for 30 min) on the compressive,

in-plane shear, impact properties and vibration characteristics of flax- and linen-fabric reinforced epoxy composites was

investigated. Test results show that alkali treatment enhanced the compressive strength and compressive modulus,

in-plane shear strength and shear modulus, and specific impact strength of both flax- and linen-epoxy composites.

However, after the treatment, the impact strength and damping ratio of the flax and linen composites decreased. The

reduction in impact strength and damping ratio is believed to be attributed to the improved fibre/matrix interfacial

adhesion, as analysed by scanning electron microscope.

Published in: Business, Technology

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
993
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
31
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Journal of Reinforced Plastics and Composites http://jrp.sagepub.com/Effect of alkali treatment on vibration characteristics and mechanical properties of natural fabric reinforced composites Libo Yan Journal of Reinforced Plastics and Composites 2012 31: 887 DOI: 10.1177/0731684412449399 The online version of this article can be found at: http://jrp.sagepub.com/content/31/13/887 Published by: http://www.sagepublications.com Additional services and information for Journal of Reinforced Plastics and Composites can be found at: Email Alerts: http://jrp.sagepub.com/cgi/alerts Subscriptions: http://jrp.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Citations: http://jrp.sagepub.com/content/31/13/887.refs.html >> Version of Record - Jul 17, 2012 What is This? Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 2. Article Journal of Reinforced Plastics and CompositesEffect of alkali treatment on vibration 31(13) 887–896 ! The Author(s) 2012 Reprints and permissions:characteristics and mechanical properties sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0731684412449399of natural fabric reinforced composites jrp.sagepub.comLibo YanAbstractIn this article, the effect of alkali treatment (with 5 wt. % sodium hydroxide solution for 30 min) on the compressive,in-plane shear, impact properties and vibration characteristics of flax- and linen-fabric reinforced epoxy composites wasinvestigated. Test results show that alkali treatment enhanced the compressive strength and compressive modulus,in-plane shear strength and shear modulus, and specific impact strength of both flax- and linen-epoxy composites.However, after the treatment, the impact strength and damping ratio of the flax and linen composites decreased. Thereduction in impact strength and damping ratio is believed to be attributed to the improved fibre/matrix interfacialadhesion, as analysed by scanning electron microscope.KeywordsNatural fabrics, composite, mechanical properties, vibration, scanning electron microscope fracture and failure behaviour of technical flax fibres.Introduction They found that the failure mechanism of flax fibre is aThere has been a growing interest in the use of bio- complex sequence consisting of axial splitting of thefibres to replace manmade carbon/glass fibres as technical fibre along its elementary constituents,reinforcement in polymer composites for engineering radial cracking of the elementary fibres and multipleapplication.1 The advantages of bio-fibres are they are fracture of the elementary fibres.7 Bos et al. concludedcost-effective, have low energy consumption, bio- that the flax fibre had a complex structure, which con-degradability, low density with high specific strength sisted of cellulose, hemicelluloses, pectin, lignin andand stiffness and are readily available.2 In the recent other components.8years, research on nano-composites shows that bio- Flax fibres as composite reinforcement are not con-composites have the potential as the next generation sidered only in the form of monofilament configur-of structural materials.3 Currently, bio-composites are ation.9 Polymer matrix, reinforced by woven flaxmainly applied in the automotive industry. There was fabric, is the form of composites used commonly inapproximately 43,000 tonnes of bio-fibres utilized as structural applications such as boats. It is reportedreinforcement materials of composites in the that a 50% (by volume) flax fibre racing boat had com-European Union (EU) in 2003.4 This amount increased pleted the France-to-Brazil Transat race in 15th place.10to around 315,000 tonnes in 2010, which accounted for The success in fabrication of the boat is attributed to13% of the total reinforcement materials (glass, carbonand natural fibres) in fibre-reinforced composites.5 Theexplosive consumption in bio-composites is an indica- Department of Civil and Environmental Engineering, The University oftion of their wider application in the future. Auckland, Auckland, New Zealand Among the bio-fibres, flax is a promising candidateto replace glass fibre. The tensile strength of flax fibres Corresponding author: Libo Yan, Department of Civil and Environmental Engineering, Thewere reported up to 1500 MPa.6 Physical/mechanical University of Auckland. Level 11, Engineering Building, 20 Symondsproperties of some bio-fibres and manmade fibres are Street, Auckland, 1001, New Zealand ´given in Table 1. Romhany et al. investigated the tensile Email: lyan118@aucklanduni.ac.nz Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 3. 888 Journal of Reinforced Plastics and Composites 31(13)Table 1. Properties of natural and manmade fibres6Fibre Density Elongation (%) Tensile strength (MPa) Elastic modulus (GPa)Flax 1.5 2.7–3.2 500–1500 27.6Cotton 1.5–1.6 7.0–8.0 400 5.5–12.6Jute 1.3 1.5–1.8 393–773 26.5Hemp 1.47 2.0–4.0 690 70Sisal 1.5 2.0–2.5 511–635 9.4–22Coir 1.2 30 593 4.0–6.0Softwood kraft pulp 1.5 4.4 1000 40E-glass 2.5 0.5 2000–3500 70S-glass 2.5 2.8 4570 86Carbon 1.4 1.4–1.8 4000 230–240the fact that the woven flax fabric allows the control of Materials and methodsfibre orientation and quality control, good reproduci- Fibre and epoxybility and high productivity.11 Assarar et al. confirmedthat the tensile stress and strain at failure of flax fabric Commercial woven flax and linen fabrics were usedreinforced polymer composites were 300 MPa and because of their wide availability. Flax fabric with1.8%, respectively – putting them close to glass fibre areal weight of 550 g/m2 was obtained from Libeco,reinforced polymer composites.12 Liu and Hughes stu- Belgium. Linen fabric with areal weight of 350 g/m2died the toughness of flax fabric reinforced epoxy com- was obtained from Hemptech, New Zealand. Bothposites and concluded that the fibre volume fraction flax and linen are plain weave fabrics. Flax fabric hasdominates the toughness, rather than the microstruc- count of 7.4 threads/cm in warp and 7.4 threads/cm intural arrangement of the fibre.13 the weft direction. Linen fabric has count of 10 threads/ Bio-composites have been applied in automotive and cm in warp and 10 threads/cm in the weft direction. Theboat engineering. However, based on the best know- epoxy used is the SP High Modulus Prime 20LV epoxyledge of the author, to date rarely study on bio- system. The fabric structures and details for the resincomposites in civil engineering has been reported. In system could be found in previous study.15fact, conventional construction materials such as con-crete and steel reinforcement have some significanteffects on the environment. In the United Kingdom Alkali treatment(UK), construction process and building use not only Initially, flax and linen fabrics were cut into a size ofconsume the most energy of all sectors and create the 400 Â 300 mm2. For alkali-treated specimens, flax andmost CO2 emissions, they also create the most waste, linen fabrics were washed three times with fresh wateruse most non-energy-related resources and are respon- to remove contaminants and then dried at room tem-sible for the most pollution.14 To reduce these negative perature for 48 h. The dried fabrics were then immersedenvironmental effects of conventional construction in 5 wt. % NaOH solution (20 C) for 30 min, followedmaterials, bio-composites as potential construction by washing 10 times with fresh water and subsequentlymaterial are being investigated. three times with distilled water, to remove the remain- This article, as a part of on-going research to study ing NaOH solution. Finally, these fabrics were dried atthe feasibility of bio-composites as construction mater- 80 C in an oven for 24 h.ial, investigated the vibration characteristics (dampingratio and natural frequency) and the mechanical prop-erties (with respect to compressive strength, compres- Composite fabricationsive modulus, in-plane shear stress and shear modulus, All the composites were manufactured by vacuum bag-and the impact strength and specific impact strength) of ging technique. It consists of an initial hand lay-up of aflax and linen fabric reinforced epoxy composites. In fibre preform and then impregnation of the preformaddition, the effect of alkali treatment (with 5 wt. % with resin in a flexible bag in which negative pressuresodium hydroxide (NaOH) solution for 30 min) on is generated by a vacuum pump. Next, the compositesthe mechanical properties and the vibration character- were cured at room temperature for 24 h and placedistics of the composites were evaluated. into the Elecfurn oven for curing at 65 C for 7 h. Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 4. Yan 889Table 2. Physical properties of the composites Fabric Thickness of Thickness of Fibre volume DensityComposites layers each layer (mm) composites (mm) fraction (%) (g/cm3)Untreated flax/epoxy 6 0.712 5.049 55.1 1.273Treated flax/epoxy 6 0.705 5.021 55.9 1.158Untreated linen/epoxy 8 0.510 4.984 54.8 1.228Treated linen/epoxy 8 0.498 5.011 55.3 1.130 Accelerometer Composite cantilever plate Amplifier 5 mm 225 mm Natural Data acquisition FFT software frequencyFigure 1. Schematic view of vibration test system. vibration of a structure. Damping of a composite canFibre volume fraction be defined as the decay of the composite in vibrations.Density of the mixed epoxy given by the supplier was It is interpreted as the dissipation of the vibration energy.1.08 g/cm3. Composite density was determined by the Damping plays an important role in controlling thebuoyancy method using water as the displacement structure from excessive vibrations due to dynamic load-medium based on ASTM D792.16 The void contents ings. Therefore, understanding the vibration character-of the composites were determined according to istic of FRP composite material, like damping, hasASTM D2734.17 After obtaining the density and void industrial significance. Damping ratio – a dimensionlesscontent for each composite, the fibre volume fraction measure of damping – is a property of the composite thatfor the composite was derived from the fibre/epoxy also depends on its mass and stiffness. Vibration test wasresin weight ratio and the densities of both fibre and conducted by using an accelerometer to detect theepoxy resin matrix.18 The fibre volume fraction Vf was dynamic characteristics of the composite plates.calculated using the following equation: Figure 1 gives a schematic view of the vibration test 1 system. Three specimens with a size of 250  25  5 mm3 Vf ¼ 1 À À Vv ð1Þ (length  wide  thickness) for each composite was 1 þ Vf =Vr clamped in the form of cantilever beams with 225 mmwhere Vv is the void content of composite and Vr is the effective length span; the accelerometer was attachedvolume of epoxy resin. The calculated fibre volume on the free-end side of each cantilever laminiate, andfractions of the untreated and alkali-treated composites then stimulated the free vibration. The vibration accel-are listed in Table 2. It can be seen that the fibre volume eration time histories were recorded by the data acquisi-fractions and thicknesses of all the composites were tion software with a computer. The logarithmicapproximately 55 % and 5 mm, respectively. decrement is used for calculating the damping ratio  of cantilever laminates from the recorded acceleration time histories based on the following equation:Vibration test of compositesAs a construction material, the damping of the material 1 gi ¼ ln ð2Þis an important parameter related to the study of 2j giþj Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 5. 890 Journal of Reinforced Plastics and Composites 31(13)Figure 2. Vibration time-history: (a) Untreated flax/epoxy composite and (b) alkali-treated flax/epoxy composite.where gi is the peak acceleration of ith peak, giþj is the (length  wide  thickness) for each composite.19 Thepeak acceleration of the peak j cycles after ith peak and cross-head speed was 1.5 mm/min for each test. Anti is the time instant at i cycle in the peak acceleration, extensometer with a gauge was amounted on the speci-as shown in Figure 2(a). men for measurement of the strain. For each compos- With respect to the fast Fourier transformation ite, five specimens were tested at room temperature and(FFT), the vibration frequency spectrum was obtained the average compressive strength and compressivefrom the measured time-histories. The main peak cor- modulus were reported.responds to the natural frequency of the composite.The average damping ratio and average natural fre-quency of each composite tested on three specimens In-plane shear test of compositeswas reported. The in-plane shear test was conducted according to ASTM D3518 with a size of 250  25  5 mm3 (length  wide  thickness) for each composite.20 TheCompressive test of composites cross-head speed was 2 mm/min. To register the elong-The compressive test was carried out according to ation during the test, an extensometer with a gauge wasASTM D3410 on plates with a size of 125  25  5 mm3 placed on each specimen. For each composite, five Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 6. Yan 891specimens were tested at room temperature and theaverage shear strength and shear modulus wereobtained.Impact test of compositesThe Izod impact test was conducted according toASTM D256 on un-notched plates with a size of65  12.7  5 (length  wide  thickness) mm3 for eachcomposite.21 The impact loading was considered witha 25 J-hammer. Impact energy in J/m2 was considered.For each composite, five specimens were tested at roomtemperature and the average impact strength wasobtained.Scanning electron microscopySurface topographies of the untreated and alkali-treated composites were investigated using a scanningelectron microscope (SEM, Philips XL30S FEG,Netherland) at room temperature, operated at 5 kV.The sample surfaces were vacuum coated by evapor-ation with platinum before examination.Results and discussionVibration characteristics of compositesFigure 2 illustrates the time histories of untreated andalkali-treated flax/epoxy composites in vibrations. Theaverage damping ratio and average natural frequencyof all the composites are given in Table 3. It shows thatboth flax and linen fabric reinforced polymer compos-ites exhibit a similar pattern in damping ratio, namely, Figure 3. Surface morphology of untreated (a) and alkali-the damping ratio of the untreated composite is larger treated (b) flax fabric reinforced composites.than the alkali-treated one. Alkali treatment has anegative effect on damping ratio of both flax andlinen composites; the decrease in damping ratio of treatment increased the natural frequency of theflax- and linen-epoxy composite is 7.4% and 9.3%, composites.respectively (Table 3). For all the considered compos- Damping defines the energy dissipation capability ofites, the untreated flax-epoxy composite has the largest a material. The damping of fabric reinforced polymerdamping ratio of 1.48 %. With respect to natural composite is believed attributed to the presence of airfrequency, it is observed that both flax and linen voids (e.g. the inherent lumens of the fibres), the visco-composites possess a smaller natural frequency than elastic characteristics of epoxy matrix and/or the fibrethe corresponding treated one. Compared with the materials and the interphase between the matrix anduntreated composite, the increase in natural frequency the fibre. Interphase is defined as the region adjacentof the treated composite is believed to be attributed to to fibre surface all along the fibre length.22 Interphasethe fact that the alkali treatment reduced the mass possesses a considerable thickness and its properties are(a lower density in Table 2) and increased the stiffness different from those of embedded fibres and matrix. Itof the composite. The Young’s modulus of alkali-trea- is true that the mechanical properties (e.g. tensile andted composite was larger than that of the untreated flexural properties) of fabric fibre reinforced polymerone, which was concluded in previous study.15 From composites are highly dependent on the matrix/fibrethe relationship among natural frequency ( f ), mass interphase.15(m) and stiffness (k) of the composite, namely, pffiffiffiffiffiffiffiffiffi Fibre/matrix interphases also affect the damping off ¼ ð1=2Þ Á k=m, it is easy to derive that the alkali the composites. The decrease in damping ratio of the Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 7. 892 Journal of Reinforced Plastics and Composites 31(13)Table 3. Mechanical properties of treated and untreated compositesa Specific Compressive Compressive Shear Shear Impact impact Damping Natural strength modulus strength modulus strength strength ratio frequency (MPa) (GPa) (MPa) (GPa) (kJ/m2) (kJ/m2/gÁcm3) (%) (Hz)Untreated flax/epoxy 90.32 2.18 38.01 2.07 36.53 28.70 1.48 16.02 composite (4.30) (0.13) (2.21) (0.11) (3.24) (–) (0.06) (0.25)Treated flax/epoxy composite 93.02 2.35 41.11 2.16 33.87 29.25 1.37 16.83 (3.25) (0.20) (2.54) (0.16) (2.96) (–) (0.04) (0.16)Change due to alkali 3.0 7.8 8.2 4.2 À7.3 1.9 À7.4 5.1 treatment (%)Untreated linen/epoxy 78.64 1.88 34.06 1.84 30.62 24.93 1.29 16.94 composite (3.45) (0.09) (1.78) (0.12) (2.76) (À) (0.09) (0.12)Treated linen/epoxy composite 82.28 1.97 35.67 1.93 28.65 25.35 1.17 17.63 (4.02) (0.16) (2.06) (0.20) (2.24) (À) (0.05) (0.28)Change due to alkali 4.6 4.8 4.7 4.9 À6.4 1.7 À9.3 4.1 treatment (%)aNumbers in parentheses are standard deviations.treated composites may be attributed to the fact that treated composites mainly depends on the fibres, as thealkali treatment leads to better fibre/matrix interfaces. compressive modulus of the epoxy is 1.13 GPaFor untreated composites, there are more voids or gaps (Figure 4(b)). Compared with the untreated composites,at the fibre/matrix interfaces. In the vibration, more both alkali-treated flax and linen composites have anenergy has been dissipated due to the internal friction increase in compressive strength and compressive modu-between the fibres and the matrices where more fibre/ lus; the increase in strength is 3.0% and 4.6%, respect-matrix interfaces are involved, and thereby leads to a ively. The increase in modulus is 7.8% and 4.8%,larger damping ratio of the composites. After alkali respectively (Table 3). The enhancement in compressivetreatment, the fibre/matrix interfacial adhesion was properties of flax- and linen-epoxy composites by alkaliimproved. Consequently, the gaps at the fibre/matrix treatment is possibly due to the improved fibre/matrixinterfaces were narrowed and resulted in less energy interfacial adhesion, since alkali treatment removes thedissipation in the vibration. SEM micrographs of the hydrophilic nature of the cellulose fibre and thusuntreated and treated flax composites are shown in improves the interfacial bonding.Figure 3. For the untreated composite, there are notice- The compressive stress–strain curves of all the com-able gaps between the adjacent fibres and the matrices; posites are shown in Figure 5. It can be seen that thethis indicates a poor fibre/matrix interfacial adhesion. behaviour of all the untreated/alkali-treated flax andThese noticeable gaps are responsible for dissipating linen fabric reinforced epoxy composites under com-energy by fibre/matrix friction during the vibration. pressive loading is non-linear. Three regions could beThe insignificant gaps between the fibre and the defined approximately. In the first region, all the speci-matrix indicate the improved interfacial adhesion, as mens show a linear relationship between the stress andshown in Figure 3(b). strain. In the second region, the curves exhibit a non- linear pattern before approaching the ultimate stress. The third post-peak curves go down with a continuousCompressive properties of composites increase in strains; this reveals a ductile behaviour. TheA comparison of compressive strength and compressive predominated failure mechanism observed in the com-modulus between pure epoxy and the composites is dis- pression test was fibre micro-buckling. It should beplayed in Figure 4. The ultimate compressive strengths noted here that the strains at break of all theof all the untreated and alkali-treated composites are untreated/alkali-treated flax and linen composites arehighly dependent on the strength of the epoxy matrix, more than 8%.as shown in Figure 4(a). The compressive strength ofuntreated flax- and linen-epoxy composite is In-plane shear properties of composites90.32 MPa and 78.64 MPa, respectively, comparedwith the pure epoxy (68 MPa). For compressive modu- The in-plane shear stress–strain behaviour for bothlus, it can be seen that the stiffness of all untreated/ untreated and alkali-treated flax- and linen-epoxy Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 8. Yan 893Figure 4. Compressive strength and compressive modulus of all the composites.composites is shown in Figure 6. The average shear increase in shear modulus, respectively (Table 3). Thestrength and average shear modulus of all the compos- alkali treatment removes the impurities and waxy sub-ites are given in Table 3. The flax/epoxy composite has stances from the fibre surface and creates a roughera larger shear strength and shear modulus than the topography (Figure 3) which facilitates the mechanicallinen-epoxy composite. The shear strength and modu- interlocking. In addition, the purified fibre surface fur-lus of untreated flax- and linen-epoxy composites is ther enhances the chemical bonding between the fibre38.0 MPa and 2.07 GPa, and 34.06 MPa and and epoxy matrix because a purified fibre surface1.84 GPa, respectively. enables more hydrogen bonds to be formed between After alkali treatment, the shear strength and shear the hydroxyl groups of the cellulose at one side andmodulus of both flax- and linen-epoxy composites the epoxy groups at the other side. As a consequenceincreased. Compared to the untreated composite, the of the treatment, the fibre/matrix interfacial bondingtreated flax and linen composite experienced 8.2% quality is improved and leads to better in-plane shearand 4.7% increase in strength and 4.2% and 4.9% properties of the composites. Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 9. 894 Journal of Reinforced Plastics and Composites 31(13)Figure 5. Compressive stress–strain curve of all the composites.Figure 6. Shear stress–strain behaviour of flax- and linen-epoxy composites. The stress–strain curves can be divided approxi- Impact properties of compositesmately into two zones. The first zone up to 0.3% Impact strength of a material is defined as its ability tostrain has a purely elastic behaviour, allowing measure- resist the fracture under stress applied at high speed.ment of the modulus. The second zone is a non-linear The impact behaviour of a composite is significantlyzone until leading to the maximum shear stress. All the influenced by the interfacial bond strength, the matrixspecimens were failed because of matrix cracking and and fibre properties. The damage process caused byfibre breakage. impact load energy is dissipated by fibre/matrix Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 10. Yan 895 debonding, matrix fracture and fibre pull-out and fibre fracture, as displayed in Figure 7. It is observed that the impact strength of the untreated flax composite (36.53 kJ/m2) is larger than the untreated linen compos- ite (30.62 kJ/m2), as given in Table 3. The difference in impact strength of flax- and linen-epoxy composites is attributable to the different areal weights of the fabrics. The alkali treatment reduced the impact strength of the composites. The reduction is 7.3 % of flax compos- ite and 6.4 % of linen composite, respectively (Table 3). The decrease in impact strength may be interpreted by assuming that a better fibre/matrix adhesion results in shorter average pull-out lengths of the fibres, as observed in Figure 8. It is clear that the average fibre pull-out lengths of the untreated flax composite is longer than the alkali-treated flax one.Figure 7. SEM micrograph of failure modes of flax fabric rein- Specific impact strength is defined as the ratio offorced epoxy composites. average impact strength divided by the density of theSEM: scanning electron microscopy. composite. Table 3 indicates that the alkali treatment increased the specific impact strength of the flax and linen composites. This is because alkali treatment has a significant reduction in the density of the composites, as shown in Table 2. Conclusion Flax and linen fabric reinforced epoxy composites have been fabricated using the vacuum bagging technique. The influence of alkali treatment on the vibration char- acteristics, the surface morphologies and mechanical properties of the composites were studied. The investi- gation reveals: 1. Alkali treatment with 5 wt. % NaOH solution enhanced the compressive properties, in-plane shear properties of the flax and linen composites. However, the damping ratio and impact strength of both flax and linen composites decreased due to the treatment. 2. In vibration, the reduction in damping ratio by alkali treatment is believed to be attributed to the improved fibre/matrix adhesion resulting in less energy dissipation during the vibration, as analysed by SEM. 3. In compression, the ultimate compressive strength of flax and linen composites is highly dependent on the strength of the epoxy. The stiffness of the fabric reinforced epoxy composite mainly depends on the fibre. The compressive failure of fabric rein- forced epoxy composites exhibits a ductile fracture mode. 4. In in-plane shear test, the stress–strain behaviour ofFigure 8. SEM micrographs of impact specimens: (a) Untreated the composites exhibits a non-linear manner.flax, and (b) alkali-treated flax composites. SEM, scanning elec- 5. The impact strength of the flax composite is superiortron microscopy. to the linen composite. Alkali treatment increased Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012
  • 11. 896 Journal of Reinforced Plastics and Composites 31(13) the specific impact strength of the composites, com- 9. Van de Weyenberg I, Ivens J, De Coster A, et al. pared with their untreated composites. Influence of processing and chemical treatment of flax6. SEM study clearly reveals that the failure of fibres on their composites. Compos Sci Technol 2003; fabric reinforced composite under impact is domi- 63: 1241–1246. 10. CW. Composites world: Flax fibre racing boat completes nated by fibre fracture, fibre pull-out and matrix Transat race. http://www.compositesworld.com/news/ fracture. flax-fiber-racing-boat-completes-transat-race (accessed 10 December 2011). This study is part of a research program investigat- 11. Assarar M, Scida D, El Mahi A, et al. Influence of watering the feasibility of bio-composites as building mater- ageing on mechanical properties and damage events ofials. Next, flax fabric reinforced epoxy composite in the two reinforced composite materials: Flax–fibres andform of hollow tube as concrete confinement (i.e. flax glass–fibres. Mater Des 2011; 32: 788–795.FRP tube confined concrete) will be investigated. The 12. Van Vuure A-W, Ko F-K and Beevers C. Net-shape knit-hollow flax FRP tube will act as the permanent form- ting for complex composite preforms. Textile Res J 2003;work for the concrete core and also is expected to 73: 1–10.increase compressive strength and ductility of the con- 13. Liu Q and Hughes M. The fracture behaviour and tough-crete as the confinement. ness of woven flax fibre reinforced epoxy composites. Composites Part A 2008; 39: 1644–1652. 14. NBT. http://www.natural building.co.uk/environmenta- l_impact.html (accessed 15th December 2011).Funding 15. Yan LB, Chouw N and Yuan XW. Improving theThis research received no specific grant from any funding mechancial properties of natural fibre fabric reinforcedagency in the public, commercial, or not-for-profit sectors. epoxy composites by alkali treatment. J Reinf Plast Compos 2012; 36: 425–437. 16. ASTM. Standard test mothods for density and specificReferences gravity of plastics by displacement. ASTM D792.1. Singha A and Thakur V. Mechanical properties of natural Philadelphia, PA: ASTM, 2008. fibre reinforced polymer composites. Bull Mater Sci 2008; 17. ASTM. Standard test mothods for void content of rein- 31: 791–799. forced plastics. ASTM D2734. Philadelphia, PA:2. Herrera-Franco P and Valadez-Gonzalez A. A study ASTM, 2009. of the mechanical properties of short natural-fiber 18. Heslehurst RB. Composite structures engineering design reinforced composites. Composites Part B 2005; 36: vs. fabrication requirements. In: ACUN-5 International 597–608. Composites Conference. Developments in Composites:3. Bordes P, Pollet E and Averous L. Nano-biocomposites: Advanced, Infrastructure, Natural and Nano-composites. biodegradable polyester/nanoclay systems. Prog Polym Sci Sydney, Australia, 11–14 July, 2006. Sydney, Australia: 2009; 34: 125–155. UNSW.4. Liu Q, Stuart T, Hughes M, et al. Structural biocomposites 19. ASTM. Standard test mothods for compressive properties from flax – part II: the use of PEG and PVA as interfacial of polymer matrix composite materials with unsupported compatibilising agents. Composites Part A 2007; 38: gage section by shear loading. ASTM D3410. 1403–1413. Philadelphia, PA: ASTM, 2008.5. Carus M and Scholz L. Targets for bio-based composites 20. ASTM. Standard test methods for in-plane shear response and natural fibres, Biowerkstoff Report. ISSN 1867-1217, of polymer matrix composite materials by tensile test of a ed 8, March 2011, p.24. Æ45 laminate. ASTM D3518. Philadelphia, PA: ASTM,6. Ku H, Wang H, Pattarachaiyakoop N, et al. A 2007. review on the tensile properties of natural fibre 21. ASTM. Standard test methods for determining the izod reinforced polymer composites. Composites Part B 2011; pendulum impact resistance of plastics. ASTM D256. 42: 856–873. Philadelphia, PA: ASTM, 2010. ´ ´7. Romhany G, Karger-Kocsis J and Czigany T. Tensile frac- 22. Gibson RF, Hwang SJ and Kwak H. Micromechanical ture and failure behavior of technical flax fibres. J App modeling of damping in composites including interphase Polym Sci 2003; 90: 3638–3645. effects. In: Proceedings of the 36th International Society8. Bos H-L, Molenveld K, Teunissen W, et al. Compressive for the Advancement of Material and Process Engineering behaviour of unidirectional flax fibre reinforced compos- Symposium. San Diego, USA, 15–18 April, 1991, ites. J Mater Sci 2004; 39: 2159–2168. pp. 592–606. Downloaded from jrp.sagepub.com at The University of Auckland Library on July 17, 2012