Evaluation on fracture mechanics of mode ii treated fiber pllabased


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Evaluation on fracture mechanics of mode ii treated fiber pllabased

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME453EVALUATION ON FRACTURE MECHANICS OF MODE II TREATEDFIBER/PLLA BASED ON REAL SIZE MODEL COMPOSITEC.V. Sia1, Y. Nakai2, H. Tanaka3, D.Shiozawa41,2,3,4Department of Mechanical Engineering, Kobe University,Kobe, Hyogo, JapanABSTRACTInterfacial fracture toughness between treated fiber and matrix was investigated byusing model composite method. Oil palm fibers (OPF) were pretreated with sodiumhydroxide (NaOH) for 48 hours before the specimen fabrication process. Three oil palmfibers (OPF) from 204µm to 295µm were aligned in parallel and bonded by poly (L-latic acid)(PLLA). A significant increase in interfacial fracture toughness was found for the modelcomposite due to the increment of the resin length which bonded on the OPF. Scanningelectron microscope (SEM) observations were carried out to analyze the morphology of themodel composite.Keywords: Fracture Toughness, Oil Palm Fiber, PLLA, Model Composite1. INTRODUCTIONRenewal of interest in the research of fibers derived from natural sustainable sourcesas potential reinforcement for high performance composites has been growing in recent years.The good strengths and modulus, low density, economical viability and biodegradability ofthe natural fibers over traditional fibers make them attractive candidate for the reinforcement.Commercially, available nature fibers such as hemp, jute, oil palm, bamboo, sisal, flax, etc.are being explored in many countries [1].INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGAND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4, Issue 2, March - April (2013), pp. 453-460© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2013): 5.7731 (Calculated by GISI)www.jifactor.comIJMET© I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME454Plant-based fibers mainly consist of cellulose, hemicellulose and lignin which aremajor components of the plant cell wall [2].Since the adhesive bonding between fiber andmatrix are mainly depend on the surface roughness of the fiber, increasing the surfaceroughness us the key factor to improve the adhesive bonding. Alkali treatment of the naturalfibers is one of the chemical treatments which can remove the impurities of the fibers andincrease the surface roughness of the fiber [3-6].Recent evaluation crack propagation behavior of fiber reinforced plastics (FRP) wasbased on meso-mechanical analysis where the crack propagation in FRP was evaluated fromfracture process like matrix fracture and fiber/matrix interfacial cracking [7-9]. The crackpropagation behavior in FRP is strongly influenced by the interfacial bonding between fiberand matrix[10, 11].The objective of the present study is to evaluate Mode II interfacial fracture toughnessbetween treated oil palm fiber and PLLA composite by using the model composite method.Scanning electron microscope (SEM) was utilized to investigate the morphology of the modelcomposite.2. EXPERIMENT PROCEDURE2.1 MaterialsOil palm fibers were purchased from Ecofibre Technology Shn.Bhd, Malaysia. Theseuntreated fibers have a characteristic were approximately 150-550µm diameter and 40-150mm in length. PLLA fibers with diameter of 0.2mm were purchased from Unitika Ltd,Japan and Sodium Hydroxide (NaOH) was purchased in Hyogo, Japan.2.2 Surface TreatmentOil palm fibers were cut to approximate 50mm of length and kept in oven at21ºC ±1ºC for 24 hours for conditioning which according to ASTM D1776-04 [12]. The oil palmfibers were then soaked in 1.0M (mol/liter) alkali solution for 48 hours. The alkali treatedfibers were then washed and rinsed with distilled water for several times until the final pHwas maintained at 7.0. After that, the fibers were dried at room temperature for 48 hours.2.3 Model Composite SpecimenThree OPFs were aligned in parallel on a paper tab with a small tension force appliedon the fibers to avoid loosening of the fibers. Four PLLA fibers were placed between the 3vertical fibers as spacer to maintain the distance between OPFs. Both end points of OPFswere glued by using epoxy resin adhesive. Small amount of PLLA was melted and mountedat the edge of a sharp soldering tip and then placed the melted PLLA at mid-point in between2 OPFs. Schematic and SEM of the specimen were shown in Fig. 1 and 2 respectively. Thematrix length of the test specimens was from230 to 5700µm and the angle of the fibers, 2θwhich shown in Fig.1(b) for bonding section was from 60 to 180 degrees.
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME455(a) (b)Fig.1 Schematics of model composite specimen. (a) Top view, (b) Cross-section viewFig.2 SEM image of the model composite2.4 Mode II Interfacial Test MethodUniaxial tensile strength, tensile modulus and elongation at break of the oil palmfibers were carried out using Tohei MT201 tensile test machine. A gauge length of 20mmwas employed with a crosshead speed of 9mm/min and 50N load.Fig.3 shows the schematic of double shear specimen model. By simplifying thecomposite model into section (a), (b) and (c), the strain energy of the model composite can beobtaind as below.ܷ ൌ ܷ௔ ൅ ܷ௕ ൅ ܷ௖ ሺ1ሻwhereUa, Ub and Ucare the strain energy of the section (a), (b) and (c). The equation of Ua, Uband Ucare stated below.ܷ௔ ൌ2ܲଶ݊ߨ‫ܦܧ‬ଶܷ௕ ൌ2ܲଶ‫ܮ‬ߨ‫ܦܧ‬ଶܷ௖ ൌ2ܲଶ݉ߨ‫ܦܧ‬ଶሺ2ሻwhereE and D are the tensile modulus and diameter of oil palm fiber respectively, P is theapplied force, L, m and n are the length of the section in Fig.3.
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME456The energy release rate at crack tip A and B are given by the following equation.‫ܩ‬஺ ൌ12θ‫ܦ‬·dd݉ሺܷ௔ ൅ ܷ௕ ൅ ܷ௖ሻ ൌ12θ‫ܦ‬൬dܷ௖d݉െdܷ௕d‫ܮ‬൰ ൌܲଶ6ߨ‫ܦܧ‬ଷθሺ3ሻ‫ܩ‬஻ ൌ12θ‫ܦ‬·dd݊ሺܷ௔ ൅ ܷ௕ ൅ ܷ௖ሻ ൌ12θ‫ܦ‬൬dܷ௔d݊െdܷ௕d‫ܮ‬൰ ൌ2ܲଶ3ߨ‫ܦܧ‬ଷθሺ4ሻSince the value of GB is larger than GA, the crack must start propagate from the point B (Fig. 3).Fig.3 Schematic of double shear specimen model.3. RESULT AND DISCUSSIONThe SEM the fiber before and after alkali treatment is exhibited in Fig. 5(a) and (b).NaOH treatment leads to the irreversible mercerization which will improve the fiber surfaceadhesive characteristics by removing natural and artificial impurities, thereby producingrough surface topography (Fig. 5(b)). Same observationhas been reported in Sreekala et al.[6] and Moshiul et al.[13]’s research.(a) (b)Fig.4 SEM micrographs of the surface of oil palm fiber. (a) Untreated OPF, (b) Treated OPF(24h, 1.0M NaOH).
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME457Fig. 5(a), (b), (c) and (d)illustrates the relationship between interfacial fracturetoughness and diameter of fibers, angle of bonding interface of treated fibers/PLLA, spacingbetween treated fibers and matrix length respectively. The highest value of the interfacialfracture toughness obtained from the double shear test is 108.6J/m2, and the minimum valueof the interfacial fracture toughness is 14.7J/m2. While the average interfacial fracturetoughness is 61.2J/m2. The scatter plots in Fig. 5(a), (b) and (c) clearly shows that interfacialfracture toughness does not depend on the fiber diameters, angle of bonding interface andspacing between fibers. However, interfacial fracture toughness of the composite model doesdepend on the matrix length (Fig. 5(d)).(a) (b)(c) (d)Fig. 5 Variations of interfacial fracture toughness as a function of (a) diameter of OPF, (b)angle of bonding interface of OPF/PLLA, (c) spacing between OPFs and (d) matrix lengthfordouble shear specimen model.020406080100120200 220 240 260 280 300FraactureToughness,G(J/m2)Fiber Diameter (µµµµm)02040608010012090 105 120 135 150 165 180FraactureToughness,G(J/m2)Angle of bonding interface, 2θ (º)0204060801001200 20 40 60 80 100FraactureToughness,G(J/m2)Spacing between fibers, t (µµµµm)0204060801001200 1 2 3 4 5 6FractureToughness,G(J/m2)Matrix Length, L (mm)
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME458As can be seen in Fig. 5(d), interfacial fracture toughness of the composite model wasfound to be increased with the increase of matrix length. The maximum fracture toughnesswas obtained when matrix length is about 2.3mm. At this point, the matrix length and processzone reach the optimum state where the maximum plastic deformation occurred. After that,the interfacial fracture toughness decreased and observed to beconstantwhen L > 3.0mmwhere the mean value of the interfacial fracture toughness is 70.9J/m2. The process zone wasindependent of the matrix length when L > 3.0mm.Other studies reveal that the interlaminarfracture toughnesswasaffectedby bond thickness of the composites. From the data analysis,they found the similarscatter plots (Fig. 6)where the fracture toughness will keep constantafter bond thickness is larger than the process zone [14, 15].Fig. 6 Relationship between fracture toughness and bond thicknessFig.7 shows the SEM of the fracture surface at the initial crack tip of the treatedfiber/PLLA model. The matrix was more found on the surface of the outer fiber (Fig. 7(b)). Itmeans that the crack propagated along the interface between center fiber and matrix.(a) (b)Fig. 7 Fracture surface of the specimen. (a) Center fiber (b) Outer fiber.
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4594. CONCLUSIONA new model composite method is introduced for Mode II test, which evaluate theinterfacial fracture mechanics of treated fibers/PLLA composite. In this research, theinterfacial fracture toughness of the composite model only affected by matrix length.However,the value of interfacial fracture toughness is independent and constant after thematrix length is more than 3.0mm.REFERENCES[1] A.K. Mohanty, M. Misra. L.T. Drzal, Natural fibers, biopolymers and biocomposite(BocaRaton, FL: CRC Press, 2005).[2] S. Shinoj, R.Visvanathan, S. Panigrahi, M. Kochubabu. Oil palm fiber (OPF) and itscomposite: A review. Industrial Crops and Products, Vol. 33, 2011, 7-22.[3] A. Roy, S. Chakraborty, S.P. Kundu, R.K. Basak, S.B. Majumder, B Adhikari,Improvement in mechanical properties of jute fibers through mild alkali treatment asdemonstrated by utilization of the Weibull distribution model, Bioresource TechnologyVol. 107, 2012, 222-228.[4] J. Gassan, A.K. Bledzki Alkali treatment of jute fibres: relationship between structureand mechanical properties, Journal of Applied Polymer Science, Vol. 71, 1999, 623–629.[5] H. Gu, Tensile behaviours of the coir fibre and related composites after NaOHtreatment, Materials and Design, Vol. 30, 2009, 3931–3934.[6] M.S Sreekala, M.G Kumaran, R. Joseph, S. Thomas. Stress-relaxation behaviour incomposites based on short oil-palm fibres and phenol formaldehyde resin. CompositesScience and Technology,Vol. 61(9), 2001, 1175–1188.[7] J.H. Crews, K.N.Shivakumar, I.S.Raju, A fibre-resin micromechanics analysis of thedelamination front in a double cantilever beam specimen, PhaseInteraction inComposite Materials, 1992, 396-405.[8] F. Dubois, R.Keunings, DCB testing of thermoplastic composites: Anon-linear micro-macro numerical analysis, Composites Science and Technology, Vol.57(4), 1997, 437-450.[9] H. Tanaka, Y.Nakai, Three-dimensional micromechanics analysis of strain energyrelease rate distribution along delamination crack in FRP, Proc. 4thAsian-AustralasianConf. onComposite Materials, 2004, 439-444.[10] M.Kotaki, M.Hojo, N. Tsujioka, H.Hamada, effect of surface treatmentoninterlaminar/intralaminar crack growth behavior of CFRP laminates, Proc. 4th JapanInternational SAMPE Symposium, 1995, 1008-1013.[11] M.Hojo, N.Tsujioka, M.Kotaki, H.Hamada, Z. Maekawa, S.Ochiai, Effect ofinterfacial strength on interlaminar and intralaminar fracture toughness ofCFRPlaminates, Proc. COMP95, 1995, 30-36.[12] ASTM, ASTM D1776-04, Standard practice for conditioning and testing textiles,American Society for Testing and Materials, 2004, Pennsylvania, USA.[13] A.K.M. Moshiul Alam, M.D.H beg, D.M. Reddy Prasad, M.R. Khan, M.F. Mina,Structures and performance of simultaneous ultrasound and alkali treated oil palmempty fruit bunch fiber reinforced poly(lactic acid) composites. Composites: Part A,Vol. 43, 2012, 1921-1929.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME460[14] F. Ozdil, L.A.Carlsson, Mode I interlaminar fracture of interleaved graphite/epoxy,Journal of Composite Materials, Vol. l6(3), 1992, 432-459.[15] H. Chai, Bond thickness effect in adhesive joints and its significance for mode Iinterlaminar fracture of composites, Composite Materials: Tasting and design (7thConf.), ASTM STP 893, 1986, 209-231.[16] Ercan Serif Kaya, Takuro Katayama and Toshitaka Yamao, “Seismic Characteristics ofthe Folded Cantilever Shear Structure”, International Journal of Civil Engineering &Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 58 - 79, ISSN Print: 0976 – 6308,ISSN Online: 0976 – 6316.[17] Sharad V. Kshirsagar and Dr. Lalit B. Bhuyar, “Signature Analysis of CrackedCantilever Beam”, International Journal of Advanced Research in Engineering &Technology (IJARET), Volume 3, Issue 2, 2012, pp. 594 - 603, ISSN Print: 0976-6480,ISSN Online: 0976-6499.[18] Maridurai T, Shashank Rai and Shivam Sharma and Palanisamy P, “Analysis of TensileStrength and Fracture Toughness using Root Pass of Tig Welding and SubsequentPasses of Smaw and Saw of P91 Material For Boiler Application”, InternationalJournal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012,pp. 594 - 603, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.