IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 Flexural Properties of Glass and Graphite Particles Filled Polymer Composites A. A. Ibrahim College of Technical -Bag hdad, Foundation of Technical Education Recei ved in Oct. 20, 2010 Accepted in December 14, 2010 Abstract The effects of reinforcing p olymers with glass and graphite p articles on enhancing their flexural p rop erties are invest igated. Five comp osites were fabricated usin g the sa me p olymer matrix material with differ ent volume fractions of reinforcement p articles. They comp rise glass p articles and graphite p articles each havin g volume fractions of 20% and 30% as well as a hy brid comp osite having 10% glass and 10% gr aphite. Three-p oint bending tests using a Universal Testing M achine were carried out on sp ecimens of the above mentioned comp osites, as well as sp ecimens of the p olymer matrix material to determine their fle xural p rop erties. The exp erimental test results indicate that the flexural st iffness of all the comp osites were markedly higher than that of t he matrix material. As for the flexural st rength, comp osites with 20% glass, 30% graphite and the hy brid comp osite maintained higher flexural strength than the matrix material. Keywords: Poly mer comp osites, Flexural prop erties, Glass and graphite p articles Introduction A comp osite is basically a syst em comp osed of two or more different individual p hases with distinctive characteristics. All comp osites have two basic co mponents, the matrix or host , and the reinforcement or fi ller. The matrix is t he element givin g shap e to t he composite, and p erforms as a load transfer medium to the filler. The filler is design ed to op timize selected mechanical p rop erties of the composite [1]. The mechanical and p hysical p rop erties of p oly mers can be significantly enhanced by adding various t yp es of fiber or p article reinforcements. Some of t he primary advantages of co mposite materials are high st rength to weight ratio, h igh bendin g st iffness, corrosion resistance, excellent fatigu e char acterist ics (comp arable to metals) and good thermal insul ation p rop erties [2]. Particle reinfor ced p olymeric comp osite materials are bein g used increasingly in a variety of modern engineering app lications and this trend is likely to continue due to the fact that these materials p ossess a number of highly desirable engineer ing p rop erties that can be exp loited to design st ructures with high demand on their p erformance. To cop e with t he obvious limitations of IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 p oly mers, for example, low st iffness and low st rength, and to exp and their app lications in different engineering areas, differ ent typ es of p articulate fillers are often added to p rocess p oly mer comp osites, which normally combine the advantages of their constituent p hases. Particulate fillers modify the mechanical and thermal prop erties of p olymers in many way s [3-5]. Particle filled p oly mer comp osites have become att ractive because of their wide app lications and low cost. Incorp orating inorganic min eral fillers into p last ic resin imp roves various p hy sical p rop erties of the materials such as mechanical st rength, modulus and heat deflection temp erature [6]. The objective of this work is to invest igate the flexur al (b endin g) p rop erties of p oly mer comp osites reinforced with glass and graphite p articles. It involves st udy ing the eff ect of vo lume fraction and ty p e of reinforcement p articles on the flexur al st rength, st iffness (modulus of elasticity ) and failure strain of the composites as comp ared to the poly mer matrix material. The flexural st rength (σ), flexural st iffness (E) and failure st rain (ε) are calcu lated by the followin g relationships [7]: where, P is the app lied load, L is the sp an of the sp ecimen, b is t he width of specimen and h is the thickness of specimen. where, is t he slope of the initial linear portion of the load-deflection curve. where, δ is the deflection at mid sp an of the sp ecimen. Materials and Methods Materials The matrix material used in this work is a thermoset epoxy resin type Conbextra Ep-10 supp lied by Fosroc Chemicals Company [8]. It is characterized by its low viscosity which facilitates its mixing with reinforcement materials, low creep characterist ics under sustained loading, resistance to repetitive dy namic loads, non-shrinkage which ensures comp lete surface contact and bond, r esistance to a wide range of chemicals, h igh tensile, comp ressive and flexural st rength. The hardener used with this ep oxy resin is M etap heny lene Diamine, which is a liqu id material with low viscosity and transp arent color. It is added to the resin in a ratio of 1:3 [9]. The reinforcement fillers used are glass and gr aphite p articles. Fume silica (Aerosil 200) sup p lied by Evonik Indust ries [10] was used to p revent the p recipitation of the reinforcement p articles. A small amount of this material (1% of total volume fraction) was added to the composite. S pecimen preparation Hand lay -up molding was emp loyed for fabricating the matrix material as well as the comp osites. The mold used in this work for cast ing p rocess was made of galv anized st eel with dimensions of (200, 80 and 4 mm). The mold was cleaned and a st icker fablon was p laced on the inside walls of the mold to p revent the sticking of the polymer material inside the mo ld. The poly mer matrix material was p repared by mixing the ep oxy resin with t he hardener in a 3 :1 ratio at room temp erature; a glass rod was used for gently st irring the mixture to avoid the formation of bubb les in the p olymer. Then the mixture was p oured into the mold. Finally , the mold was k ept on a level p lane and a galv anized steel cover p late was p laced on top of the mold to ensure obtaining a constant t hickness of material. In addition to t he poly mer matrix material, five composite materials were p repared. Composites 1, 2, 3 and 4 contain 20% glass p articles, 30% glass p articles, 20% graphite p articles and 30% IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 graphite p articles resp ectively. While comp osite 5 is a hy brid which contains 10% glass p articles and 10% graphite p articles. For p reparing comp osite materials, the epoxy resin was mixed with the hardener and p oured into t he mold in the same procedure described above. Then, the reinforcement filler p owder with the desired vo lume fraction was mixed with 1% fu me silica and added to the epoxy resin and mixed in a similar manner. All cast materials were left in the mold for 24 hrs at room temp erature to comp lete their solidification. Then, the cast materials were remov ed from the mold and placed in an oven at 50°C for three hrs t o p erform curing [9]. Finally, the cast materials were cut into flexur al sp ecimens according to ASTM standards as shown in Fig.1 [7]. Instrumentations A Universal Testing M achine Typ e Gunt WP300 was used for conducting flexural tests on sp ecimens of the matrix material and the five comp osites. For each material 5 replicates were tested. The flexural test p erformed in this work is t he three-point bending test in accordance with ASTM D-790 standard [7]. In this test, the sp ecimen is simply supp orted on two cylindrical b ars 100mm apart (sp an of sp ecimen) and the load is app lied at mid-sp an via a third cylindrical bar fitt ed to t he Universal test ing machine mov ing gr ip. Load is app lied until failure of the sp ecimen took p lace. The test rig also incorp orates a data acquisition un it and a comp uter disp lay of the load-deflection curve of each sp ecimen tested. The test rig is shown in Fig.2. Results and Discussion The flexural test results of the matrix material and the five composites are p resented in the form of st ress-stain curves as shown in Fig.3. It is noted that the matrix material fo llowed a ductile behavior to failure, with a formation of a definite "knee" in the curve indicating substantial yield, while all the composites followed a similar (almost identical) brittle behav ior to failure. The initial lin ear elast ic st ress-strain curve is followed by a non-linear behav ior p rior to britt le failure. This is in agreement with results of p revious invest igations [11and12]. The onset of nonlinear deflection coincided with the formation of micro-porous zone (or crack) in the comp osite material. Britt le behavior of p articulate comp osites is attributed to filler p articles which act as stress concentrators [11]. The flexural modulus, ultimate flexural st rength and failure st rain of tested materials are p resented in Table-1. It is noted that all comp osites p ossess markedly a higher modulus of elasticity than the matrix material. The increase in the modulus of elasticity of comp osites 1-5 as comp ared to the ep oxy resin matrix material is 28%, 36%, 40%, 136% and 60% resp ectively. These results imp ly that t he enhancement in flexural modulus of elast icity of comp osites is a function of filler volume fraction and st iffness; it increases with the increase in filler vo lume fraction and its st iffness. The effect of filler volume fr action is v erified by comp arin g st iffness of composites reinforced with the same filler but with different volu me fr actions. The stiffness of comp osite 2 (30% glass) is high er than that of comp osite 1 (20% glass) by 6%, while the st iffness of comp osite 4 (30% graphite) is higher than that of composite 3 (20% graphite) by 68%. As for the effect of filler st iffness on comp osite st iffness, it is observed that comp osites reinforced with the graphite p articles have higher st iffness than those reinforced with equivalent volume fraction of glass p articles, knowing that graphite is much stiffer than glass. The stiffness of comp osite 3 is higher than that of comp osite 1 by 9%, and the st iffness of comp osite 4 is high er than that of composite 2 by 84%. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 Previous invest igations [12-16] confir med that the modulus of elasticity of p articulate comp osites increases with the volume fraction of f iller, because hard f iller p articles have much high er st iffness than the p oly mer matrix material, and also due to better surface area for interaction between the filler p articles and the p olymer matrix. The effect of f iller typ e and volume fr action on the flexur al st rength of composites is not as evident as it was for comp osite stiffness. The ultimate flexural st rength of comp osites 1, 4 and 5 increased by 18, 6 and 58% resp ectively in comp arison with the matrix material, while comp osites 2 and 3 suffered from reduction in flexur al st rength of 20 and 14% resp ectively. Previous invest igations [12-16] also reported that the ultimate strength of p article filled comp osites might be higher or lower than the polymer matrix material. In view of Fu et al [15]; the ultimate st rength of a composite depends on the weakest fracture p ath throughout the material. Hard p articles affect the st rength in two way s. One is the weakening effect due to the st ress concentration they cause, and another is the reinforcin g effect since they may serve as barriers to crack growt h. In some cases, the weakening effect is p redominant and thus the comp osite strength is lower than the matrix; and in other cases, the reinforcing effect is more significant and then the comp osites will have st rengths higher than the matrix. Prediction of the st rength of comp osites is difficult. The difficulty arises because the st rength of comp osites is determined by the fracture behaviors which are associated with the extreme values of such p arameters as interface adhesion, st ress concentration and defect size/sp atial distributions. Thus, the load-bearing cap acity of a particulate comp osite dep ends on the strength of the weakest p ath throughout the microstructure, rather than the statistically averaged values of the microstructure p arameters [15]. As for failure st rain, it was found that all comp osites have lower failure st rain than the matrix material, and that the failure strain is inversely p rop ortional to t he filler volume fraction and filler st iffness. Similar results were reported by several invest igators [12, 13 and 16]. Sr eekanth et al [13] att ribute the reduction of failure st rain with the increase of filler content to the interference of filler in the mobility or deformability of the matrix. This interference is created through the p hy sical interaction and immobilization of the p oly mer matrix by the p resence of mechanical restraints, thereby reducing the elongation at break. Review of flexural p rop erties of all the comp osites subjected to flexural tests in this work, reveals that Composite5 which is a hy brid comp osite comp rising 10% glass and 10% graphite offers the best flexural p rop erties. The flexural st iffness and st rength of this comp osite are 60% and 58% higher than those of the matrix material. Conclusions The flexural p rop erties of p oly mer comp osites reinforced with glass and graphite p articles have been evaluated. All comp osites have higher st iffness than the p oly mer matrix material. The st iffness of the composites is directly p rop ortional to the volume fraction and st iffness of fillers. The ultimate flexural st rength of three of the comp osites is higher than that of p oly mer matrix material, while two comp osites have lower ultimate flexur al st rength than the p oly mer matrix material, irrelevant to volume fraction or typ e of fillers. The failure strain of all comp osites is lower than that of t he p oly mer matrix material; t he failur e st rain is inversely p rop ortional to t he stiffness and volume fraction of fillers. The hy brid comp osite reinforced with 10% glass p articles and 10% graphite p articles p resents the best overall flexural p rop erties. It has the highest ultimate flexural st rength as well as an excellent stiffness and a st rain to failure comp arable to that of t he p olymer matrix material. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 Re ferences 1. Hernandez-Luna,and Alejandro. M ay (2003). Structure p rop erty and deformation analysis of p olyp ropy lene montmorillonite nanocomp osites. A dissertation p repared for the degr ee of Doctor of Philosop hy , University of North Texas. 2. My lavarap u, Phani Sury a Kiran. December (2007). Characterization of advanced comp osites- A nondestructive approach. A dissertation p repared for the degree of Doctor of Philosop hy , Louisiana State University . 3. Curtu, I and M otoc Luca, D. (2009). Theoretical and Exp erimental Ap p roach of multiphase comp osite materials. In DAAAM International Scientific Book, B. Katalinic, Ed. Vienna: DAAAM International Publishing, 349-362. 4. M ilhans, J. (2009). M odeling of the effective elastic and thermal p rop erties of glass-ceramic solid oxide fuel cell seal materials. M aterials and Design, 30 : 1667-1673. 5. Wang, M . and Pan, N. (2008). Predictions of effective p hy sical p rop erties of comp lex multiphase materials. M aterials Science and En gineering, 63 : 1-30. 6. Bose, Sury asarathi and M ahanwar, P.A. (2004). Effect of p article size of filler on p rop erties of Ny lon-6. Journal of M inerals & M aterials Characterization & Engineering, 3(1): 23-31. 7. Shah, V. (1984). Handbook of p last ics t esting technology . John Wiley & Sons Inc. 8. Fosroc International Limited. December (2000). Data sheet 22, Conbextra EP, CI/SfB: q4. www.fosrocuk.com. (UV) البنفسجیة فوق األشعة تأثیر دراسة .(2009) .حسین رغد محمد، شاكر و مجدي، حسن محمد؛ ضیاء، بلقیس 9 . ى د .اإلیبوكسي لمتراكبات المیكانیكیة الخصائص بعض عل ، المجل 27المجلد,.ز.15العدد ، 27 مجلة الھندسة والتكنولوجیا ,www.evonik.comJanuary 2009. Data sheet Aerosil 200. 10 15 العدد, th s. 24Evonik Indust rie/. 11. Nie, Shihua; B asaran, C emal; Hut chins, Clyde S; and Ergun, Hale. (2006).Fa ilure M echanisms in PMMA/ATH Acry lic Casting Disp ersion. Journal of the M echanical B ehavior of M aterials, 17( 2): 79-96. 12. Sapuan, S.M .; Harimi, M . and M aleque M . A. October( 2003). M echanical p rop erties of epoxy / coconut shell filler p article comp osites. The Arabian Journal for Science and Engineer ing, 28, (2B). 13. Sreek anth, M .S.; Bambole, V.A.; M haske, S.T. and M ahanwar, P.A. (2009). Effect of Particle Size and Concentration of Fly ash on Prop erties of Poly ester Thermop last ic Elastomer Composites. Journal of M inerals & M aterials Characterization & En gineering, 8(3): 237-248. 14. Sideridis, E.; Ky top oulos, V.N.; Prassianakis, J.N. and Sakellar is, I. Ap ril (2008). Acoust ic and M echanical p rop erties of p articulate comp osites. 3rd International Non Dest ructive Test ing Sy mposium and Exhibition, Ist anbul Turkey. 15. Fu, Shao-Yun; Fen g, Xi-Qiao; Lauke, Bernd and M ai, Yiu-Wing. (2008). Effects of p article size, p article/matrix interface adhesion and p article loading on mechanical p rop erties of p articulate–p oly mer comp osites. Comp osites: Part B 39 () pp 933–961. 16. Akinci, A. January (2009). M echanical and morphological prop erties of basalt filled polymer matrix comp osites. Archives of materials scien ce and engineering 35 issue 1, p p 29-32. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 Table(1): Flexural modulus, ul timate flexural strength and failure strain of tested materials Material Fle xural modul us (G Pa) Fle xural strength (M Pa) Fail ure strain (%) M atrix material (ep oxy resin) 2.5 25 1.2 Composite 1 (20 % glass) 3.2 29.5 1 Composite 2 (30 % glass) 3.4 20 0.65 Composite 3 (20 % graphite) 3.5 21.4 0.75 Composite 4 (30 % graphite) 5.9 26.5 0.55 Composite 5 (10 % glass and 10% graphite) 4 39.6 1.1 Fig.(1): S tandard flexural test specimen Fig.(2): Flexural test-rig with an exploded view of the matrix material test specimen under three-point bending load IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL.24 (1) 2011 Fig.(3): Typical flexural stress-stain curves of tested materials 2011) 1( 24المجلد مجلة ابن الهیثم للعلوم الصرفة والتطبیقیة مركبة بولمیریة معززة بدقائق الزجاج والكرافیت خواص األنحناء لمواد احمد عالءالدین ابراهیم هیئة التعلیم التقني، بغداد -الكلیة التقنیة 2010تشرین االول 20 استلم البحث في 2010كانون االول 14 في البحث قبل خالصةال .خواصها األنحنائیة فيأجریت هذه الدراسة لمعرفة تأثیرتعزیز المواد البولیمریة بدقائق الزجاج والكرافیت مادة أساس ومعززة بكسور حجمیة مختلفة من دقائق المادة نفسها المادة البولیمریة عمالخمسة مواد مركبة باست حضرت الى مادة مركبة عن" فضاللكل منها % 30و% 20مقداره لئة، وهي تشمل دقائق الزجاج ودقائق الكرافیت وبكسر حجميالما .كرافیت% 10زجاج و % 10هجینة تحتوي على عن النقاط الثالث باستخدام جهاز أختبار جامع على عینات من المواد المذكورة أعاله أضافة يأجریت أختبارات األنحناء ذ .لمادة المالئة لتحدید خواصها األنحنائیةا .أظهرت نتائج األختبارات العملیة أن جساءة األنحناء لجمیع المواد المركبة كانت أكبر بشكل ملحوظ من المادة األساس امتلكت كرافیت والمادة المركبة الهجینة % 30زجاج وال % 20متانة األنحناء، فأن المواد المركبة ذات ال الى أما بالنسبة .متانة أنحناء أكبر من المادة األساس مواد مركبة بولیمریة، خواص انحناء، دقائق زجاج وكرافیت: یةمفتاح كلمات