Dry Slide Wear Behavior of Graphite and SiC, TiO 2 Filled the Unidirectional Glass-Epoxy Composites Dry Slide Wear Behavior of Graphite and SiC, TiO 2 Filled the Unidirectional Glass-Epoxy Composites A. Madhanagopal a and S. Gopalakannan b a Department of Mechanical Engineering, University College of Engineering Arni, Anna University,Tamilnadu 632326, India b Department of Mechanical Engineering, Adhiparasakthi Engineering College, Melmaruvathur,Tamilnadu 603319, India Summary This study determines the friction and the wear properties of the unidirectional glass epoxy composite with Gr, SiC TiO 2 powder by using pin on disk apparatus. This tribological data is obtained in dry sliding condition for a constant sliding time of 30 minutes. Test specimens are prepared using hand lay-up process and by varying the different (2, 5, 7) percentage each of graphite and SiC, TiO 2 particles addition for the combination of fiber and matrix. The tests are performed by varying the operating parameters of contact pressure (p) and velocity (v). The composites (2% 5%, and 7%) are worn by dry sliding at the steel counter face under ambient conditions. The coefficient of friction reaches maximum of 0.78 at 2 kg load, 2 m/s velocity with testing time duration of 24 min. whereas 5%, 7% sample shows the coefficient of friction 0.28, 0.25 respectively. The specific wear rate value drops to 0.79 (mm 3 /N-m 10-6 ) at 2 kg load at 2 m/s velocity for the 5% specimen. The maximum reduction in the specific wear rate at 3 kg load, 1m/s velocity is 32.7 percentages, 5.63 percentages for the 5,7 percentage specimen compared to 2% specimen for the graphite and SiC, TiO 2 particle filled composite specimen respectively. The SEM images are also taken to support the results. Keywords: Wear, Epoxy, Glass fiber, Gr, SiC and TiO 2 filler particles 1. Introduction Composite is defined as the material in which two or more distinct materials are combined together but uniquely identifiable in the mixture, its mechanical performance and properties are superior to those of the constituent material acting independently. Composite materials are used in applications where friction and wear are important parameters. Examples range from gears, seals and bearings, brakes and artificial joints. Composite materials are often preferred because of their low weight, easy process ability, high strengthto-density ratio and high chemical resistance. K. Srinivasa et al. 1 presents the tribological behaviour of epoxy composites containing the particulate fillers. The synergic effect of hybrid filler Gr-SiC is to improve the wear resistance when compared with that of Gr/SiC. The improvement in wear resistance for the composite containing 5%SiC 35%Graphite is 85% when compared with epoxy, 25% over composite containing 40%Gr and 36% over 40%SiC. The composites containing 5% Gr and 35% SiC exhibits highest wear resistance. M. Sudheera et al. 19 have enhanced mechanical and wear performance of epoxy/glass composites with PTW/graphite hybrid fillers epoxy/glass composite containing two different micro-fillers was developed by vacuum bagging technique. The effect of ceramic whisker (7.5 wt.%) and solid lubricant filler (2.5 wt.%) on mechanical and dry sliding wear behavior of epoxy/glass composites was studied it has been proven that the maximum reduction of about wear rate 49% and under a load of 90 N, this is due to addition of ceramic whiskers. 2. Experimental 2.1 Compositions in the Composite Table 1. Percentage contribution of filler and glass epoxy Sample Fiber and Graphite (G) SiC wt.% Tio 2 wt.% Material Matrix (E) wt.% wt.% 2% 94 2 2 2 5% 85 5 5 5 7% 79 7 7 7 a E -mail :madgopal2@gmail.com Smithers Information Ltd., 2017 Polymers & Polymer Composites, Vol. 25, No. 3, 2017 193
A. Madhanagopal and S. Gopalakannan 2.2 Specimen Preparation Epoxy resin is mixed with the hardener is mixed by 10:1 under ambient condition. Different specimens have been manufactured by adding different percentage of 2%, 5% and 7% graphite powder and are mixed with epoxy resin. As per the required dimensions wooden mould is prepared. Then, the resin is poured inside the mould with glass fibers. It is allowed to solidify for 24 hrs. Pin on disk machine is a versatile unit designed according to ASTM G99 to evaluate the wear and friction characteristics on a variety of material exposed to sliding contacts in dry or lubricated environments. The sliding friction test occurs between the stationary pin and a rotating disk. Normal load, rotating speed and the wear track radius can be varied. Electronic sensor monitors the wear and the tangential force of friction as a function of load, speed, lubricating conditions and the environment. Table 2. The variation of velocities and sliding distance with respect to wear track diameters and speeds Speed (rpm) Wear track diameter (mm) Velocity (m/s) Sliding distance (m) 636 30 1 1798. 1275 30 2 3605. Figure 1. Composite specimens. 1. 2% of graphite filled glass epoxy specimen; 2. 5% of graphite filled glass epoxy specimen; 3. 7% of graphite filled glass epoxy specimen Figure 2. Experimental setup. (A) Composite specimen, (B) Rotating disk; (C) Electronic displacement sensor; (D) Frictional force measuring sensor; (E) Loading point The coefficient of friction can be calculated from the following equation: µ=f/w where W - Normal load (N), F- Frictional force (N) (mm 3 /N-m) where W Normal load (N) m - Mass reduction (kg) l - Sliding distance (m) ρ- Material density (kg/mm 3 ) 3.1 Coefficient of Friction From Graphs 1-3 it is commonly understood that the increase of filler content reduces the coefficient of friction, it increases with respect to load. Graph 1. Variation of coefficient of friction with respect to time (sec) under 1 kg load, 1 m/s velocity. 3. Results and Discussions The following graphs are drawn for the various samples at a constant load and velocity conditions, the sliding distance (1797 m) and the time (30 min) remains constant. 194 Polymers & Polymer Composites, Vol. 25, No. 3, 2017
Dry Slide Wear Behavior of Graphite and SiC, TiO 2 Filled the Unidirectional Glass-Epoxy Composites Graph 2. Shows the variation of coefficient of friction with respect to time (sec), under 2 kg load, 1 m/s velocity Graph 3. Shows the variation of coefficient of friction with respect to time (sec), under 3 kg load, 1 m/s velocity Figure 3. Microscopical view of the 2% sample. 1. Resin surrounding the broken glass fibers; 2. wear of the epoxy resin; Broken glass fibers From Figure 3 it shows that bulging of glass fibers and the resin comes out from the specimen and stays around the broken glass fibers. When the fiber ends are exposed to the steel counter face it causes the remarkable rise in surface roughness of the steel counter face. This again continues with increase in load which leads to the fiber deformation and the loss of binder material hence contributing to coefficient of friction. Graphs 4-6 are drawn for the various samples at a constant load and velocity conditions, the sliding distance (3603 m) and the time (30 min) remains constant. The sliding distance and load increases the more and more the possibility for reduction in the coefficient of friction due to the lubricating effects of graphite particles. It is due to increase in loss of binder material which is rich in powder particles. But this is may not be appreciable in case of 2% sample as compared to 5, 7% filled composite samples. From the above graphs and SEM image shows increase of load causing the bulging effect and also resin is worn out between the fibers leaving the fiber ends exposed. Since the glass fibers are brittle and the exposed ends are expected to be fragmented easily by rubbing action. This increases breakage of fibers and creates the debris of glass particles which acts as the third body abrasives causing rise in coefficient of friction and mass loss. Graph 4. Variation of coefficient of friction with respect to time (sec) under 1 kg load, 2 m/s velocity Polymers & Polymer Composites, Vol. 25, No. 3, 2017 195
A. Madhanagopal and S. Gopalakannan Graph 5. the variation of coefficient of friction with respect to time (sec), under 2 kg load, 2 m/s velocity Graph 6. shows the variation of coefficient of friction with respect to time at under 3 kg load, 2 m/s velocity 3.2 Specific Wear Rate The possible effect for the filler particles contribution to the reduction of the coefficient of friction is due to the lubricating effect of the particles. It is again reduces the shear force is induced in the contact area of the composite pin this leads to reduction in specific wear rate. During sliding the wear the frictional energy is a dominant because of this heat is generated, which determines the contact temperature could greatly affect mechanical properties of the polymer composite and consequently influences the wear performance also if the Tio 2 percentage is more this again reduces the amount of heat generation and decreases the wear rate due to thin film formation at the steel counter face. In case of glass epoxy composites, polymer matrix consists of wear debris of the pulverized glass particles on metallic counter surface. This particles can either lost to the contact zone or remain there for a fixed time as a transfer layer. In such a cases, the polymer component can cushion the surface asperities and reduce the effective roughens. But the pulverized glass particles can act as a third body abrasive leading to enhanced roughing of the counter surface, due to this the specific wear rate and coefficient of friction will increase. But here this trend is different with the presence of TiO 2 graphite and SiC micron particles. Table 3. Variation of specific wear rate (mm 3 /N-m 10-6 ) for 2, 5, and 7% samples velocity at 1 m/s for various loads Sample/ 2% 5% 7% Load (kg) 1 9.72 3.17 9.2 2 6.48 3.17 4.6 3 3.24 1.06 3.06 Table 4. Variation of specific wear rate (mm 3 /N-m 10-6 ) for 2,5,7% samples velocity at 2 m/s for various loads Sample/ 2% 5% 7% Load (kg) 1 4.85 3.17 3.05 2 3.23 0.79 3.06 3 2.69 1.58 2.04 4. ConclusionS Comparing performance various percentage of filler added glass epoxy composite shows their wear pattern and they are plotted as graphs. The mechanism involved for change of trend is identified and discussed in detail with help of SEM image. Among the three loads and two speed conditions the coefficient of friction reaches maximum of 0.78 at under 2 kg load, 2 m/s velocity with testing time duration of 24 min. whereas 5%, 7% sample shows the coefficient of friction 0.28, 0.25 respectively. 196 Polymers & Polymer Composites, Vol. 25, No. 3, 2017
Dry Slide Wear Behavior of Graphite and SiC, TiO 2 Filled the Unidirectional Glass-Epoxy Composites Graph 7. Variation of specific wear rate (mm 3 /N-m 10-6 ) for 2,5,7% samples velocity at 1 m/s for various loads Graph 8. Variation of specific wear rate (mm 3 /N-m 10-6 ) for 2,5,7% samples velocity at 2 m/s for various loads The increase in load causes increase specific wear rate at less sliding speeds (636 rpm). It is because of the polymer matrix consisting of wear debris of the pulverized glass particles on metallic counter surface. When the sliding speed reaches 1275 rpm, load 2 kg, 3 kg the specific wear rate reduces. Since at high loads and speeds the filler particles can either lose to the contact zone or remain there for a fixed time as a transfer layer. In such cases the polymer component can cushion the surface asperities and reduce the effective roughness. It is also understood that for the glass epoxy composite, the filler addition shows the appreciable reduction in the coefficient of friction and the specific wear rate is optimum only at 5% beyond which specific wear rate increases. These are the positive marks, which makes the particles filled composites suitable for Tribological applications. References 1. Srinivas K, (2014) et al. Wear Behaviour of Epoxy Hybrid Particulate Composites Procedia Engineering, 97, 488 494. 2. B. Suresha, G. Chandramohan (2006) The Role of Fillers on Friction and Slide Wear Characteristics in Glass-Epoxy Composite Systems, 5(1), 87-101. 3. Chang Z. et al. (2006) Epoxy nanocomposites for the Enhancement of the wear resistance by nano-tio2 particles Elsevier publications, Wear, 650, 345-357. 4. Friedrich K. and Renicke R., (1998) Friction and wear properties of polymer based composites Me. Compo. Mater. 34, 456-548. 5. Halpin J.C. et al. (1984) Primer on composite materials, analysis Technomic publishing, 7 588-954. 6. Jaydeep Khedkar, et al. (2002) Materials Science and Engineering, Elsevier publications, Wear, 252, 361-369. 7. Klaus Friedrich, et al. An Tribology of polymeric nano composites Engineering series 55 10-25. 8. Mary Kathryan Thoms, et al. (2006) A proposal for the calculation of wear Tribology intrall. 52 4-13. 9. Mallick P.K., et al. (1993) Fiber reinforced composite materials manufacturing and design Mannl. ekker. lnc 14 14-56. 10. Mathew Naveen V., et al. (2007) Directionally oriented warp knit GFRP composites Elsevier publications, Wear, 263, 930-938. 11. Potter K., (1997) An Introction to composite products Hand book. 12. Rong M.Z., et al. (2001) Microstructure and tribological behavior of polymeric nanocomposites, Ind. Lubr. Tribol. 53, 72 77. 13. Subesha B. (2008) The role of fillers on tribological behaviour of fiber reinforced epoxy composite system Elsevier publications, Wear, 4 467-498. 14. ASTM standard test methods for the pin on disk tester Standards specifications ASTMG99 at www. koehherinstrument 15. Sawyer G.W., et al. (2003) A study on the friction and wear behaviour of PTFE filled with alumina nanoparticles, Elsevier publications, Wear, 254, 573 580. 16. N. Mohan, C. R. Mahesha, R. Raja (2014) Tribo- mechanical behaviour of SiC filled glassepoxy composites at elevated Temperatures International Journal of Engineering, Science and Technology 6(5) 44-56. 17. A. Molazemhosseini et al. (2013) Tribological performance of PEEK based hybridcomposites reinforced with shortcarbon fibers andnanosilica Wear, 397 404 18. Bhagwan D. Agarwal and Lawrence J. Broutma (1995) Analysis and Polymers & Polymer Composites, Vol. 25, No. 3, 2017 197
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