IMPACT DAMAGE, HARDNESS AND TRIBOLOGY CHARACTERIZATION OF EPOXY RESIN BASED COMPOSITES REINFORCED WITH BASALT FIBERS IN COMBINATION WITH TiO 2

Transcription

1 T. Narendiranath Journal of Chemical Babu, Technology R.V. Mangalaraja, and Metallurgy, S. Saravanan, 51, 6, D. 2016, Rama Prabha IMPACT DAMAGE, HARDNESS AND TRIBOLOGY CHARACTERIZATION OF EPOXY RESIN BASED COMPOSITES REINFORCED WITH BASALT FIBERS IN COMBINATION WITH TiO 2 AND SiC T. Narendiranath Babu 1, R.V. Mangalaraja 2, S. Saravanan 3, D. Rama Prabha 4 1 School of Mechanical Engineering, VIT University Vellore, India narendiranathbabu.t@vit.ac.in 2 Department of Materials Engineering Faculty of Engineering, University of Concepcion Concepcion, Chile 3 Department of Chemical Engineering National Institute of Technology Trichy, India 4 School of Electrical Engineering, VIT University Vellore, India Received 17 July 2015 Accepted 03 June 2016 ABSTRACT Impact damage, hardness characterization, frictional and wear behavior of epoxy resin based composites reinforced with basalt fibers in combination with TiO 2 and SiC were investigated using an impact testing machine, a hardness testing machine and a pin on disc machine. The basalt contained different fillers and short fibers whose presence varied in steps of weight percentage from 23 % to 50 %. It was fabricated using the conventional hand-layup technique followed by the light compression moulding technique. The frictional behavior of the composite specimen was determined by testing on a pin on disc test machine under different operating conditions. The present investigation focused on the determination of the friction coefficient of epoxy resin based composites reinforced with basalt fibers in combination with the fillers. The effects of basalt short fibers content and load were examined under dry conditions. The results showed that the friction coefficient decreased with the filler contents increase. The hardness and the impact damage of epoxy resin reinforced with basalt fiber was examined and it was found that its reinforcement with basalt fiber along with fillers such as titanium oxide, silicon carbide, barium sulphate and graphite made it more advantageous than other specimens. Keywords: basalt fiber, impact behavior, hardness, wear resistance. INTRODUCTION Composite materials are in limelight nowadays due to their applications ranging from automobile to aerospace industries. Fiber matrix composites have received increased research interests over several years due to their excellent mechanical and thermal properties compared with the conventional materials [1]. Recently, they have become candidates for critical structural applications because of possessing a combination of superior mechanical properties such as better elastic modulus, tensile strength, high temperature stability and wear resistance in comparison with the parent matrix fibers [2]. The fiber matrix is considered a potential engineering material for various tribological applications due to its excellent mechanical and tribological properties [3]. It is usually reinforced with high strength and high modulus materials which may be in the form of fibers, whiskers, or particulates. The addition of fillers reinforcement to a fiber matrix improves its strength and stiffness [4]. When compared to the continuous fiber reinforced composites, short fiber reinforced composites offer several advantages such as improved anisotropy, ease of fabrication, and lower cost [5]. 677

2 Journal of Chemical Technology and Metallurgy, 51, 6, 2016 The increase in demand for lightweight, stiff and strong materials has led to the development of fibers reinforced with fillers. Among them, basalt fibers are not only less expensive but also a lead-free material which makes them environmentally friendly [6]. In addition, these basalt fibers possess excellent mechanical and tribological properties and so they are considered as potential engineering materials for various wear related applications since the friction and wear occurring in the machinery components affect their performance as well as their life [7]. Their tribological properties can be further improved by strengthening their capability [8-10] and corrosion resistance by reinforcement with SiC, TiO 2, and BaSO 4. Therefore, the investigation of the tribological behavior of basalt fibers with filler based materials becomes increasingly important. A pin on disc wear testing machine was used to investigate the tribological behavior of fiber composites and matrix alloy over a load range of 3 kgf - 9 kgf and at 700 rpm rpm. The wear resistances of sample 2 matrix, particulate reinforced composites are superior to that of other samples. In view of the above discussion, an attempt has been made to develop a basalt fiber composite and study the effect of basalt short fibers content in presence of TiO 2, BaSO 4 and SiC as fillers. The study focuses further on the hardness characteristics, the coefficient of friction and wear of the materials obtained under dry lubricated conditions. EXPERIMENTAL Materials Basalt fibers made of 360 gsm with a diameter of 5 μm-10μm were used. A medium viscosity epoxy resin ( LY556) and a room temperature curing polyamine Table 1. Composites compositions and designations. hardener (HY951) both supplied by Ciba Geigy India Ltd. composed the matrix system investigated. Titanium oxide, barium sulphate and silicon carbide particulates were used as fillers. Fabrication The basalt fibers were reinforced separately in epoxy resin to prepare the fiber reinforced composites. The composition and designation of the composites prepared for this study are listed in Table 1. The fiber material was mixed with Epoxy LY 556 resin in different percentages. The fabrication of the composite pin was carried out by the conventional hand-layup technique followed by the light compression moulding technique. Low temperature curing Epoxy LY556 Resin of Young modulus of 3.42 GPa and density of 1200 kg m -3 was used. It was mixed with HY951 hardener for hardening and support in a weight ratio of 10:1 as recommended. The basalt fibers had Young modulus of 72.5 GPa and density of 2500 kg m -3. They were mixed thoroughly with the epoxy resin. The laminate prepared was of a size 250 mm x 250 mm x3 mm. It was then heated aiming hardening in a furnace at 100 C for 2 hours. The cast of each composite was cured under a load of about 50 kg for 24 hours prior to its removal from the mould. A releasing agent (silicon spray) was used to facilitate the removal. Then the cast was post cured in the air for another 24 hours. Specimens of suitable dimensions for physical and mechanical characterization and abrasive wear testing were cut using a diamond cutter. Utmost care was taken to maintain uniformity and homogeneity of the composites. All the specimens were prepared in correspondence with ASTM standards. The specimens were of dimensions of 10 mm in diameter and 30 mm in length. S. No. Designations Basalt Fibre Epoxy Resin Titanium oxide Silicon carbide Barium sulphate Graphite 1 Sample Sample Sample Sample Sample

3 T. Narendiranath Babu, R.V. Mangalaraja, S. Saravanan, D. Rama Prabha Emery paper of grade 60 was used to provide necessary surface finish. Fabrication Process 1. The major component of basalt fiber is Epoxy LY556 (Resin). 2. Hardener HY951 is used for hardening and support. 3. Resin and the hardener are mixed in the ratio of 10:1 and the mixture made up is called MATRIX. 4. Tool is prepared by standard method. 5. Apply the matrix on glass cloth which is wrapped around the mandrel. 6. Ensure that the proper weighing has been done. 7. Clamp the tool die for 2 hrs at ambient temperature condition. 8. The sample is then furnace heated at 100 C for 2 hours for hardening. 9. Take out and cool the specimen until it reached the room temperature. 10. Flash is removed from the sample. 11. Demoulding i.e., the clamp is removed from the specimen. 12. Cut the specimen to the appropriate dimension as per experimental needs. 13. Emery paper of grade 60 is used to provide necessary surface finish. Experimental setup Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to the resistance to bending, scratching, abrasion or cutting. Procedure for Rockwell hardness test The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load usually 10 kgf. When equilibrium has been reached, an indicating device, which follows the movements of the indenter and thus responds to changes in depth of penetration of the indenter, is set to a datum position. While applying the preliminary minor load, an additional major load is applied with resulting increase of penetration. After reaching the equilibrium again, the additional major load is removed but the preliminary minor load is still maintained. The removal of the additional major load allows a partial recovery, and so it reduces the depth of penetration. The permanent increase of penetration depth, resulting from the application and removal of the additional major load, is used to calculate the Rockwell hardness number. Procedure for Charpy Impact test The Charpy test determines the resistance of a material against shocks. The test temperature is very important because the resistance decreases while decreasing the temperature. The temperature at which the resistance suddenly drops to a lower value, i.e. the shifting from ductile to brittle fracture, is called the transition temperature. It is important for the designer to know the location of the transition temperature. As a matter of fact, operating below this temperature will increase the risk of fracture. The test consists of breaking a test piece notched in the middle and supported at each end just by giving one blow from a swinging pendulum under conditions defined by corresponding standards. The energy absorbed is determined in joules. It is a measure of the impact strength of the material. The test bar, which is notched in the center, is located on two supports. The hammer will fracture the test bar and the absorbed energy (Kg-m) is an indication for the resistance of the material to shock loads. Experimental Procedure for Pin on Disc Machine This test method describes a laboratory procedure for determining the wear of materials, which are undergoing the sliding process, using a pin-on-disc machine. Materials are tested in pairs under nominally non-abrasive conditions. A pin on disc is an instrument that measures the tribological quantity, such as wear behavior, between two surfaces in contact. Table 2 shows the test rig parameters. A pin-on-disc test setup is used for slide wear experiments. The surface of the sample (5mm 5 mm) glued to a pin of 10 mm diameter and 30 mm length comes in contact with a hardened disc of hardness 60 HRC. The counter surface disc wa made of En31 steel. It had a diameter of 165 mm, it was 8 mm thick and its surface roughness (Ra) was of 1.6 μm. The test was conducted on a track of 115 mm diameter for a specified test duration, load and velocity. Prior to testing, the test samples were rubbed against a 600-grade SiC paper. The surfaces of both the sample and the disc are cleaned prior to the test with a soft paper soaked in acetone. The pin assembly 679

4 Journal of Chemical Technology and Metallurgy, 51, 6, 2016 was initially weighed using a digital electronic balance (0.1 mg accuracy). The test was carried out by applying the normal load at different sliding velocities. At the end of the test, the pin assembly was again weighed using the same balance. A minimum of three trials were conducted to ensure repeatability of test data. The friction force at the sliding interface of the specimen was measured at an interval of 5 min using a frictional load cell. The coefficient of friction was obtained by dividing the frictional force by the applied normal force. The aim for conducting this test was to investigate the effect of load and velocity on the tribological behavior. The bearing velocities were kept within the interval of 2.5 m s m s -1, while the bearing loading varied up to 9 kgf. RESULTS AND DISCUSSION This work was aimed to investigate the impact, the hardness, the wear and friction of epoxy resin composites reinforced with basalt fibers and fillers of TiO 2 and SiC. Aiming a comparison, the wear properties of plain basalt epoxy were also evaluated under identical test conditions. This work helps to understand the function of different fillers (titanium oxide, barium sulphate and silicon carbide) of basalt epoxy composites. It is believed it helps to understand the function of different fillers of basalt epoxy composites. Rockwell Hardness Test Result The Rockwell Hardness test was performed for all five specimens at 100 Kgf. Three trials were taken for each specimen. The steel indenter was used to carry out the test. The hardness of the composite increased with increase of the content of the fibers and fillers. This can be assigned to the tight bonding between the resin, the fibers and the fillers such as titanium oxide, silicon carbide and graphite powder which resist penetration [5]. Table 3 shows the results of the Rockwell Hardness Test. It is seen that specimen 2 has the highest hardness of 41.1 HRB when compared to that of the other specimens. Charpy Impact test The impact test is carried out using a charpy testing machine to find out the impact energy value i.e., the energy required for breaking the composite specimen determining their impact strength. The values of the Table 2. Test rig parameters. S.No Description Details 1 Speed Min 200 rpm, max 2000 rpm 2 Normal Load 200N max 3 Frictional Force 200N max 4 Wear ± 2mm 5 Wear Track Diameter Min 50mm, max 100mm 6 Sliding Speed Min 0.3m/sec, max 10m/sec 7 Preset Timer 99/59/59 hr/min/sec 8 Specification Size (Pin) Ø3,4,5,6,8,10 & 12mm 9 Wear Disc Size Dia 165mm 8mm Thick, EN-31 Hardened To 60hrc, Ground To Surface Roughness 1.6Ra 10 Environmental Chamber This chamber prevents oil spillage and collects debris after test 11 Software Winducom Software Interface Comport 680

5 T. Narendiranath Babu, R.V. Mangalaraja, S. Saravanan, D. Rama Prabha latter are given in Table 4. The results show that the impact strength of the hybrid composites improves with increase of the fiber and particulate loading [7]. Furthermore, these results show that the hybrid composite of specimen 2 containing epoxy resin reinforced with basalt fibers and fillers such as titanium oxide, silicon carbide, barium sulphate and graphite has the highest impact strength of 7 Kg-m. The friction coefficient and the wear rate of the pure and the filled basalt fiber composites sliding against a metal disc are comparatively shown in Figs It can be seen that the friction coefficient and the wear rate of the filled basalt fabric composites decreases when compared with that of the unfilled one. It is clear that the graphite is more beneficial than TiO 2 and BaSO 4 in decreasing the friction coefficient and increasing the wear resistance of the composites in case they are incorporated as single additives. Besides, it is worth noting that further addition of TiO 2, SiC and graphite to epoxy resin composites can enhance the friction reduction and anti-wear properties of the basalt fabric composites to a greater extent. In case of TiO 2 this is attributed [7] to the positive contribution of nano-oxide particles to the development of a thin and uniform transfer film and the formation of a transfer film of better adherence on the counterpart steel disc during sliding. The graphs show also that the friction coefficient of basalt fiber filled with TiO 2, and graphite decreases by 15 %, while the corresponding wear rate decreases by 17 % when to those of the pure basalt fabric composites. These results suggest that the simultaneous addition of graphite in the presence of TiO 2, SiC improves significantly the friction reduction and the anti-wear abilities of basalt fiber composites due to the synergistic effects. The tribological properties of the different composites vary differently with the loads variation. The friction coefficient of the unfilled basalt fabric composites increases with increase the load up to 9 Kgf. Further load increase results in dropping out of the basalt fibers from the matrix during the friction process. This leads to a severe abrasive wear and results in increase of the friction coefficient. In case of 9 kgf load, the friction coefficient decreases slowly because of the micro-melting and mechanical deterioration caused by the friction heat [9]. The wear rate of the unfilled basalt fiber composites increases from 3 Kgf to 9 Kgf. The results presented show also that the adhesion between the fiber and matrix deteriorates with load increase. This provides pulling out or peeling off of the pulverized basalt fibers, which is accompanied by composites wear resistance decrease. It is also seen that the friction coefficient and the wear rate of TiO 2 and SiC filled basalt fabric composites increases when the load exceeds 6 Kgf. The friction coefficient and the wear rate of graphite filled basalt fabric composite decreases with load increase. In case of simultaneous addition of TiO 2, SiC and graphite, the friction coefficient and the wear rate of the composites decreases. Adhesive wear predominates with load increase which is generally less dangerous for polymer composite sliding surface. Film formation is generated on the counterpart of the metal surface under dry sliding conditions. Its quality may increase with load increase. These studies also suggest that the formation of transfer films can be enhanced at higher load, which in turn can shorten the running-in period. Hence, it is favorable for improving the tribological properties of Table 3. Results of the Rockwell Hardness Test. S. No. Specimen Hardness of Trial 1/ HRB Hardness of Trial 2/ HRB Hardness of Trial 3/ HRB Average Hardness/ HRB 1 Specimen Specimen Specimen Specimen Specimen

6 Journal of Chemical Technology and Metallurgy, 51, 6, 2016 polymer composites. The further increase of the load applied results in wear debris formation but the thin layer on the worn surface excludes deterioration of the tribological properties. It is clearly seen that the composites have lower friction coefficients and wear rates with increase of the sliding speed. In case of a high sliding speed, there is not enough time to produce more adhesive points because of the shorter surface contact. As a result, the friction force component from adhesion can be greatly decreased which brings about easier formation of a transfer film as rupturing becomes difficult under these conditions. Moreover, the decrease of the friction coefficient and the wear rate affect the surface softening caused by frictional heat [5]. It is assumed that the interfacial temperature is a crucial factor determining the tribological characteristics of polymer composites under a small load. Figs present the friction coefficient of various basalt fabric composites as a function of the sliding time and the load. For all the fabric composites, the friction coefficient appears within the running-in period. It is present during the following steady-state period. Its Table 4. Charpy test рesults. Wear and Friction Test Results. S. No Designation of Specimen Impact Energy (Kg-m) 1 Specimen Specimen Specimen Specimen Specimen 5 4 initial value is much higher. It becomes stable when a balance between the formation and peeling-off of the transfer films formed on the counterparts is reached. The friction coefficient curves of the pure basalt fiber composites and basalt fiber with fillers are more fluctuant indicating the highly inhomogeneous and unstable characteristics of these fabric composites. The periodic plowing and rolling action of the debris may also be responsible for this behavior. Fig. 1. Wear test at 700 rpm and 3 kgf load. Fig. 3. Wear test at 700 rpm and 9 kgf load. Fig. 2. Wear test at 700 rpm and 6 kgf load. Fig. 4. Wear test at 800 rpm and 3 kgf load. 682

7 T. Narendiranath Babu, R.V. Mangalaraja, S. Saravanan, D. Rama Prabha Fig. 5. Wear test at 800 rpm and 6 kgf load. Fig. 9. Wear test at 900 rpm and 9 kgf load. Fig. 6. Wear test at 800 rpm and 9 kgf load. Fig. 10. Friction test at 700 rpm and 3 kgf load. Fig. 7. Wear test at 900 rpm and 3 kgf load. Fig. 11. Friction test at 700 rpm and 6 kgf load. Fig. 8. Wear test at 900 rpm and 6 kgf load. Fig. 12. Friction test at 700 rpm and 9 kgf load. 683

8 Journal of Chemical Technology and Metallurgy, 51, 6, 2016 Fig. 13. Friction test at 800 rpm and 3 kgf load. Fig. 16. Friction test at 900 rpm and 3 kgf load. Fig. 14. Friction test at 800 rpm and 6 kgf load. Fig. 17. Friction test at 900 rpm and 6 kgf load. Fig. 15. Figure test at 800 rpm and 9 kgf load. Fig. 18. Friction test at 900 rpm and 9 kgf load. CONCLUSIONS The fabrication of hybrid reinforced polymer composites is carried out by a hand-layup method. The composite specimens are investigated aiming to determine the impact strength, hardness and wear resistance. The results from the various tests confirm that the resistance of the basalt hybrid composites improves with increase of the fiber and filler content. The characterization of the composites reveals that the friction and wear resistance increases with increase of the particulate content in the hybrid composites. A significant improvement in the mechanical properties of the composites with increase of the fiber, fillers and constant particulate loading is also observed. The addition of graphite along with titanium oxide, barium sulphate, and silicon carbide to epoxy resin reinforced with basalt fiber results in better performance when compared to that of the other specimens. This in turn provides its application in cases where a material of high tensile strength and hardness as well as low friction coefficient and wear rate is required. 684

9 T. Narendiranath Babu, R.V. Mangalaraja, S. Saravanan, D. Rama Prabha REFERENCES 1. Kunal Singha, A short Review on Basalt Fiber, Int. J. of textile science, 4, 2012, B. Wei, S. Song, H. Cao, Strengthening of Basalt fibers with SiO 2 - epoxy composite coating, Mater. Des., 32, 2011, S. SrinivasaMoorthy, K. Manonmani, Fabrication and characterization of TiO 2 particulate filled Glass Fiber reinforced polymer composite, Materials Physics and Mechanics, 18, 2013, C.P. Samal, J.S. Paihar, D. Chaira, The effect of milling and sintering techniques on mechanical properties of Cu-graphite metal matrix composite prepared by powder metallurgy route, Journal of Alloys and Compounds, 2, 2013, V.Fiorel, T.scalicil, G. Di Bella, A. Valenzal, A review on basalt fiber and its composites, Composites Part B: Engineering, 74, 2015, Nihat Kabay, Abrasion resistance and fracture energy of concretes with basalt fiber, Construction and Building Materials, 50, 2014, R. Petrucci, C. Santulli, D. Puglia, F.Sarasini, L. Torre, J.M. Kenny, Mechanical characterisation of hybrid composite laminates based on basalt fibers in combination with flax, hemp and glass fibers manufactured by vacuum infusion, Composites Part B, 69, 2015, Hancock, Paul and Skinner, Brian J. Basalt, United Kingdom, Y. Zhang, C. Yu, P.K. Chu, F. Lv, C. Zhang, J. Ji, Mechanical and thermal properties of basalt fibre reinforced poly(butylene succinate) composites, Mater. Chem. Phys., 133, 2012, M. Urbanski, A. Lapko, A. Garbacz, Investigation on concrete beams reinforced with basalt rebars as an effective alternative of conventional R/C structures, Procedia Eng., 57, 2013,