Effect of Short Glass Fiber and Fillers on Dry Sliding Wear Behaviour of Thermoplastic Copolyester

Effect of Short Glass Fiber and Fillers on Dry Sliding Wear Behaviour of Thermoplastic Copolyester
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  Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   71 EFFECT OF SHORT GLASS FIBER AND FILLERS ON DRY SLIDING WEAR BEHAVIOUR OF THERMOPLASTIC COPOLYESTER ELASTOMER COMPOSITES R. Hemanth 1 , Prakash Sam Thomas 2 , B. Suresha 3 , M. Sekar 4   1, 2, 4 Karunya School of Mechanical Science, Karunya University, Coimbatore, India 3 Department of Mechanical Engineering, National Institute of Engineering, Mysore, India ABSTRACT  The dry sliding wear behaviour of thermoplastic copolyester elastomer (TCE) reinforced with fibers and fillers were slid against a steel counterface of a pin-on-disc tribometer. The filler and fiber reinforcements used are polytetrafluroethylene (PTFE), short glass fiber (SGF), short carbon fiber (SCF), silicon carbide (SiC), and alumina (Al 2 O 3 ). The parameters like filler content, sliding velocity and sliding distance on the specific wear rate have been investaigated. In this study, a plan of experiments based on the techniques of Taguchi was performed to acquire data in a controlled way. An orthogonal array L 27  (3 13 ) and analysis of variance (ANOVA) were applied to study the influence of process parameters on the specific wear rate of TCE based composites. The experimental results reveal that the effect of filler content was the major parameter on specific wear rate, followed by the sliding distance. The sliding velocity, however, was found to have a neglecting effect. The worn surface topographies show asssorted features like tendency of the matrix to adhere towards the fiber, network of microcracks, less debris formation, agglomeration of debris and broken fibers on the sliding distance and velocity employed. Keywords:  TCE Based Composites, Taguchi’s Design of Experiments, Specific Wear Rate, Worn Surface Morphology. 1.   INTRODUCTION Polymers and their composites possess a unique combination of physical properties that are either unattainable or difficult to reproduce in metal and ceramic materials. Polymer composites occupy a considerable market share nowadays as one of the most common engineering materials. They provide a combination of various advantages, such as ease in manufacturing, cost effectiveness and excellent performance, which cannot be attained by metals, ceramics, or polymers alone [1]. In recent years, polymer composites have been extensively used to replace metallic materials in engineering applications involving friction and wear. The advantages of polymers such as self lubricity, light weight, corrosion resistant and ease of processing have allowed them to be the best choice [2]. Thermoplastic elastomers (TPE’s) concern large industrial and commercial fields, as well as academic and applied research. They are novel constructional polymers, which are physically cross-linked materials made up of a thermoplastic and an elastomer. Applications include flexible couplings, ski boots, gears, high pressure hose lines, outer coverings for wire and optical fiber cables, seals, etc. [3]. The choice of an appropriate matrix is of great importance in the design of wear resistant polymer composites. The concept of adding particles of micro or nanoscale into polymers is one of the most intriguing subjects in the recent decades. Fiber reinforcements like glass, carbon, and aramid fibers have frequently been applied in order to improve mechanical properties. Solid lubricants (polytetrafluroethylene and graphite) are proved to be very helpful in developing   INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 9, September (2014), pp. 71-80 © IAEME: Journal Impact Factor (2014): 7.5377 (Calculated by GISI)   IJMET   © I A E M E    Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   72 a transfer film between the two counterparts and could drastically reduce the frictional coefficient of the composites [4]. Polytetrafluroethylene (PTFE) possesses low coefficient of friction, low stick–slip and high levels of anti-adhesive properties, which make it a potential candidate for adhesive wear process. Unfortunately, PTFE has the following drawbacks: low Young’s modulus, high visco-elasticity and poor wear resistance [5]. While, short fibre reinforcements, such as carbon, glass and aramid fibers, could effectively improve the wear resistance of polymer composites by undergoing most of the load during sliding processes. Short glass fiber (SGF) exhibited better adhesive wear performance in severe operating conditions (applied load, sliding velocity, and sliding distance) [6]. Short carbon fiber (SCF), is widely advocated as a decisive reinforcement component, show a remarkable capability to increase the wear resistance [7]. Silicon carbide (SiC) particles have shown an increased wear resistance in dry sliding (adhesive) wear of polymer composites [6]. The alumina (Al 2 O 3 ) particles in polymer would strengthen the mechanical properties of polymer composites [8]. The objective of this research work is to evaluate the influence of fibers and fillers on wear rate and influence of independent parameters such as sliding distance, filler content, and sliding velocity on wear performance of thermoplastic copolyester elastomers (TCE) reinforced composites using design of experiments (DOE). The fibers and fillers reinforcements used in TCE are SGF, SCF, PTFE, silicon carbide (SiC), and Al 2 O 3 . DOE was applied to study the various parameters affecting the specific wear rate. The information generally comprises the relationship between product and process parameters and the desired performance characteristic. In any process, the desired testing parameters were either determined based on experience or by use of a handbook. It, however, does not provide optimal testing parameters for a particular situation. Thus, numerous mathematical models based on statistical regression techniques have been constructed to select the proper cutting or testing conditions. The Taguchi’s design can further simplify by expending the application of the traditional experimental designs to the use of orthogonal array. This method is a simple, efficient and systematic approach to optimize designs for performance, quality and cost [9]. Majority of research studied detailed experimental work i.e., the effect of one factor by keeping all other factors fixed, this approach is not advisable because in an actual environment there will be combined effects of interacting factors influencing the abrasive wear. Hence in this investigation an attempt is being made to study the interacting effects of factors along with the main effect. In this paper, influence of filler content, sliding distance and sliding velocity on the specific wear rate of TCE based composites was explored using Taguchi’s design of experiments. Dry slidng wear tests were carried out on a pin-on-disc tribometer. Tribological tests were carried out at room temperature, adopting L 27  ortogonal array. The experimental results were analyzed by using analysis of means and variance of the influence of factors. 2.   MATERIALS AND METHODS 2.1   Materials In the present research work, the materials used for making polymer composites are TCE as matrix material, SGF as fiber reinforcement, PTFE, SCF, SiC and Al 2 O 3  as filler reinforcement. The sources of these materials are listed in Table 1. 2.2   Fabrication of composites The polymer granules, fibers and fillers were dried at 75º C for 10 h in an oven before compounding. Selected compositions were mixed and extruded in Barbender co-rotating twin-screw extruder (Make: CMEI, Model: 16CME, SPL, chamber size 70 cm 3 ). The mixing speed of 100 rpm was maintained for all the compositions. The extrudates from the die were quenched in cold water and then pelletized. In the melt blending, the temperature profile of the extrusion were zone1 (200º C), zone 2 (210º C), zone 3 (220º C), zone 4 (240º C) and zone 5 (260º C) respectively. The extrudates of the compositions were pelletized using pelletizing machine. The details of the composites fabricated for present investigation are given in Table 2. The pellets of the extrudates were pre-dried at 100º C in vacuum oven for 24 h and injection moulded in a reciprocating screw injection moulding machine (Windsor, 50 T), to produce test specimens. The processing temperature at zone 1 (220º C) and zone 2 (250º C) were maintained respectively. The mould temperature was maintained at 35º C. Table 1:  Supplier details of the materials procured Polymer/Filler Source and supplier TCE Gargi Enterprises, Bengaluru PTFE Du Pont Co. Ltd. SGF Fine organics, Mumbai SCF Fine organics, Mumbai SiC Carborundum India Ltd. Al 2 O 3   Triveni groups  Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   73 2.3   Wear testing The dry sliding wear tests were performed on a pin on disc tribometer (Magnum Engineers, Bengaluru) setup as per ASTM G 99-05 standard. The photograph of the test apparatus is shown in Fig. 1. Table 2:  Constituents of TCE based composites Fig. 1:  Photograph of the Pin on Disk apparatus showing 1) steel counterface, 2) sample holder and 3) load cell Wear test samples of size 6 mm × 6 mm × 2.5 mm are glued to steel pin of 6 mm diameter and 30 mm length and comes in contact with (EN31 grade, 62 HRC, 1.6 µ  Ra) rotating disc. Prior to testing, the samples were polished against medium grade sand paper (600 grit size) to ensure proper contact with counter face. Test parameters are given below in Table 3. Normal load throughout the experiment is kept constant at 40 N; the pin along with the specimen was then weighted in an electronic balance (0.1mg accuracy). Before and after wear testing, samples were cleaned with the acetone to remove wear debris. Table 3:  Test conditions for the present study Weight loss of the test samples gives the measure of sliding wear loss. Volume loss was calculated from measured weight loss using density data of the test specimen. Sl. No. Matrix material (wt %) Composition (wt %) TCE Particulate fillers 1 80 20 PTFE 2 68 12 PTFE + 20 SGF 3 60 10 PTFE + 17.5 SGF + 2.5 SCF + 5 SiC + 5 Al 2 O 3   Parameters Units Tested values Sliding velocity m/s 0.5, 1.0 and 1.5 Sliding distance m 2000, 4000 and 6000 Normal load N 40 constant  Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   74 The specific wear rate ( W  s ) was calculated using equation (1).  D LV W  s ×=  (1) where, V the volume loss in mm 3 , L the load in Newton, D the sliding distance in m. 2.4. Experimental Design Design of experiments (DOE) is the powerful analysis tool for modelling and analyzing the influence of the control factors on the performance output. The most important stage in the design of experiment lies in the selection of the control factors [9]. Taguchi uses a special design of orthogonal arrays to study the entire process parameter space with only a small number of experiments [10]. The Taguchi design of experiment approach eliminates the need for repeated experiments and thus saves time, material and cost. The most important stage in the design of experiment lies in the selection of the control factors. The Taguchi approach to experimentation provides an orderly way to collect, analyze, and interpret data to satisfy the objectives of the study. In the design of experiments, one can obtain the maximum amount of information for the amount of experimentation. Taguchi parameter design can optimize the performance characteristics through the setting of design. Three parameters namely filler content (A), sliding velocity (B), and sliding distance (C). The Table 4 given below indicates the factors and level. The experiments were conducted as per the orthogonal array with level of parameters given in each array row. The experimental observations are transformed into signal-to-noise (S/N) ratio. There are several S/N ratios available depending on the type of characteristic, which can be calculated as logarithmic transformation of the loss function. Table 4:  Control factors and levels used in the experiment For lower is the better performance characteristic S/N ratio is calculated as per the given formula: - n yns  ∑ −= 2 log10  (2) Where “ n ” is the number of observations and “  y ” is the observed data. “Smaller is the better” characteristic, with the above S/N ratio transformation, is suitable for minimization of wear rate. The sliding wear test results were subject to the analysis of variance (ANOVA). The purpose of ANOVA is to investigate parameters which significantly affect the performance characteristic. With DOE and ANOVA analysis; the optimal combination of wear parameters is predicted to acceptable level of accuracy. The optimal process parameters obtained from the parameter design [11]. The use of ANOVA is to analyze the influence of wear parameters like (A) filler content, (B) sliding velocity, and (c) sliding distance. 3.   RESULTS AND DISCUSSION 3.1   Analysis of control factor Analysis of the influence of each control factor (A, B, and C) on the specific wear rate was performed with a so-called S/N response table, using a Minitab 16 computer package. Table 5 shows the experimental plan and their results with calculated S/N ratios for the specific wear rate of TCE based composites. The right side of the table included the results of the specific wear rate and the calculated S/N ratio. Overall mean for S/N   ratio was found to be 224.1818 dB. The response table of the specific wear rate is presented Control factors Level I II III Units A : Filler content 15 32 40 % B : Sliding velocity 0.5 1 1.5 m/s C : Sliding distance 2000 4000 6000 m
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