CHAPTER 3 MATERIALS, PROCESSING AND EXPERIMENTATION

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1 68 CHAPTER 3 MATERIALS, PROCESSING AND EXPERIMENTATION 3.1 INTRODUCTION This chapter deals with materials, testing equipments and experimental methods implemented in the current study. The type of matrix, reinforcement material and the fillers used for fabricating hybrid composites has been discussed. The experiment details for (i) mechanical tests such as hardness test, tensile test, flexural test and also dynamic mechanical analysis test (ii) dry sliding wear tests and (iii) two-body and three-body abrasive wear tests of unfilled and silane-treated SiC filled C-E hybrid composites are discussed in the following sections. 3.2 MATERIALS Composites are made of reinforcing fibers or fillers and matrix materials. Matrix surrounds the fibers, acting as load transferring medium and thus protecting those fibers against chemical and environmental attack. For the present study, following materials have been considered for preparing composites.1) Matrix material: Epoxy resin 2) Reinforcement material: Bidirectional carbon fabric and 3) Filler material: Silane-treated SiC particulates Matrix Materials Epoxy is the matrix materials used and it consists of medium viscosity epoxy resin (LY 556) and HY 951 room temperature curing

2 69 hardener along with diluent DY 02. All these materials are supplied by Hindustan Ciba Giegy Ltd, Mumbai, India. The properties of the materials are listed in Table 3.1. In general, the thermoset polymeric epoxy resin consists of superior properties such as good mechanical properties, enhanced chemical and corrosion resistance and ease of processing. Due to its wide applications, epoxy resin was selected as the matrix material for the current study. Table 3.1 The ingredients of matrix system Ingredients Epoxy Resin Trade name Chemical name LY 556 Diglycidal Ether of bisphenol A (DGEBA) Hardener HY 951 Triethylenetetramine (TETA) Density (g/cm 3 ) Supplier Hindustan Ciba Giegy Ltd Fiber Materials The bi-directional carbon fabric is considered as reinforcement material in this study. The main properties of the carbon fibers are highlighted in Table 3.2. Table 3.2 Properties of carbon fibers Properties Carbon (T300) Specific gravity (g/cm 3 ) Fabric weight (g/m 2 ) 300 Fiber diameter (µm) 8-10 Tensile strength (MPa) Tensile modulus (GPa) Strain to failure (%) 2.9

3 Filler Materials In the present study, silane-treated silicon carbide particulates have been selected as a filler and second reinforcement material. The addition of hard silane-treated SiC particles provides the improved strength, stiffness, wear resistance, fatigue resistance, thermal conductivity and reduced thermal expansion properties to composites. The physical and mechanical properties of Silicon Carbide (SiC) are shown in Table 3.3. Table 3.3 Physical and mechanical properties of used silicon carbide (SiC) particles Properties Value Density 3.2 g/cm 3 Particle size 5 10 µm Shape Tetrahedral Moh s hardness 9.5 Filling mass kg/m 3 Thermal dissociation point 2300 C Crystallographic lattice hexagonal and phase 3.3 PREPARATION OF THE COMPOSITES Preparation of Composite Test Samples A mould of size 550 mm 550 mm 6 mm was prepared using mild steel plates. Interior surfaces of the moulds were finely polished and chrome plated. All the surfaces of the moulds were layered with Teflon sheet. The part coming in contact with surface of the composite to be cast, were smeared with a uniform layer of silicone releasing agent in order to facilitate the release of the composite slab. The bi-directional carbon fabric (diameter 6 8 µm)

4 71 reinforced with the LY556 Epoxy resin matrix materials, added with HY951 room temperature curing hardener and diluent DY021 (all supplied by Hindustan Ciba Giegy) have been considered for panel fabrication. Ten layers of fabric were used to obtain about 3 mm thick laminates. Particulate-filled carbon fabric-reinforced epoxy composite was prepared by hand lay-up procedure, followed by compression moulding. The filler material used is SiC powder of size 5 10 µm. The SiC filler was treated with 2% organo-reactive silane coupling agent Carbon Fabric and Particulate Reinforced Epoxy Composites Carbon fabric (T-300), which is compatible with epoxy resin, has been used as the reinforcement. The epoxy resin was mixed with the hardener in the ratio 100:12 by weight. The dry hand lay-up technique as shown in Figure 3.1 was used to fabricate the composite. Figure 3.1 Hand lay-up technique setup

5 72 The stacking procedure involved placing the fabric one above other with the resin mix well spread between the fabrics. A porous Teflon film was placed on the completed stack. To ensure uniform thickness of the sample, a spacer of size 3 mm was used. The mould plates were coated with a release agent in order to avoid damage to the solidified panel upon separation. Figure 3.2 Compression moulding The panel was prepared by hand lay-up technique and followed by compression moulding as shown in Figure 3.2. The total assembly was kept in a hydraulic press at a pressure of 0.5 MPa and was allowed to cure for a day at room temperature. Subsequently, post curing was done at a temperature of 70 ± 5 C for 3 hours in a hot air circulated furnace. The panel thus prepared has a size 500 mm 500 mm 3 mm. Figure 3.3 shows the flow chart of processes involved in the composite preparation. To prepare the silane-treated SiC filled C-E composites, silane-treated SiC filler was mixed with a known amount of epoxy resin. The particulars of the composites made are shown in

6 73 Table 3.4. The test samples as per ASTM standard were prepared from the laminate using a diamond tipped cutter. Densities of the composites were determined with the help of a high precision electronic balance (Make: Mettler Toledo, Accuracy: g) using Archimedes principle. Bi-directional Carbon fabric Epoxy resin + Silane-treated SiC particulates Hand layup technique technique Compression molding Curing Composite laminate Figure 3.3 Processes involved in the preparation of composite laminate Table 3.4 Composites selected for the present study Material (Designation) Fiber (wt.%) Matrix (wt.%) Filler (wt.%) Density (g/cm 3 ) ASTM D792 Carbon-epoxy (C-E) Carbon (60±2) Epoxy (40±2) % SiC filled carbonepoxy (5SiC-C-E) Carbon (60±2) Epoxy (35±2) SiC (5) % SiC filled carbonepoxy (10SiC-C-E) Carbon (60±2) Epoxy (30±2) SiC (10) EXPERIMENTAL SETUP USED FOR MECHANICAL TESTS The mechanical tests involved in this present study are explained in the following sections.

7 Hardness test and Tensile test The mechanical properties such as tensile and hardness properties were investigated using Instron testing machine (ASTM D638) and Durometer(ASTM D2240) respectively. As per the ASTM D2240, Durometer (Hiroshima make Hardness tester) was used to measure Shore hardness of the samples. On different places of the samples, six readings were taken and the average value was recorded for each materials. Uniaxial tensile test was conducted using an Instron testing machine according to ASTM D638. The tensile tests were performed at a crosshead speed of 5 mm/min (quasistatic). Five samples were tested for each composition of the composites. The results reported are thus the average of five readings, and the relative deviations in mechanical properties were below 8%. Both the load and cross head displacements were recorded using a software and a data acquisition computer. Mechanical properties such as tensile strength, modulus and elongation were determined. The dimensions of the test specimen as per ASTM D638, type M-I are listed below. All dimensions are in mm Flexural Test Flexural test was conducted on an Instron universal testing machine using centre-loading flexure fixture according to ASTM D790 standard three

8 75 point bending method. The flexure tests were performed at crosshead speed of 2.4 mm/min. Five samples were tested for each composition of the composites. The dimensions of the test specimen as per the ASTM D790 are 90 mm 12.7 mm 3 mm. Both the load and cross-head displacements were recorded using software and a data acquisition computer. 3.5 EXPERIMENTAL SETUP USED FOR DRY SLIDING WEAR TEST A pin-on-disk setup (Make: DUCOM ASTM G-99 standard, TR-20-M26 was used for the dry sliding wear tests and schematic diagram and the photo graphic view of the same is shown in Figures 3.4 and 3.5 respectively. Figure 3.4 Schematic diagram of the Pin-On-Disc wear test rig indicating the various parts of the wear setup

9 76 Figure 3.5 Photographic view of the Pin-On-Disc wear test rig A surface (6 mm 6 mm 3 mm) of the composite specimen glued to a pin of 6 mm diameter and 22 mm length has contact with a hardened alloy steel disc with a hardness value of 62 HRC and surface roughness (Ra) of µm, as shown in Figure 3.6. Figure 3.6 Composite sample with pin assembly and the steel countersurface on which sliding takes place

10 77 The summary of the experimental conditions used for this study are listed in Table 3.5. The test samples were polished against a 600 grade SiC paper to ensure proper contact with the countersurface. The surfaces of both the samples and the disc were cleaned with a soft paper soaked in acetone and thoroughly dried before the test. The pin assembly was initially weighed to an accuracy of g in an electronic balance (Mettler Toledo). The difference between the initial and final weights is the measure of the sliding wear loss. In general, the sliding process can be divided into two stages namely; a running-in stage and a steady wear stage. In most cases, the sliding behavior in the steady stage is a matter of primary concern as it determines the wear life and thus, the overall applicability of the component. Therefore, in this study, the values of friction coefficient and weight loss refer to the mean values in the steady stage. Also, each result is an average value from at least three repeated tests. The results reported are thus the average of three readings, and the relative deviation in wear loss was observed to be below 12%. The wear was measured by loss in weight, which was then converted into wear volume using measured density data. The specific wear rate (k s ) was calculated through the following equation: K s V L D 3 m / Nm (3.1) wherev is the volume loss (m 3 ),L is the applied load (N) and D is the sliding distance (m).

11 78 Table 3.5 Details of the dry sliding wear conditions selected for this study Materials C-E 5 SiC-C-E 10 SiC-C-E C-E 5 SiC-C-E 10 SiC-C-E I-Group test for different loads &sliding distances S.No Load (N) Sliding velocity (m/s) Sliding Distances (m) II-Group test for different loads and sliding velocities Number of tests 42 number of tests 18 number of tests

12 EXPERIMENTAL SETUP USED FOR ABRASIVE WEAR TEST Two-Body Abrasion Two-body abrasive wear tests were performed using a Pin-on-disc wear test rig according to ASTM-G 99 standards. Test samples were prepared after proper cutting and polishing to 6mm x 6mm x 3mm size. Prior to testing, the test samples were polished against a 600 grade SiC paper to ensure proper contact with the countersurface. The composite sample was abraded against the water silicon carbide (SiC) abrasive papers of 150 and 320 grit size at 10 and 20 N loads for abrading distances of 75,150 and 225 m in multi pass condition. Figure 3.7 shows the photographic view of the two-body abrasive wear process on Pin-on-Disc wear test rig. Figures 3.8 (a) and (b) shows the SEM images of the abrasive particles embedded on the abrasive paper (150 and 320 grit size) before the test. The embedded hard SiC particles abrade the test samples. During the test, the sample is so placed in such a way that the fibers are parallel and anti-parallel with respect to abrading direction and the abrading plane. The weight loss measurements were carried out for three abrading distance of 75,150 and 225 m. Before and after the test, the test samples were cleaned by soft paper immersed in acetone and thoroughly dried. The weight loss of the sample was measured using the electronic balance with the accuracy of g (Mettler Toledo). The wear was measured by the loss in weight, which was then converted in to wear volume using the measured density data. The specific wear rate was calculated from the Equation (3.1). The detail of testing conditions for this study is shown in Table 3.6.

13 80 Sample holder Sample with Pin Abrasive sheet with rotating disc Figure 3.7 Photographic view of the two-body abrasive wear process a b SiC particles (150 grit size) SiC particles (320 grit size) Figure 3.8 (a) 150 grit and (b) 320 grit SiC papers used before abrasion test Table 3.6 The details of the two-body wear test conditions followed for this study Conditions/experiments Varying load conditions Varying abrading distance (m) conditions Applied load (N) 10 and 20 75,150 and 225 m Speed (RPM) Abrasive paper 150 grit size 320 grit size

14 Three-Body Abrasion Three-body abrasive wear test was conducted using the ASTM G-65 standard, rubber wheel abrasive wear tester (Magnum Engineers, Bangalore). The schematic diagram and the photographic view of the rubber wheel abrasive wear tester are shown in Figures 3.9 and 3.10 respectively. The abrasive test samples as per the ASTM G65 of size 70 mm 27 mm 3 mm were also prepared from the plate using the diamond tipped cutter. Details of the three-body wear test conditions employed for this study is shown in Table 3.7. Figure 3.9 Schematic diagram of three body rubber wheel abrasive wear tester

15 82 Figure 3.10 Photographic views of the rubber wheel abrasive wear tester rig For this test, AFS 60 grade silica sand have been used as abrasive particles with sharp edges and angular in shape ( µm) and its SEM image as shown in Figure The abrasive particles were fed in between the contact surfaces of rotating wheel and the sample. Figure 3.11 SEM image of the abrasive particles (Silica sand)

16 83 Before the test, the samples were cleaned using acetone liquid and dried; further, the initial weight of the samples was measured using a digital electronic balance (Mettler, Toledo) with a high accuracy of 0.1 mg. The samples were then fitted in the sample holder. The silica sand of AFS 60 grade was introduced between the sample and the rotating rubber wheel (constant speed 200 rpm) prepared by chlorobutyl rubber tyre (hardness: Durometer-A 58-62) with the feed rate of 255 ± 5 g/min. The load by the way of lever arm exerts the force on the specimen holder and the specimen where it is pressed against the rotating wheel while the controlled flow of the sand particles abrades the sample surface. The rotation of the abrasive rubber wheel rotates such that its contacting surface rotates in the direction of the sand flow. The lever arm which holds the sample at one end and carries the load at other end makes the sample position approximately tangential to the outer diameter of the rubber wheel and normal to the load applied. For each test condition, three tests were performed and the average values obtained were recorded. The tests were conducted for the abrading distances in the steps of 160, 320 and 480 m. The tests were also repeated for two different loads (25 and 35 N). After the test, the samples were again cleaned by acetone and dried. The final weight of the samples was measured using a digital electronic balance. The differences between the initial and final weights of the samples give the value of wear loss. The wear loss obtained from the above method was converted to wear volume loss using the measured density data of the samples. The specific wear rate (K s ) was calculated using the Equation (3.1).

17 84 Table 3.7 The details of three-body wear test conditions employed for this study S.No Parameters Details 1 Applied load (N) 25 and 35 2 Abrading distances (m) 160,320 and Speed (RPM) EXPERIMENTAL SETUP FOR DYNAMIC MECHANICAL ANALYSIS Dynamic Mechanical Analysis (DMA) was carried out as per the standard ASTM D using test setup DMA Q800 V 7.4 (TA Instruments, USA). The schematic diagram of the DMA Q800 is shown in Figure DMA 800 is a controlled stress with combined motor and transducer machine, in which motor applies force and displacement sensor measures strain. The signals of force and amplitude were recorded by the machine; the stiffness is obtained from force and amplitude. The storage modulus is obtained using the stiffness data. Figure 3.12 DMA Q800 instrument

18 85 The DMA instrument was operated in the single cantilever clamp mode which is used to test the SiC-filled and unfilled C E samples. DMA instrument operates at a frequency of 1 HZ and strain at an amplitude of 25 µm. The test was performed in the temperature range of 25 C to 250 C and at a temperature ramp of 2 C per minute. From each material, three samples with the size of 90 mm 12 mm 3 mm were prepared using the diamond tipped cutter. The DMA test was conducted for all samples. Also, the storage modulus and glass transition temperatures were recorded and revealed. 3.8 VISUAL MACRO OBSERVATION Hardness, Tensile, flexural and impact tested samples were first subject to observation using the regular photography technique. This method came in handy during the characterization of failures, especially in tension failed samples in different stages of crack propagation. 3.9 SCANNING ELECTRON MICROSCOPY Wear characterization of the worn surfaces of unfilled C E composite and silane-treated SiC-filled C E hybrid composites samples were studied using the scanning electronic microscope (JEOL, model JSM 840A), which is shown in Figure Figure 3.13 Scanning Electron Microscopy

19 86 Before the examination, a thin gold film was coated on the worn out surface by sputtering to get a conducting layer. Figure 3.14 shows the experimental flow chart which lists all the tests conducted to characterize the mechanical and tribological properties of the composite. Mechanical study Fabrication of composites Tribological study Mechanical properties (hardness, tensile and flexural strength) Dynamic mechanical properties Adhesive wear Dry sliding wear test Two-body wear test Abrasive wear Three-body wear test Fractographic analysis using SEM Viscoelastic properties, (glass transition temperature, storage modulus, loss modulus and tandelta) Effect of load, sliding velocity, sliding distance and filler wt. % Worn surface morphology using SEM Results and discussion Effect of applied load, abrading distance, abrasive grit size and filler wt. % Worn surface morphology using SEM Effect of applied load, abrading distance and filler wt. % Conclusions Figure 3.14 Experimental flow chart