THERMAL CONDUCTIVITY AND THERMAL EXPANSION COEFFICIENT OF GFRP COMPOSITE LAMINATES WITH FILLERS K. Devendra $ and T. Rangaswamy & $ Asst. Professor, Dept. of Mech. Engineering, SKSVMACET, Laxmeshwar, KA, India. & Professor, Department of Mechanical Engineering, GEC, Hassan, KA, India $ Corresponding Author:devenk93@gmail.com Abstract This research paper compares the thermal conductivity and thermal expansion coefficients of glass fiber reinforced epoxy composite laminates (GFRP laminates) made using the Hand layup technique. The composite laminates were fabricated by filling with varying concentrations of fly ash, stone powder, aluminium oxide (Al 2 O 3 ), magnesium hydroxide (Mg (OH) 2 ), Silicon carbide particles(sic) and hematite powder. The test results show that fly ash filled GFRP laminate exhibited low thermal conductivity. GFRP laminates filled with SiC exhibited maximum thermal conductivity and minimum thermal expansion coefficient. Keywords: GFRP Laminates, Fillers, Coefficients, Properties 1. Introduction Polymer matrix composites (PMC) are used in military, automotive, and civil infrastructure applications because of their overall good thermal, mechanical, electrical properties, low weight, and low cost compared to conventional materials. The favorable specific properties of fiber reinforced polymer composites are based on the low density of the matrix resins used, and the high strength of the embedded fibers. Fibers reinforced polymer composite (FRP) relatively low cost and ease of fabrication. These composites are considered as replacements for metal materials. In recent years there have been an increasing number of applications such as communication, satellites, high density electronics, and advanced aircraft requiring more effective and light weight thermal management materials [1]. The temperature fields in composites materials cannot be determined unless the thermal conductivity of the media is known and for any material a low thermal expansion is ideally required [2, 3]. In this context the study of thermal properties of composites are desirable. Now-a-days specific fillers/additives are added to enhance and modify the quality of composites as these are found to play a major role in determining the mechanical and thermal behavior of the composites. These fillers will changes the some properties and reduce the processing cost significantly low. In the present investigation an attempt has been made to utilization of fly ash, stone powder, aluminium oxide (Al 2 O 3 ), magnesium hydroxide (Mg (OH) 2 ), Silicon carbide Vol. 2, No. 5, August-September 2013 39
particles (SiC) and hematite powder as filler materials and effect of these filler materials on thermal properties of E-Glass fiber reinforced epoxy composite laminates was determined 2. Experimentation 2.1. Materials The matrix material used for the fabrication of GFRP laminates was low temperature curing epoxy resin (ARALDITE (L-12)) and corresponding hardener (K-6). E-glass fiber (7- mill) was taken for incorporation as reinforcement in the laminates. Fly ash, stone powder, aluminium oxide (Al 2 O 3 ), magnesium hydroxide (Mg (OH) 2 ), Silicon carbide particles (SiC) and hematite powder were used as filler materials. 2.2. Fabrication of GFRP Composite Laminates Hand lay-up techniques has been adopted for preparing the E-glass /Epoxy based composite laminates filled with varying concentrations (0, 10 and 15 Vol. %) of Fly ash, stone powder, aluminium oxide (Al 2 O 3 ), magnesium hydroxide (Mg (OH) 2 ), Silicon carbide particles (SiC) and hematite powder. The volume fraction of fiber, epoxy and filler materials were determined by considering the density, specific gravity and mass. Fabrication of the GFRP laminates was done at room temperature and the laminates were cured at room temperature. 2.3. Specimen Preparation The prepared GFRP laminates were taken from the mold and specimens were prepared for thermal conductivity and thermal expansion coefficient tests according to ASTM standards. The specimens were cut from the GFRP laminates using diamond tipped cutter. Three identical test specimens were prepared for tests. 2.4.Thermal Conductivity Thermal conductivity measurements are carried out under steady state condition. According to ASTM E1530 disc shaped specimens with diameter of 50mm and thickness of 10mm are used in the instrument for thermal conductivity measurements. A known constant heat is applied from one side of the specimen. When the thermal equilibrium is attained and the system approaches to steady state situation, the temperature of top and bottom surfaces were measured by using thermocouples installed on top and bottom surfaces of the specimen. Knowing the values of heat supplied, temperatures and thickness the thermal conductivity was determined by employing one-dimensional Fourier s law of conduction. All measurements are carried out approximately in the similar temperature range, i.e., 25-90 o C 2.5.Thermal Expansion Coefficient Measurement Thermal expansion coefficient test specimens had length and thickness 90mm and 10mm respectively. The linear thermal expansion test was performed over the temperature range of 30 o C to 90 o C using electric furnace. The samples were slowly heated from 30 to 90 0 C in the electric furnace and kept at 90 0 C for 10 min. Thermal Expansion Coefficient is then given by the relationship Vol. 2, No. 5, August-September 2013 40
Where = α=thermal Expansion coefficient (/ o C) L= Original length of the sample (mm) L= Change in length of the sample (mm) T= Temperature change ( o C) ----------- (1) Table 1. List of Fabricated GFRP Laminates with Constant 50% E-Glass Fiber Volume GFRP Filler Materials Epoxy (%Volume) Laminates (% Volume) GE 50 Nil GEF 1 40 10% Fly Ash GEF 2 35 15% Fly ash GES 1 40 10% Stone Powder GES 2 35 15% Stone Powder GEA 1 40 10% Al 2 O 3 GEA 2 35 15% Al 2 O 3 GEM 1 40 10% Mg(OH) 2 GEM 2 35 15% Mg(OH) 2 GESI 1 40 10% SiC GESI 2 35 15% SiC GEH 1 40 10% Hematite GEH 2 35 15% Hematite 3. Results and Discussion Thermal properties tests were conducted according to ASTM standards. Thermal properties such as, thermal conductivity and thermal expansion coefficient of GFRP laminates were determined. 3.1. Thermal Conductivity Thermal conductivity is the property describing a material s ability to transfer heat. It is well known that thermal conductivity of the GFRP composite laminates is dependent on such factors as epoxy-filler interaction and filler characteristics, namely type and shape of filler. Vol. 2, No. 5, August-September 2013 41
Figure 1. Thermal Conductivity From the test results, it was observed that the thermal conductivity of GFRP laminates decreases with increase the addition of fly ash content. GFRP laminate filled with 15% volume fly ash exhibited the minimum thermal conductivity of 1.23 W/m o C this is due to the fly ash contains some percentage of silica and phosphate and these two acts as thermal resistance to heat flow. GFRP laminate filled with 10% volume SiC exhibited maximum thermal conductivity of 3.515 W/ m o C. From the literature review we can observed that SiC particles having good thermal conductivity property because better interconnectivity between the SiC particles due to this reason SiC filled composite laminate exhibiting high thermal conductivity. Hematite filled GFRP laminates exhibited high thermal conductivities because the hematite powder contains the iron particles and this particle having capability to conduct more heat. 3.2. Thermal Expansion Coefficient The thermal expansion coefficient of GFRP composite laminates is linked to its crystalline structure [3]. From the results it was observed that increase the adding of fillers to GFRP laminates leads to decreases in thermal expansion coefficient. GFRP laminates filled with 15% volume fly ash, Al 2 O 3, Mg (OH) 2 and SiC exhibited less thermal expansion coefficients this may be by adding the more fillers in materials providing good filler matrix interaction in the system, fine dispersion of particles in the materials and the filler binds the matrix and obstruct the expansion of polymer chains at high temperature [5]. The many studies have shown that composites with higher filler content exhibited lower thermal expansion coefficient. GFRP laminate filled with 15% volume SiC exhibited minimum thermal expansion coefficient of 3.70 10-6 / o C when compared with other filled GFRP laminates this is due to the SiC particles having high rigidity, good dimensional stability and fine dispersion of SiC particles in the GFRP laminate [5]. From the test results it was indicated that when increasing the addition of more stone powder to the GFRP laminates increases the thermal expansion coefficients because the addition of stone powder decreases the connectivity between particles and adhesion between filler and matrix [3, 5]. Vol. 2, No. 5, August-September 2013 42
Figure 2. Thermal Expansion Coefficients Table 2. Comparison of Thermal Properties of GFRP Laminates GFRP Laminates Thermal Conductivity (W/m o C) Thermal Expansion Coefficient (/ o C) GE 2.89 1.96 10-5 GEF 1 1.69 1.85 10-5 GEF 2 1.23 1.48 10-5 GES 1 2.34 1.85 10-5 GES 2 1.58 2.59 10-5 GEA 1 1.32 2.40 10-5 GEA 2 1.72 1.66 10-5 GEM 1 1.56 2.44 10-5 GEM 2 2.38 1.11 10-5 GESI 1 3.51 7.40 10-6 GESI 2 2.76 3.70 10-6 GEH 1 2.45 1.85 10-5 GEH 2 3.06 1.85 10-5 4. Conclusions In the present work, E-Glass/Epoxy based composite laminates filled with varying concentrations of six various fillers were prepared and the effect of these fillers on thermal conductivity and thermal expansion coefficient were investigated. Experimental study reveals the following conclusions. 1. Experimental results show that GFRP laminate filled with 15% volume fly ash exhibited minimum thermal conductivity of 1.23 W/m o C. 2. GFRP laminate filled by 10% volume SiC exhibited maximum thermal conductivity of 3.51 W/m o C. Vol. 2, No. 5, August-September 2013 43
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