Evaluation of Thermal Properties of E-Glass/ Epoxy Composites Filled By Different Filler Materials
This paper compares the values of the thermal and fire resistance properties of composites made using the hand layup technique. E-Glass fiber reinforced epoxy composites was fabricated by filling varying concentration of aluminum oxide (Al2O3), magnesium hydroxide(Mg(OH)2), silicon carbide (SiC), and hematite powder. The main aim of this work was to determine the thermal conductivity, thermal expansion coefficient, time to ignition and flame propagation rate of composites. Experimental results show that Al2O3 and Mg (OH)2 filled composites exhibited low thermal conductivities. Composites filled by SiC particles exhibited low thermal expansion coefficient when compared with other filled composites. Fire test results indicated that increase the loading of Al2O3, Mg (OH)2, and hematite powder increase the time to ignition and reduces the flame propagation rate of composites.
Studying the Ultrasonic Properties, DC Conductivity and Coefficient of Thermal Conductivity of PVA-Egg Shells Composites
The polymer composite used in the present study were made of polyvinyl alcohol (PVA) as a matrix and Iraqi egg shells as filler. Polymer composites were fabricated by mixing PVA with (5, 10, 15, 20, 25, 30, 40 and 50) wt.% of egg shells powder by using a magnetic stirrer at temperature 90 0 C for 4hr to obtain homogeneous solution then samples were prepared by casting techniques. The ultrasonic measurements (transmittance, absorption coefficient and relaxation amplitude, acoustic impedance, compressibility and compressibility) of composites were carried out by using ultrasound technique. Measurement of DC conductivity and coefficient of thermal conductivity were done as a function to wt. % of egg shells. It was found that the samples contain additives of eggshells 5%, 10%, 20% and 30%, the attenuation decreased by increasing frequency up to 40 KHz and then increased after this frequency; while the sample contains 15% of the eggshells, the attenuation not alter significantly with increasing frequency. Sample with 50 % egg shell has two peaks at 20 and 30 kHz. As can be seen that the samples which contain a proportion of eggshells 5, 10, 20, 25, 30 and 40%, the transmittance coefficient increases with increasing frequency up to 40 kHz and then decreases and  relaxation amplitude decreases with increasing frequency from 5 to 50 KHz. Generally observed acoustic impedance decreases with increasing eggshells except percentage 20%, where the highest value for the impedance. Compressibility generally increases with increasing of eggshells up to 40 % and then decreases. The electrical conductivity increase as concentrations of egg shells increase up to 30 % then conductivity decreases at 40 % then increases slightly at 50 %. It was found that coefficient of thermal conductivity increases with increasing of egg shells up to 40 % then decreases. Keywords: PVA, egg shells, ultrasonic properties, dc conductivity, coefficient of thermal conductivity.
Prediction of fiber orientation and microstructure of woven fabric composites after forming
The forming of fabric composites into complex parts such as double-curvature shells leads to complex redistribution and reorientation of fibers in the composite. This results in variations in thermal and mechanical properties of the material, which, in turn creates complex residual stresses and deformations of the part as a function of temperature change. Consequently, it is usually very difficult to perform any structural analysis of these composites. In order to predict the thermo-mechanical behavior of fabric composites, a numerical program has been developed in this work to predict the redistribution of the woven fibers and the resin in parts with complex shapes. A brief description of the approach used for the calculation and display of the variations in microstructure throughout the part is presented in this paper. The change in microstructure is discussed in terms of various possible mechanisms such as fiber orientation, fiber slippage, thickness variation, fiber volume fraction throughout the molded part. In parts containing double curvatures, the intraply shear deformation that occurs during the forming process involves a surface area reduction of the ply. Consequently, in single-die molding, there is a ply thickness increase and a variation of fiber volume fraction. The comparison between numerical prediction and experimental measurements is presented by examining the microstructure of different composite systems with a room curing-temperature, molded by hand lay-up on a rounded top cone die. The results revealed that the prediction agrees with the actual variation in the properties of the molded composites. However the accuracy of computation is limited by the variations of the composite's characteristics due to handling and processing. In the structure investigated, these variations can be as high as 20%.