20.2.3 Measurements of the Density of the Specimens All of the measurements of the density of the specimens were carried out by pycnometer (digital density meters, Webb and Orr, 1997 work with helium gas) after post curing and the results were then compared. 20.2.4 Measurements of Dielectric Properties Dielectric properties: Values of capacitance and dissipation factor (Permittivity (ε0) and dielectric loss angle tangent (tanδ) were investigated using a Dielectric Thermal Analyzer (Rheometric Scientific) at three different frequencies (1, 10 and 100 kHz) in the temperature range from room temperature up to 300 C. The temperature was increased at a rate of 1 C/min. Data were collected at temperature intervals of 5 C. The samples used for these tests had a diameter of approximately 30 mm and were 1.5 mm thick. 20.2.5 Nanoindentation: Creep and Wear Tests Creep tests using a nanoindenter were performed on the four composites manufactured. On each sample 20 indents were performed on a 5 4 grid with a Berkovich indenter. The indents were spaced 50 μm along the 5 indent side and 75 μm along the 4 indent side. The load was increased at a rate of 1 mN/s to the max load and kept at the maximum load for 500 s then unloaded. Two maximum loads of 20 and 50 mN were used in these tests. Scratch testing capability of a nanoindenter is utilized to perform relatively fast wear tests to compare the wear behavior of the different samples. In the wear tests conducted a conical tip with a 90 cone angle was used. Wear tests were run under a normal load of 20 mN applied over a linear track of 500 nm for 50 cycles. 20.3 Results and Discussions 20.3.1 Microstructure and Fracture Surfaces of the Compositions Measurements of the density for four different compositions are given in the Table 20.3. First of all, addition of glass bubbles to the structure slightly influences the density. Overall the densities of the four compositions do not vary from one another too much. The changes observed, although very slight, follow the increase in boron and alumina in the compositions. The influence of the reinforcements on the mechanical behaviour of four compositions is shown in Table 20.4. Based on these results EBAL III exhibits higher compression resistance with respect to the other compositions. It appears that synergistic effect of boron and alumina is resulting in higher resistance to compression as evidenced by the compositions EBAL III and EBAL IV. With this limited testing, it is difficult to make a clear interpretation on the influence of reinforcements on the resistance of the composition. However, addition of glass bubbles tends to decrease density and increase plastic deformation of the material. These values should be necessitating supplementary tests. More efficient effect of boron reinforcement is observed on the compression resistance. General microstructures in the transverse direction of the four compositions are shown in Fig. 20.1 (left column). All of the compositions have shown a homogenous distribution of the reinforcements in the structure. Essentially, all of the microstructures show that the adhesion of the rubber to the epoxy matrix is very successfully carried out after the simple chemical treatment. Table 20.2 Composition of the epoxy-rubber based composites Epoxy-rubber based composition ! I II III IV Reinforcements (wt%) Boron 5 5 10 5 Alumina 5 5 5 10 Glass bubbles – 5 5 5 20 Low-Cost Production of Epoxy Matrix Composites Reinforced. . . 165
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