prematurely in the grips due to adhesive failure between the tab material and the specimens. However, elastic properties were obtained from these tests. The experimental results for each specimen configuration and temperature were then used to develop the RSMs based on the analysis of variance (ANOVA) procedure. 4.4.2 Analysis of Variance (ANOVA) The RSMs for predicting the elastic properties as a function of temperature were developed using the statistical software Stat-Ease ® Design Expert ® V.8 [9]. This software was used to generate the ANOVA tables and to perform the regression analyses to develop the RSMs. Each RSM was calculated for its overall significance to estimate the elastic properties with respect to temperature. The overall significance of each model was evaluated at a 0.05 level of significance. The models were then assessed for lack-of-fit due to possible significant terms not included in the model. The coefficients of multiple determinations, R2, were also considered in assessing the adequacy of the RSM. 4.4.3 Response Surface Models (RSMs) Longitudinal Modulus. No significant differences between each consecutive temperature were observed for the longitudinal modulus obtained from the [0]8 specimens, as shown in Fig. 4.4. The ANOVA table for the longitudinal modulus in Table 4.4 shows the model was not significant with a p-value of 0.9781 (greater than 0.05). Hence, no response surface model was obtained for this material property. Experimentally, the longitudinal modulus did not show much variation with respect to increasing temperature. This was expected since the tensile load was applied along the fibers and the fibers are not highly temperature dependent in the range considered (24–166 C). Table 4.3 Longitudinal, transverse, and shear moduli and Poisson’s ratio obtained at 24, 71, 118, and 166 C Run Temperature ( C) Longitudinal modulus, E1 (GPa) Transverse modulus, E2 (GPa) Shear modulus, G12 (GPa) Poisson’s ratio (ν12) 1 118 152.9 7.2 6.4 0.34 2 166 150.7 7.1 4.5 0.29 3 71 152.1 8.4 8.4 0.33 4 166 141.3 7.3 4.4 0.33 5 24 142.0 8.8 9.6 0.31 6 24 146.3 8.9 9.5 0.30 7 166 140.3 7.4 4.8 0.32 8 71 145.2 8.6 8.0 0.33 9 24 147.7 9.4 8.6 0.33 10 118 134.8 7.9 5.4 0.30 11 118 140.9 8.1 4.9 0.31 12 71 132.6 8.1 8.6 0.36 100 120 140 160 180 200 0 50 100 150 200 Longitudinal Modulus (GPa) Temperature (°C) [0]8 Specimens Fig. 4.4 The experimental longitudinal modulus as a function of temperature 4 Elastic Properties of CYCOM 5320-1/T650 at Elevated Temperatures Using Response Surface Methodology 33
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