PSI - Issue 45

Quan Jiang et al. / Procedia Structural Integrity 45 (2023) 117–124 / Structural Integrity Procedia 00 (2022) 000 – 000

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4.2. Charpy impact strength of injection-molded SGFRTPs Figure 4 portrays the Charpy impact strength evaluation results. Error bars in the figure represent the standard deviations. The value of a iN tended to increase with the increase in fiber content. Furthermore, the addition of maleic anhydride-modified polymer, which is compatible with the matrix, showed a tendency to increase the value. This trend is consistent with results reported by Kallel et al. (2018) for PP/GF-30wt%.

Fig. 3. IFSS determination results

Fig. 4. Charpy impact test results.

5. Discussion 5.1. Energy dissipation mechanism at impact loading of SGFRTP

Figure 5 presents the results of phase contrast microscope observations of the notch tip area. As these photographs show, fiber pull-out was observed near the notch tip in all specimens of the compositions examined for this study. As the fiber content increased, the number of pulled-out fibers tended to increase. Figure 6 presents the results of digital microscopic observation. These photographs, which were taken with magnification that accommodates viewing of the entire fractured surface, indicate that lines are drawn through the entire fractured surface of all the specimens of the compositions examined for this study. These findings suggest that the main mechanism of impact energy dissipation in the studied compositions is fiber pull-out. To confirm this conjecture, we calculated the critical fiber length L c under the corresponding IFSS results. L c was expressed using the following equation (5). In that equation, σ f represents the fiber tensile strength. Also, d represents the fiber diameter. Figure 7 shows the average fiber pull-out length, l p , average fiber length, L f , as measured from the phase contrast microscope observation. In addition, L c , as calculated by using equation (5). The error bars in the figure show the standard deviation. Actually, l p and L f tended to become shorter with increasing fiber content. Also, because of the decreasing trend of IFSS, L c tended to become longer with increasing fiber content. The shear stress inside the fiber reaches its maximum value at half of the fiber length. In other words, theoretically, a nearly 2:1 relation can be found between L f and l p had been reported by A. Kelly et al. (1965). The relation between L f and l p obtained in this study exhibits the same relation. In addition, all fiber content and materials by L c are longer than L f , which means that the yield condition of SGFRTPs is dominated by fiber pull-out. From these results, one can infer that the energy dissipation mechanism in the Charpy impact test of the compositions studied in this paper is attributable to fiber pull-out. 2 f IFSS  c d L  (5)