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Chao-Tsai Huang,Jia-Hao Chu,Wei-Wen Fu,Chia Hsu,Sheng-Jye Hwang 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.3
During the past two centuries, due to too fast growth of the human population, the pollution made by human has seriously impacts on our environment, particularly, for the CO2 emission. To diminish the CO2 emission problem, one of the effective solutions is applying lightweight material, such as the fiber-reinforced plastics (FRP), to replace metal in the manufacturing of transportation vehicles. However, since the reinforced function of the fibers inside plastic matrix is very complex, it is not easy to be visualized and managed. Specifically, the connection from microstructures of the fibers to the physical properties of the final product is far from our understanding. In this study, we have proposed a benchmark with three standard specimens based on ASTM D638 with different gate designs. This system is used to study the fiber microstructures and associated mechanical properties using numerical simulation and experimental studies. Results showed that the tensile properties (including tensile modulus and tensile stress) of all three ASTM standard specimens can be improved significantly in the appearance of the fibers. Moreover, the tensile properties variation of the finished parts associated with the microstructures of the short fibers based on the gate design have been also investigated. Specifically, the tensile modulus and the strength of the Model I are greater than that of Model II, while Model III is much less than others because of its double gate effect. The reason why the tensile modulus and the strength of the Model I is greater than that of Model II is due to some entrance effect. That entrance effect will further provide flow-induced fiber orientation to melt and then enhance the tensile properties of Model I. To confirm the observation, a series simulation and experimental studies have been performed. Specifically, the fiber orientation distribution is predicted using CAE, and verified using micro-CT scan and image analysis by Avizo software. Hence, the correlation from fiber microstructure feature (particularly in fiber orientation) to tensile modulus and tensile stress for fiber reinforced thermoplastic (FRP) in injection molding process can be validated.
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Chao-Tsai Huang,Jun-Zheng Wang,Cheng-Hong Lai,Sheng-Jye Hwang,Po-Wei Huang,Hsin-Shu Peng 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.4
Fiber reinforced thermoplastics (FRP) have been widely used in automotive industry. However, how does the flow-fiber coupling effect influence the micro fiber orientation and further affect the geometrical shrinkage of the final part that is not fully understood yet. In this study, a complex center-gated plate has been applied to study the influence of the flow-fiber coupling effect on the fiber orientation variation and the geometrical change through numerical simulation. Then the practical verification through the micro-computed tomography (micro-CT) and image processing technology was carried out. Results show that in the presence of the flow-fiber coupling the required spruce pressure will be higher compared to no coupling case. In addition, the melt flow front pattern will be changed from “convex-flat” to “convex-concave” under the influence of this coupling. Moreover, in the presence of the flow-fiber coupling effect, the wider core width for fiber orientation tensor in the flow direction (A11) can be obtained from upstream to downstream regions for the same model. However, in the downstream region (i.e. in the FR), the flow-fiber coupling effect is more significantly due to the action of less shear rate in that region. Finally, through the measurement of the left–right asymmetrical shape of the FR for Model I (or Model II), the reason is that the flow-fiber coupling effect will switch the fiber orientation from the flow direction (A11) dominate to the cross-flow direction (A22) dominate. This asymmetrical fiber orientation distribution will further create that asymmetrical shrinkage shape of final part. The correlation between fiber orientation and geometrical shrinkage can be achieved.
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