環氧樹脂、酚醛樹脂等高分子材料為複合材料常用之基材，但電熱與機械性質不佳，通常得加入補強材料改善之。石墨具有耐高溫、良好之機械性質、及優越之導電性與導熱性等物理性質，比起奈米碳管而言價格更為低廉、也更容易製備。本研究主要使用環氧樹脂和20 μm天然石墨以及膨脹石墨製備天然石墨/環氧樹脂複合材料以及膨脹石墨/環氧樹脂複合材料，並將8層碳纖維加入25 wt%之天然石墨/環氧樹脂製備碳纖維複合材料。改變20 μm天然石墨或膨脹石墨比例，探討20 μm天然石墨或膨脹石墨含量對整體複合材料之機械性質與導電性質之影響，並且利用修正型哈賓-蔡(Halpin-Tsai)方程式嵌合楊氏係數與20 μm天然石墨體積百分比的關係。由實驗結果可知，40 wt%的20 μm天然石墨/環氧樹脂複合材料，在機械性質方面，楊氏係數提升成201.11倍、撓曲模數提升成270.14倍，但拉伸強度降低21.36 %、撓曲強度降低34.65 %。在導電性質方面，體積電阻率從3.14×107 Ω-cm下降至2.57×101 Ω-cm，降低了99.99%；20 wt%膨脹石墨/環氧樹脂複合材料，在機械性質方面，楊氏係數提升成105.07倍、撓曲模數提升成150.91倍，但拉伸強度降低23.88%、撓曲強度降低31.74 %。在導電性質方面，體積電阻率從3.14×107 Ω-cm下降至2.72×103 Ω-cm，降低了99.99%。而8層碳纖維加入25 wt%之天然石墨/環氧樹脂複合材料在機械強度、體積電阻率、氣體滲透度、密度皆符合美國能源局2015年所規範之雙極板標準。在分析方面，建立三維模型，以有限單元套裝軟體ANSYS分析模擬天然石墨/環氧樹脂之等效楊氏係數。

Mechanical stength, electrical conductivity, thermal conductivity of matrix used in polymeric composite materials are not so good. Graphite with good mechanical properties, low electrical resistivity, high temperature resistance is cheaper than carbon nanotubes. This study used epoxy, 20 μm natural graphite, expanded graphite, and carbon fiber to fabricate natural graphite/epoxy and expanded graphite/ epoxy composites and carbon fiber/natural graphite/epoxy composites. Different percentages, (0, 10, 15, 20, 25, 30, 35, 40 wt%) of natural graphite and (0, 10, 15, 20 wt%) of expanded graphite in composites, was assessed to discuss the effect on their mechanical and electric properties. Modified Halpin–Tsai equation was used to fit the Young’s modulus and flexural modulus of the natural graphite/epoxy composites by adopting an orientation factor and an exponential shape factor in the equation. The results of 40 wt% natural graphite/epoxy composites showed that the Young’s modulus increased 201.11%, the flexural modulus increased 270.14%, the tensile strength decreased 21.36%, the flexural strength decreased 34.65%, the volume resistance decreased 99.99%. The results of 20 wt% expanded graphite/epoxy composites showed that the Young’s modulus increased 105.07%, the flexural modulus increased 150.91%, the tensile strength decreased 23.88%, the flexural strength decreased 31.74%, the volume resistance decreased 99.99%. And results of carbon fiber/natural graphite/epoxy composites’ properties satisfied the bipolar plates 2017 targets of US Department of Energy. In addition, the Young’s modulus of natural graphite/epoxy composites were also analyzed using the finite element software ANSYS.

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