PSI - Issue 26

E. Solfiti et al. / Procedia Structural Integrity 26 (2020) 187–198

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E. Solfiti and F. Berto / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 4: (a) Thermal conductivity in the in-plane direction against bulk density and (b) thermal conductivity in the out-of-plane direction against bulk density: 1. Py et al. (2001),2. Wei et al. (2010), 3. Liu et al. (2013), 4. Olives and Mauran (2001), 5. Bonnissel et al. (2001), 6. Papyex ® , 7.Grafoil ® , 8. Chen and Chung (2014).

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Fig. 5: Temperature dependence of thermal conductivity: 1. Ho et al. (1972), 2. Chen et al. (2011a), 3. Grafoil ® , ρ = 1.12 g / cm 3 , 4. Papyex ® , ρ = 0.7 - 1.1 g / cm 3 , 5. Sigraflex ® , ρ = 1 g / cm 3 .

the polycrystalline trend and follow the same behavior on the whole range of temperature. In the out-of-plane direc tion instead appears more similar to PG perpendicular to the main orientation of crystals. Copper and aluminum own values higher than FG although in the same order of magnitude but, more fundamental, they cannot hold the same working temperature of FG. For example, their melting point results indeed equal to 1357 ◦ C and 933 ◦ C respectively [Ho et al. (1972)], which is considerably lower than 2500 ◦ C. The e ff ect of increasing temperature acts on lattice vibrations of graphite being useful for the conductivity at low temperature but having the opposite e ff ect at high tem perature. FG in the in-plane direction seems to inherit the same e ff ect whereas in the out-of-plane direction it keeps a constant trend with small variations around a stable average. Despite the microstructure of PG is highly crystalline and the manufacturing process is totally di ff erent from flexible graphite foils, it is possible to intuitively capture not only that FG owns a mixed behavior among the two extreme bounds of PG but it holds such feature along the whole working range of temperature. To design the conductivity in a material has a fundamental relevance in order to im prove the heat transfer capability and to better understand the heat transfer mechanism of FG. The atomic mechanism of heat transfer is not well-known indeed and only Chen and Chung (2014) suggested a contribution of the crystalline