Creep and Mechanical Energy Dissipation of Exfoliated Graphite
Qurishi, Adeel Ul Haq
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Exfoliated graphite (EG) refers to graphite that has a degree of separation between the carbon layers in a graphite. The structure of EG is cellular and its cell walls are viscoelastic due to the shear and the associated interfacial friction between the graphite layers. This viscoelastic nature of its cell walls allows it to dissipate energy, making it an attractive material for vibration damping. The thesis addresses the creep behavior of exfoliated graphite which is enabled by its cellular structure. The approach involves experimental characterization and mathematical modelling of its creep behavior. The creep-recovery experiment is conducted for a range of compressive stresses (6 - 25 kPa) showing a recovery of (37-30%). A decreasing trend in creep compliance is also observed with the increase in solid fraction. A generalized Voigt model which contains a series of spring and dashpots connected in parallel is used to represent the material. Schapery's collocation method and Emri-Tshcoegl \textquotesingle s algorithm are used to fit the experimental creep data. The latter is preferred as it avoids any negative coefficients. The time-dependent creep compliance is used to calculate the overall flexural strain which provides an estimate of equivalent sliding displacement. A pseudo coefficient of friction µ is introduced to estimate the force of friction at the interfaces. The value is chosen such that the analytical values of energy dissipation fits well with the experimental results. This modelling approach is expected to work well for materials having large interfaces where significant sliding is possible.