Abstract

Laser Flash Method (LFM) is commonly used to measure the thermal diffusivity of homogeneous and isotropic materials, but it can be also applied to macroscopically inhomogeneous materials, such as composites. When composites present thermal anisotropy, as fiber-reinforced, LFM can be used to measure the effective thermal diffusivity (aeff) in the direction of heat flux. In the present work, the thermal behavior of composites during thermal diffusivity measurements with the LFM was simulated with a Finite Element Model (FEM) using commercial software. Three composite structures were considered: sandwich layered (layers arranged in series or parallel); fiber-reinforced composites; particle composite (spheres). Numerical data were processed through a non-linear least-square fitting (NL-LSF) to obtain the effective thermal diffusivity of the composite. This value has the meaning of "dynamic effective thermal diffusivity". Afterward, the effective thermal conductivity (?eff) is calculated from the dynamic effective thermal diffusivity, equivalent heat capacity and density of the composite. The results of this methodology are compared with the analytically calculated values of the same quantity, which assume the meaning of "static effective thermophysical property". The comparison of the dynamic and static property values is so related to the inhomogeneity of the samples, a deviation of the temperature vs time trend from the solution for the perfectly homogeneous sample gives information about the sample's lack of uniformity.

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