Characterisation of anisotropic materials by steady-state and modulated thermal ellipsometry

摘要

A new lock-in thermography method for the measurement of in-plane principal diffusivities of orthotropic materials is proposed. Two-dimensional synchronous detection is performed on the elliptical thermal field which develops around a point periodically heated by a laser beam. Diffusivities are inferred from the slope of the phase lag profiles. The approach was validated on a duralumin (isotropic) sample and then applied on a unidirectional carbon/epoxy sample. The aspect ratio of the surface isotherms is determined by the anisotropy of the heated material. Therefore, possible in-depth variations of the anisotropy unavoidably alter the aspect ratio distribution. An inversion method was thus recently proposed to monitor internal fibre orientation changes in composites. Results obtained with a continuous-fibre carbon/epoxy sample and with an injection-moulded short-fibre sample are reported.