Determination of in-plane and through-the-thickness coefficients of thermal expansion in composite angle brackets using digital image correlation

A procedure for the simultaneous determination of in-plane and through-the-thickness coefficients of thermal expansion (CTEs) in composite angle brackets is presented. Carbon fibre/epoxy samples are heated and digital image correlation is used to determine the in-plane strains and out-of-plane displacements in one side of each sample. In-plane CTEs are obtained from the average in-plane strains measured at different temperatures. Through-the-thickness CTE is obtained from the angular distortion of the samples at different temperatures, which is determined from the out-of-plane displacements. One quasi-isotropic and two unidirectional samples are used. Unidirectional samples allow the material’s in-plane CTEs in orthotropic directions to be determined. Material’s in-plane CTEs permit predicting an in-plane CTE value for the quasi-isotropic sample that agrees with the experimental measurements. Conversely, results obtained for the through-the-thickness CTE in all samples show a significant dispersion. This fact is attributed to the manufacturing distortions present in the curved part of the samples.