On the reliability of residual stress measurements in unidirectional carbon fibre reinforced epoxy composites. (May 2021) - Magnier, A.
Abstract: The present work introduces a novel methodology to analyse non-uniform residual stresses in composite materials. For robust determination of stresses in complex structures made of different layers, it is first necessary to prove that residual stress analysis in a single layer structure can reliably be accomplished. In present work a unidirectional carbon fibre reinforced epoxy is investigated. For residual stress determination, the integral incremental hole drilling method is used. It is revealed that the standard evaluation formalism for non-uniform stress analysis in isotropic structures is not applicable. A novel methodology based on the formalism for uniform stress analysis in orthotropic materials is introduced and applied for determining non-uniform residual stress states in depth. For calibration, a known load is induced by bending of samples. By comparing data obtained with the known bending stresses, the reliability of measurements is analysed and the novel formalism introduced is validated. Highlights: Residual stress measurements in composite material are challenging. Use of classical X-ray diffraction method is not possible as the material is not a single crystal structure. Use of the incremental hole drilling method for isotropic structure is not applicable. New orthotropic formalism for the incremental hole drilling method is introduced. The calculated coefficients and new methodology are experimentally validated.