On the reliability of residual stress measurements in unidirectional carbon fibre reinforced epoxy composites

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.