Determination of residual stress in composite laminates using the incremental hole-drilling method

The cooling conditions used in the forming process of composite materials play an important role in the creation of residual stress. In this study, a new method for measuring residual stress in composite laminates is presented. Three cooling conditions were used to produce different residual stress levels. Residual stresses in [0₂/90₂]_s and [0₈] laminate have been measured by the incremental hole-drilling method combined with 3-D finite element modelling. A software which quickly calculates all the coefficients for each increment was developed. The automatic procedure can be used to calculate the calibration coefficient for any type of laminate (ply number, mechanic characteristics, ⋯) and whatever the number of increments and their depths. The different results show that this method provides access to the in-depth distribution and through thickness of residual stress in the laminate with a good accuracy and practicality.