Development of an Integral Method for Determination of Non-uniform Residual Stresses in Laminated Composites

A new method for determination of residual stresses in the bottom layers of laminated composites is developed. In this method the residual stresses are determined by performing a consecutive drilling of laminated composites in the center of the rosette and recording the strains after drilling each layer. The depth of the hole in each step is equal to the thickness of each layer and the maximum depth of driling is equal to the diameter of the hole. The integral method has been used for determination of the residual stresses because these stresses are distributed non-uniformly through the thickness of each layer. A computer program for simulation and calculation of the calibration factors of the incremental hole drilling process of laminated composites is presented. The calibration factors correlate the released strains to the residual stresses in each layer. The released strains in the incremental hole drilling process are divided in two parts. The first part is due to the released strain by increasing the holes depth and changing the geometry of the hole. The second part is due to the released strain from each layer by drilling the same layer. In this method, by calculating the calibration factors using the integration method and performing a finite element method, the residual stresses in each layer of laminated composites are calculated.