effects of free edge interlaminar shear stress on the residual stresses of polymer composites using hole drilling method

in the traditional hole drilling method the in-plane stresses are studied in detail and the interlaminar stresses are not taken seriously. the interlaminar stresses on the free edge of composite materials are important and can cause matrix cracking and delamination. inserting holes in composite laminates causes free edges and it can induce interlaminar shear and normal stresses. in this research, using a finite element method and the simulated hole drilling method for isotropic and orthotropic materials, the three dimensional state of stresses are studied. the number of steps for hole drilling, the uniform and non-uniform pre-stresses, and uniaxial and biaxial stresses are considered. the results show if the number of drilling steps changes from one to four, the ratio of the maximum three-dimensional stresses to the induced uniaxial stress is changed. the mechanical properties of each layer, number of layers, and the stacking sequence are important parameters for laminated composites. therefore, unidirectional plies under uniaxial and biaxial state of stresses are considered. then, the interlaminar stresses for the cross-ply, angle-ply and quasi-isotropic laminated are studied. the effects of interlaminar stresses on the residual stresses on the point of measurement of strains by strain gauges are studied in detail.