More accurate evaluation of curing residual stress field considering interphase characteristics

In this research, the effects of bonding conditions between fiber and resin on thermal residual stress field of polymer composites have been studied. For this purpose, a three phase composite has been considered includes fiber, matrix as well as the interphase between them. First, by employing the available analytical predictions for elastic properties of the interphase and based on micromechanical equations, the mechanical properties of the three phase orthotropic layer is obtained. By applying these properties to the available exact solution, calibration factors of the central hole-drilling method for unidirectional composites with four different materials have been reached. Simulation of the central hole-drilling method in composite laminates considering various interphase thicknesses leads to prediction of an equivalent calibration factors matrix for the laminate. Finally, by using the available experimental data for residual strains, thermal residual stresses are calculated according to different bonding conditions. Analytical results show that for carbon/epoxy composite, bonding conditions affect all of the calibration factors importantly, while for boron/epoxy, glass/epoxy and aramid/epoxy composites some of these factors are not sensitive to these conditions. Thus, for carbon/epoxy laminates, getting away from perfect bonding conditions, gives rise to a noticeable decrease in residual stress field (about 903), while these variations are lower in glass/epoxy composite (about 113). Main of this reduction is occurred when the composite is considered as a three-phase material, even if the interphase is very narrow.