Prediction of calibration factors of the hole-drilling method for orthotropic composites including hybrid interphase region

Abstract

This paper investigates the effects of hybrid interphase region on the calibration factors of the hole-drilling method for orthotropic composites. For this purpose, a three-phase composite has been considered which includes fiber, matrix as well as the interphase between them. 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 composite can be obtained. These properties are applied to the available exact solution in order to determine the calibration factors for the three-phase orthotropic plate. Four different composites have been considered in order to study the interphase influences on the calibration factors matrix. 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 interphase thickness. Sometimes, bonding conditions change some of the calibration factors considerably between 30 and 50%. Consequently, when a central hole-drilling experiment is performed in an orthotropic layer, the precision of residual stresses measurement is identically dependent on the elastic properties and the thickness of the hybrid interphase.