اندازه گيري كرنشهاي رهاشده و محاسبه تنشهاي پسماند در چند لايه هاي كامپوزيتي به روش انتگرال

Residual Strains Measurement and Calculating Residual Stresses in Composite Laminates Using the Integral Method

In this study, the integral method has been employed in order to calculate the non-uniform residual stresses in various composite laminates. The integral method is a well established technique for isotropic materials. In this research, the method is extended and examined for composite materials. In the integral method, the residual stresses in each lamina are determined by consecutive drilling at the center of the rosette which is mounted on the surface of the laminated composites and recording the strains in each layer afterwards. The calibration coefficients for each stage of drilling are determined by simulating the incremental hole drilling process. The calibration coefficients of the integral method separate the residual strains of each layer from the strains measured in each stage of the drilling and, hence, increase the accuracy of calculating the residual stresses in each layer. In this study, samples of symmetric and un-symmetric cross ply and quasi isotropic laminated composite are examined. The residual stresses in each layer of composite samples are determined through measuring the released strains in consecutive steps of the drilling. The experimental measurements are then compared with the predictions of the classical laminate theory. The agreements between the two results validate the integral method for calculating the residual stresses in laminated composite materials..