Estimation of Residual Stresses in Laminated Composites by Slitting Method Utilizing Eigen Strains

The manufacturing parameters such as curing process cause residual stresses in polymeric laminated composites. Therefore, an accurate method of measurement of residual stresses is essential for the design and analysis of composites structures. The slitting method is recently used for measurement of the residual stresses in laminated composites. However, this method has some drawbacks such as high sensitivity to noise of measurements and high scattering in the final results, which necessitate using of normalization techniques. Moreover, the form of polynomials, used in the conventional slitting method for calculation of the stiffness matrix, has a significant effect on final results. In this paper, it is shown that the major reason of the drawbacks of the slitting method in calculating the residual stresses is a direct use of the elastic released strains recorded by strain gages. In the present study, instead of direct calculation of residual stresses from the elastic released strains, eigen strain distribution as a constant and invariant field has been calculated from the recorded elastic strains. Then, by using the calculated eigen strain field in a finite-element model, the residual stress filed was obtained. Also, instead of using polynomials to calculate the compliance, a superposition method was used. The results show that the new method decreases the sensitivity of the final results to noise and scattering of the experimental data. It means that the normalization methods are not needed any more.