Micro-area Experimental And Numerical Analysis On Laminated Composites Single-lap Stitched Joint

The main subjects of this paper are to research the co-curing single-lap stitiched composites joint using experimental method and numerical analysis. In the experimental part, we firstly research the displacement measurement precision of digital image correlation technique (DIC), and then apply DIC on the deformation measurements in micro areas of the single-lap stitched composites joint. In the numerical simulation part, FEM is used to research the effect of stitch line and resin fillet on the stress distribution of the single-lap stitched composites joint, and the effect of stitch line on the crack extension after an initial crack become to be in the specimen.DIC, developed from 1980s', has become a popular experimental technique in experimental mechanics due to its simplicity and flexibility. The measurement precision is a key issue in the current research of DIC. It is universally accepted that the displacement measurement precision of DIC is affected by many factors. The influence of dark current of CCD and the sub-pixel interpolation methods on the displacement measurement precision of DIC are analyzed. The effect of dark current is analyzed by the statistics. As a result, the quantitative relation between the vibration of gray value and the displacement value is got. The effect of interpolation algorithm is analyzed by thinking an interpolation algorithm as a set of filters. The transfer function and interpolation error of some interpolation algorithms are got. The results are helpful for improving the displacement measurement precision of DIC.Laminated composites stitched single-lap joint is common joint type in composites structures. It is useful for us to know the stress distribution in the several areas of the joint when is loaded. In this work, DIC is applied to measure the deformation of the specimen in several important micro areas. As results, the strain fields on the different positions of the specimen are measured. Additionally, FEM is used to research the behavior of the joint. The effects of stitch line and resin fillet on the stress fields of the specimens are analyzed. Moreover, the virtual crack closure technique (VCCT) is applied to analyze the effect of stitch line on the energy release rate when there is an initial crack in the specimen, and the effect of stitch line on the crack extension. The main function of stitch line in the single-lap joint is clarified.