Assessing 3D shear stress-strain properties of composites using Digital Image Correlation and finite element analysis based optimization

This work presents a method which uses the full-field measurement capability of Digital Image Correlation (DIC) for a simultaneous assessment of non-linear shear stress--strain relations for composites in all three principal material planes. The method, which employs a small rectangular plate torsion specimen, advances our ability to measure 3D material properties compared to the previous methodology that was able to use only small regions of the specimen surfaces in the material characterization. The new methodology takes full advantage of the full-field measurement. Material stress-strain constitutive modeling is relying on the DIC data including the in-plane as well as out-of-plane strain components; and on iterative finite element model (FEM) updating based on the Levenberg-Marquardt algorithm for minimization of weighted least squares error between the DIC-measured and the FEM-predicted strains. Results include the in-plane and two interlaminar stress-strain curves simultaneously captured for a practical carbon/epoxy tape material system.