On the prediction of the bi-axial failure envelope of a UD CFRP composite lamina using computational micromechanics: Effect of microscale parameters on macroscale stress-strain behavior

A computational micromechanics based Finite Element (FE) analysis methodology is presented to predict the bi-axial failure envelope of a unidirectional (UD) carbon-epoxy composite ply. In order to estimate the effect of various microscale parameters that are influencing the macroscopic stress-strain behavior, under individual load cases, detailed numerical studies are conducted using a 3D RVE (Representative Volume Element) model. The constituent epoxy matrix plastic deformation in the RVE is captured using the linear Drucker-Prager plasticity model. The effect of the fiber-matrix interface damage, followed by frictional sliding of the constituent materials on the computed interface tractions is captured using the cohesive zone damage model combined with the Coulomb friction law, which is implemented into Abaqus using VUMAT. From the detailed FE analysis of the RVE under individual load cases, it is observed that the predicted macroscopic stress-strain behavior is sensitive to the fiber-matrix interface properties as well as the in-situ epoxy stress-strain behavior. Hence, using a coupled experimental-computational micromechanics approach the interface and the in-situ epoxy material properties are calibrated and validated. Using the calibrated interface and in-situ epoxy material properties, the bi-axial (transverse tension/transverse compression - in-plane shear) failure envelope of a UD composite ply is estimated. Comparing the predicted damage profiles and the failure envelope with the experimental results leads to good agreement and validates the proposed numerical methodology.