Revealing complex aspects of compressive failure of polymer composites - Part II: Failure interactions in multidirectional laminates and validation

The compressive failure of multidirectional laminates can be considered as an interaction of four failure mechanisms: fiber kinking, fiber splitting, matrix cracking and delamination. The interaction of these four failure mechanisms is responsible for the macroscopically observed nonlinear behavior and ultimate failure of the structure. In this paper, a numerically efficient 3D Finite Element modeling approach is presented combining the benefits of homogenizing material models and micromechanical modeling strategies. The micro model is used to resolve the regions which are prone to fiber kinking. In all other regions, a single UD ply is considered as a continuum (i.e. in a homogenized way) and the material properties are represented using a transversely-isotropic constitutive model. At both scales, fully 3D elastic-plastic material models regarding nonlinearities and failure under multiaxial loading conditions are used. With this approach, the progressive failure of multidirectional laminates under compressive loading can be simulated in detail considering the complete kinking process and the progression of kink bands. The sequence and interaction of the different failure mechanisms is studied and discussed. In order to validate the numerical results, the nonlinear stress-strain response and ultimate failure stress of selected carbon epoxy laminate layups is predicted and compared with experimental results.