Abstract
<p>In this Ph.D. work, a 3D orthotropic augmented finite element method (A-FEM) that can model arbitrary ply cracking, including matrix cracking and fiber rupture/kinking, was formulated and implemented into a commercial code ABAQUS as a user-defined element. The 3D orthotropic A-FEM can work with 3D cohesive zone model-based interface elements to model coupled intra-ply cracking and delamination. Furthermore, the 3D A-FEM has been extended to account for curved or non-planar composite laminates, which is a critical improvement because the crack configuration in non-planar laminated structures can be very complicated due to instantaneous variation of the local fiber direction, and there have been few models can cope with such complexity.<br />
The developed 3D orthotropic A-FEM has been subjected to a rigorous validation procedure. The verification tests start from a single element under monotonic loading and further extend to single aligned and off-axial ply with various crack propagation tests. Crack initiation, propagation, and its coupled evolution with interlaminar delamination have also been tested using angle-ply specimens.<br />
After successful validations, the 3D orthotropic A-FEM was employed to analyze six numerical models provided by our industrial collaborator. All these models were multi-directional laminates with various ply orientations and shapes. The A-FEM simulated results were in good agreement with the collaborator's experimental results. For those non-planar specimens, a newly formulated two-step rotation process has been developed to calculate the instantaneous fiber orientations so that the respective crack configurations can be correctly predicted. This new subroutine successfully predicted a composite radius structure's crack paths and failure with two different stacking sequences. Additionally, this subroutine was successfully used to study the effects of a possible production imperfection in the radius region and then compared to a perfect radius region model.</p>