Three-dimensional stress analysis of variable angle tow composite laminate using hybrid brick elements

Variable angle tow (VAT) composites manufactured using continuous tow shearing (CTS) technique exhibits smooth thickness variation across the plane of the laminate as a function of fiber angle variation. These VAT laminates have a flat surface on one side and a curved surface on the other side resulting in asymmetric cross-section about the mid-surface of the laminate. Mostly shell-based finite elements have been used for modeling the VAT panels, and they neglect the thickness variation introduced by manufacturing in the stress analysis of laminates. In this work, the use of hybrid brick elements for three-dimensional stress analysis of VAT laminates manufactured using CTS technique is studied. A user-defined element subroutine is written for the 8-node and 27-node hybrid brick elements in the ABAQUS finite element software. The numerical performance of the hybrid brick elements in computing the stress solution of composite laminates is evaluated by studying benchmark problems and the results are compared with the displacement brick element. The influence of mesh distortion, shear locking and boundary layer effect in the stress solution evaluated by hybrid elements are studied. VAT laminate with thickness variation is modeled using the hybrid brick elements and the effect of asymmetric cross-section on the through-thickness stress field is investigated. The influence of the fiber angle distribution as well as thickness variation on the phenomenon of stress redistribution across the plane of the laminate for different VAT configuration is studied. Further, the numerical results of VAT laminate with thickness variation obtained using hybrid brick elements are compared with the experimental results available in the literature. The results from this numerical study will help the engineer in designing efficient VAT laminates fabricated using CTS technique.