Finite Element Analysis of Free-Edge Delamination in Laminated CompositeSpecimens

摘要

A mixed-type finite element formulation based on minimization of potentialenergy, and ensuring continuity of displacements as well as tractions, is developed to analyze the free-edge delamination problem in composite laminate coupons under uniform longitudinal strain. in this model, compatible cubic interpolation functions, originally proposed by Felippa for plate bending analysis, were used for defining the displacement field within each element. To ensure traction continuity, the nodal displacement components and their gradients normal to element boundary were transformed to a mixed set of degrees of freedom through appropriate displacement-traction relationships. Thus, for global assembly, the nodal degrees of freedom include interlaminar traction components at the corner nodes, as well as traction components at the mid-side nodes of each element. This ensures continuity of displacement and traction along interelement boundaries as well as across laminate interfaces. Also, traction-free boundary conditions can be specified in a point-wise sense. (continued) The procedure is verified by application to four-ply laminate specimens. The displacement and stress fields from the continuous traction finite element procedure are compared with solutions by Pagano's procedure which is based on a totally different theoretical approach. Application of the proposed method to multilayer coupons is shown to be successful in modeling some failure phenomena observed in the experiments. The method has potential for obtaining accurate estimates of stresses in laminated composites and, hence, for better understanding of damage and failure mechanisms.