This article describes the application of interface elements to the prediction of progressive delamination in composite materials. The work has been implemented in two separate commercial finite-element computer packages, ABAQUS [1] and LUSAS [2]. In the former case, this has been achieved via a "user subroutine", while in the latter case the elements are embedded directly within the system, either in the standard "release version" of the code or in a research version, to which the authors have access and in which they have implemented various algorithms directly. Comparisons are made with a range of experimental results for composite material specimens. In addition to the finite-element solutions, closed-form results are also presented that are based on a corrected beam theory.

An approach employing decohesive models with mixed damaged scale and using total fracture energy was developed to simulate the delamination process of a stiffened fibre-composite panel and a repaired composite sandwich panel. Two decohesive material models - a bilinear interfacial decohesive function and the other a cubic polynomial interfacial decohesive function - were developed by using total fracture energy G_c, and based on using interface elements. In comparison with traditional numerical methods in fracture mechanics, this approach automatically predicts the failure load, crack path and the residual stiffness in the fracture process. Applications in this article are delamination analysis of a stiffened fibre-composite panel under four-point bending conditions and a repaired composite sandwich panel under four-point bending test. Comparisons between modeling predictions and experimental observations show that these decohesive models perform well. This article compares the problem of numerical convergent failure between two decohesive material models.