Progressive Damage Analyses of SkinStringer 9) Debonding.pdf

PROGRESSIVE DAMAGE ANALYSES OF SKIN/STRINGER DEBONDING C. G. Dávila, P. P. Camanho, and M. F. de Moura Abstract The debonding of skin/stringer constructions is analyzed using a step-by-step simulation of material degradation based on strain softening decohesion elements and a ply degradation procedure. Decohesion elements with mixed-mode capability are placed at the interface between the skin and the flange to simulate the initiation and propagation of the delamination. In addition, the initiation and accumulation of fiber failure and matrix damage is modeled using Hashin-type failure criteria and their corresponding material degradation schedules. The debonding predictions using simplified three-dimensional models correlate well with test results. INTRODUCTION The fracture process of high performance composite laminates is quite complex, involving both intralaminar damage mechanisms (e.g. matrix cracking, fiber fracture) and interlaminar damage (delamination). The basic failure mechanisms that can induce failure in a laminated composite are: matrix tensile/compressive cracking, fi- ber-matrix shearing, fiber tensile failure, fiber microbuckling, and delamination. To simulate damage growth accurately, a failure analysis must be able to predict all failure modes and apply a corresponding reduction in material stiffness. The objective of the proposed paper is to demonstrate a methodology that can cal- culate the strength of composite structures by predicting the growth of all major dam- age modes, including delamination and ply damage. The effectiveness of the method- ology for modeling the debonding of skin/stringer is assessed. The failure of these specimens is clearly dominated by delamination. However, other damage mechanisms such as transverse matrix cracking are also present and the simulation of their interac- tion with the initiation and growth of delamination needs to be included in the analy- ses. Delamination is simulated with decohesion elements and ply da