Paper number 124

MODELLING R-CURVE EFFECTS IN DELAMINATION DAMAGE MECHANISMS

V. Q. Bui¹, E. Marechal², H. Nguyen-Dang³

1,3 Department of Fracture Mechanics-Laboratory of Aeronautic & Spatial Techniques (LTAS)
University of Liège, 21 Ernest Solvay Street, B-4000 Liège, Belgium
2 SAMTECH Company
25 Frère-Orban Boulevard, 4000 Liège, Belgium

Summary

The presence of imperfect interlaminar interfaces in laminated composites is an essential condition for delamination initiation and propagation. Besides, for a complete characterisation of delamination resistance, the R-curve effect, i.e. the increase of the interlaminar fracture energy Gc as delamination propagates, should be taken into account. Rather than defining the interlaminar fracture energy by one single value Gc, it turns out that both an initiation value Gc (ini), and a steady-state propagation value Gc (s/s-prop) need to be considered. By reducing the description of all interlaminar damage mechanisms within a so-called "equivalent damaged area", damage models associated to weakened interfaces are developed using "steady-state R curves" to simulate the evolution of energy release rates in the damage zone. These models have been integrated into the SAMCEF F.E. package and successfully applied to the modelling of standard delamination tests like Double Cantilever Beam (DCB) and End Loaded Split (ELS) specimens. The importance of taking R-curve effect into account in the numerical simulation is demonstrated by comparing the predicted results with the experimental data.

Keywords

laminates, delamination, damage mechanics, imperfect interface, interface finite element, R-curve, modelling.