A modified cohesive zone model for fatigue delamination in adhesive joints: Numerical and experimental investigations

A modified cohesive zone model (CZM) has been developed to simulate damage initiation and evolution in Fibre-Metal Laminates (FMLs) manufactured in-house but based on the Glare (R) material specifications. Specimens containing both splice and doubler features were analysed under high cycle fatigue loading. The model uses a novel trapezoidal traction-separation law to describe the elastic-plastic behaviour of this material under monotonic and high-cycle fatigue loading. The model is implemented in the software Abaqus/Explicit via an user-defined cohesive material subroutine. Several models of increasing complexity were investigated to validate the proposed approach. A two-stage experimental testing programme was then conducted to validate the numerical analyses. Firstly, quasi-static tests were used to determine the ultimate tensile strength (UTS) of a series of specimens with and without internal features. Secondly, high-cycle fatigue tests were conducted on both laminate types with variable load amplitude so that S-N curves could be built. Tests were monitored using digital image correlation (DIC) for full-field strain mapping and acoustic emission (AE) sensing to detect the initiation and propagation of damage during quasi-static and fatigue tests. Good correlation was observed between predicted onset and growth of delaminations and the history of cumulative AE energy during the tests, which supports the validity of the cohesive modelling approach for FMLs.