• Delamination
• fatigue
• mixed mode Cohesive Element
• UMAT

One of the most common failure modes for laminated composite structures is delamination, or interlaminar cracking. The development of predictive, reliable and robust numerical and experimental analysis tool for quasi-static and cyclic mixed mode delamination of CFRPs is the major focus of the work.
In this study, the capabilities of commercial FE code Abaqus with implementation of the Cohesive Zone Model and customized user-subroutines (UMAT) was assessed. Benchmark delamination propagation results for several specimen configurations were generated and compared with previous works. The results demonstrated that the Cohesive Zone Approach implementation in Abaqus was capable of accurately replicate the benchmark delamination growth results.
The sensitivity of the interface element has also been tested with respect to input parameters, such as interface element length, interface element strength, initial stiffness, damage initiation and damage evolution criterion. The behaviour of the delamination between plies has been also described by a user subroutine, which contains a failure criterion for the delamination both for static and cyclic loading condition. The results showed a good agreement with Cohesive Zone formulation in Abaqus and with experimental results available in literature. Each ply has been assumed as an orthotropic homogenized continuum and a layer of cohesive elements has been placed in specimen mid-plane.