A novel numerical methodology for the simulation of unstable debonding growth in aerospace stiffened composite panels

The growth of interlaminar damage under various loading conditions can be a significant factor in the integrity of aerospace composite components. This phenomenon can be extremely dangerous under cyclic loading conditions, potentially leading to structural collapse due to the rapid decrease in strength and stiffness of the material with loading cycles. In order to enhance comprehension of the mechanisms underlying damage evolution and interaction in composite materials, a combination of numerical and experimental methodologies is frequently employed. This approach facilitates the development of safe composite components for aerospace applications. Indeed, the most advanced fatigue numerical tools simulate the evolution of damage in composite structures by adopting static analyses in conjunction with appropriate material properties degradation rules. The numerical analyses are typically conducted under load control, thereby accounting for the cyclical nature of the applied load. This simulation approach is often inadequate when dealing with unstable interlaminar damage growth phenomena, which are related to sudden variations in geometry and damage status. An accurate simulation of unstable damage growth necessitates the utilisation of a tool that accounts for dynamic effects, including mass and damping matrices, which are typically incorporated into transient analysis. However, transient analyses are computationally expensive and may require a considerable investment of time to complete. The current methodologies for simulating interlaminar damage evolution have yet to achieve a satisfactory level of robustness and effectiveness for this highly dynamic event. Accordingly, the objective of this research is to simulate a dynamic phenomenon, such as the propagation of fatigue-driven unstable delaminations, using a more efficient static approach. In particular, this study aims to introduce an efficient numerical methodology that can overcome the issues related to the sudden variations of geometry and damage status. The proposed methodology employs the Virtual Crack Closure Technique (VCCT) and the Paris’ law to utilise a series of nonlinear iterations, with a hybrid displacement-load control approach, in order to emulate the highly dynamic behaviour associated with unstable interlaminar damage growth. The proposed methodology has been implemented in the ANSYS FEM software via the parametric APDL language and has been successfully preliminary tested on an artificially debonded composite stiffened panel under compression-compression fatigue loading conditions.