Analysis of load-displacement curves of an adhesive-reinforced composite patch repaired plate using the combination of XFEM and CZM techniques

Since the development of the eXtended Finite Element Method (XFEM), Cohesive Zone Modelling (CZM), and the Virtual Crack Closure Technique (VCCT) for damage analysis in repaired structures, it has now become easy to validate experimental tensile tests carried out on damaged and repaired plates with a composite patch. In most cases, these tensile tests can be expensive and time-consuming due to surface preparation, cleaning, polishing, adhesive application, and the crosslinking time of the adhesive, which must be carefully considered. The analysis of damage in structures assembled by adhesive bonding is crucial to predicting their behavior under various loading conditions. Moreover, the analysis of experimental curves is in most cases translated a global behavior without taking into account the details that can influence the results. With the introduction of techniques (XFEM, CZM and VCCT), it is now possible to model different forms of damage, accounting for several mechanical and geometric parameters of the plate, patch, and adhesive. This work aims to analyze the behavior under tensile loading of a 2024-T3 aluminum plate presenting an initial crack of different lengths emanating from a central circular notch. This plate is repaired by a carbon/epoxy type patch through an adekit A140 adhesive. The combined use of XFEM to track damage in the plate and CZM for adhesive debonding allowed the acquisition of tensile load-elongation curves and the assessment of damage inflicted by loading on the plate. The results demonstrate that the combined use of XFEM and CZM techniques enables the identification of the adhesive debonding impact on the load transfer to the patch and consequently on the strength of the repaired structure. Furthermore, these highlight that the decrease in the effectiveness of the composite patch with increasing crack size is directly linked to the progressive deterioration of both the plate and the adhesive strength.