Novel FGM-USDFLD approach in Graded Cohesive Zone Modeling (GCZM): Predicting debonding and crack propagation in composite-patched notched plates

Abstract

This study uses a graded adhesive approach to investigate the efficacy of composite patch reinforcement on a notched aluminum plate. The methodology employs the volumetric fraction concept of Functionally Graded Materials (FGM) to develop a Graded Cohesive Zone Model (GCZM). A variable field, introduced through a Fortran-based USDFLD subroutine, adapts the formulation of this GCZM. Patch debonding is simulated via adhesive damage using the Cohesive Zone Model (CZM). At the same time, crack initiation and propagation within the plate are modeled using the Extended Finite Element Method (XFEM) implemented in ABAQUS finite element software. The adhesive behavior is characterized by a triangular traction-separation law, with the GCZM incorporating gradation in both shear and normal separation modes relative to the notch radius. The GCZM concept is compared against two non-graded cases, Araldite 420 and AV138 adhesives, with one case replicating a previous study. Three gradation concepts are explored: C-1, where the more resistant Araldite 420 is located at the notch; C-2, at the extremity; and C-3, where it is at both the notch and extremity. These configurations aim to homogenize load transfer to the composite reinforcement and elucidate how different GCZM concepts influence debonding between the plate and composite reinforcement. By implementing USDFLD, this work effectively demonstrates the impact of gradation concepts and volumetric fraction indices on the competition between debonding and crack initiation in the plate. The results provide valuable insights into optimizing adhesive properties for enhanced structural integrity in composite-reinforced metallic structures.