Composite Patch Repair of Cracked Aluminum Structures

Abstract

A bonded composite patch repair of damaged metallic structures has many advantages over traditional welding and bolted patch repair, such as no new stress concentration, design flexibility, high fatigue and corrosion resistance, and low cost. The effectiveness and reliability of a repair are highly reliant on the patch design, bondline properties, and processing and fabrication parameters. To explore an optimal repair within a design space, most of the current modeling and simulations are performed based on a single failure mechanism along the bondline without considering other aging and damage mechanisms in the composite patch and aluminum structures. A Hybrid Structure Evaluation and Fatigue Damage Assessment (HYSEFDA) toolkit based on an Abaqus/Implicit platform has been developed to access the residual strength and fatigue life of a composite patch repaired metallic structure. A mesh independent, phantom-paired element based extended finite element method (XFEM) and a cohesive spring element is employed to describe the discrete cracks in the metallic layer and the adhesive interface between the metal layer and the composite patch, respectively. A virtual crack closure technique (VCCT) approach is adopted to extract the energy release rate at the crack tip and delamination front, which is tracked by a developed geometrical mapping algorithm. In order to capture other damage and aging mechanisms, a continuum damage mechanics (CDM) approach is applied to characterize inter and intra ply damage. In addition, the plasticity induced crack closure effect is also investigated by implementing a plastic hardening model into the HYSEFDA toolkit. The HYSEFDA toolkit is used to evaluate the fatigue life of an aluminum plate repaired by E-Glass epoxy composite patch tested by the Naval Surface Warfare Center, Carderock Division. Parametric studies are performed to examine the effects of patch damage on the bridging of a fatigue crack in an aluminum plate.