On Stress Concentration on Edges of Defect Holes in Plates and Critical Issues on Filling-in Repairs

Abstract

Repair is now increasingly used for damaged structures due to its distinguished advantages in prolonging the service life of structures, substantial saving in materials, and preservation of related crucial resources. This work presents a novel filling-in repair procedure for localized damages in panel structures, and conducts a series of theory and numerical studies to examine the repair effects in terms of stress concentration. It aims providing some fundamental understandings important in the design of repairing procedures for effective filling-in repairs to mitigate stress concentrations. First, the damaged zone (or cracks) is “cut-off” by simply drilling a hole through the panel to remove possible stress singularity. The hole is then filled-in with a circular patch of slightly smaller diameter made of similar material of the panel using adhesives. Stress concentration is then investigated to reveal the possible ranges of the stress concentration factors (SCF), through both analytical and numerical means using finite element (FE) models. The repair effects are then examined for repaired plates with filled-in holes in terms of SCF reduction, comparing with plates with open-holes. Both aluminum and composite plates are studied, and the filling-in repairs are carried out using epoxy adhesives. It is found that the SCF increases with the adhesive thickness, decreases with hole radius and Young’s modulus of adhesives. Parametric studies are performed to produce two-stage curve-fitted formulae for SCF predictions from given hole radius, physical properties and thickness of the adhesive layer, which are useful for the design and assessment of the repairs, leading to a prolonged life of services of structures.