Fracture and fatigue of bonded composite repairs
Abstract
Bonded composite repair has been recognized as an effcient and economical method to extend the service life of cracked aluminum components. An accurate tool for investigating the stress intensity factor in the cracked aluminum structure after repair is needed. The use of 3D finite elements is computationally expensive. In this thesis, a simple analysis method using Mindlin plate theory is presented. Specifically, the aluminum plate and composite patch are modeled separately by the Mindlin plate finite element while the adhesive layer is modeled with effective springs connecting the patch and aluminum plate. Constraint equations are used to enforce compatibility of the patch-adhesive and adhesive-aluminum plate interfaces. Comparison of the present stress intensity factors for the aluminum crack with a plane boundary element analysis and a 3D finite element analysis are made. The effects of thermal residual stresses arising from the thermal coefficient mismatch of the patch and aluminum plates are examined. Large deflection theory is used to study the effect of different variables including the thermal residual stresses and host and repair plate thicknesses. A procedure for calculating the strain energy release rate along the debond front at the aluminum-adhesive interface is proposed. Experiments on aluminum 2024-T3 plate, AS4/3501-6 carbon/epoxy composite patch, and FM73 adhesive include determining debonding observations using an ultrasonic C-scan. Tests are conducted to examine the metallic and debond crack growth interaction on both symmetric and unsymmetric repairs.
Degree
Ph.D.
Advisors
Sun, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering
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