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Picture for Fatigue Loading of Test Specimens with Galvanically Induced Corrosion Damage Provides New Insight to Guide Fracture Mechanics Modeling
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Fatigue Loading of Test Specimens with Galvanically Induced Corrosion Damage Provides New Insight to Guide Fracture Mechanics Modeling

Product Number: 51324-20989-SG
Author: Thomas Curtin; Sharon Mellings; Ivan Karayan; Robert Adey; Joe Indeck
Publication Date: 2024
$40.00
Airframe structural components commonly experience galvanic damage at dissimilar metal connections following deterioration of insulating sealants or breakdown in coating protection systems. Of particular concern is the often-hidden corrosion damage that occurs inside fastener holes. Aggressive electrolytes can develop in these occluded spaces leading to the formation of multiple crack initiation sites and a compromise in the structural integrity of the component. To investigate this type of damage, laboratory testing was undertaken to evaluate fatigue life in AA 7075-T651 dog-bone specimens that included side holes fitted with CFRP inserts. The CFRP insert was used to introduce galvanic damage under thin film atmospheric corrosion conditions but removed prior to actual fatigue testing. Fatigue tests were conducted under constant amplitude loading, at R-ratios of 0.05, 0.6, and 0.89, in both air and 4.5M NaCl solution. Using a three-dimensional, fatigue crack growth (FCG) program, BEASY, complex crack propagation path evolution, and transition from surface flaw to through-crack was accurately represented. By selecting appropriate crack growth kinetics, the environmental effects on fatigue life were quantitatively determined for different modeling scenarios. Fractographic images of crack initiating features (corrosion pits, constituent particle clusters) were used to guide the location and sizing of initial flaws. Fatigue crack growth kinetic data, collected in both air and NaCl solution, was used to drive crack growth simulations. Modeling scenarios included the propagation of both single dominant flaws and multiple interacting flaws; the FCG life was evaluated for each case. This modeling work provides new insight for understanding how advanced fracture mechanics modeling capability can be used to improve life prediction of corroded components.