A numerical simulation is presented in this paper on the performance of crack
retarders bonded to integral metallic structures. The work is described in two
main parts. First, a novel modeling approach employing the finite element method
has been developed for simulating the various failure mechanisms of a bonded
structure and for predicting fatigue crack growth life. Crack growth in the
substrate and the substrate/strap interface disbond failure are modeled in the
framework of linear elastic fracture mechanics. A computer code interfacing with
the commercial package MSC NASTRAN has been developed and validated by
experimental tests. Second, the effectiveness of different strap configurations
on crack growth retardation has been modeled; these include different strap
materials, strap dimensions, and their locations on the substrate. The research
has included two substrate materials and four strap materials, and at this stage
the specimens were cured at room temperature. Strap stiffness and adhesive
toughness are found to be the most influential parameters in designing crack
retarders. A design tool has been developed based on the numerical simulation to
achieve optimal crack retarder design in terms of prescribed fatigue life target
and minimum structural weight added by the bonded reinforcement
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