The extended finite element method is adopted for fracture analysis of delamination problems in fiber-reinforced polymer (FRP) reinforced beams. In this method, the stress singularities near the debonding crack tip are modeled by newly proposed orthotropic bimaterial enrichment functions, while crack faces and the material interface simulated by the Heaviside function and the weak discontinuity enrichment function, respectively. The orthotropic crack tip enrichments are utilized in orthotropic FRP plate and in a reduced isotropic form in the beam. The strain energy release rate is numerically evaluated using mixed-mode stress intensity factors which are evaluated by the means of domain interaction integral approach. The accuracy of this approach is examined through some numerical examples and the results are compared with available reference results.
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