Debond crack growth in fatigue along fiber in UD composite with broken fibers

Assuming that Paris law is applicable for individual debond crack propagation along the fiber/matrix interface, the related strain energy release rate in a unidirectional composite is analysed using FEM and also using simple analytical considerations based on self-similar debond crack propagation. Model with axial symmetry consisting of three concentric cylinders is used: partially debonded broken fiber in the middle is surrounded by matrix cylinder which is embedded in a large block of effective composite with properties calculated using rule of mixtures and Halpin-Tsai expressions. It is shown for pure mechanical loading that the fiber elastic properties have a huge effect on the released energy, whereas fiber content in the composite in the considered realistic range has effect only for short debonds. The interaction between debonds approaching from both fiber fragment ends is investigated and related to material properties and geometrical parameters. It is shown that the self-similar debond propagation model gives slightly overestimated values of the strain energy release rate which may be related to interaction effects not included in the analytical model.Godkänd; 2008; Bibliografisk uppgift: USB; 20081208 (ysko