Abstract
The stress intensity factor (S.I.F) has widely been used in the evaluation of material strength in the presence of a crack. When a crack in a composite material is treated as a crack in a homogeneous anisotropic material, the derived S.I.F can only be used in characterizing the material properties at macroscopic scales. To characterize the material behavior at microscopic scales, the presence of the inhomogeneities around the crack tip must be taken into consideration. In this thesis, an idealized case for a fibrous composite is studied. The crack is assumed to be normal to the fiber direction and subjected to Mode-I loading. To avoid numerical difficulty, the crack tip is taken to be rounded with a finite radius of curvature. The near-tip stress distribution at the microscopic scale is determined by ANSYS and Matlab, then the associated microscopic S.I.Fs are extracted by two different numerical approaches. We have found that the larger modulus of elasticity in the fiber has higher S.I.Fs than the smaller one in the matrix. Clearly, most of stress is supported by fibers in a composite material. It is concluded that for the same macro-S.I.Fs, the micro-S.I.Fs may be significantly different depending on the crack tip position and the elastic properties of the constituent phases of the composite.