Effect of Fiber-Matrix Interphase Defects on Microlevel Stress States at Neighboring Fibers

ABSTRACT: A fiber with inferior interphase proFrties generates higher stresses at the fiber matrix interfaces of neighboring fibers. In this paper detailed calculations are pre-sented for this erect. The mechanical behavior of the interphase between fibers and matrix is modelled by continuity of tnctions and a linear relation between displacement differences across the interphase and the conjugate tractions. The proportionality con-stants characterize the stiffness and the strength of the interphase. For acell of the conipos-ite which contains a cluster of fibers, calculations have been carried out by the use of the boundary element method. Four cases have been considered: ( I) perfect composite. (2) a single fiber in the composite with lower interphase stiffness, (3) a single fiber in the coni-posite with interphase cracks and l o w r interphase stiffness, and (4) a missing fiber in the composite. The interface stresses for neighboring fiben: have been calculated. Also, for the case of the fiber with an interphase crack the strain energy density near the crack tip has been calculated and the condition for crack propagation has been discussed. INTRODUCTIOS H E UNDERSTANDIKG OF the strength properties of fiber-reinforced compos- T ites, particularly with regard to the role played by interfaces and interphases