Stress singularity analyses of interface ends in micro-mechanics tests

Singular stress fields exist in the interface ends of micro-mechanics test specimens, which are used to measure the interfacial shear strength (IFSS) in fiber composites. With the aid of asymptotic and variable separation, the stress singularities near the axisymmetric interface ends are studied. The results show that the α-β diagram of the stress singularity exponents for the push-in specimen can be divided into two areas, singular and non-singular. The oscillatory singular area may appear in the diagram of a pull-out specimen. In the micro-droplet specimen, the oscillatory area is dependent not only on Dundurs parameters but also on the angle between the boundaries of the matrix and fiber. The general forms of angular distribution functions are derived in this paper. By the use of axisymmetric BEM and the obtained angular distribution functions, the numerical results of stress distribution near the interface end and the stress intensity factors are obtained. It is concluded that, theoretically, the interfacial shear strength (IFSS) cannot be determined by the existing interfacial micro-mechanics tests.