Fracture Mechanics of the Microbond and Pull-out Tests

The properties of the fiber/matrix interface in composites have an influence on their overall performance. Common methods for studying the interface are micromechanical tests that load a single fiber/matrix interface to failure. Two popular tests are the microbond test [1] and the single-fiber, pull-out test [2]. In a microbond test a droplet of matrix is sheared off the fiber by pulling the fiber while restraining the droplet. In a pull-out test, the end of a fiber is embedded in a polymer and pulled until failure while restraining the matrix. A common interpretation of these tests is to reduce the load at failure to an interfacial shear strength (ISS) by dividing the applied load by the total interfacial area. Physically this term is the average interfacial shear stress at the time of failure. ISS has some use in qualitative work; it is less useful for fundamental characterization of the interface.