A microbond method for determination of the shear strength of a fiber/resin interface

The shear strength of the fiber/resin interface in a fiber-reinforced composite is usually determined by measuring the force needed to pull a single fiber axially out of the solid matrix. To make such pull-out measurements, however, the length of embedded fiber must be small enough so that the fiber does not break before it pulls free. This is difficult to achieve by conventional methods with fibers of small diameter, such as the high-strength glass, Aramid, and carbon fibers now extensively used in practice. The approach taken is to deposit a droplet of the matrix resin on the fiber and to support the cured droplet appropriately during pull-out. Successful shear debondings are obtained in most trials, and the nature of the recorded force curves during the trial distinguishes between proper shear debonding and slipping of the droplet or fiber breakage. Interfacial bond strength results for an epoxy resin and several fiber types are adequately reproducible and are reasonable in light of the nature of the fiber surfaces, indicating that the microband method may be generally applicable.