In situ determination of the fiber–matrix interface tensile strength

A single-fiber test specimen to measure the tensile strength of a glass fiber–epoxy interface is introduced. The fiber is oriented perpendicular to the loading axis through the thickness of the specimen. Tensile testing was conducted in situ in a scanning electron microscope. The stress state at the fiber–matrix interface was determined using 3D finite element stress analysis (FEA). The effects of mechanical loading and cure shrinkage of the matrix material are included in the FEA. It was observed that debond initiation occurs on the loading axis where the tensile stress acting on the fiber–matrix interface is maximum. Based on the measured load at onset of debonding and finite element stress analysis, the tensile strength of the fiber–matrix interface was about 36.6 MPa.