Characterization of fiber/matrix interface strength: applicability of different tests, approaches and parameters

Different approaches to interface strength characterization in fibrous composite materials by means of micromechanical tests are analyzed. Special attention is paid to single fiber pull-out and microbond techniques. For these tests, advantages and disadvantages of stress-based and energy-based models of interfacial debonding and corresponding adhesional parameters (local interfacial shear strength, critical energy release rate, adhesional pressure) are discussed. The following analytical models developed to measure these parameters as well as to determine the interfacial frictional stress are considered in detail: (1) the use of the debond or “kink” force from the force-displacement curves; (2) two-parameter fit of experimentally measured maximum pull-out force as a function of embedded length; and (3) models assuming two-stage debonding with imperfect interface at the second stage. The analysis is illustrated by our own experimental data on adhesion of polymer and cement matrices to different reinforcement fibers.