Finite element evaluation of the microbond test: meniscus effect, interphase region, and vise angle

An axisymmetric finite element model (FEM) was used to determine the stresses that develop during a microbond test of a glass fiber/polymer matrix composite system. The complete bead shape including the meniscus that occurs as the bead wets to the fiber was included in the FEM to determine the influence of the bead geometry on the resulting stresses. Significant differences in the stress fields were found near the fiber/bead contact point due to the geometry and resulting z-location of the vise. In addition, the vise angle and interphase properties were varied to examine their influence. As the vise angle increases, the combined state of stress decreases considerably. The effect of the interphase, while not as significant as the effect of the vise angle, did produce a 10% variation in von-Mises stress at the fiber/bead contact point for the properties used. It was found that the ratio of the maximum shear to average shear equaled 4 near the fiber/bead contact point. At this location the interfacial material has yielded with a von-Mises stress 8× the average shear. Finally, results are provided showing the average interfacial shear stress value obtained by the FEM is within 2% of the theoretical solution.