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Zhandarov, S. ; Mäder, E.
Peak force as function of the embredded length in pull-out and microbond tests: effect of specimen geometry

We have derived the equations which explicitly express the peak force, Fmax, and the apparent interfacial shear strength, tauapp, measured in the pull-out and microbond tests, as functions of the embedded length. Three types of test geometries were considered: (1) a fiber embedded in a cylindrical block of the matrix material; (2) microbond test with spherical matrix droplets; and (3) pull-out test in which the matrix droplet had the shape of a hemisphere. Our equations include the local interfacial shear strength (IFSS), taud, and the frictional interfacial stress, tauf, as parameters; the effect of specimen geometry appeared in the form of dependency of the effective fiber volume fraction on the embedded length. The values of taud and tauf were determined by fitting our theoretical curves to experimental Fmax (le) plots by using the least squares method. Our analysis showed how the local IFSS and the frictional interfacial stress affected the measured Fmax and tauapp values. In particular, it was revealed that intervals of embedded lengths could exist in which frictional interfacial stress had no effect on Fmax and tauapp, even if the tauf value was high. We also derived an equation relating the scatter in the interfacial strength parameters (taud and tauf) to the scatter in tauapp, which is experimentally measurable, and proposed a procedure to determine the standard deviations of tauB>d and tauf from experimental pull-out and/or microbond test data.

Journal of Adhesion Science and Technology 19



December 2005


Composite Materials