Abstract
The fiber-matrix interface can play an important role in the performance of a composite, and consequently, it has been the subject of considerable study. One of the experiments often used to characterize the strength or quality of the interface is the single-fiber fragmentation test. The models used to analyze the data from this test involve a number of assumptions, one of which is the constitutive behavior of the matrix resin. To evaluate this assumption, a fragmentation apparatus was modified to include a load cell so both stress and strain could be measured during the experiment. Surprisingly, the results show that not only is the behavior viscoelastic, but virtually all of the fragmentation takes place in a range where the response is non-linear. To characterize this behavior, single-step, stress-relaxation experiments were conducted on a resin system often used in such tests. The results indicate that a simple power law model with strain-dependent parameters could describe the behavior over a very wide range of conditions. By using this characterization and the strain history, a crude fit to the actual loading curve in a fragmentation test could be obtained. In order to achieve quantitative agreement, however, a modified power law model was required. Such a relationship was shown to describe the loading curve for two quite different loading procedures.