Viscoelastic properties of a resin commonly used in the single fiber fragmentation test

The fiber-matrix interface can play an important role in the performance of a composite, and consequently, it has been the subject of considerable stu dy. One of the experiments often used to characterize the strength or quali ty 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 a ssumption, a fragmentation apparatus was modified to include a load cell so both stress and strain could be measured during the experiment. Surprising ly, the results show that not only is the behavior viscoelastic, but virtua lly all of the fragmentation takes place in a range where the response is n on-linear. To characterize this behavior, single-step, stress-relaxation ex periments were conducted on a resin system often used in such tests. The re sults indicate that a simple power law model with strain-dependent paramete rs could describe the behavior over a very wide range of conditions. By usi ng this characterization and the strain history, a crude fit to the actual loading curve in a fragmentation test could be obtained. In order to achiev e 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.