Fiber-matrix adhesion in single-fiber model composites

A single-fiber fragmentation test is a useful technique to provide a measure of fiber-matrix adhesion. A four-point bending test was used to determine the final fragmentation length for the glass fiber-polycarbonate system.; Surface treatment of the glass fiber with a mold release agent decreased the interfacial adhesion and caused an increase in fragment length. Fragment lengths from the four-point bending test were compared with those from a tensile test. Good agreement was obtained from the two tests. The effect of fiber diameter on fragmentation length also was examined. The full fragment length increased linearly with the fiber diameter.; Applied forces for a resin droplet adhering to a fiber were calculated in terms of the strain energy release rate G of the fiber-resin interface. Finite element analysis was performed using the ADINA code. Results for the displacement were compared with the experimental results for a silicone rubber sphere adhered to a steel rod. Good agreement was obtained. Force versus displacement relationship of the model fiber composite was non-linear.; Therefore, a non-linear fracture mechanics approach was used. Two types of bonding, poor and good, were considered in the present study. The force required to propagate a crack was compared with the values predicted by theory and an empirical method. Good agreement was obtained. Further crack growth required a large force. Thus, in this system the crack propagates in a stable manner. Two different fracture modes were observed in the model. One is adhesive fracture along the interface for poor bonding. In the other fracture mode, for good bonding, both adhesive and cohesive failure occurred competitively along the interface.; Calculated results for force versus displacement as a function of vise hole radius gave good agreement with the experimental results. Stiffness decreases as the vise gap increases from 2.1 mm to 3.8 mm.; The force required to propagate a crack was predicted by an empirical method at all stages of crack growth and for a range of dimensions.; By using the values of pull-out force from several fiber-epoxy microbond tests, values of fracture energy G{dollar}sb{lcub}rm c{rcub}{dollar} were estimated from the empirical calculation. These values tend to be rather low, i.e., 10-20 J/m{dollar}sp2{dollar}.