抄録
Tensile strength of polypropylene composites reinforced with a natural jute fiber having different chopped lengths and surface treatment was measured. Three kinds of fiber treatments were applied to change the interfacial strength between fiber and matrix. The fragmentation test was also conducted with single jute fiber to determine the interfacial shear strength quantitatively. In situ micro observations of the fracture progress were carried out for single fiber notched specimens under tensile loading. It was found that there is the most effective interfacial strength to improve the tensile strength, nevertheless a few change is observed in fiber strength due to the treatment. For an interfacial strength lower than that of the most effective value, an interfacial debonding led a fatal failure of the composite. In opposite, for an interfacial strength higher than that, the fiber broke down at front of crack tip before the crack reached to the jute fiber. The most effective interfacial strength was shifted to higher value according to the shortening of fiber length. The opitimum state of the composite strength would be obtained by a combination of a low interfacial shear strength long and a low strength jute fibers. This result was explained with the applied stress to the fiber at interfacial failure calculated with the energy release ratio.
