Abstract
At the present, there are many kinds of methods to evaluate the interfacial strength of composites, for example, fragmentation test of a single fiber, single fiber pull-out test, torsion test and shear test. But there are few non-destructive methods. Therefore, as a new method for evaluation of the interfacial strength of composites, the interfacial strength was studied from viewpoint of balance stress. The balance stress of the composites occurs by viscoelastic properties of the material, and it reflects strongly the stress redistribution between fibers and resin. The balance stress depends on the degree of the stress transition from resin to fibers, and so it is obtainable from a viscoelastic model consisting of three elements. The theoretical values of the balance stress agreed with the experimental results. Two types of composites made of the same epoxy resin were prepared. One was a coupling treated on the fiber and the other was untreated. The balance stress of the treated composite was large due to strong adhesion at the interface. It is clear that the relative interfacial strength of composites can be estimated by the balance stress.
