INFLUENCE OF STRESS RELAXATION AND SWELLING TO DEFORMATION AND DESTRUCTION OF INTERFACIAL REGION BETWEEN FIBER AND RUBBER OF SHORT FIBER-RUBBER COMPOSITES

The fatigue behavior of short fiber-rubber composites was studied by stress relaxation. The stress relaxation test of composites was carried out in the direction of fiber orientation under 5, 10, 15 MPa of initial stress and 4, 80, 400%/min of initial strain rate. The faster the initial strain rate, the higher the modulus of composites in stress-strain curves. This phenomenon seems to be caused by delay of flow of the interfacial region between fiber and rubber under deformation process. On the other hand, the faster the strain rate, the larger the stress decay at initial stage. It suggests that the interfacial region contains the large distortion under the fast strain.The stress relaxation tests and the observation of rupture surface for rubber matrix and composite after swelling by toluene were undertaken in order to understand the properties of the interfacial region. It seems that the composites include the weak bond between fiber and rubber matrix, because the stress relaxation of composites after swelling is smaller than that of composites before swelling. From the results of the observation of the fracture surface, it seems that the fracture of composites are caused by propagation of nuclei, which is initiated by the destruction of interfacial region, to the other interfacial region.