抄録
High-Polymer and rubber are important materials. Evaluation method of stress-strain behavior of them is demanded in order to use them with reliability. But it is difficult especially in unloading process and in fatigue. And the mechanical properties of high-polymer and rubber are deteriorated more easily than that of metal. The constitutive equation that can consider the deterioration and that can evaluate deformation in unloading process is demanded. Nitrile Butadiene Rubber (NBR) is hard rubber used as O-ring and gasket, etc. In this study, the deterioration tests of NBR in water at 60C for 0 month, 3 months, 7 months, 9 months and 12 months were carried out. Compression tests of NBR in water at 25C were carried out with deteriorated material. VBO model, one of constitutive equation, is applied to evaluate the deformation of them. The mechanical properties used in VBO model were taken from the constant-strain-rate tests and relaxation tests. And the influence of deterioration to mechanical properties used in VBO model was obtained. The stress-strain curve simulated with VBO model well corresponded to that of test in loading process, but didn’t in unloading process. Therefore we improved VBO model with the strain acceleration term. We showed the probability that the improved model could evaluate the stress-strain behavior in unloading process.
