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Effects of temperature (24°, 37°, and 50°C) and cyclic rate (0.8, 2, and 5 Hz) on fatigue behavior were studied on two different segmented polyether polyurethanes immersed in a plasma-analogous cholesterol-lipid solution. Dynamic fatigue tests were carried out under conditions of 50% mean strain and 10% strain amplitude. Changes in the mean stress and the ratio of stress amplitude to strain amplitude were significantly larger at 50°C than at 24° and 37°C. In the initial stage of fatigue testing, changes in these variables appeared earlier at higher cyclic rates. However, the long-term dynamic fatigue behavior was dependent on the duration of testing rather than on the repetition number or the cyclic rate. These results imply that the fatigue testing in the cholesterol-lipid solution of 50°C at the cyclic rate of 5 Hz might be useful for the prediction of long-term behavior of these materials under actual service inside the body.
segmented polyether polyurethane, elastomer, cholesterol-lipid solution, servo-hydraulic tester, stress relaxation, fatigue test, accelerated testing, durability
Professor, Osaka University, Osaka,