It is well known that high strength steels have the duplex S-N property consisting of a couple of S-N curves in short life and long life regions. Fatigue crack occurs at the specimen surface in the short life region, whereas the crack takes place at the interior inclusion in the long life region. In this study, a probabilistic model on the statistical aspect on the interior inclusion induced fracture in the very high cycle regime was constructed by combining distribution characteristics of size and location of the interior inclusions. Two-parameter Weibull distribution was accepted as distribution of the inclusion size, and the random distribution was assumed for the location of the interior inclusions. By numerical calculations based on this model, probabilistic S-N property in the interior inclusion induced fracture was analyzed for the bearing steel of SUJ2. Analytical distributions of the fatigue strength at several stages of cyclic loading and of the fatigue life at several stress levels are in good agreement with the experimental results reported by many researchers.

Rice-duck farming is a well-known environmentally friendly rice cultivation. Ducks swim around the paddy field,eat weeds and insects, and release waste into the paddy field thus improving soil fertility resulting higher yields. The objective of this study is to realize "artifact-animal collaboration" in rice-duck farming. An autonomous mobile robot automatically guides a duck flock to weed area and ducks eat weeds effectively. Effectiveness of visual and auditory stimuli is evaluated through imprinting and guidance experiments in comparison with findings in the field of ethology. Finally, effective guide functions, design requirements and operational conditions of the autonomous mobile robot are clarified.