In order to investigate fatigue characteristics of vulcanized natural rubber (NR), fatigue
tests are carried out under various stress ratios R (R = minimum stress / maximum stress). It was
considered that the fatigue cracks were initiated from flaws in very early stage of total life. The
fatigue damage process was almost the fatigue crack propagation process and it is independent of R.
The crack growth rate was proportional to the crack length to about the first power, when the crack
length was defined as the length of the direction perpendicular to the loading direction. Miner’s rule
was examined to observe the fatigue crack behavior and checked by using two-step loading fatigue
tests experimentally. It seems Miner’s rule has a possibility to predict fatigue lives.
The finite element method is applied to two-dimensional elastic-plastic analyses for underclad crack problems. The analyses are performed for rectangular specimens with an underclad crack, which are composed of A533B class 1 steel and a clad material, to obtain the fracture mechanics parameter J-integral and the stress distribution ahead of a crack tip. The Q-factor proposed by O’Dowd and Shih is calculated from the stress distribution ahead of a crack tip, and the constraint effect of a crack tip due to a clad material or the effect of a clad material on the fracture toughness of a base material is discussed in terms of the Q-factor. Clad thickness, crack length, and the material property of a clad material are varied to examine their effects.
In order to clarify the hydrogen effect on the fatigue strength at 10 7 cycles in a plain specimen of type 316L austenitic stainless steel, rotating bending fatigue tests in laboratory air and plane bending fatigue tests in 1.0 MPa dry hydrogen gas and in air at 313 K were carried out. The main results obtained are as follows. The observed fatigue behavior showed that the fatigue strength at 10 7 cycles in both environments is determined by the non-propagation of a fatigue crack of the order of the grain size. Also, the strength at 10 7 cycles in hydrogen gas is slightly higher than that in air. In the region of high-cycle fatigue, the fatigue life in hydrogen gas is longer than that in air, which is mainly caused by the longer crack initiation life in hydrogen gas. The crack propagation life in hydrogen gas is shorter than that in air but has only a small ratio to the fatigue life in this region.
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