| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1987: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1986: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
The concept of the environmental fatigue fracture toughness proposed by the author, through the research "Basic Study on Fatigue Design for Offshore Structure", Project No.58460080, has been developed for a low temperature environment from room temperature to 77K.
It is cleared that this value governs the fatigue cracking behavioru of the material at low temperature. The fatigue characteristic stress intensities Ke and Kv, can be proposed as controlling stress intensities, where the region 2 and the region 3 fatigue crack propagation starts, respectively.
Since the correlations between the fatigue fracture toughness and the Ke, Kv, a method of teh estimation of the fatigue crack growth curve, covering the entrire range of stress intensity can be also presented. This method can be utilized to determine the threshold stress intensity factor in a low temperature environment.
The proposed characteristic stress intensitiy Kv corresponds to the K value where the static mode of fracture begins to superimpose to the fatigue crack propagation. The other fatigue characteristic stress intensity, Ke, is the K value where the cyclic plastic zone size equals to the grain diameter of the material. This implies that both of the Ke and threshold stress intensity, Kth, are linearly related to the <delta>yROO<d>, where, <delta>y is yield stress and d grain diameter, as indicated by the experiment.
The fatigue crack propagation in the brittle material, such as silica glass, is fundamentally the same as that in static loading condition. This behaviour is explained by the low value of the Kv, meaning that the crack propagation of this material mainly controlled by the region 3 crack propagation.
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