変動ひずみ条件下における316LC鋼の高温疲労特性(<特集>高温強度)

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In order to clarify the validity of the previously proposed creep-fatigue life prediction model based on the strain range partitioning concept, the applicability of the proposed model to type 316LC steel was examined. Two-step variable PP type straining(high-low and low-high)tests were conducted at 700℃, and the experimental results were compared with those predicted by the proposed model. In both high-low and low-high tests, 1.0% was chosen as the higher strain range, and 0.8%, 0.4% and 0.3% were chosen as the lower strain ranges. Furthermore, PP type small crack growth behavior in smooth bar specimens was observed at 700℃ under constant strain range by the surface replica technique and compared with that predicted by the proposed model. The high-low and low-high test results could be predicted by the linear damage rule(LDR) when the lower strain range was 0.8%. On the other hand, when the lower strain range was 0.4% or 0.3%, the deviation of experimental data from the LDR prediction was found. That is, the sum of the life ratio of the first and second step straining was smaller than unity in the high-low tests, whereas it was larger than unity in the low-high tests. These experimental results were well explained by the proposed fatigue life prediction model, in which it was assumed that the crack initiation life is not negligible when the inelastic strain range is smaller than the critical strain range, (Δε_<pp>)_<cr> and it was found that the proposed model was successfully applied to type 316LC steel. The value of (Δε_<pp>)_<cr> was 0.23%. The experimentally obtained small crack growth curves were well predicted by the proposed model using the correction factor, with which the macro through crack growth rate in the CCT specimen was converted into the small surface crack growth rate in the smooth bar specimen.
1995-01-15

変動ひずみ条件下における316LC鋼の高温疲労特性(<特集>高温強度)

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