熱応力のみによる円筒の熱ラチェット変形挙動とその評価法の提案

抄録

Thermal ratcheting tests were performed on SUS304 large stainless steel cylinder specimens (610 mm in diameter), which were subjected to axially shifting temperature. In the experiment, we investigated the effects of four types of shifting temperature distributions : cold-front cycling and hot-front cycling with large movements, changing temperature distribution with fast movement, and no movement (stationary) cycling. Considerable thermal ratcheting strain was observed in the early cycles, but became saturated after many cycles. The increment in thermal ratcheting strain during each cycle, Δε, can be expressed as an inverse power law of the number of cycles N, such that Δε=C·N^-m(C, m are constants). During stationary cycling, the thermal ratcheting strain became saturated after several cycles and was very small. The relationship between transversed distance l and ratcheting strain Δε is explained quantitatively. A method for evaluating thermal ratcheting strain accumulated after a large number of cycles is proposed and its possibilities are examined. Under changing temperature distribution conditions, thermal ratcheting strain can be conservatively estimated by considering temperature distribution with shifting constant maximum stress.