SM41Aの高温疲労に及ぼす温度変動の影響

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In the temperature range from R.T. to 500℃, the characteristic curves of high temperature fatigue strength of mild steel SM41A showed the maximum stress at 400℃ (so called the "peaking temperature") and the minimum ones at 150℃ and 500℃. Based on these results, the following four model conditions were adopted as the temperature variations. In model A, the specimens were held N_h cycles at 500℃ and then dropped to 150℃, while in model B N_h cycles at 150℃ and then raised to 500℃. Model C was a convex type such as the specimens were held at 150℃ in the first 30 minutes, then raised to 500℃, held there for N_h cycles and downed to 150℃ again. Model D was the same type as model A except the initial temperature was held at the peaking temperature instead of 500℃. The rotary bending fatigue tests were made under these temperature conditions at three stress levels. By taking the cumulative cycle ratio as the abscissa and log N_h/log N_<500> as the corresponding ordinate, we constructed log log N_h/log N_<500> versus Σn/N diagrams expressing the relation among repeated stress, hold-time and fatigue life simultaneously. The main results obtained from these diagrams were as follows: (1) The fatigue life at the second temperature was higher than those at the constant temperature both 150℃ and 500℃ for model A, B and C. (2) The fatigue life at the second temperature in model A was appreciably higher than that in model B. (3) For model D, with increasing hold-cycles N_h the fatigue strength reached the maximum value at the peaking temperature. (4) According to the microphotographs of specimens, a great deal of etch pits and slip bands were found in model D, while in the case of model A and C, they were not so much. They were hardly observed in model B.
社団法人日本材料学会の論文
1975-12-15

SM41Aの高温疲労に及ぼす温度変動の影響

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