| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1991: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1990: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
The aim of this study is to clarify the ductile-brittle transition behavior in sheet specimens of carbon steels under mode I-II mixed-mode loading condition. Mixed-mode tests were carried out on center cracked sheet specimens of S50C and HT50 (thickness=1.6mm) under various mixed-mode loading condition in the ductile-brittle transition temperature region using the testing method proposed by the present investigator. In the proposed testing method, it is possible to keep the ligament width constant irrespective of the angle between the tensile loading direction and the crack plane, and thus, to separate the influence of the loading direction and that of the ligament width on the ductile-brittle transition behavior. In order to investigate the influence of the ligament width, the crack length was varied for a constant specimen width, and the specimen width was varied for a constant ratio of the specimen width to the crack length. Furthermore, the results obtained in this study were compa
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red with that obtained in the investigator's another study using the conventional mixed-method testing method in which a slant center cracked specimen is employed.
The principal results of the study are summarized as follows.
(1) The fracture appearance varied with decreasing temperature as follows independent of the loading direction : (i) a ductile crack initiates and then extends, (ii) a ductile crack initiates and then extends as a brittle cleavage crack, and (iii) a cleavage crack initiates and extends.
(2) The direction of the cleavage crack almost coincided with the estimation of the maximum tangential stress criterion.
(3) The relationship between the mieses equivalent stress obtained at the maximum load and temperature under the mode II loading condition was shifted to lower temperature than that under the mode I loading condition.
(4) The mieses equivalent stress obtained at the maximum load in the temperature range with the fracture appearance of (i) and (ii) were almost constant independent of the loading direction, the crack length, and the specimen width.
(5) The upper limit temperature below which cleavage fracture can occur showed a tendency to decrease with increasing the mode II component in the case of S50C, but it was almost constant independent of the loading direction in the case of HT50, and there was little influence of the crack length and the specimen width on the results. Less
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