Influence of Loading Condition and Ligament Width on the Ductile-Brittle Transition Behavior under Mixed-Mode Loading Condition (in the case of Mode I-II Mixed-Mode Condition)

本研究的目的是阐明碳钢薄板试件在I-II复合型加载条件下的韧脆转变行为。采用作者提出的试验方法，对S50C和HT50(厚度=1.6 mm)中心裂纹薄板试件在韧脆转变温区不同的复合加载条件下进行了复合型试验。在所提出的测试方法中，无论拉伸加载方向与裂纹面之间的夹角如何，都可以保持韧带宽度不变，从而将加载方向和韧带宽度对韧脆转变行为的影响分开。为了考察韧带宽度的影响，在固定试件宽度的情况下改变裂纹长度，在固定试件宽度与裂纹长度的比率下改变试件宽度。此外，本研究所得结果为Compa…本研究的主要结果总结如下：(1)断裂形态随温度的降低而变化，与加载方向无关：(I)延性裂纹萌生后扩展，(Ii)延性裂纹萌生后作为脆性解理裂纹扩展，解理裂纹的萌生和扩展。解理裂纹的方向与最大切向应力准则的估计基本一致。(3)在II型加载条件下，最大载荷下的Mieses等效应力与温度之间的关系向低于I型加载条件下的温度移动。(4)在(I)和(II)断裂形态的温度范围内，在最大载荷下得到的Mieses等效应力几乎不变，与加载方向、裂纹长度、温度无关。(5)在S50C的情况下，发生解理断裂的上限温度随着II型成分的增加而有降低的趋势，而在HT50的情况下，它几乎不随加载方向的变化而变化，裂纹长度和试件宽度对结果的影响很小。较少

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 … More 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