中文摘要：

基于拉伸扭转组合变形理论及平面应力状态理论,推导了低碳钢试件在轴力及扭矩作用下断裂时主应力及其主方向的计算公式。该文设计了3种拉扭加载速率的试验方案,通过试验得到了相应的扭矩、轴力、应变及扭转角的时间曲线,观察了试件破坏时的断面特征,并将试验值与理论计算结果进行了比较。结果表明,随着加载速率的增加,低碳钢的延伸率增加,断面收缩率减小;抗拉强度、屈服极限和扭转强度提高,断裂时的主应力及主方向值增大,试件破坏时的主方向与理论计算结果的变化规律一致。

英文摘要：

Based on the tension- torsion composite deformation theory and plane stress state theory, the calculation formulas of the principal stress and its main direction of corresponding to failure of low carbon steel specimen under axial force and torque were deduced. We designed three kinds of experimental programs with different tension - torsion loading rates. By experiments, we had got the time curves of torsion moment of axial force, strain and twist angle. We observed the section characteristics corresponding of the specimen failure and we compared the calculated solution with the experimental results. The resluhs indicate that with the increase of loading rate, the elongation of low carbon steel increases and the shrinkage rate decrease; the tensile strength, yield limit and torsional strength are improved; and the principal stress and principal direction value at the time of fracture are also increased. The principal direction of the specimen failure is consistent with the theoretical calculation result.