中文摘要：

对建筑用Q235结构钢分别在单轴和多轴载荷下进行低周疲劳试验，并利用测得的试验结果对寿命评估方法进行研究。研究结果表明：在相同VonMises等效应变幅值下，材料的比例拉扭路径疲劳寿命高于单轴拉压疲劳寿命，而非比例路径疲劳寿命低于单轴拉压疲劳寿命。按等效应变法进行寿命预测，在非比例加载路径下的预测结果远远超出2倍寿命安全范围区；按临界面法的KBM和Socie模型进行寿命预测能够得到较好的结果，但对圆形路径的高应变幅区得到的结果则过高估计了材料的寿命。在考虑循环过程临界面法向应变影响的基础上，提出了一个改进的考虑临界面拉伸影响的模型，其对比例和非比例路径循环下低周疲劳寿命的评估与实测吻合较好。

英文摘要：

Low cycle ted, and the fatigue fatigue tests on Q235 steel under uniaxial and muhiaxial loadings were conduc- life evaluation formulas were studied based on experiments. The low-cycle ex- perimental results of strain show that the fatigue life of the metal under proportionally muhiaxial load- ing is longer than that under uniaxial loading, but the fatigue life of the metal under non-proportion- ally muhiaxial loading is shorter under the condition of given Von Mises＇ equivalent strain amplitude controlled by machine. Using the equivalent strain approach to evaluate the low-cycle fatigue life, it can be found that the life value under non-proportionally muhiaxial loading was 2 times larger than that given in the experiments. Adopting KBM or though the life prediction become better evidently, Socie model of the critical plane approach, al- over estimation is still inevitable for the low-cycle fatigue under round loading path with large strain amplitude. Based on the consideration of the ten- sion effect on normal of the critical plane during the cycle, a modified critical plane model is pro- posed, in which the tension factor can be determined directly by using the given parameters for acertain loading path. And the life evaluation given by the present model agrees with the experimental result.