中文摘要：

以Q235钢制U型缺口板试样为研究对象,用有限元方法计算其缺口根部等效应变幅对应的试样标距段位移,以此控制试验机进行拉压循环疲劳试验.然后用局部应力应变法对试验测得的寿命结果进行分析.结果表明：无论用有限元还是修正Neuber公式计算缺口根部的应力应变,局部应力应变法的疲劳寿命评估只适用于缺口半径较大的试样;对缺口半径较小试样的估计寿命明显低于实测值,且有限元法比修正Neuber法更保守.进而又对试样缺口区域应变梯度的影响进行了探讨：参照有限元计算的应变梯度,利用Taylor模型估算了缺口根部的屈服应力和流动应力;在此基础上重新计算应变分布并估计试样的疲劳寿命,结果证实考虑应变梯度影响可改善缺口试样的疲劳寿命估计.

英文摘要：

The low-cycle fatigue behavior of Q235 steel U-shape notched plate specimens is experimentally studied in this paper.The low-cycle fatigue experiments under tension-compression loading are conducted by controlling the elongations of specimen＇s gauge section which are calculated by finite element method（FEM）prior experiments.Then the local stress-strain method is adopted to analyze the fatigue life.According to the results,it is found that when the stress and strain near notch root region are obtained by FEM or modified Neuber method,the local stress-strain method only is applicable to the fatigue life assessment of specimens with larger notch radius,the estimated life is obviously lower than the experiementally obtained fatigue life for those specimens with smaller notch radius,and the fatigue life is more seriously underestimated by FEM than by modified Neuber equation.For this,the effect of strain gradient on the fatigue life of notched specimen is taken into account.The famous Taylor＇s model is adopted to estimate the raises of yield stress and flow stress due to high strain gradient in notch root region,by which the strain distribution in the notch root region is recalculated.The fatigue life estimation taking the influence of strain gradient into account is found to be improved for all notched specimens.