Q235钢缺口试样拉压低循环疲劳的实验研究

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。

EXPERIMENTAL INVESTIGATION ON TENSION-COMPRESSION LOW CYCLE FATIGUE OF Q235 STEEL NOTCHED SPECIMENS

Q235 steel U-shape notched plate specimens are taken as subject investigated. 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 lives by test. According to the results, it is found that: whether FEM or modified Neuber method is taken to calculate stress and strain of notch root region, for fatigue life assessment the local stress-strain method is applicable only to the specimens with larger notch radius; the estimated lives obviously lower than test data for those specimens with smaller notch radius, and more serious in life estimation for the strain in notch root evaluated by FEM than by modified Neuber equation. On this basis, the effect of strain gradient for notched specimen is investigated. The famous Taylor’s model is applied to estimate the raise of yield stress and flow stress due to the high strain gradient in notch root region, by which the strain distribution of specimen is recalculated. The fatigue life estimation taken the influence of strain gradient into account is found improved for all notched specimens.