Liu Dezheng, Li Yan, Xie Xiangdong, Zhao Jing
Hubei Key Laboratory of Power System Design and Test for Electrical Vehicle, Hubei University of Arts and Science; Xiangyang 441053, China.
School of Urban Construction, Yangtze University, Jingzhou 201800, China.
Materials (Basel). 2019 Jul 2;12(13):2130. doi: 10.3390/ma12132130.
The effect of pre-corrosion pits on residual fatigue life for the 42CrMo steel (American grade: AISI 4140) is investigated using the accelerated pre-corrosion specimen in the saline environment. Different pre-corroded times are used for the specimens, and fatigue tests with different loads are then carried out on specimens. The pre-corrosion fatigue life is studied, and the fatigue fracture surfaces are examined by a surface profiler and a scanning electron microscope (SEM) to identify the crack nucleation sites and to determine the size and geometry of corrosion pits. Moreover, the stress intensity factor varying with corrosion pits in different size parameters is analyzed based on finite element (FE) software ABAQUS to derive the regression formula of the stress intensity factor. Subsequently, by integrating the regression formula with the Paris formula, the residual fatigue life is predicted and compared with experimental results, and the relationship of the stress intensity factor, pit depth, and residual fatigue life are given under different corrosion degrees. The fatigue life predicted by the coupled formula agrees well with experiment results. It is observed from the SEM images that higher stress amplitude and longer pre-corroded time can significantly decrease the residual fatigue life of the steel. Additionally, the research work has brought about the discovery that the rate of crack extension accelerates when the crack length increases. The research in this paper also demonstrates that the corrosion pit size can be used as a damage index to assess the residual fatigue life.
采用加速预腐蚀试样在盐环境中研究了预腐蚀坑对42CrMo钢（美国牌号：AISI 4140）残余疲劳寿命的影响。对试样采用不同的预腐蚀时间，然后对试样进行不同载荷的疲劳试验。研究了预腐蚀疲劳寿命，并用表面轮廓仪和扫描电子显微镜（SEM）检查疲劳断口，以确定裂纹形核位置，并确定腐蚀坑的尺寸和几何形状。此外，基于有限元软件ABAQUS分析了应力强度因子随不同尺寸参数腐蚀坑的变化情况，推导了应力强度因子的回归公式。随后，将回归公式与Paris公式相结合，预测了残余疲劳寿命，并与实验结果进行了比较，给出了不同腐蚀程度下应力强度因子、坑深和残余疲劳寿命的关系。耦合公式预测的疲劳寿命与实验结果吻合良好。从SEM图像可以看出，较高的应力幅值和较长的预腐蚀时间会显著降低钢的残余疲劳寿命。此外，研究工作还发现，裂纹扩展速率随裂纹长度的增加而加快。本文的研究还表明，腐蚀坑尺寸可作为评估残余疲劳寿命的损伤指标。
