基于数字图像相关技术的 SLM-IN718 细观表面裂纹扩展机制研究

Combined with digital image correlation (DIC) technique, in-situ fatigue tests with different stress ratios (R=0.1 and R=-1) at room temperature were carried out to analyze the mesoscopic surface crack propagation mechanism of selected laser melted Ni-based superalloy (SLM-IN718) in the very high cycle fatigue regime. The results show that, firstly, the DIC analysis results indicate that a plastic strain zone, similar to a butterfly shape, appears at the crack tip when SLM-IN718 is loaded, which is consistent with the result by the Von Mises yield criterion. Secondly, the strain field characteristics and displacement field characteristics in front of the crack tip are analyzed for SLM-IN718, the crack opens when the load reaches 53% and 29% of the maximum load under R=0.1 and R=0, respectively. In addition, a model considering the crack closure effect is developed to evaluate the plastic zone size in front of the crack tip, the calculated values are in good agreement with the measured values. Finally, the surface crack propagation mechanism of SLM-IN718 under low stress conditions is discussed based on DIC analysis results.