| dc.description.abstract | This study focuses on the fatigue crack growth properties of Inconel 718 workpieces fabricated by Selective Laser Melting (SLM). It investigates the effects of stress ratio (R), overload load, and crack closure on fatigue crack growth. Additionally, the study evaluates the applicability and accuracy of different fatigue crack growth prediction models. Furthermore, it analyzes the causal relationship between failure mechanisms and fatigue crack growth.
The results demonstrate that the fracture toughness of SLM Inconel 718 workpieces in this study can achieve 179 MPa√(＂m＂ ), which is higher than that of the forged Inconel 718 alloy. The fatigue crack growth rate under constant amplitude load increases with stress ratio. The fatigue crack growth rate begins to show a noticeable retardation phenomenon when the overload ratio is greater than 2.0. When the maximum stress intensity factor of the load history is less than 30 MPa√(＂m＂ ), the average material coefficient p in Wheeler model equals to 1.01. While maximum stress intensity factor higher than 30 MPa√(＂m＂ ), the p value increases with increasing stress intensity factor (ΔK). In the crack closure model, the crack closure factor increases with the rise of stress ratio or ΔK, and the relationship is expressed as U = 0.014ΔK + 0.579R + 0.377. Under variable amplitude loading, the predicted fatigue crack growth life is better by crack closure models (including Elber, Schijve, and the proposed model in this study), with an average error of about 25%. When ΔK is below 33 MPa√(＂m＂ ), the fatigue crack growth curve predicted using proposed model shows the best fit with experimental data. With respect to the load sequence effect, the load history with arranging stress ratio in a decreasing order has smaller fatigue damage. The reason for this is that the first high stress will induce compressive residual stress and reduce the fatigue damage of the subsequent low stress. Conversely, arranging the stress ratio in an increasing order leads to a decrease in fatigue life. On the fatigue fracture surfaces, it can be seen that there are obvious differences in the spacing of fatigue striation caused by constant amplitude load, variable amplitude load and overload load. The influence of metallurgical defects within SLM workpieces on crack growth rate and fracture surfaces is also visibly evident. The effect of the metallurgical defects in the SLM workpiece on the crack growth rate and fracture surface can also be clearly observed. | en_US |