| Summary: | The three-dimensional small crack growth behavior of selective laser melting (SLM) TC4 alloy was investigated by in-situ observation fatigue test method, and the long crack growth curve was measured by load reduction method under the same experimental conditions. The results show that at the early stage of small crack growth, the fatigue crack growth(FCG) rate fluctuates obviously under the influence of microstructure, and the FCG path is zigzag. With the increase of crack length, the influence of microstructure decreases, and the FCG path is straight, and the FCG rate increases steadily with the crack length. Internal defects can still reduce alloy fatigue life. Considering the small and long crack growth data, it is demonstrated that the small crack can still propagate under threshold value of long crack, and under the same stress intensity factor amplitude ΔK, small crack growth rate is higher than that of long crack. There is a typical "small crack effect", thus the small crack behavior should be considered when fatigue life prediction is carried out.
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