增材制造316钢高周疲劳性能的微观力学研究

由于增材制造逐层累积的工艺特点, 其成形材料力学性能往往不同于传统减材制造材料. 在航空航天、核工业以及医疗领域中, 对增材制造材料疲劳性能的研究不足导致其很难作为主承力件使用, 这制约着增材制造技术的进一步推广使用. 本文以增材制造316钢为对象, 通过仿真手段研究其高周疲劳性能, 研究表明循环载荷下滑移带与晶界处的裂纹萌生是增材制造316钢材料发生高周疲劳的主要原因. 根据提出的微观力学模型研究了增材制造316钢的高周疲劳性能, 其中分别使用唯象学晶体塑性理论和弹塑性内聚力模型模拟晶粒和晶界的力学行为. 为了准确评估增材制造316钢的高周疲劳性能, 本文针对于晶粒和晶界分别采用Papadopoulos疲劳准则和一种基于安定性理论的介观疲劳准则同时考虑位错滑移和晶界对疲劳性能的影响. 最后, 为了验证所提微观力学模型的有效性, 本文对比了增材制造316钢和轧制316钢高周疲劳性能的仿真结果. 与实验结果相同, 仿真结果显示增材制造316钢相较于轧制316钢具有更好的高周疲劳性能. 

MICROMECHANICAL STUDY OF THE HIGH CYCLE FATIGUE PROPERTY OF ADDITIVE-MANUFACTURED 316 STEEL

Due to the layer-by-layer process, the mechanical performance of the additive-manufactured part is often different from that produced by traditionally manufactured process. In the field of the aerospace, nuclear and medicine, additive-manufactured parts are difficult to serve as the main load-bearing structure due to the lack of the study about the fatigue property, which limits the generalizability of additive manufacturing technology. Here, the simulation method is adopted to study the high cycle fatigue property of the additive-manufactured 316 steel. The research results show that the crack initiation at the slip bands and grain boundaries is the main cause of the high cycle fatigue for the additive-manufactured 316 steel. In this paper, a micromechanical model is proposed to study the high cycle fatigue property of AM 316 steel, where the mechanical responses of grains and grain boundaries are calculated by the phenomenological crystal plasticity theory and elastoplastic cohesive zone model, respectively. For fatigue assessment, Papadopoulos fatigue criterion and a shakedown-theory-based fatigue criterion are adopted to consider the effect of dislocation slips and grain boundaries on the fatigue property, respectively. Finally, in order to verify the validity of the proposed micromechanical model, the simulation results of AM and rolled 316 steel are compared. As same as the experimental results, the simulation results show that AM 316 steel has a better fatigue property compared with rolled one.