The study aims to estimate the role of surface defects in the fatigue life of age-hardened and unmachined additively manufactured 18Ni300 maraging steel and to verify the effectiveness of stress-based life prediction models. Axial-torsional cyclic loading paths involving in-phase and out-of-phase cases are applied. Scanning electron microscopy and micro-computed tomography are performed to detect the fatigue crack initiation sites and paths. The effectiveness of the classic models and a physics-constrained Gaussian process for regression in fatigue life prediction is estimated. Results show that the intrinsic orientation of the surface defects affects the fatigue mechanism by increasing the material sensitivity to axial stress. Additionally, the steel is insensitive to the phase shift between the axial and torsional loading components. The hydrostatic stress and the integrated shear stress amplitudes over the critical plane are pointed as the most effective load-related quantities for life prediction.

中文翻译：

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表面缺陷对增材制造未加工18Ni300马氏体时效钢多轴疲劳寿命的关键作用

该研究旨在评估表面缺陷在时效硬化和未加工增材制造的 18Ni300 马氏体时效钢疲劳寿命中的作用，并验证基于应力的寿命预测模型的有效性。应用涉及同相和异相情况的轴向扭转循环加载路径。进行扫描电子显微镜和微型计算机断层扫描来检测疲劳裂纹萌生位置和路径。估计了疲劳寿命预测中回归的经典模型和物理约束高斯过程的有效性。结果表明，表面缺陷的固有取向通过增加材料对轴向应力的敏感性来影响疲劳机制。此外，钢材对轴向和扭转载荷分量之间的相移不敏感。临界平面上的静水应力和积分剪应力幅值被认为是寿命预测的最有效的载荷相关量。