Abstract

The surface characteristics of direct energy deposition (DED)-Arc specimens have been previously explored, revealing the dual effect of the surface topography on fatigue strength. This effect includes a reduction in the nominal load-bearing cross-section due to the waviness of the surface and the initiation of fatigue cracks at combined geometric and metallurgical notches from the surface. To complement these findings, this study focuses on the fatigue life and crack initiation of milled DED-Arc samples, e.g., after removal of the geometric notches. Fatigue tests on DED-Arc specimens validate the impact of surface topography on fatigue strength, emphasizing the significance of surface characteristics in determining structural integrity. The additional tests conducted on milled surfaces provide insights into the failure mechanisms specific to these samples. Fracture surface analysis, microstructure characterization, and hardness measurements are performed. For both surface conditions, cracks originate in the interlayer zone, where local hardness is reduced. In unmilled specimens, this is due to the stress concentration effect, and in milled samples, this is due to softened interlayer zones. The fatigue life of milled specimens is comparatively high, demonstrating the importance of optimizing surface characteristics for improved fatigue resistance.

Highlights

1. Both, unmilled and milled specimens, show crack origins in the interlayer areas. For unmilled specimens, this is because of the local stress concentration in the notch; for milled specimens, it was shown that soft zones between the layers act as the weakest link.

2. The fatigue strength of unmilled test coupons is significantly lower than those of milled specimens.

3. Unmilled samples exhibit multiple crack origins.

中文翻译：

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铣削和未铣削表面高强度钢 DED-Arc 试件疲劳试验结果比较

摘要

先前已经探索了直接能量沉积（DED）-电弧样品的表面特征，揭示了表面形貌对疲劳强度的双重影响。这种效应包括由于表面的波纹度而导致的标称承载横截面的减小以及在表面的几何和冶金缺口处产生疲劳裂纹。为了补充这些发现，本研究重点关注铣削 DED-Arc 样品的疲劳寿命和裂纹萌生（例如，去除几何凹口后）。DED-Arc 样品的疲劳试验验证了表面形貌对疲劳强度的影响，强调了表面特性在确定结构完整性方面的重要性。在铣削表面上进行的额外测试可以深入了解这些样品特有的失效机制。进行断裂表面分析、微观结构表征和硬度测量。对于这两种表面条件，裂纹均起源于层间区域，该区域的局部硬度降低。在未铣削的样品中，这是由于应力集中效应，而在铣削的样品中，这是由于软化的夹层区域。铣削样品的疲劳寿命相对较高，这表明优化表面特性对于提高抗疲劳性的重要性。

强调

1. 未铣削和铣削的样品均显示裂纹起源于层间区域。对于未铣削的样品，这是因为缺口处存在局部应力集中；对于铣削样品，研究表明层之间的软区域是最薄弱的环节。

2.未铣削试样的疲劳强度明显低于铣削试样。

3. 未铣削的样品表现出多个裂纹源。