Abstract

Additive manufacturing (AM) offers design freedom and ability to fabricate parts of complex shapes which are not often possible with the conventional methods of manufacturing. In an AM part, even with optimum build parameters, a complete elimination of defects is not possible and this makes it hard to fully deploy the AM technology to build load bearing parts operating under cyclic loading conditions. Many of these defects are < 1 mm in size and are categorised as ‘small cracks’. Local interaction of cracks with microstructural features and closure effects at the wake of the crack tip are some of the factors which make the growth behaviour of small and long cracks different. A crack growth life prediction method, which effectively considers the small crack growth behaviour, has been discussed in this paper. This proposed method includes a detailed finite element-based crack growth simulation using the ANSYS SMART fracture technology. The lifing calculations utilise the modified NASGRO equation and small crack growth data which was obtained from the published long crack growth data, corrected for closure effects. The predicted stress versus number of cycles curves were compared against the fatigue test results for the AM specimens in Ti–6Al–4V material. A good correlation between the predictions and test results suggests that the proposed method can be used to assess the small crack growth life of AM parts where the fatigue effects of cyclic loading can be quite significant.

中文翻译：

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添加剂制造的Ti-6Al-4V材料中疲劳小裂纹扩展的模拟

摘要

增材制造（AM）提供了设计自由度和制造复杂形状零件的能力，而这是常规制造方法通常无法做到的。在AM零件中，即使具有最佳的构建参数，也无法完全消除缺陷，这使得难以完全采用AM技术来构建在循环载荷条件下运行的承重零件。其中许多缺陷的尺寸小于1毫米，被归类为“小裂纹”。裂纹与微观结构特征的局部相互作用以及裂纹尖端后的闭合效应是使小长裂纹的生长行为不同的一些因素。本文讨论了有效考虑小裂纹扩展行为的裂纹扩展寿命预测方法。该提议的方法包括使用ANSYS SMART断裂技术进行的基于有限元的详细裂纹扩展模拟。提升计算使用修改后的NASGRO方程和从已发布的长裂纹扩展数据中获得的小裂纹扩展数据，并针对闭合效应进行了校正。预测的比较了Ti-6Al-4V材料中AM试样的应力与循环次数曲线与疲劳测试结果。预测与测试结果之间的良好相关性表明，所提出的方法可用于评估AM零件的小裂纹扩展寿命，其中循环载荷的疲劳效应可能非常显着。