Wire and Arc Additive Manufacturing (WAAM) is a direct-energy deposition technique (unlike SLM or EBM) that builds up a part in a layer-by-layer fashion, each layer being constituted of interlaced weld beads. It is the best suited Additive Manufacturing (AM) technique for large structures thanks to its high deposition rate (5 kg/h). The resulting material shows a rough surface, strong residual stress induced by its complex thermal history, a heterogeneous microstructure marked by the different weld passes as well as defects formed by gas pockets. Despite their rarity, pores are found to have a first-order influence on the fatigue life of machined specimens. The discrepancy in their size (> 100 μm) and position is responsible for a considerable scatter that makes classical fatigue tests ineffective. The aim of this study is to propose a novel approach to take into account the effect of rare WAAM-induced defects in high cycle fatigue. To achieve this, numerical porous structures are generated from the knowledge of the real pore population determined by tomography. Their fatigue performances are predicted via a two-scale probabilistic model identified on experimental self-heating results, on which pores have no influence. In that sense, the probabilistic model describes the behavior of a virtually healthy material. Then, by computing a database of representative pore cases, the whole bundle of Wöhler curves for each numerical porous structure is determined. Finally, the numerical fatigue scatter is in close agreement with experimental data, and it is shown that the ranking in pore criticality according to the model matches the fractography observations.

线材和电弧增材制造（WAAM）是一种直接能量沉积技术（与SLM或EBM不同），它以逐层的方式构建零件，每一层都由交错的焊道组成。由于其高沉积速率（5 kg / h），它是最适合大型结构的增材制造（AM）技术。所得材料显示出粗糙的表面，由其复杂的热历史引起的强大的残余应力，以不同的焊道标记的异质微观结构以及由气穴形成的缺陷。尽管孔非常稀少，但发现孔对加工样品的疲劳寿命具有第一级影响。它们的尺寸（> 100μm）和位置的差异造成了很大的分散，这使得传统的疲劳测试无效。这项研究的目的是提出一种新方法，以考虑到罕见的WAAM诱导的缺陷在高周疲劳中的作用。为了实现这一点，从通过层析成像技术确定的实际孔隙总数的知识中生成了数值多孔结构。通过在实验自热结果上确定的两级概率模型预测其疲劳性能，该模型对孔没有影响。从这个意义上讲，概率模型描述了实际上健康的材料的行为。然后，通过计算代表性孔隙情况的数据库，确定每个数值多孔结构的整个Wöhler曲线束。最后，数值疲劳散布与实验数据非常吻合，