Defects introduced during additive manufacturing currently control fatigue resistance and lead to a large scatter in lifetime, with pancake shaped lack of fusion (LOF) defects being particularly potent. In this study the fatigue crack propagation life of selective laser-melted (SLM) AlSi10Mg alloy is considered in cases where single cracks and multiple cracks can initiate from LOF defects under high cycle fatigue (HCF). Firstly, the aspect ratios of initially long fatigue cracks were determined for critical LOF defects obtained from X-ray CT renderings using the critical defect regularization method, and the response surface method used to obtain the stress intensity factor of the crack front quickly and continuously. Then a single crack propagation model considering the evolution of the crack aspect ratio established to predict the crack propagation life which is in good agreement within in situ X-ray CT imaging of the crack front when a single crack is dominant. The crack propagation phase was predicted to represent 35–60% of the total fatigue life representing a larger fraction at high stress amplitudes. Multiple cracks were found to initiate cracks at the larger stress amplitudes. In cases where multiple cracks arise this is non-conservative and so a synergistic multiple fatigue crack growth (smFCG) model was developed based on multiple defects measured a priori by X-ray CT to depict the competitive cracking effect. Compared with the single crack model, the smFCG model predicts a shorter propagation life (by 5–10%) when multiple defects are involved since it considers all the initial defects within the crack initiation region. Given the propensity of large numbers of defects in AM material this approach may be more appropriate in many cases.

增材制造过程中引入的缺陷目前控制着抗疲劳性，并导致寿命中的大量分散，其中煎饼形未熔合 (LOF) 缺陷尤为严重。在这项研究中，选择性激光熔化 (SLM) AlSi10Mg 合金的疲劳裂纹扩展寿命被考虑在高周疲劳 (HCF) 下 LOF 缺陷可能引发单个裂纹和多个裂纹的情况下。首先，利用临界缺陷正则化方法和响应面法，快速、连续地获取裂纹前沿应力强度因子，对X射线CT渲染得到的临界LOF缺陷确定初始长疲劳裂纹的纵横比。就地单个裂纹占优势时裂纹前沿的 X 射线 CT 成像。裂纹扩展阶段预计占总疲劳寿命的 35-60%，在高应力幅度下占更大比例。发现多个裂纹会在较大的应力幅度下引发裂纹。在出现多个裂纹的情况下，这是不保守的，因此基于 X 射线 CT 先验测量的多个缺陷开发了协同多重疲劳裂纹扩展 (smFCG) 模型，以描述竞争性裂纹效应。与单裂纹模型相比，smFCG 模型在涉及多个缺陷时预测更短的传播寿命（5-10%），因为它考虑了裂纹萌生区域内的所有初始缺陷。