The relative fatigue resistance of different polycrystalline microstructures can be evaluated using fatigue indicator parameters (FIPs) that serve as surrogate measures for the fatigue crack formation driving force. This typically requires simulating many grains/phases to capture sufficient microstructure heterogeneity. Thus, the concept of a representative volume element (RVE) for fatigue-related properties has remained computationally prohibitive and elusive. Alternatively, ensembles of statistical volume elements (SVEs) can be simulated to build up the extreme value fatigue response. A crucial consideration in these types of crystal plasticity finite element method (CPFEM) simulations is the nature of applied boundary conditions. Fatigue crack formation has been experimentally observed to occur either at or near the free surface or throughout the specimen volume, depending on the material microstructure, surface conditions, and the fatigue regime (e.g., low cycle, transition, or high cycle fatigue). The recently developed open-source PRISMS-Fatigue framework (Yaghoobi et al. in NPJ Comput Mater 7:38, 2021) enables the simulation of very large microstructures that may be used to study fatigue RVE characteristics. The available multi-point constraints in PRISMS-Fatigue impose periodic boundary conditions that can appropriately distinguish between the bulk and surface driving forces for fatigue crack formation. We demonstrate the efficacy of these multi-point constraints in microstructure-sensitive CPFEM simulations and compare the extreme value fatigue crack driving force response using various boundary conditions, microstructures, and crystallographic textures. The effects of applied boundary conditions on different mechanical responses such as the macroscopic stress–strain response, local measures of plastic slip, and corresponding FIPs are studied. The results provide guidance for microstructure-sensitive crystal plasticity fatigue studies and demonstrate the advanced capabilities of PRISMS-Fatigue to model large volumes of material microstructure.

可以使用疲劳指标参数 (FIP) 作为疲劳裂纹形成驱动力的替代措施来评估不同多晶微观结构的相对疲劳强度。这通常需要模拟许多晶粒/相以捕获足够的微观结构异质性。因此，用于疲劳相关属性的代表性体积元素 (RVE) 的概念在计算上仍然令人望而却步且难以捉摸。或者，可以模拟统计体积元素 (SVE) 的集合以建立极值疲劳响应。在这些类型的晶体塑性有限元方法 (CPFEM) 模拟中，一个关键的考虑因素是应用边界条件的性质。根据材料微观结构、表面条件和疲劳状态（例如，低周疲劳、过渡疲劳或高周疲劳），已经通过实验观察到疲劳裂纹的形成发生在自由表面处或附近或整个试样体积。最近开发的开源 PRISMS-Fatigue 框架（Yaghoobi et al. in NPJ Comput Mater 7:38, 2021）可以模拟非常大的微结构，这些微结构可用于研究疲劳 RVE 特性。PRISMS-Fatigue 中可用的多点约束施加周期性边界条件，可以适当地区分疲劳裂纹形成的体驱动力和表面驱动力。我们证明了这些多点约束在微观结构敏感 CPFEM 模拟中的有效性，并使用各种边界条件、微观结构和晶体结构比较了极值疲劳裂纹驱动力响应。研究了应用边界条件对不同机械响应的影响，例如宏观应力应变响应、塑性滑移的局部测量和相应的 FIP。结果为微观结构敏感的晶体塑性疲劳研究提供了指导，并证明了 PRISMS-Fatigue 对大量材料微观结构进行建模的先进能力。研究了应用边界条件对不同机械响应的影响，例如宏观应力应变响应、塑性滑移的局部测量和相应的 FIP。结果为微观结构敏感的晶体塑性疲劳研究提供了指导，并证明了 PRISMS-Fatigue 对大量材料微观结构进行建模的先进能力。研究了应用边界条件对不同机械响应的影响，例如宏观应力应变响应、塑性滑移的局部测量和相应的 FIP。结果为微观结构敏感的晶体塑性疲劳研究提供了指导，并证明了 PRISMS-Fatigue 对大量材料微观结构进行建模的先进能力。