AI 中文总结
研究中子辐照钨中应变速率敏感性和变形长度尺度效应的耦合，采用球形纳米压痕等方法及CPFE建模，校准并验证模型，发现应变速率和压痕深度分别控制不同方面，该框架可用于相关材料本构建模。
AI 中文摘要
在应变速率控制的球形纳米压痕过程中，塑性变形受本构应变速率敏感性和变形长度尺度的耦合演化支配，使得应变速率的内在影响难以通过实验分离。本文使用球形纳米压痕、原子力显微镜、高分辨率电子背散射衍射（HR-EBSD）和晶体塑性有限元（CPFE）建模研究了未辐照和中子辐照的单晶钨中的这种耦合。纳米压痕实验在每秒3.2e-5至3.2e-3的应变速率下进行。原子力显微镜和高分辨率电子背散射衍射对表面堆积、残余晶格应变和几何必要位错（GND）分布进行了量化。使用单一实验条件校准了一个包含热激活滑移、GND强化、辐照诱导障碍强化和应变依赖软化的应变梯度CPFE框架，并在所有其余应变速率下进行了验证，无需进一步调整参数。然后使用经过验证的模型独立改变应变速率和压痕深度。模拟结果表明，应变速率主要控制热激活塑性流动所需的应力，而压痕深度控制塑性区演化、堆积和GND积累。辐照增加了障碍强度并促进了变形局部化，同时与常见的热激活机制保持一致。该框架还预测了多晶立方体的压缩响应，证明了在不同加载条件和长度尺度下的可转移性，为瞬态加载下辐照硬化材料的本构建模提供了坚实的基础。
英文摘要
Plastic deformation during strain-rate-controlled spherical nanoindentation is governed by the coupled evolution of constitutive strain-rate sensitivity and deformation length scale, making the intrinsic influence of strain rate difficult to isolate experimentally. This coupling is investigated in unirradiated and neutron-irradiated single-crystal tungsten using spherical nanoindentation, atomic force microscopy, high-resolution electron backscatter diffraction (HR-EBSD), and crystal plasticity finite element (CPFE) modeling. Nanoindentation experiments were performed at strain rates from 3.2e-5 to 3.2e-3 per second. AFM and HR-EBSD quantified surface pile-up, residual lattice strain, and geometrically necessary dislocation (GND) distributions. A strain-gradient CPFE framework incorporating thermally activated slip, GND hardening, irradiation-induced obstacle hardening, and strain-dependent softening was calibrated using a single experimental condition and validated across all remaining strain rates without further parameter adjustment. The validated model was then used to independently vary strain rate and indentation depth. Simulations show that strain rate primarily controls the stress required for thermally activated plastic flow, whereas indentation depth governs plastic-zone evolution, pile-up, and GND accumulation. Irradiation increases obstacle strength and promotes deformation localization while remaining consistent with a common thermally activated mechanism. The framework also predicts the compression response of a polycrystalline cube, demonstrating transferability across loading conditions and length scales, providing a robust basis for constitutive modeling of irradiation-hardened materials under transient loading.
Comments70 pages, 12 figures
