用数字图象相关和晶体塑性有限元模拟表征滑移和孪晶活动：对正交$α$ -铀的应用
Characterisation of slip and twin activity using digital image correlation and crystal plasticity finite element simulation: Application to orthorhombic $α$-uranium
摘要：
校准和验证晶体塑性材料模型是一项重大挑战，特别是对于具有许多潜在滑移和孪晶系统的材料。在这里，我们使用数字图像相关的粗晶粒$α$ -铀在拉伸试验与晶体塑性有限元模拟。这种方法使我们能够确定的临界解析剪切应力，和硬化率的不同的滑移和孪生系统。本构模型是基于位错密度作为状态变量和模拟的几何构造从电子背散射衍射图像，提供形状，尺寸和晶粒的取向，允许虚拟和真实的实验之间的直接比较。一个优化算法是用来找到的模型参数，再现每个晶粒的平均应变的演变，随着负载的增加。一个拉伸杆，包含四个晶粒对齐的负载方向，被用来校准模型与8个未知参数。然后，通过模拟第二个拉伸杆中的应变分布，独立验证该方法。不同的机制的双系统的硬化进行了评估。最活跃的孪晶系统的潜在硬化是由共面孪晶和滑移决定的。最活跃的滑移系的硬化速率低于细粒$α$ -铀。该方法可用于其它粗晶材料的临界分辨剪应力和硬化参数的识别。
英文摘要：
Calibrating and verifying crystal plasticity material models is a significant challenge, particularly for materials with a number of potential slip and twin systems. Here we use digital image correlation on coarse-grained $α$-uranium during tensile testing in conjunction with crystal plasticity finite element simulations. This approach allows us to determine the critical resolved shear stress, and hardening rate of the different slip and twin systems. The constitutive model is based on dislocation densities as state variables and the simulated geometry is constructed from electron backscatter diffraction images that provide shape, size and orientation of the grains, allowing a direct comparison between virtual and real experiments. An optimisation algorithm is used to find the model parameters that reproduce the evolution of the average strain in each grain as the load is increased. A tensile bar, containing four grains aligned with the load direction, is used to calibrate the model with eight unknown parameters. The approach is then independently validated by simulating the strain distribution in a second tensile bar. Different mechanisms for the hardening of the twin systems are evaluated. The latent hardening of the most active twin system turns out to be determined by coplanar twins and slip. The hardening rate of the most active slip system is lower than in fine-grained $α$-uranium. The method developed in the present research can be applied to identify the critical resolved shear stress and hardening parameters of other coarse-grained materials.
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