Materials World Network: Physically Based Approach for Predicting and Minimizing Damage Nucleation in Metals

预测损伤成核并评估其是否会导致致命缺陷的能力是计算塑性学的主要目标之一。 然而，大多数损伤的建模是基于预先存在的缺陷或裂纹的假设，并且迄今为止开发的建模方法预测损伤的增长而不是成核。 虽然不均匀变形被理解为是损伤成核的前兆，但不均匀变形和损伤成核之间的步骤并不清楚。如果不均匀变形建模准确，那么它是不可能的损伤成核和随后的损伤增长可以自信地预测。 从目前对晶界处的非均匀变形和变形传递的理解的回顾来看，损伤成核机制的识别将需要（i）界面两侧的晶体取向，（ii）边界取向和结构（能量），（iii）边界两侧的激活变形系统，以及（iv）界面两侧晶粒中的应力-应变梯度历史。 本研究考察了具有简单微观结构的金属和合金，这些金属和合金具有固有的低延展性（在这种情况下是钛和双相钢），从而提供了获得明确识别损伤成核机制所需的基于滑移系统的信息的最佳机会。本研究计划的目标是：（1）确定在变形路径的背景下识别强边界和弱边界的基本规则（2）以跟踪边界强度作为局部应力和应变历史的函数的模型的形式定量地表达规则。 (3)将晶界强度规则应用到细观变形的计算模型中。 这是在一个联合研究项目中完成的，该项目涉及密歇根州立大学（MSU）和位于德国杜塞尔多夫的马克斯·普朗克研究所（MPIE），在那里存在相互有用的技能，当融入国际合作研究计划时，可以达到上述目标。 这项研究是基于获得足够详细的数据集，使损伤成核机制在多晶体边界可以清楚地识别。 使用最先进的方法，允许比较提供补充信息的多种实验方法。 数据集的比较有助于量化的分辨率和可信度的取向成像显微镜，连续切片，三维X射线成像，电子沟道衬度成像（ECCI）和背散射电子成像。 这些丰富的数据集有助于在计算模型中自信地预测损伤成核之前所需的模型开发。这项工作是由三个博士。在密歇根州立大学的Bieler和Crimp教授以及马克斯·普朗克研究所的Philip Eisenlohr和Franz Roters博士的指导下， 两个实验室之间进行了广泛的交流，以整合实验和分析方法，以实现这些目标。 需要对先进材料和部件的复杂加工和服务条件进行多尺度建模，以支持推动世界经济的所有技术创新。 很难想到材料加工的一个方面比能够可靠地预测损伤成核对社会的影响更大。 在设计环境中成功实施可靠的损伤成核模型将减少浪费，加快高附加值制成品的上市时间，提高技术和工程各个方面的安全性和经济性。 该奖项由国际科学与工程办公室共同资助。

The ability to predict damage nucleation and evaluate whether it will lead to a fatal flaw is one of the major goals of computational plasticity. However, most modeling of damage is based upon the assumption of pre-existing flaws or cracks, and the modeling approaches developed so far predict the growth rather than the nucleation of damage. While heterogeneous deformation is understood to be a precursor to damage nucleation, the step between heterogeneous deformation and damage nucleation is not clearly understood. If heterogeneous deformation is not modeled accurately, then it is unlikely that damage nucleation and subsequent damage growth can be confidently predicted. From a review of current understanding of heterogeneous deformation and deformation transfer at grain boundaries, identification of mechanisms of damage nucleation will require quantitative knowledge of (i) the orientations of crystals on either side of the interface, (ii) the boundary orientation and structure (energy), (iii) the activated deformation systems on either side of the boundary, and (iv) the stress-strain gradient history in the grains on either side of an interface. This research examines metals and alloys with simple microstructures that have an intrinsically low ductility (in this case titanium and dual phase steels) and thus provide the best opportunity to gain the slip-system-based information needed to clearly identify damage nucleation mechanisms. The goals of this research program are: (1) Identify fundamental rules for identifying strong and weak boundaries in the context of a deformation path (2) Express rules quantitatively in the form of models that track boundary strength as a function of local stress and strain history. (3) Implement grain boundary strength rules into computational models of mesoscale deformation. This is accomplished in a joint research project involving Michigan State University (MSU) and Max Planck Institut fr Eisenforschung (MPIE) in Dsseldorf, Germany, where mutually useful skills are present which can reach the above goals when integrated into an international cooperative research program. The research is based upon obtaining sufficiently detailed data sets so that damage nucleation mechanisms in polycrystal boundaries can be clearly identified. State of the art methodologies are used, which permit comparisons of multiple experimental methodologies that provide complimentary information. Comparison of data sets helps quantify the resolution and credibility of orientation imaging microscopy, serial sectioning, three-dimensional x-ray mapping, electron channeling contrast imaging (ECCI) and backscattered electron imaging. These rich data sets facilitate model development that is needed before damage nucleation can be predicted with confidence in computational models. The work is carried out by three Ph.D. students under the guidance of Profs Bieler and Crimp at MSU, and Drs. Philip Eisenlohr and Franz Roters at the Max Planck Institut fr Eisenforschung. Extensive exchanges between the two laboratories occur in order to integrate experimental and analytical methods to reach these goals. Multi-scale modeling of sophisticated processing and service conditions of advanced materials and components is needed to support all technological innovations that drive the world economy. It is difficult to think of an aspect of material processing that affects society more than being able to reliably predict damage nucleation. Success in implementing credible models of damage nucleation in design environments will lead to reduced waste, accelerated time to market for highly value-added manufactured goods, improved safety and economy in all aspects of technology and engineering. This award is co-funded with the Office of International Science and Engineering.