Mesoscale Plasticity: Dislocation Patterns, Stochastic and Size Effects

推进和加速材料发现取决于我们开发模型的能力，该模型可以快速调查大的材料空间以优化性能，并在可验证的模拟的基础上设计产生所需机械行为的制造工艺。特别令人感兴趣的是由尺寸在几纳米到几百微米范围内的多尺度结构部件组成的系统的材料特性。这包括微型机电系统、微型植入物和微电子设备。在较小的尺度下，测量的力学性能随尺寸的减小而变化很大。虽然现有的模型可以预测确定性的值，但分析模型通常隐含地假设数据中的噪声是由于微尺度测试技术固有的困难造成的。然而，无论实验进行得多么优雅，实验都显示出大量的随机行为。该奖项支持基础研究，以开发解释随机现象的预测模型，以确保验证技术和模拟工具很好地配对。更广泛的影响将是在我们的实验室中创造一个种族、性别和民族出身的多样化环境。这个项目为学生和初级研究人员提供了在跨学科环境中参与研究和教育体验的机会，在来自力学和材料科学的教师的共同建议下解决他们的论文问题。研究活动将发展力学和材料科学的理论和测试方案，作为材料建模和实验验证的指标。我们的假设是，小体积塑性变形是随机的、锯齿状的和非均匀的。这种效应的产生是由于底层微观结构的随机性，如位错、晶粒度、界面和晶界，以及由加载条件和形态缺陷引起的应力梯度，以及局域化和位错图案的形成。我们将开发解释这些现象的模型，以便验证技术和模拟工具能够很好地配对。为此，该项目将解决以下五个问题。1)可观察到的随机现象的根本原因是什么：塑性、局部化、图案化和锯齿状流动？2)变形机制和缺陷-表面相互作用如何在小体积内对强度、韧性和损伤做出贡献？3)在什么形态和微观结构条件下，变形行为从确定性转变为随机性？4)我们如何量化和模拟长度尺度上的随机行为？5)我们如何将这种理解转化为中尺度的随机尺寸相关塑性模型？

Advancing and accelerating materials discovery depends on our ability to develop models that can allow rapid investigation of large materials spaces to optimize properties, and to design manufacturing processes that yield the desired mechanical behavior on the basis of verifiable simulations. Of particular interest are the material properties of systems which consist of multiscale structural components whose dimensions lie in the range of a few nanometers to a few hundred micrometers. This includes micro-electro-mechanical systems, micro implants and microelectronic devices. At small length scales the measured mechanical properties vary significantly with decreasing dimensions. While existing models can predict deterministic values, analytical models often implicitly assume that noise in the data is due to difficulties inherent in microscale testing techniques. However, experiments show a significant amount of stochastic behavior no matter how elegantly the experiments are performed. This award supports fundamental research to develop predictive models that account for stochastic phenomena to ensure that validation techniques and simulation tools are well paired. Further broader impact will be the creation of a diverse environment in our laboratories in terms of race, gender, and national origin. This project offers students and junior researchers opportunities to participate in a research and education experience in an interdisciplinary environment, tackling their thesis problems with co-advisement from faculty drawn from both mechanics and materials science.The research activities will develop mechanics and materials science theories and testing schemes as metrics for material modeling and experimental validation. Our hypothesis is that plastic deformation in small volume is stochastic, serrated and heterogeneous. Such effects would arise from the stochastic nature of the underlying microstructure such as dislocations, grain size, interfaces and grain boundaries, from stress gradients arising from loading conditions and morphological defects, and the formation of localized and dislocation patterns. We will develop models that account for such phenomena so that validation techniques and simulation tools are well paired. Towards this end, this project will address the following five questions. 1) What are the underlying causes of the observed stochastic phenomena: onset of plasticity, localization, patterning, and serrated flow? 2) How do deformation mechanisms and defect-surface interactions contribute to strength, toughness, and damage in small volumes? 3) Under what morphological and microstructural conditions does the deformation behavior transition from deterministic to stochastic? 4) How can we quantify and model stochastic behavior across length scale? 5) How can we translate this understanding into a mesoscale stochastic size-dependent plasticity model?