GOALI: Micromechanics Experiments and Modeling of Shape Memory Response in Ni-Ti Based Alloys

GOALI：镍钛合金形状记忆响应的微观力学实验和建模

• 批准号: 0907561
• 负责人: Michael Mills
• 金额: $ 37.5万
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0907561&HistoricalAwards=false
• 关键词: GOALI; Micromechanics; Experiments; Modeling; Shape

TECHNICAL SUMMARY:Shape memory alloys are materials with remarkable properties that stem from a martensitic transformation. One of the fundamental aspects of shape memory and pseudoelastic behavior that is not well understood is how the matrix accommodates the large strain associated with the transformation. Theoretically, accommodation may be achieved either by matrix plasticity or by inducing other transformation variants. This three-year GOALI proposal will develop new, fundamental insight into the pseudoelastic shape memory behavior of several Ni-Ti based alloys, including a ternary Ni-Cu-Ti, in collaboration with GM Research. The focus will be on alloys that undergo different martensite transformations and exhibit disparate functional fatigue properties. The approach is to meld innovative micron-scale mechanical tests and advanced microstructural characterization with analytic and novel microstructure-based modeling. Uniaxial deformation of focused-ion-beam-machined microcrystals will be used to probe the static and cyclic response as a function of matrix crystal orientation, and in order to directly measure the mechanical response (stress, strain, work output) for individual variants. Post-mortem characterization using transmission electron microscopy of the remnant substructure will be coupled with analytic modeling of the possible transformations. This approach will also yield directly the relative conditions for martensite transformation versus matrix plasticity over a range of component sizes. A new microstructure-based finite element approach will be developed that explicitly tracks local, discrete phase transformations coupled with rate-dependent crystal plasticity. For the first time, this will enable the treatment of size effects and the generation of local plasticity associated with transformations?a crucial step to understand and enhance pseudoelastic and shape memory response. The proposed effort integrates advanced characterization at The Ohio State University and the GM Research center with new experimental techniques at two DOE labs ? high temperature nanoindentation/pillar testing at Oak Ridge National Laboratory and in situ pillar testing at the National Center for Electron Microscopy.NON-TECHNICAL SUMMARY:Shape memory alloys (SMAs) are materials with remarkable properties that include the ability to bend and stretch to large extent under an applied load, then spring back to their original shape when the load is removed. In addition, SMAs can change shape when heated, after which they may either maintain their newly acquired shape or return to their original shape after cooling back down to room temperature. The automotive industry has recognized the phenomenal potential of SMAs since they are remarkably simple actuation devices compared with conventional motorized actuators. For instance, they could be used as small, ?solid-state? motors that could be used to reconfigure a wide range of components, greatly reducing the complexity of such systems. However, commercially available SMA materials are not presently operated at their full potential due to degradation in their shape-changing capabilities after experiencing many temperature or stress cycles (?functional fatigue?). This program is designed to develop a fundamental understanding of the materials science aspects associated with this degradation process, as well as the development of modeling capabilities to predict and improve the functional fatigue performance for automotive, medical and other applications. A vigorous program of interchange between OSU and GM will stimulate efficient transfer of knowledge and will provide ample mechanisms for experiencing both academic and industrial environments. In an exciting outreach effort, we will develop a high school inquiry-based teaching module about shape memory alloys and their applications. Several mechanisms insuring insertion of this module into local high schools have also been defined.

技术摘要：形状记忆合金是一种具有源自马氏体转变的卓越性能的材料。形状记忆和伪弹性行为的基本方面之一尚未得到充分理解，即矩阵如何适应与变换相关的大应变。理论上，调节可以通过基质可塑性或通过诱导其他变换变体来实现。这项为期三年的 GOALI 提案将与 GM Research 合作，对几种 Ni-Ti 基合金（包括三元 Ni-Cu-Ti）的伪弹性形状记忆行为产生新的、基本的见解。重点将放在经历不同马氏体转变并表现出不同功能疲劳性能的合金上。该方法将创新的微米级机械测试和先进的微观结构表征与基于分析和新颖的微观结构的建模相结合。聚焦离子束加工微晶体的单轴变形将用于探测作为基体晶体取向函数的静态和循环响应，并直接测量各个变体的机械响应（应力、应变、功输出）。使用透射电子显微镜对残余子结构进行尸检表征，并将与可能的转变的分析模型相结合。这种方法还将直接得出在一定范围的部件尺寸上马氏体转变与基体塑性的相对条件。将开发一种新的基于微观结构的有限元方法，该方法可以明确跟踪局部离散相变以及速率相关的晶体塑性。这将首次实现尺寸效应的处理以及与变换相关的局部可塑性的生成——这是理解和增强伪弹性和形状记忆响应的关键一步。拟议的工作将俄亥俄州立大学和通用汽车研究中心的先进表征与能源部两个实验室的新实验技术相结合？橡树岭国家实验室的高温纳米压痕/柱测试以及国家电子显微镜中心的原位柱测试。非技术摘要：形状记忆合金 (SMA) 是具有卓越性能的材料，包括在施加的载荷下能够在很大程度上弯曲和拉伸，然后在去除载荷时弹回原来的形状。此外，SMA 在加热时可以改变形状，之后它们可以保持新获得的形状，也可以在冷却至室温后恢复到原来的形状。汽车行业已经认识到 SMA 的巨大潜力，因为与传统电动执行器相比，它们是非常简单的执行设备。例如，它们可以用作小型“固态”？电机可用于重新配置各种组件，从而大大降低此类系统的复杂性。然而，商用 SMA 材料目前尚未充分发挥其潜力，因为在经历多次温度或应力循环（“功能疲劳”）后，其变形能力会下降。该计划旨在加深对与这种降解过程相关的材料科学方面的基本了解，并开发建模功能来预测和改善汽车、医疗和其他应用的功能疲劳性能。俄勒冈州立大学和通用汽车之间的积极交流计划将促进知识的有效转移，并为体验学术和工业环境提供充足的机制。在一项令人兴奋的推广工作中，我们将开发一个关于形状记忆合金及其应用的高中探究式教学模块。还确定了几种确保将该模块插入当地高中的机制。