Towards a Scientific Understanding of Fatigue Damage Tolerance in Shape Memory Materials

科学理解形状记忆材料的疲劳损伤耐受性

• 批准号: 1709515
• 负责人: Huseyin Sehitoglu
• 金额: $ 38.94万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1709515&HistoricalAwards=false
• 关键词: Towards; Scientific; Understanding; Fatigue; Damage

Non-Technical AbstractShape memory alloys can "remember" their original shape and return to their pre-deformed shape when heated. They are utilized mainly in biomedical applications. They undergo a structural transformation under the application of temperature or stress. Under repeated transformations or cyclic loadings, shape memory alloys can undergo mechanical fatigue. Fatigue is the progressive deterioration of metals under cyclic loading, resulting in damage due to cracking and ultimately failure. This can negatively affect the actuation performance in many applications. Therefore, the purpose of this project is to advance the science-based knowledge of fatigue progression in such alloys by developing a fundamental approach to estimate the fatigue threshold stress intensity as a function of key material parameters. The work will address how the material variables affect the macroscopic fatigue parameters such controlling crack advance. The impact of this work is to remove the empiricism associated with fatigue threshold determination in shape memory materials. The proposed modeling will reveal understanding that can advance prediction of fatigue damage. This research will examine the most important shape memory material NiTi which is not well understood, and then consider new classes of promising alloys that currently remain untested. The proposed research recognizes the need for revamping education in this field with outreach efforts to high school students. A novel project is proposed to build a small fatigue machine using rapid prototyping methodology. The students will learn how to build the machine during the summer camp and observe the failure of alloy wires under fatigue. Technical AbstractFundamental understanding of shape memory alloy (SMA) fatigue damage tolerance has not been established despite the significance of these alloys. The lack of understanding of fatigue hinders the widespread use of SMAs and has confined SMA utilization to very few compositions. This project is an effort on modeling from atomistic to micro- mechanical scales to develop a superior understanding of fatigue thresholds in shape memory alloys (SMAs). This science-based methodology of fatigue-damage prediction is one of the challenges that the shape memory community faces especially under varying stress in endovascular stents and potential applications such as elastocaloric cooling where the SMAs could see thousands of cycles. The work requires deep knowledge of several fields- physics of fatigue, atomistic models and shape memory behavior. The proposal will utilize modeling at atomic scale via ab-initio calculations as well as molecular dynamics to understand: (i) the role of elastic anisotropy (including cubic, tetragonal and monoclinic lattices), (ii) the role of dislocation-mediated slip resulting in irreversibility, residual martensite, and residual austenites, and their role in producing crack closure forces. The alloys to be considered such as NiTi and CoNiAl exhibit different crystal lattices, ordering and transformation stresses as a function of composition and heat treatment. To verify the models at various length scales, electron microscopy in meso-scale fatigue experiments will be utilized. Only the confluence of these techniques can provide the needed insight to advance the current knowledge of mechanical fatigue of SMAs. This proposal will evaluate two shape memory alloy systems with experiments (NiTi and Co-Ni-Al with varying compositions). The proposed experiments consider very fine measurements of displacements at crack tips allowing determination of crack advance. Concurrently, the focus will be on theoretical developments to compute the crack closure forces due to transformation strains which will account for the elastic moduli tensors, anisotropy of internal tractions, and transformation and plasticity zones. The proposal plans to predict the fatigue crack advance under three different material conditions: (i) monolithic austenitic state (ii) martensitic state (detwinned and self-accommodated cases) and (iii) stress- induced transformation (austenite to martensite) conditions. The study of these three material conditions will provide a complete spectrum of understanding of SMA fatigue behavior. A novel project is proposed for students to build a small fatigue machine using rapid prototyping methodology and test SMA wires under high-speed rotation. The curvature of the wire dictates the strain amplitude and the rotation of the wire generates cyclic loading that alternates between tension and compression and ultimately results in fatigue failure. The students will learn how to build the machine during the summer camp and observe the failure of SMA wires under fatigue.

非技术形状记忆合金可以“记住”它们的原始形状，并在受热时恢复到其预先变形的形状。它们主要用于生物医学应用。它们在温度或应力的作用下经历结构转变。在反复相变或循环载荷作用下，形状记忆合金会发生机械疲劳。疲劳是指金属在循环载荷作用下的逐渐恶化，导致因开裂而造成的损伤，最终失效。在许多应用中，这可能会对驱动性能产生负面影响。因此，本项目的目的是通过开发一种基本的方法来估计疲劳门槛应力强度作为关键材料参数的函数，从而促进对这类合金疲劳过程的科学认识。这项工作将研究材料变量如何影响宏观疲劳参数，如控制裂纹扩展。这项工作的影响是消除了与形状记忆材料疲劳阈值确定相关的经验主义。所提出的模型将揭示可以促进疲劳损伤预测的理解。这项研究将考察最重要的形状记忆材料NiTi，这是一种尚未被很好理解的材料，然后考虑目前仍未测试的新的有前途的合金类别。拟议的研究认识到有必要改革这一领域的教育，努力扩大到高中生。提出了一种利用快速成型技术制造小型疲劳试验机的新方案。学生们将在夏令营期间学习如何制造机器，并观察合金丝在疲劳下的失效情况。技术摘要尽管形状记忆合金(SMA)具有重要意义，但对这些合金的疲劳损伤容限还没有建立基本的了解。对疲劳的缺乏了解阻碍了SMA的广泛使用，并将SMA的使用限制在很少的成分中。该项目致力于从原子尺度到微观力学尺度的建模，以更好地了解形状记忆合金(SMA)的疲劳阈值。这种基于科学的疲劳损伤预测方法是形状记忆界面临的挑战之一，特别是在血管内支架和潜在应用(如弹性热能冷却)中的不同压力下，SMA可能会看到数千个循环。这项工作需要对几个领域有深刻的了解--疲劳物理学、原子模型和形状记忆行为。该方案将通过从头计算和分子动力学在原子尺度上进行模拟，以了解：(I)弹性各向异性(包括立方晶格、四方晶格和单斜晶格)的作用，(Ii)位错介导的滑移导致不可逆性、残余马氏体和残余奥氏体数的作用，以及它们在产生裂纹闭合力方面的作用。NiTi和CoNiAl等合金表现出不同的晶格、有序化和相变应力随成分和热处理的变化。为了验证不同长度尺度下的模型，将利用细观疲劳实验中的电子显微镜。只有这些技术的融合才能提供所需的洞察力，以促进对SMA机械疲劳的现有知识。本方案将通过实验对两种形状记忆合金系统(NiTi和Co-Ni-Al)进行评价。建议的实验考虑了对裂纹尖端的位移进行非常精细的测量，从而确定裂纹的推进。同时，重点将集中在计算相变应变引起的裂纹闭合力的理论发展上，这将考虑弹性模张量、内力的各向异性以及相变和塑性区。该方案计划预测三种不同材料条件下的疲劳裂纹扩展：(I)整体奥氏体态；(Ii)马氏体态(孪晶和自容情况)；(Iii)应力诱导相变(奥氏体向马氏体)。对这三种材料条件的研究将提供对SMA疲劳行为的完整理解。提出了一个新的项目，以供学生使用快速成型方法制造一台小型疲劳试验机，并在高速旋转下测试SMA丝。钢丝的曲率决定了应变幅度，钢丝的旋转产生了在拉伸和压缩之间交替的循环载荷，最终导致疲劳破坏。学生们将在夏令营期间学习如何制造机器，并观察SMA钢丝在疲劳状态下的失效情况。

项目成果

Unraveling Frequency Effects in Shape Memory Alloys: NiTi and FeMnAlNi

• DOI: 10.1007/s40830-021-00335-0
• 发表时间: 2021-06
• 期刊: Shape Memory and Superelasticity
• 影响因子: 2.2
• 作者: R. Sidharth;A. Mohammed;W. Abuzaid;H. Sehitoglu

Nano-twinning enhanced room temperature fatigue crack growth in single crystalline CoCrFeMnNi high entropy alloy

单晶 CoCrFeMnNi 高熵合金中纳米孪晶增强室温疲劳裂纹扩展

• DOI: 10.1016/j.intermet.2020.106919
• 发表时间: 2020
• 期刊: Intermetallics
• 影响因子: 4.4
• 作者: Sidharth, R.;Abuzaid, W.;Sehitoglu, H.
• 通讯作者: Sehitoglu, H.

Relationship Between Functional Fatigue and Structural Fatigue of Iron-Based Shape Memory Alloy FeMnNiAl

铁基形状记忆合金FeMnNiAl功能疲劳与结构疲劳的关系

• DOI: 10.1007/s40830-020-00283-1
• 发表时间: 2020
• 期刊: Shape Memory and Superelasticity
• 影响因子: 2.2
• 作者: Sidharth, R.;Wu, Y.;Brenne, F.;Abuzaid, W.;Sehitoglu, H.
• 通讯作者: Sehitoglu, H.

Superelasticity of (TiZrHf)50Ni25Co10Cu15 high entropy shape memory alloy

• DOI: 10.1016/j.scriptamat.2020.04.017
• 发表时间: 2020-09
• 期刊: Scripta Materialia
• 影响因子: 6
• 作者: J. Yaacoub;W. Abuzaid;Florian Brenne;H. Sehitoglu

Deshielding effects on fatigue crack growth in shape memory alloys- A study on CuZnAl single-crystalline materials

• DOI: 10.1016/j.actamat.2019.06.042
• 发表时间: 2019-09
• 期刊: Acta Materialia
• 影响因子: 9.4
• 作者: Y. Wu;J. Yaacoub;F. Brenne;W. Abuzaid;D. Canadinc;H. Sehitoglu