Flexural Fatigue of Saline Ice

盐冰的弯曲疲劳

• 批准号: 1947107
• 负责人: Erland Schulson
• 金额: $ 52.85万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1947107&HistoricalAwards=false
• 关键词: Flexural; Fatigue; Saline; Ice

The sea ice cover on polar oceans is cyclically bent owing to the action of ocean waves, rather like the back and forth bending of a paper clip. Just as a paper clip will eventually break with repeated bending, so too may the sea ice cover. This type of breaking is termed fatigue failure, a mode of failure that occurs without warning. Fatigue failure of the sea ice cover and its attendant breakup into many small pieces can imperil on-ice navigation by humans and animals, can increase the rate at which the ice cover melts, and can reduce the protective barrier from ocean waves afforded Arctic coastal villages and their indigenous people. In other words, as sea ice retreats and oceanic fetch increases, the propensity for fatigue failure and its consequences is expected to increase owing to an increase in ocean wave amplitude and, hence, in ice stress. This project will investigate the fatigue failure of ice under bending. Its intellectual merit resides in describing, and then understanding, a destructive phenomenon about which little is known. More broadly, the project provides insight and, ultimately, predictive models for the stability of Antarctic ice shelves and the integrity of the lithosphere of icy satellites that possess putative oceans, such as Jupiter’s Europa and Saturn’s Enceladus. This project builds upon a preliminary study in the laboratory which showed that when subjected to flexing under four-point loading at the rate of one cycle every ten minutes (0.1 Hz), plates of both saline ice and freshwater ice at -10 degrees C exhibit erratic behavior, failing in some tests after as few as two to three cycles and in others after two thousand cycles. While fatigue life of materials in general is known to be somewhat variable, the magnitude of the variability that we noted seems unusually large. More surprising still is the observation that the flexural strength of ice that survived many cycles actually increases, by as much as a factor of two. This cyclic strengthening is opposite to fatigue weakening that has been reported in the literature from in-situ studies of flexed beams of Antarctic sea ice. We hypothesize that the difference between in-situ and laboratory behavior may reflect the role on fatigue life of thermal-mechanical history, particularly of stress-induced micro-cracks produced in natural settings. The goal of this project is to test this hypothesis in a systematic manner by introducing into test specimens different populations of micro-cracks and then exploring their role, cognizance being taken of possible annealing/blunting effects with time. Variables will include micro-crack density, salinity (0-7 ppt), temperature (-25 to-3 degrees C), flexing frequency (0.01 to 1.0 Hz), stress (0.1 to 1 MPa) and hold time between cracking and flexing (1 to 48 hrs).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

由于海浪的作用，极地海洋上的海冰会周期性地弯曲，就像回形针来回弯曲一样。就像回形针最终会因反复弯曲而断裂一样，海冰也可能会断裂。这种类型的断裂被称为疲劳失效，这是一种没有预警的失效模式。海冰的疲劳破坏和随之而来的分裂成许多小块，可能危及人类和动物的冰上航行，可能增加冰盖融化的速度，并可能减少为北极沿海村庄和土著居民提供的抵御海浪的保护屏障。换句话说，随着海冰的退缩和海洋海水的增加，由于海浪振幅的增加和冰应力的增加，预计疲劳破坏的倾向及其后果将会增加。本项目将研究冰在弯曲作用下的疲劳破坏。它的知识价值在于描述，然后理解，一个知之甚少的破坏性现象。更广泛地说，该项目为南极冰架的稳定性和拥有假定海洋的冰冻卫星（如木星的木卫二和土星的土卫二）岩石圈的完整性提供了见解，并最终提供了预测模型。该项目建立在实验室的一项初步研究的基础上，该研究表明，当以每十分钟一个周期（0.1 Hz）的速率在四点载荷下进行弯曲时，盐冰和淡水冰的板在-10摄氏度下表现出不稳定的行为，在一些测试中，只有两到三个周期，而在其他测试中，经过2000个周期。虽然材料的疲劳寿命通常是可变的，但我们注意到的变异性的幅度似乎异常大。更令人惊讶的是，经过多次循环的冰的弯曲强度实际上增加了两倍之多。这种循环强化与南极海冰弯曲梁的原位研究文献中报道的疲劳弱化相反。我们假设，现场和实验室行为之间的差异可能反映了热力学历史对疲劳寿命的作用，特别是在自然环境中产生的应力诱导微裂纹。该项目的目标是通过在试样中引入不同种群的微裂纹，然后探索它们的作用，随着时间的推移，对可能的退火/钝化效应进行认知，以系统的方式验证这一假设。变量包括微裂纹密度、盐度（0-7 ppt）、温度（-25 -3摄氏度）、弯曲频率（0.01至1.0 Hz）、应力（0.1至1 MPa）以及开裂和弯曲之间的保持时间（1至48小时）。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Freeze Bond Failure Under Tensile Stress due to Flexural Loading

由于弯曲载荷导致的拉伸应力下的冻结粘合失效

• 发表时间: 2021
• 期刊: Proceedings of the 26th International Conference on Port and Ocean Engineering under Arctic Conditions
• 作者: Andrii Murdza, Arttu Polojärvi

A flexible and springy form of ice

• DOI: 10.1126/science.abj4441
• 发表时间: 2021-07
• 期刊: Science
• 影响因子: 56.9
• 作者: E. Schulson

Rapid Healing of Thermal Cracks in Ice

• DOI: 10.1029/2022gl099771
• 发表时间: 2022-08
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: A. Murdza;E. Schulson;C. Renshaw;Arttu Polojärvi

Ice fracturing

冰压裂

• DOI: 10.1063/pt.3.5270
• 发表时间: 2023
• 期刊: Physics Today
• 影响因子: 3.5
• 作者: Schulson, Erland M.

Behavior Under Cyclic Loading of Freshwater Ice and Sea Ice With Thermal Microcracks

• DOI: 10.1029/2023gl102889
• 发表时间: 2023-05
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: A. Murdza;E. Schulson;C. Renshaw