Shear Thickening: Insights from Far-From-Equilibrium Phenomena

非技术摘要非连续剪切增稠液，如玉米淀粉和水，对冲击表现出惊人而有用的反应。它们在撞击时会变成固体状，例如可以阻止撞击的物体，或支持人在流体表面上奔跑，但在撞击前后保持流体状。该项目包括研究这种冲击响应的受控实验室实验，目的是更好地了解堵塞材料的行为。这项工作的应用包括冲击保护材料的设计，以及改进的悬浮流处理。这项研究计划包括对研究生和本科生进行科学过程的培训和参与。对当地公立学校学生的宣传包括针对妇女和代表性不足的少数民族的科学和工程教育的讲座演示。技术摘要本项目的目标是了解不连续剪切增稠液的动态行为(包括冲击响应和在表面运行的能力)。最近发现，在撞击物体的前方，会形成一个暂时堵塞的物质区域，并使其传播。研究小组结合测力和地表堵塞区域的图像进行了实验，以确定应力响应是否与到达边界的堵塞锋面相关，以及如何相关。实验通过测试应力响应是否与其他干扰系统中边界或粒子的硬度成比例来研究强烈应力响应背后的物理机制。研究小组还进行了实验，以确定冲击下剪切增稠转变处的临界剪切率。这是通过不同冲击速度和流体粘度的冲击实验来检验的。通过这些实验，可以建立描述非连续剪切稠化流体动态行为的本构关系。这些实验得到了低维模型的补充，以连接和解释不连续剪切增稠流体的各种动态行为。这个低维模型需要通过碰撞实验的模型系统的测量获得的刚度和松弛时间作为输入。

Non-technical abstractDiscontinuous Shear Thickening fluids such as cornstarch and water exhibit an amazing and useful response to impact. They become solid-like in response to impact and can, for example, stop an impacting object, or support a person running on the surface of the fluid, but remain fluid-like before and after impact. This project involves controlled laboratory experiments to study this impact response and aims to develop a better understanding of how jammed materials behave. The applications of this work include the design of materials for impact protection, as well as improved suspension flow processing. This research program includes the training and participation of graduate and undergraduate students in the scientific process. Outreach to local public school students includes lecture-demonstrations focusing on science and engineering education for women and underrepresented minorities.Technical abstract The goal of this project is to understand the dynamic behavior of Discontinuous Shear Thickening fluids (including impact response and the ability to run on the surface). It has recently been found that a transiently jammed region of material can develop and propagate in front of an impacting object. The research team carries out experiments with a combination of force measurements and images of the jammed region at the surface to determine if and how the stress response correlates with the jammed fronts reaching the boundaries. The experiments investigate the physical mechanism behind the strong stress response by testing if the stress response scales with the stiffness of the boundary or particles as in other jammed systems. The research team also carries out experiments to determine the critical shear rate at the shear thickening transition under impact. This is tested with impact experiments for different impact velocities and fluid viscosities. A constitutive relation describing the dynamic behavior of Discontinuous Shear Thickening fluids can be developed from these experiments. The experiments are complimented by low-dimensional modeling to connect and explain the various dynamic behaviors of Discontinuous Shear Thickening fluids. This low-dimensional model requires as input a stiffness and relaxation times, obtained from measurements of the model system of impact experiments.