Concrete Micromechanics Validated with In-Situ Stress and Strain Measurements

本研究将研究混凝土在微米到厘米长度尺度上的力学响应，以验证用于预测其行为和破坏的理论和计算模型。混凝土是世界上最常见的建筑材料，广泛的研究工作正在进行中，以提高其弹性和环境友好性。混凝土由颗粒和夹杂物组成，它们具有不同的性质和尺寸，从纳米到厘米不等，在机械加载过程中相互作用。这些相互作用的结果被微观力学领域的理论和计算模型所捕获。虽然基于微观力学的理论准确地预测了混凝土的许多力学特性，但这些理论背后的假设尚未在小长度尺度上得到验证。此外，确定精确的混凝土计算建模所需的分辨率仍然具有挑战性。该研究项目将采用新的、先进的x射线测量来评估从微米到厘米的混凝土的响应，以测试微观力学理论的假设，并为研究团体提供验证模型的高保真数据。本研究的结果有望改善混凝土力学响应的预测，并促进对其特性的理解。研究结果还将用于研究生工程课程的高级概念教学，并为对STEM职业感兴趣的代表性不足的高中生提供研究机会。本研究包括在实验室和同步加速器设施中对混凝土试件在机械加载过程中的应力和应变进行微米至厘米长度尺度的原位x射线断层扫描和衍射测量。这些测量将用于验证和扩展微观力学理论，如Eshelby的包含理论和Mori-Tanaka的理论，以及它们在长度尺度上的潜在假设。例如，测量结果将用于检查作为推导均质材料性能的中间变量的平均夹杂应力是否准确，以及单个夹杂应力偏离平均值的程度。测量结果还将用于检查具有不同微观结构精细化水平的中尺度模型的准确性，解决与此类模型中必须捕获的长度尺度相关的开放问题。该项目的成果将是对混凝土跨长度尺度的应力和应变变化的基本理解，中尺度建模的指导，以及用于整个研究界使用的理论和模型的校准和验证的高保真数据集。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。

This research will examine the mechanical response of concrete at micrometer to centimeter length scales to validate theories and computational models used to predict its behavior and failure. Concrete is the world’s most-common building material and extensive research efforts are on-going to improve its resiliency and environmental friendliness. Concrete is composed of particles and inclusions with varying properties and dimensions ranging from nanometers to centimeters that interact during mechanical loading. The results of these interactions are captured by theories and computational models in the field of micromechanics. While micromechanics-based theories accurately predict many mechanical properties of concrete, the assumptions underlying these theories have not been validated at small length scales. Furthermore, determining the resolution needed for accurate computational modeling of concrete is still challenging. This research project will employ new, advanced x-ray measurements to assess the response of concrete from micrometers to centimeters, to test the hypotheses underlying micromechanics theories, and to provide the research community with high-fidelity data for validating models. The results of this research are expected to improve predictions of concrete’s mechanical response and promote understanding of its properties. The research results will also be used to teach advanced concepts in a graduate engineering course and to provide research opportunities to under-represented high school students interested in STEM careers.This research consists of making in-situ x-ray tomography and diffraction measurements of stress and strain at micron to centimeter length scales during mechanical loading of concrete specimens at laboratory and synchrotron facilities. These measurements will be used to validate and extend micromechanics theories, such as Eshelby’s inclusion and Mori-Tanaka’s theories, and their underlying assumptions across length scales. For instance, the measurements will be used to examine whether average inclusion stresses used as intermediate variables in deriving homogenized material properties are accurate and to what degree individual inclusion stresses deviate from the average. The measurements will also be used to examine the accuracy of mesoscale modeling with varying levels of microstructural refinement, addressing open problems related to the length scales that must be captured in such models. The outcomes of the project will be a fundamental understanding of stress and strain variability across length scales in concrete, guidance for mesoscale modeling, and high-fidelity datasets for calibration and validation of theories and models used throughout the research community.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.