EAGER: Submicron Fracture Toughness Measurements for Cement Paste using Focused Ion Beam (FIB) and Nanoindentation

这项早期概念探索性研究（EAGER）奖的研究目标是使用聚焦离子束（FIB）研磨样品结构的纳米压痕实验来测量亚微米长度尺度下水泥浆的断裂韧性。对水泥和混凝土材料的断裂和塑性破坏进行建模通常涉及引入微裂纹的概念，微裂纹扩展并最终合并以在更大尺度上引起材料破坏。这些裂缝的小规模和它们周围的体积给测量和建模带来了许多挑战。 需要新的实验技术来定量评估准脆性破坏机制，在小尺度上，管理微裂纹，并最终材料失效。研究任务将开始与实验方法的发展，以创建使用FIB铣削样品微结构。微柱，缺口梁，和楔形分裂的几何形状将被尝试作为替代品。接下来，这些样品结构将使用纳米压痕设备进行测试，以施加载荷并测量位移。将对这些数据进行分析，以提供强度和断裂韧性特性。最后，将收集样品数据，以建立测量特性的初步统计模型，重点是测量材料特性的能力，这些特性在每个阶段内是可重复的，但在阶段之间是可区分的。水泥生产产生的二氧化碳占全球总排放量的3- 5%，但如果混凝土设计得更能抵抗准脆性破坏，这一比例可能会大幅降低。混凝土的损伤和破坏通常是通过调用水泥浆体中存在的微裂纹来模拟的，但是这些微裂纹的性质以及导致微裂纹的材料行为还没有得到很好的理解。如果了解微裂纹的起源，则可以理解并防止极端荷载条件或耐久性问题（包括碱-硅反应、冻融循环、钢筋腐蚀和延迟钙矾石形成）导致的混凝土损坏。关于破坏行为的基本起源的新知识将使改性和新材料的合理设计成为可能，从而更有效地利用自然资源和更具可持续性和弹性的结构。 该项目的研究是实现这一总体目标的重要的第一步，并将使未来的研究能够更广泛地表征水泥和混凝土在小长度尺度上的破坏行为。开发的技术将适用于广泛的其他材料，包括页岩和碳酸盐等沉积岩，以及骨骼，牙齿和贝壳等生物材料。

The research objective of this Early-concept Grant for Exploratory Research (EAGER) award is to measure the fracture toughness of cement paste at submicron length scales using nanoindentation experiments with Focused Ion Beam (FIB) milled sample structures. Modeling fracture and plastic failure of cement and concrete materials often involves introducing the concept of microcracks, which propagate and eventually coalesce to cause material failure at larger scales. The small scale of these cracks and the volumes around them pose many challenges for measurements and modeling. New experimental techniques are required to quantitatively assess the quasi-brittle failure mechanisms at small scales that govern microcracking and eventually material failure. Research tasks will begin with development of experimental methods to create sample micro-structures using FIB milling. Micropillars, notched beams, and wedge-splitting geometries are will be tried as alternatives. Next, these sample structures will be tested using nanoindentation equipment to apply loads and measure displacements. This data will be analyzed to deliver strength and fracture toughness properties. Finally, sample data will be collected to build a preliminary statistical model of measured properties, focusing on the ability to measure material properties that are repeatable within each phase but distinguishable between phases. The production of cement generates between 3-5 percent of total carbon dioxide emissions worldwide, but this could be significantly reduced if concrete is engineered to be more resistant to quasi-brittle failure. Damage and failure of concrete is often modeled by invoking the existence of microcracks in cement paste, but the properties of these microcracks and the material behaviors that lead to microcracks are not well understood. Concrete damage from extreme loading conditions or from durability issues including alkali-silica reaction, freeze-thaw cycles, reinforcement corrosion, and delayed ettringite formation that lead to microcracking may be understood and prevented if the origins of microcracking are understood. New knowledge about the fundamental origins of failure behaviors of will enable rational design of modified and new materials that will lead to more efficient use of natural resources and more sustainable and resilient structures. The research in this project represents an important first step towards this overall goal, and will enable future research to more broadly characterize the failure behavior of cement and concrete at small length scales. The techniques developed will be applicable to a wide range of other materials, including sedimentary rocks such as shale and carbonates, and biological materials such as bones, teeth, and shells.