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

这一早期概念探索性研究奖章的研究目标是利用聚焦离子束(FIB)球磨样品结构的纳米压痕实验，在亚微米尺度测量水泥浆体的断裂韧性。模拟水泥和混凝土材料的断裂和塑性破坏通常涉及引入微裂纹的概念，这些微裂纹扩展并最终结合在一起，导致更大范围的材料破坏。这些裂缝的小范围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控制微裂纹和最终材料破坏的小尺度准脆性破坏机制。研究任务将从开发使用FIB球磨制造样品微结构的实验方法开始。微柱、切口梁和楔形劈开几何形状将作为替代方案进行试验。接下来，这些样品结构将使用纳米压痕设备进行测试，以施加载荷和测量位移。这些数据将被分析以提供强度和断裂韧性特性。最后，将收集样本数据以建立测量属性的初步统计模型，重点是测量在每个阶段内可重复但可在不同阶段区分的材料属性的能力。水泥生产产生的二氧化碳占全球总排放量的3%-5%，但如果混凝土被设计成更能抵抗准脆性破坏，这一比例可能会显著降低。混凝土的损伤和破坏通常是通过考虑水泥浆体中微裂纹的存在来模拟的，但是这些微裂纹的性质和导致微裂纹的材料行为还没有被很好地理解。如果了解微裂缝的起源，则可以了解极端加载条件或耐久性问题造成的混凝土损坏，包括碱-硅酸反应、冻融循环、钢筋腐蚀和延迟钙矾石形成导致的微裂缝。对失效行为的根本根源的新知识将使改性和新材料的合理设计成为可能，这些材料将导致更有效地利用自然资源，以及更可持续和更有弹性的结构。该项目的研究代表着朝着这一总体目标迈出的重要的第一步，并将使未来的研究能够更广泛地表征水泥和混凝土在小尺寸下的破坏行为。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.