Fracture initiation in FCC and BCC metals during tribology

根据目前对金属磨损的科学认识，裂纹的起裂机制与表面疲劳有关，这种疲劳发生在金属经历反复加载循环的过程中。然而，我使用微裂纹进行的初步基础实验表明，即使在第一次摩擦行程中，裂纹也会产生。此外，我观察到裂纹的演化与晶粒的取向有关：当一个晶粒中出现裂纹时，尽管两个晶粒受到相同的载荷，另一个晶粒却没有裂纹。本项目研究了一种工程FCC钢及其相应的BCC模型合金在无润滑接触下裂纹扩展的基本机制以及微裂纹与微塑性的相互作用。通过辅助模拟的千分尺实验，我将确定晶粒取向相关的裂纹形成、裂纹扩展速率和随后的加载。随着对单个微磨粒裂纹萌生的基本理解，人们可以更好地理解宏观摩擦学，即众多微磨粒的综合接触和相互作用。这种宏观尺度上的改进可以减少磨损和摩擦，从而降低更换成本、噪音和能源消耗。

According to the current scientific understanding of wear of metals, the crack initiation mechanism is linked to surface fatigue, which occurs as the metal experiences repeated loading cycles. However, my preliminary fundamental experiments using a microasperity reveal that cracks can develop even during the first friction stroke. Moreover, I observed that the crack evolution is grain orientation dependent: while cracks develop in one grain, another grain is crack free although both grains experience the same loading. This project investigates the basic mechanisms of crack growth and the interaction of micro-cracks and micro-plasticity in unlubricated contacts of an engineering FCC steel and a corresponding BCC model-alloy. Using micrometer experiments with auxiliary simulations, I will determine grain orientation dependent crack formation, the crack growth rate and subsequent loading. With the fundamental understanding of crack initiation due to a single microasperity, one can acquire a better understanding of macroscale tribology, which is the combined contact and interaction of a multitude of microasperities. This improved macroscale understanding can result in a reduction of wear and friction and, hence, in a reduction of replacement costs, noise and energy consumption.