EAGER: Development of an Experimental Methodology to Probe Crack Tip Chemistry and Electrochemistry

美国的基础设施老化问题正受到越来越多的关注，这些应用中使用的金属，包括铝和钢，必须经受住苛刻的机械载荷和腐蚀性环境条件。当机械载荷在腐蚀性环境中存在时，可能会发生称为环境辅助开裂(EAC)的现象。EAC是由于机械应力和外部腐蚀环境的有害相互作用而发生的材料退化，导致应力水平低于预期的裂纹萌生和裂纹扩展快于预期。例行安全检查以检查损坏是维护成本的一个组成部分，如果部件故障和寿命预测模型通过包括EAC的影响提高准确性，则可以降低维护成本。这一早期概念探索性研究(AGERGE)奖支持开发一种实验技术，该技术可以直接探测和改变不断增长的裂纹内的环境条件，提供一个工具来生成增强寿命预测模型所需的数据和知识。环境辅助裂纹(EAC)是通过裂纹尖端附近的腐蚀和机械过程发生的。因此，对裂纹尖端条件的了解对于理解EAC的驱动机制至关重要。在广泛的材料系统和外部环境中，对裂纹环境的实验验证很少。该奖项下的工作将开发一种实验方法，用于探测和/或改变正在增长的EAC裂纹内的化学和电化学(pH和电化学势)条件，以实现直接探测裂纹尖端条件并了解在广泛的合金和整体环境条件下的EAC机制的短期和长期研究计划。为此，研究小组将重新设计腐蚀疲劳断裂力学标本，使其具有小孔(直径1毫米或更小)，用于插入能够测量pH和电化学势的微电极，或用于提取或注入用于化学分析的电解液的管子。

Ever growing attention is being given to the issue of aging infrastructure in the United States, and metals utilized in these applications, including aluminum and steel, must withstand demanding mechanical loads and corrosive environmental conditions. When mechanical loads are present with a corrosive environment, a phenomenon referred to as environment assisted cracking (EAC) can occur. EAC is material degradation that occurs because of the deleterious interaction of mechanical stresses and an external corrosive environment causing crack initiation at stress levels lower than expected and crack growth faster than expected. Routine safety inspections to check for damage are a component of maintenance cost that could be reduced if component failure and life prediction models increased accuracy by including the effects of EAC. This EArly-concept Grant for Exploratory Research (EAGER) award supports the development of an experimental technique that can directly probe and alter the environmental conditions within a growing crack, providing a tool to generate the data and knowledge necessary to enhance life prediction models.Environment Assisted Cracking (EAC) occurs via corrosion and mechanical processes localized near the crack tip. Therefore, knowledge of crack tip conditions is vital to understanding the mechanism driving EAC. Little experimental verification of the crack environment over a wide range of material systems and external environments has been done. The work under this award will develop an experimental methodology for probing and/or altering both the chemical and electrochemical (pH and electrochemical potential) conditions within a growing EAC crack to enable both short-term and long-term research initiatives that directly probe crack tip conditions and understand EAC mechanisms in a wide range of alloy and bulk environment conditions. To do this, the research team will re-design a corrosion fatigue fracture mechanics specimen to have small holes (1 mm or less in diameter) used to insert micro-electrodes capable of measuring pH and electrochemical potential or tubing to extract or inject electrolyte for chemical analysis.