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

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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.