Microstructural burns on chrome-plated, high-strength steel are a serious risk to structural integrity and adversely affect safety, maintenance costs, and asset availability. These burns are insidious as they are difficult to detect without expensive processing and inspection methods. Ongoing research by our team (SBIR AF172-001; contract FA8222-19-C-011) shows that metallurgical burns caused by abusive grinding in 300M steel (a common alloy for aircraft landing gear) can reduce fatigue capability beyond a factor of five. Under our recently-completed AFWERX Phase 1 program, we verified that eddy current (EC) testing was able to identify burn locations without having to remove chrome plating or employ more specialized techniques such as Barkhausen noise. The latter is difficult to interpret and requires complicated, expensive equipment not available to most inspectors. On the other hand, EC is widely available at USAF maintenance depots, and inspectors are experienced with EC systems. Preliminary results are very promising but merit further study. This proposed effort focuses on more rigorous extraction and interpretation of EC scan data and the development of mitigation schemes for variations in magnetic permeability. A primary goal of this proposed work is to establish the common ground between fatigue damage thresholds for grinding burns and EC detection thresholds. Successful development and integration of this technology stands to greatly increase reliability of newly manufactured and overhauled components. Many customers are poised to benefit tremendously from this technology include defense aviation, commercial aviation, and power generation. Risks to success are greatly reduced by the fact that our team, APES and Southwest Research Institute, have already developed reliable methods for generating grinding burns and characterizing damage caused by these burns using destructive methods. The proposed program evolves this work to characterize the burns using EC technology through the chrome plating, the presence of which currently hinders reliable and timely detection.
