Review of Progress in Quantitative Nondestructive Evaluation
During manufacture, rotating jet‐engine components are shaped into their final configurations by machining operations which may include turning, drilling and broaching. Anomalous machining conditions, such as a loss of lubricant or a damaged cutting tool, can result in an altered near‐surface microstructure, shortening the useful life of the component. In this paper we report on preliminary attempts to detect anomalous machining damage using ultrasonic surface acoustic waves (SAWs). Two pulse∕echo immersion setups are considered: normal‐incidence acoustic microscopy (Method 1); and oblique‐incidence SAW backscatter (Method 2). Each method is applied to pairs of Ti 6‐4 turned coupons, one manufactured using accepted best practices; and one purposely damaged using abusive machining conditions. Representative results are presented for each method. Method 1 is very sensitive to changes in surface topology; thus near‐surface damage that is accompanied by surface topology changes can be readily detected. For detecting microstructural damage in the absence of topology changes, Method 2 is preferable. In Method 2 the transducer tilt angle is found which results in the maximum backscattered SAW “noise.” This angle is dependent on the effective surface wave speed, which in turn is influenced by the near‐surface microstructure. For a set twenty Ti 6‐4 turned coupons, Method 2 was generally able to distinguish damaged from undamaged surfaces.
American Institute of Physics
Margetan, Frank J.; Enyart, Darrel; and Thompson, R. Bruce, "Ultrasonic detection of anomalous machining damage" (2008). Center for Nondestructive Evaluation Conference Papers, Posters and Presentations. 89.