Harold E. Kautz

Quantifying Creep Damage in a Metallic Alloy Using Acousto-Ultrasonics

Due to elevated temperatures and excessive stresses, turbine components may experience creep behavior. As a result, it is desirable to monitor and assess the current condition of such components. This study used the acousto-ultrasonics (AU) method in an effort to monitor the state of the material at various percentages of expended (i.e., used-up creep life) creep life in the nickel base alloy, Udimet 520. A stepped specimen (i.e., varying cross-sectional area) was used, which allowed for a post mortem nondestructive evaluation (NDE) analysis of the various levels of expended life. The overall objectives in this study were two-fold: First, a user-friendly, graphical interface AU system was developed, and second, the new AU system was applied as a NDE tool to assess distributed damage resulting from creep. The experimental results demonstrated that the AU method was able to detect material changes as a function of expended creep life.

3-D surface profiling using focused air-coupled ultrasound

Surface topography is an important variable in the performance of many industrial components and is normally measured with diamond-tip profilometry over a small area or using optical scattering methods for larger area measurement. This article shows quantitative surface topography profiles as obtained using only high-frequency focused air-coupled ultrasonic pulses. The method is simple and reproducible because it relies mainly on knowledge and constancy of the sound velocity through the air. The air transducer is scanned across the surface and sends pulses to the sample surface where they are reflected back from the surface along the same path as the incident wave. Time-of-flight images of the sample surface are acquired (over large depths if required) and converted to depth/surface profile images using the simple relation (d=V*t/2) between distance (d), time-of-flight (t), and the velocity of sound in air (V). The system has the ability to resolve surface depression variations as small as 25 μm, is useab...