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This paper will present a review of the use of Air coupled ultrasonics for nondestructive evaluation of wind turbine blades carried out at the CNDE, Iowa State University. Results will show the use of air coupled ultrasonics to scan thick composite sections of 40m wind turbine blades including the spar cap, the leading and trailing edges. Detection of defects such as slots, holes, fiber waviness (both in-plane and out-of-plane waviness), delaminations and dry fibers will be presented. Other features like adhesive thickness and length estimation in spar cap/shear web section and the trailing edge section will also be presented. The use of air coupled UT is not limited to just detection, but also characterization of the detected defects. Results highlighting the use of ultrasonic velocity to characterize defects will be presented. This includes defining damage index in terms of velocity, as well as development of stiffness maps to show reduction in structural stiffness based on the defect. Additionally, the challenges of NDT of wind turbine blades using conventional ultrasonics will also be presented. [ABSTRACT FROM AUTHOR]

Under the sponsorship of the National Science Foundation's Industry/University Cooperative Research Center at Iowa State University, an effort was initiated in 2015 to repackage existing research-grade software into user friendly tools for the rapid estimation of signal-to-noise ratio (S/N) for ultrasonic inspections of metals. The software combines: (1) a Python-based graphical user interface for specifying an inspection scenario and displaying results; and (2) a Fortranbased engine for computing defect signals and backscattered grain noise characteristics. The later makes use the Thompson-Gray Model for the response from an internal defect and the Independent Scatterer Model for backscattered grain noise. This paper provides an overview of the ongoing modeling effort with emphasis on recent developments. These include: treatment of angle-beam inspections, implementation of distance-amplitude corrections, changes in the generation of "invented" calibration signals, efforts to simulate ultrasonic C-scans; and experimental testing of model predictions. The simulation software can now treat both normal and oblique-incidence immersion inspections of curved metal components having equiaxed microstructures in which the grain size varies with depth. Both longitudinal and shear-wave inspections are treated. The model transducer can either be planar, spherically-focused, or bi-cylindricallyfocused. A calibration (or reference) signal is required and is used to deduce the measurement system efficiency function. This can be "invented" by the software using center frequency and bandwidth information specified by the user, or, alternatively, a measured calibration signal can be used. Defect types include flat-bottomed-hole reference reflectors, and spherical pores and inclusions. Simulation outputs include estimated defect signal amplitudes, root-mean-squared grain noise amplitudes, and S/N as functions of the depth of the defect within the metal component. At any particular depth, the user can view a simulated A-scan displaying the superimposed defect and grain-noise waveforms. The realistic grain noise signals used in the A-scans are generated from a set of measured "universal" noise signals whose strengths and spectral characteristics are altered to match predicted noise characteristics for the simulation at hand. We present simulation examples demonstrating recent developments, and discuss plans to improve simulator capabilities. [ABSTRACT FROM AUTHOR]

The determination of absolute nonlinearity parameter (β) for water using a finite-amplitude method is described here. Measurements were carried out using commercial immersion transducers, thus making this technique field adaptable. Calibration of immersion transducers is based on a simplified version of the calibration technique proposed by Dace et al. With corrections for diffraction and attenuation, the nonlinearity parameter calculated for water is in good agreement with literature, providing a validation for the methods developed. The current study is aimed at progressing towards measuring the nonlinearity parameter of immersed solids using commercially available ultrasonic equipment. This work is supported by the Industry/University Cooperative Research Center members of the Center for Nondestructive Evaluation at Iowa State University. [ABSTRACT FROM AUTHOR]