In this study, the feasibility of using a scanning laser vibrometer for detecting hidden delamination in multi-layer
composites is explored. First, Lamb waves are excited by Lead Zirconate Titanate (PZT) transducers mounted on the
surface of a composite plate, and the out-of-plane ultrasonic velocity field is measured using a 1D scanning laser
vibrometer. From the scanned time signals, wave field images are constructed and processed to study the interaction of
Lamb waves with hidden delamination. In order to highlight the defect area in the image, the performance of different
image processing tools were investigated. In particular, the Laplacian image filter was found to accentuate the visual
indications of the ultrasound-defect interaction by suppressing the presence of incident waves in the wave field images.
The performance of the proposed scheme is investigated using experimental data collected from a 1.8 mm thick multilayer
composite plate and a 10 mm thick composite wing structure.
Ultrasonic Guided Waves (UGWs) are a useful tool in structural health monitoring (SHM) applications that can benefit
from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes a
SHM method based on UGWs, discrete wavelet transform (DWT), outlier analysis and principal component analysis
(PCA) able to detect and quantify the onset and propagation of fatigue cracks in structural waveguides. The method
combines the advantages of guided wave signals processed through the DWT with the outcomes of selecting defectsensitive
features to perform a multivariate diagnosis of damage. The framework presented in this paper is applied to the
detection of fatigue cracks in a steel beam. The probing hardware consists of a PXI platform that controls the generation
and measurement of the ultrasonic signals by means of piezoelectric transducers made of Lead Zirconate Titanate.
Although the approach is demonstrated in a beam test, it is argued that the proposed method is general and applicable to
any structure that can sustain the propagation of UGWs.
A crack detection technique based on nonlinear acoustics is developed in this study. Acoustic waves at a chosen
frequency are generated using an actuating lead zirconate titanate (PZT) transducer, and they travel through the target
structure before being received by a sensing PZT wafer. Unlike an undamaged medium, a cracked medium exhibits high
acoustic nonlinearity which is manifested as harmonics in the power spectrum of the received signal. Experimental
results also indicate that the harmonic components increase non-linearly in magnitude with increasing amplitude of the
input signal. The proposed technique identifies the presence of cracks by looking at the two aforementioned features:
harmonics and their nonlinear relationship to the input amplitude. The effectiveness of the technique has been tested on
aluminum and steel specimens. The behavior of these nonlinear features as crack propagates in the steel beam has also