Authors: Se Won Eun, Jong Woong Lee, Cheol Won Kong, Jae Sung Park, Young Soon Jang, Ho Sung Lee
Abstract: Edge closeout is one of the better methods for fastening composite materials to other
structures. In this paper, fastened region of Carbon/Fabric composite plate edge closeout is
mechanically tested. Finite element analysis and AE(acoustic emission) characteristics are utilized for
comparison of test and analysis. The characteristics of AE signal used in this study are hit
distributions, peak frequency of generated AE waveform and amplitude of signals. The frequency
regions for failure of composite materials are under 100 kHz and 200-300 kHz for failure initiation
and the ultimate failure occurred with frequency region of 300-400 kHz.
627
Authors: Rhys Pullin, Pete T. Theobald, Karen M. Holford, S.L. Evans
Abstract: This paper presents the findings of an investigation to determine theoretically and
empirically the wave speeds and frequency content of the two primary Lamb wave modes, the
symmetric (S0) and anti-symmetric (A0). A 2 mm thick steel plate measuring 700 mm by 700 mm
was used to perform all measurements. A broadband pulse propagated through the plate and
detected by a conical type piezoelectric receiver was used to show how the dispersive properties of
the plate influenced the detected AE signals. It was shown that the two primary Lamb wave modes
cover a very broad range of velocities, leading to a severe spreading of arrival times.
A further investigation was completed using four acoustic emission sensors to record a pencil
lead fracture, which was used as an artificial source. Reflections in the plate were shown to cause
interference in the signal that can complicate the interpretation of the arrival modes. A recorded
signal 400mm from the source was filtered into frequency bands. The arrival times of the wave
modes were determined for each frequency band and the appropriate velocities calculated allowing
a dispersion curve to be plotted experimentally. The plotted curve was shown to be a very close
approximate to the calculated curve.
53
Authors: Yong Hong, Byung Jin Kim, Dong Pyo Hong, Young Moon Kim
Abstract: Beam structures are a common form in many large structures, and therefore the real-time
condition monitoring and active control of beams will improve the reliability and safety of many
structures. However, the incipient damage, i.e. cracks, is not easy to be detected with using the
traditional methods, such as modal analysis, etc. Piezoceramic (PZT) sensors offer special
opportunities for the health monitoring of structures constructed by beams. The change of
mechanical impedance of structures along with the occurrence of damage is sensitively indicated by
the change of electro-impedance of PZT sensors. This paper presents work done on developing and
utilizing PZT sensors to detect and quantitatively assess the extent and locations of cracks occurred
in simulated structures. The PZT sensors are conducted particularly to generate the longitudinal
wave along the beam specimen, and systematic experiments conducted on statistical samples of
incrementally damaged specimens were used to fully understand the method, the cracks with
different length and location are simulated to indicate the feasibility of the detection and assessment.
To estimate the damage conditions numerically, in this paper, we propose the evaluation method of
impedance peak frequency shift F and CC (Correlation Coefficient), Cov (Covariance). The
results of experiments verify that the impedance peak frequency shift Δ F uniformly assesses the
location of cracks, and as well CC. and Cov assesses the size of cracks efficiently. The study
presents the method that is satisfied for much higher frequencies, alternate power, and minute
damages.
2431
Authors: Chao Du, Toshiaki Natsuki, Qing Qing Ni
Abstract: Based on Laminate plate theory, a formulation, including the effects of shear deformation
and rotary inertia on the characterization of plate wave propagation, was derived. The
characteristics of plate waves propagating were investigated and the influences of frequency, plate
thickness and propagating direction were clearly known. A health monitoring system was built and
the plate waves generated by lead break source were received by acoustic emission (AE) sensors.
By the wavelet transform [1], the time-frequency domain of AE signal was derived. For a certain
frequency, the first peak of the magnitude of wavelet transform indicates the arrival times of plate
waves. The locations of lead break source and the delaminations of plate were compared with the
predictions of theory.
306
Authors: Pavel Tofel, Josef Sikula, K. Hajek, Zuzanka Trojanová, L. Bumbalek
Abstract: New non-destructive testing (NDT) method is based on the effect of the ultrasonic vibrations on the electron transport in samples with macroscopic defects as cracks or defect centers affecting electrical conductivity. On the frequency given by the subtraction of exciting frequencies new intermodulation signal appears. Its value is given by electric resistance modulation by the defects and un-homogeneities in the sample structure. In our experiment we used the ultrasonic actuator with frequency fU when the period of wave is longer than the dielectric relaxation time in analyzed sample. In this case the effects of electron bunching by ultrasonic wave are negligible. The ultrasonic wave length is much larger than the electrons mean free path and the wave period is much longer than the mean free time among the electrons collision with scattering centers and defects. Then the electron transport is described by the quasi-steady state transport equation in one-electron approximation. Because of the requirement of charge neutrality, no net AC electric current with the ultrasonic wave frequency fU can be carried by the wave. Similar situation exists for samples excited by standing ultrasonic waves. The electrical conductivity varies with time due to that the cracks geometry is changed with frequency of the ultrasonic vibration. The sample conductivity is affected mainly by the presence of cracks and defects boundaries perpendicular to the electric current density vector. In our experiment the amplitude of ultrasonic vibration is so low that no new cracks are generated and then the proposed testing method belongs to NDT.
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