• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.3
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• pp.285-291
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• 2008

We have experimentally investigated the cyclic deformation in copper using ultrasonic nonlinearity. The observation and characterization of dislocation substructure have been conducted using transmission electron microscope and electron backscattered diffraction technique. The ultrasonic nonlinearity (${\beta}/{\beta}_0$) was measured by the harmonic generation technique after various fatigue cycles. The microstructural effect on the nonlinearity was discussed regarding the extent of dislocation substructures evolved from low cycle fatigue. The ultrasonic nonlinearity of copper monotonically increased with the fatigue cycles due to the evolution of dislocation cell substructures.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.268-271
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• 2004

Non-contact technique should be developed for receiving ultrasonic wave for on-line monitoring of processing defects of fiber reinforced composites, since couplant must be applied on composite materials when conventional ultrasonic testing technique was used. Restriction of conventional ultrasonic testing technique was proven by transmitting and receiving ultrasonic wave on CFRP in various direction of wave propagation with various incident angle of ultrasonic beam. Air-coupled transducer and laser interferometer were applied for non-contacting reception of ultrasonic wave in fiber reinforced composite materials. Air-coupled transducer has optimal sensitivity and frequency band of 300kHz has homogeneous characteristics on direction of wave propagation.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.3
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• pp.190-197
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• 2006

For enhancement of flaw detactability using array transducers, focusing of ultrasonic waves on a target in an inhomogeneous medium or through a complex geometry is important. But focusing can be strongly degraded by geometrical distortion of field radiated by the array transducers or by sound speed fluctuations in the propagating medium. In recent years, the time reversal technique has been proposed. Thus, in this paper, we describe the basic principal of the time reversal technique for focusing. Then, the implementation results of the time reversal technique for ultrasonic inspections using bulk waves and guided waves generated by array transducers are presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.6
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• pp.459-466
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• 2005

The scanning laser source (SLS) technique has been proposed recently as an effective way to investigate small surface-breaking defects, By monitoring the amplitude and frequency changes of the ultrasound generated as the SLS scans over a defect, the SLS technique has provided enhanced signal-to-noise performance compared to the traditional pitch-catch or pulse-echo ultrasonic methods, An extension of the SLS approach to map defects in microdevices is proposed by bringing both the generator and the receiver to the near-field scattering region of the defects, To facilitate near-field ultrasound measurement, silicon microcantilever probes are fabricated using microfabrication technique and their acoustical characteristics are investigated, Then, both the laser-generated ultrasonic source and the microcantilever probe are used to monitor near-field scattering by a surface-breaking defect.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.209-214
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• 2005

Spot welding is the most widely used in automotive and aerospace industries. The quality of weld depends upon the size of nugget between the overlapped steel plates. Recently, the thickness of the steel plates is much thinner and hence, it introduces the smaller size of nugget. Therefore, it is necessary not only to develop the criterion to evaluate the quality of weld but also to obtain the optimal welding conditions for the better performance. In this paper, the steel plates, 0.5 mm through 1.5 mm thickness, have been spot welded at different welding conditions and the nugget sizes are examined by ultrasonic technique (C-scan type). The relationships between the nugget sizes and the weldability have been investigated. The result of ultrasonic technique shows the good agreement with that of the tensile test.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.222-227
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• 2005

An efficient technique fur the calculation of guided wave dispersion curves in composite pipes is presented. The technique uses a forward-calculating variational calculus approach rather than the guess and iterate process required when using the more traditional partial wave superposition technique. The formulation of each method is outlined and compared. The forward-calculating formulation is used to develop finite element software for dispersion curve calculation. Finally, the technique is used to calculate dispersion curves for several structures, including an isotropic bar, two multi-layer composite bars, and a composite pipe.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.291-298
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• 2003

The resonant column testing is a laboratory testing method to determine the shear modulus and the material damping factor of soils. The method has been widely used for many applications and its importance has been increased. Since the establishment of the testing method in 1963, the low-technology electronic devices for testing and data acquisition have limited the measurement to the amplitude of the linear spectrum. The limitations of the testing method were also attributed to the assumption of the linear-elastic material in the theory of the resonant column testing and to the use of the wave equation for the dynamic response of the specimen. For the better theoretical formulation of the resonant column testing, this study derived the equation of motion and provided its solution. This study also proposed the improved data reduction and analysis method for the resonant column testing, based on the advanced data acquisition system and the proposed theoretical solution for the resonant column testing system. For the verification of the proposed data reduction and analysis method, the numerical simulation of the resonant column testing was performed by the finite element analysis. Also, a series of resonant column testing were peformed for Joomunjin sand, which verified the feasibility, of the proposed method and showed the limitations of the conventional data reduction and analysis method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1345-1346
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• 2011

• Nuclear industry
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• v.4 no.2 s.18
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• pp.12-19
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• 1984

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.6
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• pp.627-636
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• 2002

Identification and sizing of surface breaking vertical cracks using angle beam ultrasonic testing in practical situation quite often become very difficult tasks due to the presence of non-relevant signals caused by geometric reflectors. The present work introduces effective and systematic approaches to take care of such a difficulty by use oi angle beam ultrasonic testing models that can predict the expected signals from various targets very accurately. Specifically, the model-based TIFD (Technique for Identification of Flaw signals using Deconvolution) is Proposed for the identification of the crack tip signals from the non-relevant geometric reflection signals. In addition, the model-based Size-Amplitude Curve is introduced for the reliable sizing of surface breaking vertical cracks.