• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1531-1538
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• 2003

This paper compiles solutions of plastic $\eta$ factors and crack tip stress triaxialites for standard and nonstandard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament-to-thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental J estimation than that of the LLD, for all cases considered in the present work. Moreover, the J estimation based on the load-CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing specimen with any thickness. The effects of in-plane and out-of-plane constraint on the crack tip stress triaxiality are also quantified, so that when experimental J value is estimated according to the procedure recommended in this paper, the corresponding crack tip stress triaxiality can be estimated. Moreover, it is found that the out-of-plane constraint effect is related to the in-plane constraint effect.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.6
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• pp.557-562
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• 2009

Abrupt change of cross-section in mechanical parts is one of significant causes of structural fracture. In this paper, a hybrid method is employed to analyze the stress distribution of a discontinuous plate. The plate with an inclined crack is utilized in our experiment and the stress field in the vicinity of crack tip is calculated through isochromatic fringe order of given points. This calculation can be made handy through least-squares method integrated with complex power series representation(Laurent series) implemented on a computer program for high-speed processing. In order to accurately compare calculated results with experimental ones, both of actual and regenerated photoelastic fringe patterns are doubled and sharpened by digital image processing. The experiment results show that regenerated patterns obtained by hybrid method are quite comparable to actual patterns.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.6
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• pp.583-593
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• 2003

The effect of liquid confined in a pipe on elastic waves propagating in the pipe wall was studied theoretically and experimentally. The axisymmetric motion of the wave was modeled with the cylindrical membrane shell theory. The liquid pressure satisfying the axisymmetric wave equation was included in the governing equation as a radial load. The phase speed of the wave propagating in the axial direction was calculated, accounting for the apparent mass of the liquid. Experiments were performed in a pipe equipped with ring-shaped, piezoelectric transducers that were used for transmitting and receiving axisymmetric elastic waves in the pipe wall. The measured wave speeds were compared with the analytical ones. This work demonstrates the feasibility of using pipe waves for the determination of the density and, eventually, the flow rate of the liquid in a pipe.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.6
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• pp.559-565
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• 2003

A spectral element model-based structural damage identification method (SDIM) was derived in the previous study by using the damage-induced changes in frequency response functions. However the previous SDIM often provides poor damage identification results because the nonlinear effect of damage magnitude was not taken into account. Thus, this paper improves the previous SDIM by taking into account the nonlinear effect of damage magnitude. Accordingly an iterative solution method is used in this study to solve the nonlinear matrix equation for local damages distribution. The present SDIM is evaluated through the numerically simulated damage identification tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.8 no.1
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• pp.38-43
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• 1988

Microstructure and mechanical properties of most steels change by heat treat treatment. Such variation of stucture and properties of steel cause an impedance change on electromagnetic induction coil. The objective of this study is, by searching the relationship between the mechanical property or microstructural changes and impedance value of induction coil, to examine the applicablity of a monitoring the heat treated condition of products nondestructively.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.115-121
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• 2012

Exploration in microelectromechanical systems(MEMS) and nanotechnology requires evaluation techniques suitable for sub-micron length scale so that thermal and mechanical properties of novel materials can be investigated for optimal design of miro/nanostructures. The ultrafast optical pump-probe technique provides a contact-free and non-destructive way to characterize nanoscale thin-films, and its ultrahigh temporal resolution enables the study of heat-transport phenomena down to a sub-picosecond regime. This paper reviews the principle of optical pump-probe technique and introduces its application to the area of micro/nano-NDE.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.6
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• pp.521-526
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• 2010

Gas transmission pipelines are often inspected and monitored using the magnetic flux leakage method. An inspection vehicle known as a "pig" is launched into the pipeline and conveyed along the pipe by the pressure of natural gas. The pig contains a magnetizer, an array of sensors and a microprocessor-based data acquisition system for logging data. This paper describes magnetic flux leakage (MFL) signal processing used for detecting mechanical damages during an in-line inspection. The overall approach employs noise removal and clustering technique. The proposed method is computationally efficient and can easily be implemented. Results are presented and verified by field tests from an application of the signal processing.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1363-1371
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• 1996

This paper presents the design, fabrication, and testing of polysilicon electrostatic microactuators that resonate in the direction parallel to the silicon susbstrates. A set of six different designs has been developed using a theoretical model and design formulae developed for the mocroactuators. Microactuator prototypes are fabricated from a 2.1 $\mu{m}$-thick LPCVD polysilicon film, using a 4-mask surface-micromachining process. The prototypes are tested under a d.c. bias voltage of 45V with an a.c. drive voltage amplitude of 20 v.Measured resorant frequencies are in the ranges of 40-60 kHz, showing a good agreement to their theoretical estimates within error bounds of .$\pm$.5%. Important issues inthe design and microfabrication of the microactuators are discussed, together with potential applicaitons of the key technology involved.

• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1261-1267
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• 2003

The Steering system is the most important system for a vehicle, in terms of safety and driving feel. But in many cases, experiments to improve the steering feel using a real vehicle are very difficult in the aspects of repeatability, safety and money. Repeatability in testing steering systems is very important because the steering feel for a driver varies according to the environmental conditions. In addition to that, steering tests using vehicle are so dangerous that the driver might not concentrate on the tests. In this paper, a new steering system simulator using the front part of a steering and suspension system is described. This simulator allows cheap, safe, and repeatable testing of the steering system compared with the real vehicle test.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.11-23
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• 2011

In this study, a finite element(FE) analysis on electro-mechanical impedance response of cable-anchor connection interface under various anchor force is presented. In order to achieve the objective, the following approaches are implemented. Firstly, an interface washer coupled with piezoelectric(PZT) material is designed for monitoring cable-force loss. The interface washer is a small aluminum plate on which a PZT patch is surface-bonded. Cable-force loss could be monitored by installing the interface washer between the anchor plate and the anchorage of cable-anchor connection and examining the changes of impedance of the interface washer. Secondly, a FE model for cable-anchor connection is established to examine the effect of cable-force on impedance response of interface washer. Also, the effects of geometrical and material properties of the interface washer on impedance responses under various cable-forces are investigated. Finally, validation of the FE analysis is experimentally evaluated by a lab-scale cable-anchor connection.