Koung-Suk Kim

Measurement of shock waves using phase shifting pulsed holographic interferometer

A phase shifting pulsed holographic interferometer was applied to the experimental study of the propagation of laser-induced shock waves over metal plates. A double-pulsed ruby laser was used to generate the shock waves and to make a holographic interferogram of the wave fields. The phase shifting method with a dual-reference beam solved the sign ambiguity problem in holographic fringe patterns and allowed a quantitative evaluation of the phase of the interference patterns. The transient surface profile and propagation behavior of the shock wave over plates were investigated from the holographic fringe patterns.

An open-loop control scheme for minimization of residual vibrations of a flexible robot

The aim of this study is to develop a practical control scheme, called the three-step input method, whereby a flexible robot arm is moved from one position to another with a minimum of residual vibration when the arm reaches its defined endpoint. This work is concerned with defining a simple practical method to utilize step inputs to achieve optimum response. The optimum response is achieved by using a self-adjusting input command function that is obtained during real-time processing. The practicality of this control scheme is demonstrated by using an analog computer to simulate a simple flexible robot and conventional servo controller. The experiments focus on point-to-point movement. Also, this method required little computational effort through the intelligent use of conventional servo control technology and the robots vibration characteristics.

Non-Destructive Evaluation of Separation and Void Defect of a Pneumatic Tire by Speckle Shearing Interferometry

This paper describes the speckle shearing interferometry, a non-destructive optical method, for quantitative estimation of void defect and monitoring separation defect inside of a pneumatic tire. Previous shearing interferometry has not supplied quantitative result of inside defect, due to effective factors. In the study, factors related to the details of an inside defect are classified and optimized with pipeline simulator. The size and the shape of defect can be estimated accurately to find a critical point and also is closely related with shearing direction. The technique is applied for quantitative estimation of defects inside of a pneumatic tire. The actual traveling tire is monitored to reveal the cause of separation and the starting points. And also unknown void defects on tread are inspected and the size and shape of defects are estimated which has good agreement with the result of visual inspection.

Quantitative Evaluation of a Crack Inside of Pressure Pipeline by Shearography and ESPI

Electronic Speckle Pattern Interferometry (ESPI) and Shearography for quantitative analysis of a crack inside of pipelines are described. Shearography is used widely for non‐destructive inspection because of less sensitivity to environmental disturbance and simple interferometer. However, it is difficult to determine the defect size quantitatively because there are so many effect factors‐ shearing distance, shearing direction, and induced load, which depend on operator’s skill and crack information. These effective factors in Shearography are optimized for quantitative analysis and the size of crack is determined. And also, ESPI is used for determination of crack size quantitatively. In ESPI only induced load play an important role and the effective factor is independent on information of a crack. The displacement of object surface is obtained three‐dimensionally and differentiated numerically, which is same to result of Shearography so that crack size can be determined quantitatively without any informat...

Quantitative visualization of the laser induced plume behavior using quasi-heterodyne holographic interferometry

Abstract It is very important that we understand the dynamic behaviors of the laser induced plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. Many experimental studies have been performed in order to observe the plume behaviors using a visualization method. In this paper, we describe the visualization and quantification of the laser induced plumes by pulse holographic interferometry. A pulsed Nd : YAG laser was used for the generation of laser induced plume and a Q-switched Ruby laser was employed to record the weld plume. For qualitative visualization of the laser induced plume, we used the double-exposure holographic interferometry. Then, we chose the quasi-heterodyne holographic interferometry with the dual-reference-beam and phase shifting in order to visualize the plume quantitatively. The experimental results show the visible behavior of the laser induced plume according to a change in the output power of the pulsed Nd : YAG laser and the time delay of Q-switched Ruby laser. Finally, we obtained the quantitative results by using the dual-reference-beam.

Stress Distribution Measurement of Welding Part by Electronic Speckle Pattern Interferometry

The welding which is one of material joining methods plays an important role for development of the modern industry. The welding has several advantages such as high joint effect, high airtightness, and reduction of the materials being used. Nowadays, the applying or loading condition of the plates which are used for various mechanical structures becomes various. For applying the plates to the industrial field, its characteristics by tensile or compressive testing should be measured. Especially, the stress distribution at the welding part must be measured. During welding process, the thermal damage causes several types of defect including porosity, crack, insertion of impurities. A crack at the welding part results from these defects so that the mechanical structures could be destructive. In this paper, the butt welded S30400(STS304 in KS) specimen is prepared and the stress distribution at the welding part is measured by electronic speckle pattern interferometry (ESPI).

Non-destructive evaluation of semiconductor package by electronic speckle pattern interferometry

This paper proposes non-destructive ESPI technique to evaluate inside defects of semiconductor package quantitatively Inspection system consists of ESPI system, thermal loading system and adiabatic chamber The technique has high feasibility in non-destructive testing of semiconductor and gives solutions to the drawbacks in previous technique, time-consuming and the difficulty of quantitative evaluation In result, most of defects are classified in delamination, from which it is inferred to the insufficiency of adhesive strength between layers and nonhomogeneous heat spread The 90% of tested samples have a delamination defect started at the around of the chip which may be related to heat spread design

Characterizing the mechanical property of thin film using dynamic ESPI

Speckle interferometry is a powerful technique for the static and dynamic characterization of micromechanical devices. In this paper we emphasize its capabilities for the determination of mechanical properties of Al micro-machined thin films. Micro-tensile testing system and the modified ESPI (Electronic Speckle Pattern Interferometry) for large deformation analysis are developed. Stress-strain curves for aluminum membrane are obtained and the mechanical properties, elastic modulus and yield stress, are estimated. The results show that yield stress is similar to Al bulk material but the elastic modulus is 60% of Al bulk material.Speckle interferometry is a powerful technique for the static and dynamic characterization of micromechanical devices. In this paper we emphasize its capabilities for the determination of mechanical properties of Al micro-machined thin films. Micro-tensile testing system and the modified ESPI (Electronic Speckle Pattern Interferometry) for large deformation analysis are developed. Stress-strain curves for aluminum membrane are obtained and the mechanical properties, elastic modulus and yield stress, are estimated. The results show that yield stress is similar to Al bulk material but the elastic modulus is 60% of Al bulk material.

Composition and temperature dependence of optical energy gaps of TlGa 1− x Sb x S 2 single crystals

TlGa) 1 - x Sb x S 2 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) single crystals were grown using the Bridgman-Stockbarger method. The direct energy gaps of the single crystals were found to be 2.586, 2.459, 2.344, 2.228, 2.119, and1.987 eV for the composition x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively, at 20 K. The indirect energy gaps were found to be 2.479, 2.357, 2.232, 2.118, 1.983, and 1.871 eV for the composition x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively, at 20 K. The optical energy gaps decreased linearly with increasing composition x. The temperature dependence of the optical energy gaps for each of the single crystals was well fitted with the Varshni equation.

The electronic laser interferometry and laser heating method for residual stress determination

Residual stress is one of the causes which makes defects in engineering components and materials. These residual stresses can occur in many engineering structures and can sometimes lead to premature failures. There are commonly used methods by which residual stresses are currently measured. But these methods have a little damage and other problems; therefore, a new experimental technique has been devised to measure residual stress in materials with a combination of electronic laser interferometry, laser heating and finite element method. The electronic laser interferometer measures in-plane deformations while the laser heating and cooling provides for very localized stress relief. FEM is used for determining the heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heat-up and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.