• 한국생산제조학회지
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• 제25권6호
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• pp.401-409
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• 2016

The formation of micro-burrs in micro-milling processes causes several problems related to productivity and surface integrity. It should be minimized and suppressed by effective monitoring of the cutting conditions. This paper presents the correlation between the micro-burr length and cutting signals in the micro-milling process of an Al alloy (Al6061-T6). The acoustic emission (AE) signals and cutting force signals are acquired during the experiments. The characteristics of the cutting signals are obtained by analyzing the AE root mean square value and resultant cutting force. In addition, the micro-burr length is measured according to the cutting conditions by analyzing a scanning electron microscopy image of the machined surface. The results of this study can be used to enhance the surface quality of micro parts.

• 비파괴검사학회지
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• 제32권3호
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• pp.269-275
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• 2012

Carbon-fiber reinforced plastic(CFRP) laminates made of nano-particle-coated carbon fibers and damaged by a simulated lightning strike were tested under compression-after-impact(CAI) mode, during which the damage progress due to compressive loading has been monitored by acoustic emission(AE). The impact damage was induced not by mechanical loading but by a simulated lightning strike. Conductive nano-particles were coated directly on the fibers, from which CFRP coupons were made. The coupon were subjected to the strikes with a high voltage/current impulse of 10~40 kA within a few ${\mu}s$. The effects of nano-particle coating and the degree of damage induced by the simulated lightning strikes on AE activities were examined, and the relationship between the compressive residual strength and AE behavior has been evaluated in terms of AE event counts and the onset of AE activity with the compressive loading. The degree of impact damage was also measured in terms of damage area by using ultrasonic C-scan images. The assessment during the CAI tests of damaged CFRP showed that AE monitoring appeared to be useful to differentiate the degree of damage hence the mechanical integrity of composite structures damaged by lightning strikes.

• 비파괴검사학회지
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• 제31권6호
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• pp.609-615
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• 2011

Excitation and propagation of electromagnetic field of a cylindrical coil above an arbitrary number of conductive plates for pulsed eddy current testing(PECT) are very complex problems due to their complicated physical properties. In this paper, analytical modeling of PECT is established by Fourier series based on truncated region eigenfunction expansion(TREE) method for a single air-cored coil above stratified conductive structures(SCS) to investigate their integrity. From the presented expression of PECT, the coil impedance due to SCS is calculated based on analytical approach using the generalized reflection coefficient in series form. Then the multilayered structures manufactured by non-ferromagnetic (STS301L) and ferromagnetic materials (SS400) are investigated by the developed PECT model. Good prediction of analytical model of PECT not only contributes to the development of an efficient solver but also can be applied to optimize the conditions of experimental setup in PECT.

• 한국자동차공학회논문집
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• 제15권4호
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• pp.33-40
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• 2007

Crashworthiness design is of special interest in automotive industry and in the transportation safety field to ensure the vehicle structural integrity and more importantly the occupant safety in the event of the crash. Front side assembly is one of the most important energy absorbing components in relating to the crashworthiness design of vehicle. The structure and shape of the front side assemblies are different depending on auto-makers and size of vehicles. Thus, it is not easy to grab an insight on designer's intention when you glance at a new front side member without experiences. In this paper, we have performed the explicit nonlinear dynamic finite element analysis on the front side assembly of passenger cars to identify the mechanical roles of major parts in relation to collapse modes from the viewpoint of reverse engineering. To do this, we have performed crash FE analysis for the two different assemblies of small car and heavy passenger car and have compared dynamic behaviors of the two.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.285-286
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• 2008

In practical applications of HTS tapes for electric devices such as coils and power cables, the jointing of HTS tapes is needed. In magnet applications superconducting joints are needed to achieve very low resistance at the joint, but for power device applications, a slightly higher joint resistance may be acceptable. In this study, an economical joint with good mechanical and electrical integrity could be achieved for Bi-2223 tapes which can be applicable to electric power applications. A lap joint method has been used. The joint resistance and strength of the jointed Bi2223 tapes have been evaluated. Electro-mechanical properties of the joint sample under tension have been examined and compared with the case of the single tapes.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.82-82
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• 2007

The chemical mechanical polishing (CMP) process has been widely used to obtain global planarization of multilevel interconnection process for ultra large scale. integrated circuit applications. Especially, the application of copper CMP has become an integral part of several semiconductor device and materials manufacturers. However, the low-k materials at 65nm and below device structures because of fragile property, requires low down-pressure mechanical polishing for maintaining the structural integrity of under layer during their fabrication. In this paper, we studied electrochemical mechanical polishing (ECMP) as a new planarization technology that uses electrolyte chemistry instead of abrasive slurry for copper CMP process. The current-voltage (I-V) curves were employed we investigated that how this chemical affect the process of voltage induced material removal in ECMP of Copper. This work was supported by grant No. (R01-2006-000-11275-0) from the Basic Research Program of the Korea Science.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1846-1857
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• 2021

Ultrasonic nondestructive testing is important for monitoring the structural integrity of dissimilar metal welds (DMWs) in pressure vessels and piping in nuclear power plants. However, there is a low probability of crack detection via inspection of DMWs using ultrasonic waves because the grain structures (grain orientations) of the weld area cause distortion and splitting of ultrasonic beams propagating in anisotropic media. To overcome this issue, the grain orientation should be known, and a precise ultrasonic wave simulation technique in anisotropic media is required to model the distortion and splitting of the waves accurately. In this study, a method for nondestructive prediction of the DMW grain orientations is presented for accurate simulation of ultrasonic wave propagation behavior in the weld area. The ultrasonic wave propagation behavior in anisotropic media is simulated via finite-element analysis when ultrasonic waves propagate in a transversely isotropic material. In addition, a methodology to predict the DMW grain orientation is proposed that employs a simulation technique for ultrasonic wave propagation behavior calculation and an optimization technique. The simulated ultrasonic wave behaviors with the grain orientations predicted via the proposed method demonstrate its usefulness. Moreover, the method can be used to determine the focal law in DMWs.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.988-1003
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• 2021

Existing elastic analysis methods cannot be adhered to in order to assess the structural integrity of a reactor vessel and internals for a beyond design basis earthquake. Elasto-plastic analysis methods are required, and the factors that affect the elasto-plastic behavior of reactor materials should be taken into account. In this study, a material behavior model was developed that considers the irradiation embrittlement effect, which affects the elasto-plastic behavior of the reactor material. This was used to perform the elasto-plastic time history analyses of the reactor vessel and its internals for beyond design basis earthquake. For this investigation, appropriate beyond design basis earthquakes and reliable finite element models were used. Based on the analysis results, consideration was given to the load reduction effect and the margin change. These were transferred to the internals due to the plastic deformation of the reactor vessel.

• Advances in materials Research
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• 제8권2호
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• pp.103-115
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• 2019

Polypropylene (PP) fibers for making fabric which is used for packing cement have a high strength and high tear resistance. Due to these excellent properties the present study investigates the effect of PP fibers on the mechanical strength of concrete. Mechanical strength parameters such as compressive strength, splitting tensile strength and flexural strength are evaluated. Structural integrity of concrete using Ultrasonic Pulse Velocity (UPV) was also studied. Concrete containing PP fibers in percentage of 0%, 0.15%, 0.25%, 0.5% and 0.75% was developed with a characteristic compressive strength of 25 MPa. Concrete cubes, cylinder and prismatic specimens were cast and tested. It was found that the UPV values recorded for all specimens were of the similar order. Test results indicated the used of PP fibers can significantly improve the flexural and splitting tensile strengths of concrete materials whereas it resulted a decreased in compressive strength. The relative increase in split tensile and flexural strength was optimum at a fiber dosage of 0.5% and a mild decreased were observed in 28 days compressive strength. The findings in this paper suggested that PP fibers deriving from these waste cement bags are a feasible fiber option for fiber-reinforced concrete productions.

• 한국기계가공학회지
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• 제20권4호
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• pp.24-30
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• 2021

In this paper, a structural stability analysis of the swash plate hydraulic piston pump installed on hydraulic supply systems in marine vessels is presented. In order to verify the integrity of the pump design, a standard structural analysis technique based on the finite element method has been applied for various operating and boundary conditions. For the maximum operational torque (223 N·m) at 5°, 10°, and 15° of the swash plate angle, the maximum deformation, equivalent stress and safety factor are evaluated. The analytical results show that under current operating conditions, the structural reliability of the design has been confirmed.