• 비파괴검사학회지
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• 제37권2호
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• pp.75-83
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• 2017

In this paper, we investigate the capacity of the lock-in infrared thermography technique for the evaluation of non-uniform top layers of a silicon carbide coating with a nickel based superalloy sample. The method utilized a multilayer heat transfer model to analyze the surface temperature response. The modelling of the sample was done in ANSYS. The sample consists of three layers, namely, the metal substrate, bond coat and top coat. A sinusoidal heating at different excitation frequencies was imposed upon the top layer of the sample according to the experimental procedures. The thermal response of the excited surface was recorded, and the phase angle image was computed by Fourier transform using the image processing software, MATLAB and Thermofit Pro. The correlation between the coating thickness and phase angle was established for each excitation frequency. The most appropriate excitation frequency was found to be 0.05 Hz. The method demonstrated potential in the evaluation of coating thickness and it was successfully applied to measure the non-uniform top layers ranging from 0.05 mm to 1 mm with an accuracy of 0.000002 mm to 0.045 mm.

• 한국조명전기설비학회지:조명전기설비
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• 제9권6호
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• pp.83-90
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• 1995

본 논문에서는 자기체 현수애자 내부의 미세한 결함에 의한 관통사고 원인과 예방책을 제시하고자 PD(Partial Discharge)실험에 사용된 자기체 현수애자의 전계강도를 분석하였고, 상용주파 유중파괴 시험과 급준파 전압시험을 비교, 시험하였다. 이중 시료는 SEM(Scanning Electron Microscope)을 사용해서 단면촬영과 소재의 특성을 분석하였으며, 이종 물질간의 열팽창계수 차이로 인한 사고 진전 가능성이 큰 자기부와 금구류의 접착제로 사용하고 있는 포틀랜드 시멘트에 대하여 오토클래브 팽창도를 시험하였고, 사고 예방을 위한 내부결함 평가방법을 제시하였다.

• Advances in aircraft and spacecraft science
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• 제1권1호
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• pp.1-14
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• 2014

Physico-chemical changes of the plasma modified titanium alloy [Ti-6Al-4V] surface were studied with respect to their crystallographic changes by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM).The plasma-treatment of surface was carried out to enhance adhesion of high performance nano reinforced epoxy adhesive, a phenomenon that was manifested in subsequent experimental results. The enhancement of adhesion as a consequence of improved spreading and wetting on metal surface was studied by contact angle (sessile drop method) and surface energy determination, which shows a distinct increase in polar component of surface energy. The synergism in bond strength was established by analyzing the lap-shear strength of titanium laminate. The extent of enhancement in thermal stability of the dispersed nanosilica particles reinforced epoxy adhesive was studied by Thermo Gravimetric Analysis (TGA), which shows an increase in onset of degradation and high amount of residuals at the high temperature range under study. The fractured surfaces of the joint were examined by Scanning electron microscope (SEM).

• 한국해양공학회지
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• 제22권1호
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• pp.53-57
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• 2008

Friction welding was performed to investigate mechanical properties for Ni-base superalloy with 15 mm diameter solid bar. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bond of area and heat affected zone. And then, the nondestructive technique to evaluate the weld quality was carried out by acoustic emission(AE) and ultrasonic attenuation coefficient. The tensile strength of the friction welded joint was shown up to 90 % of the Alloy718 base metal under the condition of the heating time over 5 sec. The optimal welding conditions were n=2,000 rpm, $P_1=200$ MPa, $P_2=200$ MPa, $t_1=8$ sec and $t_2=5$ sec when the total upset length was 4.4 mm.

• 한국정밀공학회지
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• 제26권11호
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• pp.138-145
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• 2009

A suspended membrane micro fluidic heat flux sensor that is able to measure the heat flow rate was designed and fabricated by a complementary-metal-oxide-semiconductor-compatible process. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, low pass filter, and lock-in amp has enabled the resolution of 50 nW power and provides the sensitivity of $11.4\;mV/{\mu}W$. The heater modulation method was used to eliminate low frequency noises from sensor output. It is measured with various heat flux fluid of DI-water to test as micro fluidic application. In order to estimate the heat generation of samples from the output measurement of a micro fluidic heat-flux sensor, a methodology for modeling and simulating electro-thermal behavior in the micro fluidic heat-flux sensor with integrated electronic circuit is presented and validated. The electro-thermal model was constructed by using system dynamics, particularly the bond graph. The electro-thermal system model in which the thermal and the electrical domain are coupled expresses the heat generation of samples converts thermal input to electrical output. The proposed electro-thermal system model shows good agreement with measured output voltage response in transient state and steady-state.

• 열처리공학회지
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• 제16권1호
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• pp.2-9
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• 2003

The aluminum alloy which is light and has excellent thermal conductivity and iron base alloy that is remarkable heat-resistece and wear resistence properties were bonded together. The bond was created between a stationary and a rotating member by using the frictional heat generated between them while subjected to high normal forces on the interface of Al alloy and iron base alloy. The microstructure of the bonded interface of friction welding and the strength in the bonded interface formed under various bonding conditions were examined through TEM, SEM with EDX and triple bending test. In interface of bonding materials formed after various heat treatment, bonding strength was substantially different, resulting from formation of intermetallic compound or softening during annealing.

• Journal of Welding and Joining
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• 제29권1호
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• pp.52-58
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• 2011

In this paper, the direct bonding process between FPCB and HPCB was studied. By using an ultrasonic horn which is mounted on the ultrasonic bonding machine, it is alternatively possible to bond the gold pads attached on the FPCB and HPCB at room temperature without an adhesive like ACA or NCA. The process condition for obtaining more bonding strength than 0.6 Kgf, which is commercially required, was carried out as 40 kHz of frequency, 0.6 MPa of bonding pressure and 2 second of bonding time. The peel off test was performed for evaluating bonding strength which results in more than 0.8 Kgf.

• Journal of Welding and Joining
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• 제32권5호
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• pp.72-79
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• 2014

Shaped charge(SC) ammunition is a weapon that penetrates directly the target by made jet from metal liner on impacting at a target. In SC, the liner occupies significantly important role causing an explosion and penetration of the target. The Al-Ni composite coating was deposited on copper liner in a solid state via kinetic spraying to improve the explosive force. The mechanical properties, reactivity and microstructure were investigated to confirm the possibility of kinetic sprayed Al/Ni composite coating as a reactive liner material. Reactive liner using Al/Ni composite exhibited much enhanced reactivity than pure copper liner due to Self-propagating High-temperature Synthesis (SHS) reaction with significantly improved adhesive bond strength. Especially, among the Al/Ni composite coatings, AN11 (the Al versus Ni atomic percent ratio is 1:1) showed the greatest reactivity due to its widest reaction area between deposited Al and Ni.

• 대한치과교정학회지
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• 제20권2호
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• pp.283-291
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• 1990

The purpose of this study was to measure and compare tensile and shear strength for 4 types of new direct-bonding brackets and same brackets after recycling and to evaluate the change of bracket slot width after recycling. Four types of new direct-bond brackets were bonded to recently extracted human premolar teeth and the tensile and shear strength was measured by Universal Testing Machine. The brackets were recycled by chemical process and the tensile and shear test was repeated. To evaluate the change of the bracket slot width, slot width was measured by the Topcon Universal Measuring Microscope before and after recycling. Following results were obtained: 1. There was no satistically significant difference between the tensile and shear strength of recycled brackets and those of new brackets. 2. In both new and recycled brackets, the tensile and shear strength of perforated base bracket was lower than those of photoetched, foilmesh and contou-lok mesh base brackets. (P<0.01) 3. There was no statistically significant difference in bonding strengths of control group bonded only once and two times. 4. There was no statistically significant difference in the change of the bracket slow width after recycling process. 5. Of the failure, the combination type (58%) in the tensile strength and the tooth adhesive interface (65%) in the shear strength was the most common type.

• 한국표면공학회지
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• 제41권6호
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• pp.312-324
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• 2008

In this study, the functional property as a super abrasive material was secured for CBN powder by the electroless Ni-P plating on the surface of the particle. The plating solution has been prepared to control the surface morphology by regulating surfactants and process conditions. The effects of processing parameters on the surface morphology of CBN powder was discussed. The results are summarized as follows; A stable plating tendency was achieved from 1 hour after quantitatively dropping reducing agent. It was observed that more than 50% of the weight gain was obtained by Ni-P coating on the surface of CBN super abrasive powder. The morphology of the Ni-P coating layer is consisted of botryoidal and spiky type and it could be controlled by regulating processing parameters. Superior characteristic in terms of surface morphology was found in the nonionic surfactant XL-80N. It was found that XL-80N considerably decreased surface tension of CBN powder and Ni-P alloy surface then enhance wettability as well as plating rate. Metal coated CBN powder as a raw material of resin bond wheel has been developed through this investigation.