• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.342-349
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• 2010

This paper is a foundation work in developing a software for generating infrared images from a scene with various objects. The spectral radiance received by a remote sensor is consisted of the self-emitted, reflected and scattered components. In general, the self-emitted component is the most important part for generating Infrared signatures from the object. In this paper, the infrared image generation considering various surface temperature and optical surface property of a flat plate is demonstrated in MWIR($3{\sim}5{\mu}m$) and LWIR($8{\sim}12{\mu}m$) regions for different spatial resolutions of the images. Resulting spectral radiance values in the MWIR($3{\sim}5{\mu}m$) and LWIR($8{\sim}12{\mu}m$) regions arrived at the infrared sensor are compared numerically and graphically by recognizing that they are strongly dependent on the surface conditions such as the surface temperature and the surface emissivity. And these infrared images are also shown to be strongly dependent on the resolutions of the infrared imaging devices as well. This study reveals that the surface conditions are more dependent on the radiance level from the surface while the resolution of the imaging device is more responsible for identifying the shape of object.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.9
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• pp.953-958
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• 2014

The use of functionally graded materials (FGMs) may enhance thermal conductivity without reducing the desired strength in many applications such as injection molds embedding conformal cooling channels and cutting tools with heat sinks (or cooling devices). As a fundamental study for cutting tools having FGM heat sinks between M2 tool steel and Cu, six FGM specimens (M2 and Cu powders were premixed such that the relative compositions of M2 and Cu were 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 wt%) were fabricated by powder metallurgy in this study. The cross sections of these specimens were observed by optical microscopy, and then the material properties (such as thermal conductivity, specific heat, and coefficient of thermal expansion) related to heat transfer were measured and analyzed.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.43-50
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• 2017

Thermal flowfield of a micro turbojet engine was computationally investigated for exhaust nozzles with different aspect ratio and curvature. Special attention was paid to maximum and average temperature of the nozzle surface and the exhaust nozzle plume. The IR signatures of the micro turbojet engine nozzle were then calculated through the narrow-band model based on thermal flowfield data obtained through CFD analysis. Finally, in order to check the similarity of thermal flowfields and IR signature of the sub-scale micro turbojet engine model and the full-scale UCAV propulsion system, several non-dimensional parameters associated with temperature and optical property of plume were introduced. It was shown that, in spite of some differences in actual values of non-dimensional parameters, the scaling characteristics on spectral feature of IR signature and effects of aspect ratio and curvature of nozzle configuration remain similar in sub-scale and full-scale cases.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.1
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• pp.1-12
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• 1991

This study has been performed to find out the effect of austenitizing temperature, austempering temperature and its holding time, and tempering cycle on the mechanical properties such as impact resistance, hardness etc. of AISI $M_2$ Mo series high speed tool steel austempered or tempered after austempering treatment. The results obtained from the experiment are as follows ; (1) Optical micrograph has revealed that the transformation rate of bainite is delayed as the austenitizing temperature increases and that bainite is most apparently transformed at an austempering temperature of $290^{\circ}C$. (2) The amount of retained austenite during austempering has been analysed to be increased by the X-ray diffraction technique as the transformation product of bainite is increased. It has also been shown that the longer the holding time of austempering, the more the transformation quantity of bainite is formed, exhibiting, however, that the rate of bainitic transformation is considerably retarded after a certain period of holding time elapses. (3) Hardness measurement has shown that hardness values obtained after austempering increase with decreasing the amount of retained austenite. (4) The austempering and then tempering cycle has been formed to give hardness values which are more greatly improved as austenitizing temperature is increased. (5) The mechanical property of the specimen primary-tempered for 1 hour at $550^{\circ}C$ after austempering for 2 hours at $290^{\circ}C$ from the austenitizing temperature range of $1180^{\circ}C$ to $1210^{\circ}C$ have been estimated to be good values.

• Composites Research
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• v.31 no.4
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• pp.122-127
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• 2018

Sandwich composites of carbon fiber reinforced plastic(CFRP) and polymer foam will be used to automobile and aerospace industry according to increasing importance of light weight. In this study, mechanical and heat resistance properties of sandwich composites were compared with type of polymer foam (polyethylene terephthalate(PET), polyvinylchloride(PVC), epoxy and polyurethane). All types of polymer foams were degraded to 30, 60, 120, 180 minutes in $180^{\circ}C$. After heat degradation, the polymer foams were observed using optical microscope and compressive test was performed using universal testing machine(UTM). Epoxy foam had the highest compressive property to 2.6 MPa and after thermal degradation, the mechanical property and structure of foam were less changed than others. Epoxy foam had better mechanical properties than other polymer foams under high temperature. Because the epoxy foam was post cured under high temperature. As the results, Epoxy foam was optimal materials to apply to structures that thermal energy was loaded constantly.

• Composites Research
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• v.16 no.6
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• pp.41-47
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• 2003

Composites are widely used for aircraft, satellite and other structures due to its good mechanical and thermal characteristics such as low coefficient of thermal expansion(CTE), heat-resistance, high specific stiffness and specific strength. In order to use composites under condition of high temperature, however, material properties of composites at high temperatures must be measured and verified. In this paper, material properties of T700/Epoxy were measured through tension tests of composite specimens with an embedded FBG sensor in the thermal chamber at the temperatures of RT, $100^{\circ}$, $200^{\circ}$, $300^{\circ}$, $300^{\circ}$. Through the pre-test of an embedded optical fiber, we confirmed the embedding effects of an optical fiber on material properties of the composites. Two kinds of specimens of which stacking sequences are [0/｛0｝/0]$_{T}$. and [$90_2$/｛0｝/$90_2$]. were fabricated. From the experimental results, material property changes of composites were successfully shown according to temperatures and we confirmed that fiber Bragg grating sensor is very appropriate to strain measurement of composites under high temperature.

• Journal of Korea Foundry Society
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• v.11 no.4
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• pp.331-337
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• 1991

Various test specimens were prepared by austempering low alloyed Mo-Ni-Cu ductile iron blocks of high graphite nodule count at 270, 320 or $370^{\circ}C$ for 0.5, 1, 3 or 9hrs. Tensile test, CVN impact test and plane-strain fracture toughness test(compact tension specimen of 50mm W) were done for each heat treatment condition at room temperature. X-ray diffractometer and optical microscope were used to investigate the change of microstructure and relationships between microstructure and test results. The highest retained austenite volume percent at each austempering temperature was corresponded to the highest mechanical property. The highest elongation value of 17%, U.T.S. value of 1,600 MPa or $K_{IC}$ value of 90MPa${\surd}$m were reached at each optimum condition. The best heat treatment condition for fracture toughness were 3hrs' holding time combined with the austempering temperature of 270 and $320^{\circ}C$, and 1hr's of $370^{\circ}C$.

• Journal of the Korean Applied Science and Technology
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• v.32 no.2
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• pp.232-239
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• 2015

In this paper, we study the dry transfer technology utilizing PDMS (Polydimethylsiloxane) stamp of a large single-layer graphene grown on Cu-foil as catalytic metal by using Chemical Vapor Deposition (CVD). By changing the surface property of the target substrate through $UV/O_3$ treatment, we can transfer the graphene on the target substrate while minimizing mechanical damages of graphene layer. Multi-layer (1~4 layers) graphene was stacked on $SiO_2/Si$ wafer successfully by repeating thetransfer method/process and then optical transmittance and sheet resistance of graphene layers have been measured as a quality assessment.

• Transactions of Materials Processing
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• v.27 no.5
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• pp.301-313
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• 2018

In this paper, tensile test was performed on pure titanium sheet (CP Ti sheet) with HCP structure in each direction to evaluate mechanical and surface properties and analyze microstructural changes during plastic deformation. We also evaluated forming limits of Ti direction in dome-type punch stretching test using a non-contact three-dimensional optical measurement system. As a result, it was revealed the pure titanium sheet has strong anisotropic property in yield stress, stress-strain curve and anisotropy coefficient according to direction. It was revealed that twinning occurred when the pure titanium sheet was plastic deformed, and tendency depends differently on direction and deformation mode. Moreover, this seems to affect the physical properties and deformation of the material. In addition, it was revealed the pure titanium sheet had different surface roughness changes in 0 degree direction and 90 degree direction due to large difference of anisotropy, and this affects the forming limit. It was revealed the forming limit of each direction obtained through the punch stretching test gave higher value in 90 degree direction compared with forming limit in 0 degree direction.

• Journal of Korea Foundry Society
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• v.19 no.1
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• pp.38-46
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• 1999

Microstructural characteristics and strengthening behavior in Mg-5wt%Zn-0.6wtZr alloys have been investigated by a combination of optical, secondary electron and transmission electron microscopy, differential thermal analysis, and hardness and tensile, creep property measurements. The result have been compared with those of Mg-5wt%Zn alloys. The as-squeeze cast microstructure consisted of dendrite ${\alpha}-Mg$, interdendrite or intergranular $Mg_7Zn_3$ and fine dispersoids of $ZnZr_2$. The size of secondary solidification phases in Mg-5wt%Zn-0.6wtZr alloys was significantly smaller than that of the Mg-5wt%Zn alloys due to the existence of fine dispersoid of $ZnZr_2$ which also effected the refinement of grain size. TEM study showed that the main cause of age hardening is formation of fine rodlike ${\beta}_1\;'$ precipitates as well as fine $ZnZr_2$ dispersoids. Due to the observed microstructural characteristics mechanical propeties of Mg-5wt%Zn-0.6wtZr alloys was found to be superior to those of Mg-5wt%Zn alloys.