• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.10
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• pp.876-882
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• 2018

The purpose of this research is to verify the feasibility of Plastic Ball Grid Array (PBGA), one of the most popular chip packaging types for commercial electronics, under strong random vibration occurred in satellite during launch. Experiment were performed by preparing daisy chained PCB specimen, where large size PBGA were surface mounted, and the PCB was fixed to an aluminum frame which is commonly used to install the electronics parts to satellite. Then the entire sample was fixed to vibration tester. The random vibration power spectrum density employed in the tests were composed of two steps, the acceptance level of 22.7 Grms, and qualification level of 32.1 Grms with given period of time. The test results showed no solder cracks, which provided the strong structural integrity and feasibility evidences of the PBGA packaging to aerospace electronics. Numerical analyses were also performed to calculate the solder stresses and analyze their development mechanism.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.771-777
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• 2014

Injection-compression molding was used for film insert molding of an automotive door grip using films with three-dimensional embossed patterns. A vacuum mold was fabricated for vacuum-assisted thermoforming of the film, and an injection-compression mold was developed for film insert molding. Three pressure transducers were installed inside the mold cavity to measure cavity pressures. Injection-compression molding experiments under various compression strokes and toggle speeds were performed to investigate their effects on the cavity pressure and heights of the embossed patterns. The compression stroke of 0.9mm and low toggle speed resulted in a higher degree of conservation of embossed patterns. Additionally, the processing conditions for the maximum heights of embossed patterns were almost similar to those for minimum integral value of cavity pressures. The injection-compression molding process presents the opportunity to impart a soft-touch feeling of plastic parts printed with embossed patterns.

• Transactions of the KSME C: Technology and Education
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• v.1 no.1
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• pp.13-19
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• 2013

Ftheta Lens, whose image height is proportional to its field view angle, is one of the most important parts in Laser Scanning Unit(LSU). In this paper $f{\theta}$ lens design, mold production and modification method of lens design and mold are introduced. Lens design was carried out with Zemax and Special Toric surfaces were applied for lens surfaces to minimize distortion both in main and sub scanning directions. And a high precision machine with 1nm resolution was used to fabricate lens mold cores. After injection the lens was evaluated and the difference from design was examined. This difference was compensated by modifying lens design and new lens mold cores were made according to modified lens design to obtain the quality of original design.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.51 no.2
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• pp.118-122
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• 2006

This experiment was carried out on plastic pots ($40cm{\times}25cm{\times}30cm$) filled with sand soil at greenhouse using two soybean cultivars with small seed; one was Pungsannamulkong (PSNK) recognized as a tolerant cultivar against excessive water stress and the other one was Sobaeknamulkong (SBNK) recognized as a susceptible cultivar. Seed was sown with 30 plants of 2 hills, and the amount of applied fertilizer was N; 3.0 g, P; 3.0 g, and K; 3.4 g per $m^2$ with all basal fertilizations. Plants were grown under photoperiod of natural light with day temperature of $31{\pm}5^{\circ}C$ and night temperature of $22{\pm}1^{\circ}C$. The flooding treatment was done for 3, 5, 7 and 10 days by filling pots with tap water up to 1 cm above the level of the soil surface when plants were 2 days after emerging. Nitrogen uptake by leaves of soybeans decreased significantly by the flooding after 6 days. This significant reduction of N uptake by flooding was evidently recognized from the chlorosis of leaves. The dry matter of flooded soybean seedlings significantly decreased compared to non-flooded soybean seedlings at 10 days. The dry matter of roots also showed similar result of the shoot. Shoots had more N reduction than roots under the flooding. This N reduction was more pronounce in SBNK than in PSNK. Chlorophyll content of flooded soybeans showed decreasing or non-increasing tendency, and the reduction of chlorophyll content was more in SBNK than in PSNK from the flooding stress. Nitrate content of soybean seedlings with flooding stress showed decreasing tendency in shoot and root parts. Ammonium content, however, was higher in flooding stress compared to the non-flooding. Flooding caused a remarkable change in the AA (amino acid) composition and TAA (total amino acid) concentration in the leaves of soybean seedlings.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.2
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• pp.19-26
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• 2008

This study has been carried out to investigate the dynamic characteristics of RC slabs. For this purpose, the 20-node solid element has been used to discretize the RC slabs into two parts of concrete and rebar. The material non-linearity considering elasto-visco plastic model and the smeared crack model have been adopted in the finite element formulation. The applied load can handle step load, load intensity of harmonic load, area of distributed load and frequency. The frequency of harmonic load has an significant effect on dynamic behaviour in terms of displacement. As the frequency is increased, the effect of load amplitude is more serious. Especially, if the frequency of harmonic load exceeds 30 Hz, it is noted that the displacement by harmonic load is greater than that by step load. In case of harmonic load, the damping effect shows no certain tendency with respect to frequency of load. In details, the damping is effective when the frequency of harmonic load is 2 Hz, but there is no consistent tendency according to damping ratio. The dynamic response when the frequency of harmonic load is 3 Hz shows same result for undamped case as well as for damped case with 5% damping ratio. It is also noted that we can get the largest deflection for damped case with 1% damping ratio. However, there is not any damping effect when the frequency of harmonic load is greater than 4 Hz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.1
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• pp.42-48
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• 2017

Characteristics of ground-penetrating radar(GPR) signals for detecting buried pipes are investigated numerically. Transmitting and receiving parts of a GPR system, a subsurface soil and a plastic pipe filled with a dielectric material are modeled by using the finite-difference time-domain(FDTD) method. FDTD simulations for observing aspects of GPR signals are performed as a function of the diameter of the pipe and the permittivity of the filling material in the pipe. GPR signals scattered by a dielectric filled pipe appear as a superposition of two waves, such as the specular wave from the front convex surface of the pipe and the axial wave from the rear concave surface of the pipe. We show that the amplitude, the polarity, the delay time of two waves depend on the size of the pipe and the permittivity of the filling material in the pipe.

• Design & Manufacturing
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• v.14 no.1
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• pp.42-48
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• 2020

Titanium alloy has been in the spotlight as a core material in high-tech industries that require high strength and light weight because it has excellent strength and corrosion resistance and strength is higher than that of steel. Therefore, in various industries, existing steel products are intended to be replaced with titanium alloys. Titanium alloys can cause cutting tool breakage during cutting, and heat generated during cutting does not dissipate, accumulates in tools and workpieces, resulting in large wear and tear on thin workpieces. In addition, since titanium alloy is a metal with high chemical activity, the wear of the tool becomes more severe when the cutting speed is high, so machining of titanium bolt through cutting is very disadvantageous in terms of productivity. Therefore, the production of bolts using titanium alloys is being produced through a forging process to improve productivity and product quality. In this paper, hot forging molding analysis was performed on bolts used for fastening automobile parts using Ti-6Al-4V alloy, which is the most commonly used titanium alloy.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.8
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• pp.159-165
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• 2015

In this paper, we designed and tested of the passive millimeter-wave imaging system in near range. The proposed passive millimeter-wave imaging system consists two parts. The first part is a 94 GHz band millimeter imaging sensor which is coupled to an antenna, two LNAs, and a diode detector. The second part is a control unit. The control unit is consists of the 2-axes Cartesian robot, the data acquisition (DAQ), and imaging program. The 2-axes Cartesian robot should be able to scan a 2-D image of the metalic tools, IC card and plastic objects, with a raster scanning method. The passive millimeter-wave image of $20{\times}20$ pixels is acquired within less than 60s, and is immediately displayed and stored for post processing.In order to improve the image quality, interpolation methods are applied.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.125-135
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• 2012

The FE model for shot peening often assume that shots impact vertically on the engineering parts to generate compressive residual stresses. However, the shots obliquely impact on the surface in actual peening. In this work, we propose a 3D finite element (FE) model for evaluation of residual stress under angled shot peening. Using the FE model for angled multi-impact, we examine the effects of factors such as impact angle, impact pattern and the number of shots. Plastic deformation of shot is also considered. To validate the model, we then compare the FE solution with experimental result by X-ray diffraction (XRD). The proposed model will be a base of 3D multi-impact FE model with diverse impact angles.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.917-923
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• 2014

Subminiature joining bolts are required for the electronic parts of gadgets such as mobile phones and watch phones. During the miniaturization of bolt heads, it is difficult to obtain sufficient joining force owing to the risk of shear fracture of the bolt head or severe plastic deformation on the bit region. In this study, the maximum joining torque for the bit depth was predicted using finite element analysis. A shear fracture test was conducted on a wire used in bolt forming. The results of this test were subjected to finite element analysis and a fracture criterion was obtained by comparing the experimental and analysis results. The shear fracture of the bolt head during joining was predicted based on the obtained criterion. Furthermore, the maximum joining torque was predicted for various bit depths. Fracture on the boundary between the bolt head and thread was found to occur in lower joining torque as bit depth increases.