• Journal of the Korean Society for Nondestructive Testing
• /
• v.32 no.1
• /
• pp.20-26
• /
• 2012

The objective of this study is to assess plastic deformation in aluminium alloy by acoustic nonlinearity of laser-generated surface waves. A line-arrayed laser beam made by high-power pulsed laser and mask slits is utilized to generate the narrowband surface wave and the frequency characteristics of laser-generated surface waves are controlled by varying the slit opening width and slit interval of mask slits. Various degrees of tensile deformation were induced by interrupting the tensile tests so as to obtain aluminum specimens with different degrees of plastic deformation. The experimental results show that the acoustic nonlinear parameter of a laser-generated surface wave increased with the level of tensile deformation and it has a good correlation with the results of micro-Vickers hardness test and electron backscatter diffraction (EBSD) test. Consequently, acoustic nonlinearity of laser-generated surface wave could be potential to characterize plastic deformation of aluminum alloy.

• Journal of the Korean Institute of Gas
• /
• v.15 no.1
• /
• pp.30-34
• /
• 2011

This paper presents a strength safety evaluation of composite pressure container for hydrogen fuel tanks with a storage capacity of 104 liter and 70MPa pressure. The carbon fiber composite container is manufactured by an aluminum liner of Al6061-T6 and composite multi-layers of hoop winding layer in circumferential direction, $12^{\circ}C$ inclined winding layer and $70^{\circ}C$winding layer in helical direction respectively. The FEM results on the strength safety of composite fuel tanks were evaluated with a criterion of design safety of US DOT-CFFC and KS B ISO 11119-2 codes. The FEM computed results indicate that the proposed design model of 104 liter composite container is safe based on two strength safety codes. But, the computed results of carbon fiber fuel tanks based on US DOT-CFFC code is safer compared with that of KS B ISO 11119-2. Thus the hydrogen gas pressure container of 70MPa may be evaluated and designed by US DOT-CFFC code for more strength safety.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.30 no.2
• /
• pp.104-109
• /
• 2010

Lap joint friction stir welding(LFSW) is an relatively new solid state joining process. A6061-T6 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength to weight ratio and good corrosion resistance. Test methods used in this paper, lock-in thermography, a phase difference between the defect area and the healthy area indicates the qualitative location and size of the defect. In this paper, the defects detected from the thermal image of mechanical properties for weld were evaluated and compared by the lock-in infrared thermography technique.

• Journal of Aerospace System Engineering
• /
• v.17 no.5
• /
• pp.19-27
• /
• 2023

In this study, we used finite element analysis to conduct a containment capability evaluation of a turbine case. When analyzing the impact behavior of structures subjected to impact loads, it is important to consider the strain rate, as it affects the increase in flow stress. Therefore, we applied three material models (Cowper-Symonds, Johnson-Cook, and Modified Johnson-Cook) for the impact analysis. To validate these material models, we performed an impact test on an aluminum 6061 plate. By comparing and analyzing the experimental and analytical results, we determined that the Modified Johnson-Cook material model exhibited the least error. As a result, we applied this material model to evaluate the containment capability of the turbine case. This evaluation involved determining the occurrence of penetration, as well as the stress and strain induced at the collision area due to the initial velocity of the blade.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.10
• /
• pp.887-894
• /
• 2016

The thermal control device using solid-liquid phase change material (PCM) is designed, manufactured, and experimented in thermal environment chamber. The n-Hexadecane is selected as a PCM and its melting point is placed within the component working temperature range. The PCM container is made of Al6061 and has the thermal spreading fins inside. To simulate the working condition for on-orbit satellite the heat pipes are used to connect the heater and radiator and the PCM thermal control device (PCMTD) is installed at the middle portion of heat pipes. The thermal buffer mass (TBM), which is same configuration and volume with PCMTD, is also manufactured to compare the thermal control performance. As a result, the PCMTD is not only more efficient than TBM in their temperature control features but both mass and power of compensation heater are reduced.

• Composites Research
• /
• v.23 no.6
• /
• pp.14-18
• /
• 2010

Among the factors that threaten spacecraft, Micrometeoroid and Orbital Space Debris(MMOD) cause damage to spacecraft and impact velocity is about 8~70km/s. Nowadays, various Whipple Shield are studied and applied to protect spacecraft. As the materials used to Shielding System, aluminum is usually used but composite is also used increasingly. So this study compared characteristics of hypervelocity impact of Aluminum and composites through finite element analysis. The Projectile was a spherical shape using Aluminum 2017-T4, and aluminum plate was using Aluminum 6061-T6, CFRP plate was using T300/5208. Initial impact velocity of projectile was 1km/s. As a result, kinematic energy of projectile decreased to about 64J and about 63J for aluminum plate and CFRP plate, respectively after impact. Although both results is almost same about the absorption of impact energy, you can think the CFRP has good ballistic characteristic, because CFRP is lighter about 1.7 times compared with density of aluminum.

• Journal of the Korean Society for Precision Engineering
• /
• v.31 no.10
• /
• pp.889-895
• /
• 2014

Machine parts and structures of a change in the displacement and strain can be evaluated safety is one of the important factors. Typically the strain gauge has been employed to measure the displacement and strain. However, this contact-type measurement method has disadvantages that are not measured under condition of specific object shape, surface roughness and temperature. In particularly, 3 point bending and 4 point bending test not use strain gauge. So its test used cross head displacement and deflect meter. Digital Image Correlation measurement methods have many advantages. It is non contact-type measurement method to measure the object displacements and strain. In addition, it is possible to measure the Map of full field displacements and strain. In this paper, measured the 3 point bending deflection using the Digital Image Correlation methods. In order to secure the reliability, Digital Image Correlation method and universal test machine were compared.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.29 no.4
• /
• pp.344-350
• /
• 2009

The goal of this study is to introduce the theoretical background of acoustic nonlinearity in surface wave and to verify its characteristics by experiments. It has been known by theory that the nonlinear parameter of surface wave is proportional to the ratio of $2^{nd}$ harmonic amplitude and the power of primary component in the propagated surface wave, as like as in bulk waves. In this paper, in order to verify this characteristics we constructed a measurement system using contact angle beam transducers and measured the nonlinear parameter of surface wave in an Aluminum 6061 alloy block specimen while changing the distance of wave propagation and the input amplitude. We also considered the effect of frequency-dependent attenuation to the measurement of nonlinear parameter. Results showed good agreement with the theoretical expectation that the nonlinear parameter should be independent on the input amplitude and linearly dependent on the input amplitude and the $2^{nd}$ harmonic amplitude is linearly dependant on the propagation distance.

• Asian Pacific Journal of Cancer Prevention
• /
• v.14 no.10
• /
• pp.6061-6064
• /
• 2013

Objective: To explore the feasibility of pulmonary lobectomy combined with pulmonary arterioplasty by complete video-assisted thoracic surgery (VATS) in patients with lung cancer, and summarize its surgical methods. Materials and Methods: Twenty-one patients with lung cancer in Beijing Chest Hospital Affiliated to Capital Medical University from Feb., 2010 to Jun., 2013 were selected, males and females accounting for 15 and 6 cases, respectively. Ten underwent right upper lobectomy, 5 right lower lobectomy, 4 left upper lobectomy (in which left upper sleeve lobectomy was conducted for 2) and 2 left lower lobectomy. At the same time, local resection of pulmonary arterioplasty was performed for 12 patients, and sleeve resection of pulmonary arterioplasty for 9. Results: Twenty-one patients recovered well after surgery. Thoracic drainage tube was maintained for 3-8 days, with an average of 4.9 days, and hospital stays were 8-15 days, with an average of 11 days. There were no deaths in the perioperative period, and the complications like pulmonary embolism, bronchopleural fistula, chest infection and pulmonary atelectasis did not occur after surgery. Conclusions: Performance of pulmonary lobectomy and pulmonary arterioplasty together by complete VATS is a safe and effective surgical method, which can expand the indications of patients with lung cancer undergoing thoracoscopic pulmonary lobectomy, and make more patients profit from such minimally invasive treatment.

• Korean Journal of Environment and Ecology
• /
• v.25 no.3
• /
• pp.378-388
• /
• 2011

This study was done to classify the vegetation structure and ecological characteristics in Nakdong-jeongmaek. Therefore, we set up 34 plots($100m^2$) in 9km range. As a result of vegetation analysis, the vegetation of Seongsi valley was classified into the type of 6 communities i.e. Pinus densiflora community, Quercus variabilis community, Q. mongolica community, Q. serrata community, Betula schmidtii community, Larix leptolepis community. The average number of species and individuals were ranged from 8.5~10.5 and 27.5~75.6 respectively. Species diversity index(H') of groups were ranged from 0.6061~0.8736 per units, and it was highest and lowest in B. schmidtii and P. densiflora communities respectively. Similarity index of groups were slightly low. It was low in P. densiflora community, Q. mongolica community and L. leptolepis community, and lowest in Q. variabilis-Q. mongolica community.