• 한국지진공학회논문집
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• 제22권6호
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• pp.353-360
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• 2018

This paper is to investigate the micro-behavior of the double-span beams with WUF-W seismic connection under combined axial tension and moment and to propose the rational rotational capacity of it for progressive collapse-resistant analysis and design addressing the stress and strain transfer mechanism. To this end, the behavior of the double-span beams under the column missing event is first investigated using the advanced nonlinear finite element analysis. The characteristics of fracture indices of double-span beams with WUF-W connection under combined axial tension and flexural moment are addressed and then proposed the rational rotational capacity as the basic datum for the progressive collapse-resistant design and analysis. The distribution of fracture indices related to stress and strain for the double-span beams is investigated based on a material and geometric nonlinear finite element analysis. Furthermore, the micro-behavior for earthquake and progressive collapse is explicitly different.

• Structural Engineering and Mechanics
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• 제65권4호
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• 한국학교보건학회지
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• 제29권2호
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• pp.63-70
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• 2016

Purpose: The purpose of this study was to find the factors influencing adolescents' adult media engagement. The study is based on Agnew's General Strain Theory (GST) and a micro-systemic perspective. Methods: The study examined 479 middle school freshmen who participated in the fourth wave of the Korean Children & Youth Panel Survey (KCYPS) conducted by National Youth Policy Institute. Data were analyzed through descriptive statistics, factor analysis, and reliability analysis using SPSS 22.0 Ver. Also, hypothesis testing was performed via covariance-based structure equation modeling (CB-SEM) using Amos 21.0 Ver. Results: Strain factors had positive effects on adolescent depression, and depression had a positive effect on adult media engagement. Also, cell-phone dependency had a positive mediation effect between depression and adult media engagement. Conclusion: The study's result identified the factors affecting adult media engagement. Therefore, we suggest intervention programs considering adolescents' strains, depression and cell-phone dependency to improve their health.

• 대한기계학회논문집
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• 제9권1호
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• pp.1-9
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• 1985

본 연구에서는 이러한 점에도 역점을 두어서 초기 피로균열의 발생.거동을 관 찰하기 쉬운 연강을 선택하여 편진인장반복하중을 작용시켜, 연강 평골재의 표면상에 발생.성장하는 미소표면균열의 거동을 전자현미경과 광학현미경을 병용하여 표면과 파 단면을 입체적으로 조사하여, 피로균열의 초기발생상태를 조사하고, 그 성장율을 조사 하여 파괴역학적으로 해석하여 그 특성을 조사한다.

• 대한기계학회논문집B
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• 제33권7호
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• pp.535-540
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• 2009

Experiments are conducted to elucidate effects of counterflow burner diameter on flame extinction behaviors in C-curve. Present experimental results with burner diameters of 18, 26, and 50 mm in normal-gravity are compared with the numerical result of Oppdif code as well as the previous experimental results in micro-gravity. The turning point migrates to a higher global strain rate as burner diameter decreases. It is shown that the C-curve with the burner diameter of 50mm is best-fitted to the numerical result of Oppdif code and the previous micro-gravity results also excurse to the numerical result. This suggests that the precise C-curve can be obtained only with an appreciably large burner. The main reason why these differences appear is shown to be attributed to the transition of shrinking flame disk to flame hole due to strong effects of radial conduction heat loss, which is the typical extinction characteristics of low strain rate flames with a finite burner diameter in a counterflow diffusion flame.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문 발표회
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• pp.27-31
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• 2003

To maintain serviceability of concrete structure more than proper it is necessary not only predict service life through periodical monitor but also need monitoring system to recognize optimal time and method for repair. Recently, CPGFRP, replacing some GFRP with CF, is developed and used for monitoring concrete fraction. But dramatic resistance change of CPGFRP is showed below 0.5% strain and it is not small strain in terms of monitoring micro crack in concrete. In other word, monitoring with CF is not suitable in low stress hut hight stress. In this study, we accessed applicable possibility and reliability of CPGFRP composite as monitoring sense that is proved very sensitive to stress through domestic and oversea previous study. CPGFRP composite plays a role in specimen like steel and increases flexural strength. CPGFRP composite shows resistance increasement in micro crack. In particular, CPUFRP is more sensitive than strangage in low stress. Resistance change ratio curve is very similar to strain curve so sensitivity and reliability is very excellent to monitor concrete fracture.

• 한국정밀공학회지
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• 제18권5호
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• pp.90-97
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• 2001

An electronic speckle pattern interferometry (ESPI) system for measuring tensile properties under micro-tensile testing has been developed. The system consists of an optical system and an image processing system. In the optical system, optical components for measurement of in-plane deformation are arranged on the path of He-Ne laser. In the image processing system, the window-based program for acquiring speckle pattern interferometric image was developed and deformation in a small specimen is continuously evaluated during the test. Using this system, tensile strain of copper foil was measured during tensile testing. Tensile specimen had the thickness and width of 22 and 500 ${\mu}{\textrm}{m}$, respectively. Tensile properties, including the elastic modulus, yielding strength and tensile strength, of the copper were evaluated and also plastic exponent and coefficient in the Ramberg-Osgood relationship were evaluated from the stress-strain curve.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문발표회
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• pp.27-31
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• 2003

To maintain serviceability of concrete structure more than proper it is necessary not only predict service life through periodical monitor but also need monitoring system to recognize optimal time and method for repair. Recently, CPGFRP, replacing some GFRP with CF, is developed and used for monitoring concrete fraction. But dramatic resistance change of CPGFRP is showed below 0.5％ strain and it is not small strain in terms of monitoring micro crack in concrete. In other word, monitoring with CF is not suitable in low stress but hight stress. In this study, we accessed applicable possibility and reliability of CPGFRP composite as monitoring sense that is proved very sensitive to stress through domestic and oversea previous study. CPGFRP composite plays a role in specimen like steel and increases flexural strength. CPGFRP composite shows resistance increasement in micro crack. In particular, CPGFRP is more sensitive than strangage in low stress. Resistance change ratio curve is very similar to strain curve so sensitivity and reliability is very excellent to monitor concrete fracture.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.436-449
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• 2017

In this paper, the damage and failure behavior of triaxially braided textile composites was studied using progressive failure analysis. The analysis was performed at both micro and meso-scales through iterative cycles. Stress based failure criteria were used to define the failure states at both micro- and meso-scale models. The stress-strain curve under uniaxial tensile loading was drawn based on the load-displacement curve from the progressive failure analysis and compared to those by test and computational results from reference for verification. Then, the detailed failure initiation and propagation was studied using the verified model for both tensile and compression loading cases. The failure modes of each part of the model were assessed at different stages of failure. Effect of ply stacking and number of unit cells considered were then investigated using the resulting stress-strain curves and damage patterns. Finally, the effect of matrix plasticity was examined for the compressive failure behavior of the same model using elastic, elastic - perfectly plastic and multi-linear elastic-plastic matrix properties.

• 한국안전학회지
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• 제23권5호
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• pp.30-34
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• 2008

To evaluate the mechanical properties of in-service materials, tensile properties measurement using small-scaled specimen has been carried out. Tensile testing specimens with various dimensions, including standard and sub-size specimen specified in ASTM and ISO and small-scaled specimen, were prepared. Tensile strain in small-scaled specimen was measured using micro-ESPI system set up in this study. This system was used in the specimen with the parallel length of 2 mm and in subsequently measuring the strain under tensile loading. From each type of tensile specimen, stress-strain curves were determined. The dimension effect of the tensile properties was investigated comparing the tensile results obtained from standard specimens and small-scaled specimens. It was shown that the tensile strength for the small-scaled specimen is lower by 15% than those for the standard specimen.