• 한국정밀공학회지
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• 제20권11호
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• pp.142-149
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• 2003

Domain switching effect on crack growth in ferroelectric ceramics under combined electric and mechanical loading is investigated. The shape and size of the switching zone is shown to depend strongly on the relative magnitude between the applied electric field and stress field as well as on the ratio of the coercive electric field to the yield electric field. The toughening mechanism is thought to be ferroelectric domain switching leading to the development of a process zone around the crack. Crack-tip stress intensity factor induced by domain switching for the steady state crack growth is numerically obtained.

• Steel and Composite Structures
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• 제30권2호
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• pp.149-169
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• 2019

A new form of composite column, concrete-filled round-ended steel tubes (CFRTs), has been proposed as piers or columns in bridges and high-rise building and has great potential to be used in civil engineering. Hence, the objective of this paper presents an experimental and numerical investigation on the flexural behavior of CFRTs through combined experimental results and ABAQUS standard solver. The failure mode was discussed in detail and the specimens all behaved in a very ductile manner. The effect of different parameters, including the steel ratio and aspect ratio, on the flexural behavior of CFRTs was further investigated. Furthermore, the feasibility and accuracy of the numerical method was verified by comparing the FE and experimental results. The moment vs. curvature curves of CFRTs during the loading process were analyzed in detail. The development of the stress and strain distributions in the core concrete and steel tube was investigated based on FE models. The composite action between the core concrete and steel tube was discussed and clarified. In addition, the load transfer mechanism of CFRT under bending was introduced comprehensively. Finally, the predicted ultimate moment according to corresponding designed formula is in good agreement with the experimental results.

• Computers and Concrete
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• 제29권 5호
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• pp.323-334
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• 2022

In order to study the axial compression performance of basalt-fiber reinforced recycled concrete (BFRRC) filled circular steel tubular short columns, the axial compression performance tests of seven short column specimens were conducted to observe the mechanical whole-process and failure mode of the specimens, the load-displacement curves and the load-strain curves of the specimens were obtained, the influence of design parameters on the axial compression performance of BFRRC filled circular steel tubular short columns was analyzed, and a practical mathematical model of stiffness degradation and a feasible stress-strain curve equation for the whole process were suggested. The results show that under the axial compression, the steel tube buckled and the core BFRRC was crushed. The load-axial deformation curves of all specimens show a longer deformation flow amplitude. Compared with the recycled coarse aggregate (RCA) replacement ratio and the basalt fiber dosage, the BFRRC strength has a great influence on the peak bearing capacity of the specimen. The RCA replacement ratio and the BFRRC strength are detrimental to ductility, whereas the basalt fiber dosage is beneficial to ductility.

• 대한기계학회논문집A
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• 제35권6호
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• pp.609-617
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• 2011

최근 효율을 높이기 위한 플랜드의 환경이 고온, 고압으로 변화함에 따라 열하중과 기계하중을 동시에 반영한 균열 평가는 플랜트의 건전성을 위하여 반드시 필요하다. C(t)-적분은 고온 균열 평가에 있어서 천이 크리프 상태의 균열을 평가하는 중요한 요소이다. 열하중과 기계하중이 동시에 작용하는 환경에서의 C(t)-적분을 예측하는 것은 복잡하며 하중조건이 달라지는 경우에는 더욱더 복잡해진다. 본 논문에서는 열하중과 기계하중의 하중조건이 달라지는 여러 조건에 대한 C(t)-적분 평가식을 제시하였다.

• 한국세라믹학회지
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• 제28권1호
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• pp.20-28
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test($\tau$/$\sigma$= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio $\tau$/$\sigma$. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• 전력전자학회논문지
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• 제18권2호
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• pp.123-130
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• 2013

This paper proposes the switched trans Z-source inverter(STZSI) which combined the characteristics of the trans Z-source inverter(TZSI) and the switched inductor Z-source inverter(SLZSI). The proposed STZSI has the same performance compared with the SLZSI which is improved the voltage boost performance of the conventional typical X-shaped ZSI, and it has advantage that circuit structure of Z-impedance network is more simple. And, in order to step up the voltage boost factor under the condition of the same duty ratio, unlike the SLZSI adding the inductors and diodes, the proposed method is dune by changing the turn ratio of trans primary winding of Z-impedance network. To confirm the validity of the proposed method, PSIM simulation and a DSP(TMS320F28335) based experiment were performed using trans with turn ratio 1 and 2 under the condition of the input DC voltage VI=50V, duty ratio D=0.1 and D=0.15. As a result, under the same input/ouput condition, the inverter arm voltage stress of the proposed method is reduced to about 15%-22% as compared with typical X-shaped ZSI, and the elements in Z-impedance network of the proposed method is reduced as compared with the SLZSI.

• 한국지반공학회논문집
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• 제30권1호
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• pp.103-116
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• 2014

본 논문에서는 석션파일의 하중지지력 및 압밀 거동에 대한 수치해석 내용을 다루었다. 수치해석에서는 파일-지반 간 인터페이스 거동이 고려된 3차원 모델을 적용하여 석션파일의 길이 대 직경 비, 하중 형태(수직하중, 수평 및 조합하중)를 변화시키며 해석을 수행하고 그 결과를 토대로 수직 및 수평지지력 거동 특성을 고찰하였다. 아울러 임의의 수직하중이 작용하는 조건에 대해 응력-간극수압 연계해석을 수행하여 석션파일의 하중재하 후 압밀거동을 고찰하였다. 해석 결과 석션파일의 지지력은 석션파일과 지반간의 상호작용 모델링 여부에 따라 큰 차이가 발생하는 것으로 검토되어 인터페이스 모델링의 중요성이 부각되었으며 산정된 하중지지력 결과를 토대로 제시된 조합하중에 대한 파괴포락선을 제시하였다. 아울러 응력-간극수압 연계해석에 근거한 압밀해석 결과를 분석한 결과 석션파일은 주면마찰이 주 하중지지 구조인 관계로 수직하중 재하시 과잉간극수압 발생량 및 압밀침하량은 미미한 것으로 검토되었다.

• 한국임상수의학회지
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• 제37권5호
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• pp.235-241
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• 2020

We aimed to determine the effect of timed artificial insemination (TAI) protocols on the pregnancy rate per insemination and pregnancy loss compared with AI performed at detected estrus in dairy cows and Korean Hanwoo cattle under heat stress. In dairy cattle, 1,250 sets of data that underwent AI during heat stress (temperature-humidity index ≥ 72) were categorized according to their TAI protocols or as controls: 1) PGF_2α-36 h-estradiol benzoate (EB)-36 h-TAI (PG-EB group, n = 113); 2) GnRH-7 days-PGF_2α-56 h-GnRH-16 h-TAI (Ovsynch group, n = 455); or 3) GnRH-6 days-Ovsynch (G6G group, n = 136). The remaining cows underwent AI at detected estrus (AIDE group, n = 546). The probability of pregnancy per AI 45 days after AI was higher (P < 0.01) in the PG-EB (odds ratio [OR]: 1.68), Ovsynch (OR: 1.48), and G6G (OR: 1.79) groups than in the AIDE group. However, the prevalence of pregnancy loss between 30 and 45 days after AI did not differ among the groups. In Hanwoo cattle, 617 sets of data inseminated artificially under heat stress were categorized into AIDE (n = 281), PG-EB (n = 194), and combined Ovsynch or G6G (n = 142) groups. The probability of pregnancy per AI 45 days after AI and the prevalence of pregnancy loss between 30 and 45 days after AI did not differ among the groups. Thus, implementation of a TAI protocol (PG-EB, Ovsynch, or G6G) in dairy cows under heat stress improves the pregnancy rate per AI versus AIDE, whereas there is no beneficial effect of TAI on the pregnancy rate of Hanwoo cattle under heat stress.

• 대한조선학회논문집
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• 제49권4호
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• pp.350-358
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• 2012

This paper deals with accuracy of accumulated fatigue damage estimation using stochastic fatigue analysis method based on Rayleigh PDF. From full scale measurement data on an 8100TEU container vessel, zero-order spectral moments for wave- and vibration-induced energy spectral densities are determined on the probability level of 99%. 80 simulation cases in total are prepared according to the variation of ratio of zero-order spectral moments and center frequency of vibration ESD. By using inverse Fourier transformation and rainflow cycle counting for the combined ESD of wave and vibration, exact fatigue damages are derived. Fatigue damages in frequency domain based on Rayleigh PDF show large conservativeness compared to exact fatigue damages in times domain. The main cause of the excessive conservativeness is analyzed by two aspects: ratio of zero crossing and peak frequencies and ratio of initial zero order spectral moments and zero order spectral moments from rainflow stress range distributions. Finally, a guideline of applicability of Rayleigh PDF is proposed for wide band processes.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.270-270
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• 2016

We fabricated an organic-inorganic nano laminated encapsulation layer using molecular layer deposition (MLD) combined with atomic layer deposition (ALD). The $Al_2O_3$ inorganic layers as an effective single encapsulation layer were deposited at 80 degree C using ALD with alternating surface-saturation reactions of TMA and $H_2O$. A self-assembled organic layers (SAOLs) were fabricated at the same temperature using MLD. MLD and ALD deposition process were performed in the same reaction chamber. The prepared SAOL-$Al_2O_3$ organic-inorganic nano laminate films exhibited good mechanical stability and excellent encapsulation property. The measurement of water vapor transmission rate (WVTR) was performed with Ca test. We controlled thickness-ratio of organic and inorganic layer, and specific ratio showed a lowest WVTR value. Also this encapsulation layer contained very few pin-holes or defects which were linked in whole area by defect test. To apply into real OLEDs panels, we controlled a film stress from tensile to compressive and flexibility defined as an elastic modulus with organic-inorganic ratio. It has shown that OLEDs panel encapsulated with nano laminate layer exhibits better properties than single layer encapsulated in acceleration conditions. These results indicate that the organic-inorganic nano laminate thin films have high potential for flexible display applications.