• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.100-105
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• 2002

This paper predicts the material properties of spatially reinforced composites (SRC) and analyzes the thermo-elastic behavior of a kick motor nozzle manufactured from that material. To find the appropriate SRC structure for the nozzle throat that satisfies given design conditions, the equivalent material properties of the SRC are predicted using the superposition method for those of rod and matrix. Studied are the elastic behavior, temperature distribution, and thermo-elastic behavior of a kick motor nozzle composed of carbon/carbon SRC as a throat part. The elastic deformation of the nozzle composed of 3D carbon/carbon SRC shows asymmetry in a circumferential direction. However, 4D carbon/carbon SRC nozzle shows uniform deformation in the circumferential direction. Stress concentration in connecting parts of the kick motor nozzle is ultimately high due to the high temperature gradient in each connecting part. The thermo-elastic deformations of both the 3D and the 4D SRC nozzles are uniform in the circumferential direction due to the isotropy of CTE of each SRC. The deformation of the 3D SRC nozzle is a slightly smaller than that of the 4D SRC nozzle in the nozzle throat, which is favorably effective on rocket thrust. The circumferential stress is the most critical component of the kick motor nozzle. The 4D SRC nozzle having 1,1,1,1.7 diameters in each direction has the smallest circumferential stress among several SRC nozzles.

• Elastomers and Composites
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• 제50권1호
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• pp.30-34
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• 2015

Thermo-mechanical treatment process of a compressed open-cell rigid polyurethane foam (OC-RPUF), which was fabricated for the vacuum insulation panel (VIP), was studied to obtain an optimum condition for the dimensional stability by the relaxation of compressive stress. Thermo-mechanical deformation of the sample OC-RPUF was shown to occur from about $120^{\circ}C$. Yield stress of 0.36 MPa was shown at about 10% yield strain. And, densification of the foam started to occur from 75% compressive strain and could be continued up to max. 90%. Compression set of the sample restored after initial compression to 90% at room temperature was ca. 82%. Though the expansion occurred to about twice of the originally compressed thickness in case of temperature rise to $130^{\circ}C$, it could be overcome and the dimensional stability could be maintained if the constant load of 0.3 MPa was applied. As the result, a thermo-mechanical treatment process, i.e, annealing process at temperature of $130{\sim}140^{\circ}C$ for about 20 min as is the maximum compressed state at room temperature, should be required for dimensional stability as an optimum condition for the use of VIP core material.

• 한국정밀공학회지
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• 제20권10호
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• pp.183-190
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• 2003

Major device failures such as die cracking, interfacial delamination and warpage in flip chip packages are due to excessive heat and thermal gradients- There have been significant researches toward understanding the thermal performance of electronic packages, but the majority of these studies do not take into account the combined effects of thermo-mechanical interactions of the different package constituents. This paper investigates the thermo-mechanical performance of flip chip package constituents based on the finite element method with thermo-mechanically coupled elements. Delaminations with different lengths between the silicon die and underfill resin interfaces were introduced to simulate the defects induced during the assembly processes. The temperature gradient fields and the corresponding stress distributions were analyzed and the results were compared with isothermal case. Parametric studies have been conducted with varying thermal conductivities of the package components, substrate board configurations. Compared with the uniform temperature distribution model, the model considering the temperature gradients provided more accurate stress profiles in the solder interconnections and underfill fillet. The packages with prescribed delaminations resulted in significant changes in stress in the solder. From the parametric study, the coefficients of thermal expansion and the package configurations played significant roles in determining the stress level over the entire package, although they showed little influence on stresses profile within the individual components. These observations have been implemented to the multi-board layer chip scale packages (CSP), and its results are discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.188-193
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• 2000

A more accurate life prediction for gas turbine blade takes into account the material behavior under the complex thermo-mechanical fatigue(TMF) cycles normally encountered in turbine operation. An experimental program has been carried out to address the thermo-mechanical fatigue life of the IN738LC nickel-base superalloy. In the first phase of the study, out-of-phase and in-phase TMF experiments have been performed on uncoated and coated materials. In the temperature range investigated. the deposition of NiCrAlY air plasma sprayed coating did not affect the fatigue resistance. In the second phase of the study, a physically-base life prediction model that takes into account of the contribution of different damage mechanisms has been applied. This model was able to reflect the temperature and strain rate dependences of isothermal cycling fatigue lives, and the strain-temperature history effect on the thermo-mechanical fatigue lives.

• 설비공학논문집
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• 제14권11호
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• pp.914-922
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• 2002

Thermo-acoustic waves can be thermally generated in a compressible flow field by rapid heating and cooling, and chemical reaction near the boundary walls. This mechanism is very important in the space environment in which natural convection does not exist. Also this may be a significant factor for heat transfer when the fluids are close to the thermodynamic critical point. In this study, the generation and transmission characteristics of thermo-acoustic waves in an air-filled confined domain with two-step pulsed heating are studied numerically. The governing equations are discretized using control volume method, and are solved using PISO algorithm and second-order upwind scheme. For the purpose of stable solution, time step was set to the order of $1\times10_-9s,\;and\;grids\;are\;50\times2000$. Results show that temperature and pressure distributions of fluid near the boundary wall subjected to a rapid heating are increased abruptly, and the induced thermo-acoustic wave propagates through the fluid until it decays due to viscous and heat dissipation. Pressure waves have sharp front shape and decay with a long tail in the case of step heating, but these waves have sharp pin shape in the case of pulsed heating.

• 제어로봇시스템학회논문지
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• 제14권6호
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• pp.543-547
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• 2008

In the paper, we develop the ultrasonic bonding technique for LCD driver chips having small size and high pin-density. In general, the mounting technology for LCD driver ICs is a thermo-compression method utilizing the ACF (An-isotropic Conductive Film). The major drawback of the conventional approach is the long process time. It will be shown that the conventional ACF method based on thermo-compression can be remarkably enhanced by employing the ultrasonic bonding technique in terms of bonding time. The proposed approach is to apply the ultrasonic energy together with the thermo-compression methodology for the ACF bonding process. To this end, we design a bonding head that enables pre-heating, pressure and ultrasonic excitation. Through the bonding experiments mainly with LCD driver ICs, we present the procedures to select the best combination of process parameters with analysis. We investigate the effects of bonding pressure, bonding time, pre-heating temperature before bonding, and the power level of ultrasonic energy. The addition of ultrasonic excitation to the thermo-compression method reduces the pre-heating temperature and the bonding process time while keeping the quality bonding between the LCD pad and the driver IC. The proposed concept will be verified and demonstrated with experimental results.

• Elastomers and Composites
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• 제45권3호
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• pp.165-169
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• 2010

최근에 기존 고무의 장점인 유연성과 충전제에 의한 다양한 기능성과 열가소성 고무의 장점인 리싸이틀 및 성형의 용이성을 동시에 갖춘 초분자 네트워크형 열가역성 가교 탄성체가 소개되고 있다. 수소 결합과 이온 클러스터간의 결합력과 같은 열가역성 결합은 1990년부터 소개되었지만, 초분자 네트워크에서 가교 구조의 결합과 절단을 조절할 수 있는 기술이 시도된 것은 최근의 기술적 성과이다. 본 보문에서는 열가소성 탄성체의 용융 특성과 가교 탄성체의 보강 거동을 가지는 열가역성 가교 탄성체의 특징들을 정리하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.47-50
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• 2011

본 연구에서는 열/음향 불안정성 환경 모사를 위하여 수평형의 Rijke tube를 설계/제작하였고, 이를 이용하여 구현하고자 하는 주파수대의 열구배를 갖는 공진현상이 발생됨을 확인하였다. Rijke tube를 이용해 열 음향 불안정 환경을 조성한 후, 음향공을 장착하여 얻어진 감쇠특성을 상온실험 자료와 비교/분석하여 열 음향 불안정 환경에서의 음향공 감쇠특성을 확인하였다. 열/유동 환경하에서의 감쇠 시간이 상온 환경에 비해 약 40% 증가함을 확인하였으며, 이로부터 음향공 설계시 열/유동 환경이 고려되어야 함을 확인하였다.

• 국제강구조저널
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• 제18권4호
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• pp.1177-1190
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• 2018

This study presents an analytical framework for estimating the thermo-mechanical behavior of a composite beam exposed to fire. The framework involves: a fire simulation from which the evolution of temperature on the structure surface is obtained; data transfer by an interface model, whereby the surface temperature is assigned to the finite element model of the structure for thermo-mechanical analysis; and nonlinear thermo-mechanical analysis for predicting the structural response under high temperatures. We use a plastic-damage model for calculating the response of concrete slabs, and propose a method to determine the stiffness degradation parameter of the plastic-damage model by a nonlinear regression of concrete cylinder test data. To validate simulation results, structural fire experiments have been performed on a real-scale steel-concrete composite beam using the fire load prescribed by ASTM E119 standard fire curve. The calculated evolution of deflection at the center of the beam shows good agreement with experimental results. The local test results as well as the effective plastic strain distribution and section rotation of the composite beam at elevated temperatures are also investigated.

• 한국환경과학회지
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• 제33권2호
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• pp.121-129
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• 2024

The study investigated the effect of thermo-alkaline pretreatment on the solubilization of polyhydroxybutyrate (PHB) and its potential to enhance of thermophilic anaerobic digestion, focusing on biochemical methane potential (BMP) and methane production rate, using two different particle sizes of PHB (1500 ㎛ and 400 ㎛). Thermo-alkaline pretreatment tests were conducted at 90 ℃ for 24 hours with varying NaOH dosages from 0-80% (w/w). BMP tests with untreated PHB exhibited methane production ranging from 150.4~225.4 mL CH₄/g COD and 21.5~24.2 mL CH₄/g VSS/d, indicating higher methane production for smaller particle sizes of PHB, 400 ㎛. Thermo-alkaline pretreatment tests achieved a 95.3% PHB solubilization efficiency when 400 ㎛ PHB particles were treated with 80% NaOH dosage at 90 ℃ for 24 hours. BMP tests with pretreated PHB showed substantial improvement in thermophilic anaerobic digestion, with an increase of up to 112% in BMP and up to 168% in methane production rate. The results suggest that a combined pretreatment process, including physical (400 ㎛ PHB particles) and thermo-alkaline (90 ℃, 40-80% NaOH dosage, and 24 hours reaction time), is required for high-rate thermophilic anaerobic digestion of PHB with enhanced methane production.