• 한국기계가공학회지
• /
• 제15권3호
• /
• pp.28-35
• /
• 2016

Forging operations are non-stationary processes occurring because of indirect pressure, generally, under conditions of three-dimensional stress and deformation. Furthermore, due to friction and the constraints of die geometry, deformation is not homogeneous. Material flow and deformation are largely determined by the shape of the tools. It is well known that net-shape forging can improve the mechanical strength of the final product as well as reduce material waste. Oxygen-free copper that is used for electrical and electronic components has excellent electrical and thermal conductivity. Oxygen-free copper parts have a low productivity in cutting process. Thus, the forging process is performed in order to improve the low productivity in cutting process. The forging of oxygen-free copper for electrode body parts was modeled using finite element simulation and forging experiments that were conducted for producing electrode body parts at room temperature. In order to reduce the cost of cutting products, the forging was performed in a closed cavity to obtain near-net or net-shape parts.

• 대한기계학회논문집A
• /
• 제33권10호
• /
• pp.1158-1162
• /
• 2009

Fatigue limit of the copper film coated by Sn was estimated using Goodman diagram and Gerber diagram. To obtain the high cycle fatigue life curve, S-N curve, of the film, the high cycle fatigue test was carried out by applying the constant amplitude load to the film specimen with three different stress ratio of 0.05, 0.3 and 0.5 and the frequency of 40 Hz at room temperature in air. The free-standing film specimen 15.26${\mu}m$ thick was fabricated by etching process. The fatigue limits and S-N curves at the respective stress ratios were determined from the experimental works. It was shown that the S-N curves were dependent on the stress ratio and the fatigue limit was increased with decreasing the stress ratio. The dependency of the fatigue behavior was presented in empirical relationship. Using these relationships, the fatigue limit was predicted.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1997년도 추계학술대회논문집
• /
• pp.228-231
• /
• 1997

A series of load relaxation tests was performed to determine stress-strain rate curves at high temperatures. Constitutive parameters of GBS and GMD were evaluated from the curves using the recently proposed inelastic deformation theory. Tensile tests and Microsturcture investigations showed deformation behavior as the relaxation test results predicted.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2000년도 추계학술발표대회 논문집
• /
• pp.46-49
• /
• 2000

A decoupled thermo-~lezoelectric-mechanical model of composite laminates with surface bonded piezoelectric actuators, subjected to externally applied load, temperature change load, electric field load is developed. The governing differential equations are obtained by applying the principle of free energy and variational techniques. A higher order zigzag theory displacement field is employed to accurately capture the transverse shear and normal effects in laminated composite plates of arbitrary thickness.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
• /
• pp.346-349
• /
• 2006

Superstructure of reinforced concrete bridges are shortened or elongated due to creep, drying shrinkage, temperature and so on. Most of bridge superstructures are free to shortening and elongation without constraint and stresses will not be induced by creep, drying shrinkage and temperature. But if bridge superstructure are constraint due to wrong setting and functional defects of bridge bearing, very large constraint forces can be induced. In this study, PSCI-Beam by tilt-constructed with constraint and deviation of bearings are presented and the effects of time-dependent constraint stress and temperature loads are investigated.

• 대한화학회지
• /
• 제43권3호
• /
• pp.251-256
• /
• 1999

여러 온도와 압력에서 톨루엔의 점성도를 공낙하법에 의하여 결정하고 톨루엔의 점성도에 대한 온도 및 압력 의존성을 연구하였다. 톨루엔의 점성 흐름에 관한 엇갈림 변형력으로부터 엇갈림 자유 에너지, 엇갈림 엔트로피, 엇갈림 엔탈피 등을 정의하여 압력 변화에 따르는 열역학적 성질의 변화를 고찰하였다. 실험적으로 결정된 엇갈림 자유 에너지, 엇갈림 엔트로피, 엇갈림 엔탈피 등을 온도 상승에 의한 톨루엔 분자들의 열운동 효과와 압력 증가에 의한 밀도 증가 및 분자의 입체 효과에 의하여 설명하였다.

• Journal of Magnetics
• /
• 제3권1호
• /
• pp.21-30
• /
• 1998

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media, due to large Kerr rotation angle in the wavelength of a blue laser beam. however, since multilayer structure, as well as amorphous structure, is a non-equilibrium state in terms of free energy and MO recording is a kind of thermal recording which is conducted aound Curie temperature (Tc) of the recording media, when the multilayer is used for the MO recording media, changes in the multilayer structure are occurred as the amorphous structure do. Therefore, the assessment of the structural stability in the Co/Pd multilayer is crucially important both for basic research and applications. As the parameter of the structural stability in this research, modulation amplitude and particle size of the Co/Pd multilayer are measured in terms of Ar sputtering pressure and heat treatment temperature. From the results of the research, we find out that the magnetic exchange energy in the structural changes of a magnetic multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.

• Computers and Concrete
• /
• 제23권5호
• /
• pp.321-327
• /
• 2019

Experimental isotherm compressive tests show that concrete behaviour is dependent on temperature. The aim of such tests is to reproduce how concrete will behave under environmental changes within a moderate range of temperature. In this paper, a novel constitutive elastic damage behaviour law is proposed based on a free energy with an apparent damage depending on temperature. The proposed constitutive behaviour leads to classical theory of thermo-elasticity at small strains. Fixed elastic mechanical characteristics and fixed evolution law of damage independent of temperature and the material volume element size are considered. This approach is applied to compressive tests. The model predicts compressive strength and secant modulus of elasticity decrease as temperature increases. A power scaling law is assumed for specific entropy as function of the specimen size which leads to a volume size effect on the stress-strain compressive behaviour. The proposed model reproduces theoretical and experimental results from literature for tempertaures ranging between $20^{\circ}C$ and $70^{\circ}C$. The effect of the difference in the coefficient of thermal expansion between the mortar and coarse aggregates is also considered which gives a better agreement with FIB recommendations. It is shown that this effect is of a second order in the considered moderate range of temperature.

• 한국작물학회지
• /
• 제24권1호
• /
• pp.57-65
• /
• 1979

대.소맥에 대한 유리 Proline 축적의 온도범위, 장기저온처리의 경향, 저온과 수분부족에 있어서 광의재생의 여부 및 수종의 식물에 대한 종간 및 종내의 변이 등 일련의 반응생리와 축적기작에 대한 실험결과를 요약하면 다음과 같다. 1. 대맥은 8$^{\circ}C$나 그 이하의 온도에서 축적되나 소맥은 12$^{\circ}C$나 그 이하의 온도에서 Proline을 축적하였다. 2. 대.소맥에 있어서 신장억제온도와 Proline을 축적하기 시작하는 온도는 거의 일치하였다. 3. 엽절편을 5$^{\circ}C$의 저온에 둔 것은 29일 생존하였으며 그동안 Proline을 축적하였으나 2$0^{\circ}C$에 둔 것은 13일 밖에 생존하지 못하였으며 그 동안 축적은 없었다. 4. 완전식물체엽과 엽절편 공히 5$^{\circ}C$의 저온에 서의 축적은 광의재생이였다. 5. 광의재생은 Proline의 생합성을 위한 전구물질의 급여로는 대체될 수 없었다. 6. 수분부족에 의한 Proline 축적은 2$0^{\circ}C$에서는 광의재생이 아니였으나 5$^{\circ}C$에서는 광의재생이였다. 7. 저온과 수분부족에 대한 종간 및 종내의 축적변이는 높은 편이였다. 그러나 수분부족이 저온에 대한 변이보다 높았다. 8. 저온과 수분부족에 의한 Proline 축적의 기작은 상당히 상이한 것 같다.

• 한국재료학회지
• /
• 제19권6호
• /
• pp.337-343
• /
• 2009

In this study, we optimized Pb-free Sn/Ni plating thickness and conditions were optimized to counteract the environmental regulations, such as RoHS and ELV(End-of Life Vehicles). The $B_{10}$ life verification method was also suggested to have been successful when used with the accelerated life test(ALT) for assessing Pb-free solder joint life of piezoelectric (PZT) ceramic resonator. In order to evaluate the solder joint life, a modified Norris-Landzberg equation and a Coffin-Manson equation were utilized. Test vehicles that were composed of 2520 PZT ceramic resonator on FR-4 PCB with Sn-3.0Ag-0.5Cu for ALT were manufactured as well. Thermal shock test was conducted with 1,500 cycles from $(-40{\pm}2)^{\circ}C$ to $(120{\pm}2)^{\circ}C$, and 30 minutes dwell time at each temperature, respectively. It was discovered that the thermal shock test is a very useful method in introducing the CTE mismatch caused by thermo-mechanical stress at the solder joints. The resonance frequency of test components was measured and observed the microsection views were also observed to confirm the crack generation of the solder joints.