• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.398-403
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• 2005

This study investigates the change of the temperature and mechanical properties of the braking disk for the railway vehicle. The average temperature is measured about $100^{\circ}C$ and the maximum temperature is measured over $200^{\circ}C$ by non-contact sensor from Seoul to Chun-an. In the $20^{\circ}C-300^{\circ}C$, the 0.2% offset yield strengths of the disk (GC25-30 material) are a little down to the reference value, but the linear relation of tensile test result is not find from the linear change of temperature. However, JIC values have the inverse proportion to the temperature, and the JIC value at $200^{\circ}C$ decrease 30.55% from the JIC. value of the room temperature. This result means that the crack length on the braking disk is rapidly increase at $200^{\circ}C$.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.10
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• pp.57-63
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• 2014

This paper proposes an architecture of $3^{rd}$ order SDM(Sigma-Delta Modulator) with delayed feed-forward path in order to reduce the power consumption and area. The proposed SDM improve the architecture of conventional $3^{rd}$ order SDM which consists of two integrators. The proposed architecture can increase the coefficient values of first stage doubly by inserting the delayed feed-forward path. Accordingly, compared with the conventional architecture, the capacitor value($C_I$) of first integrator is reduced by half. Thus, because the load capacitance of first integrator became the half of original value, the output current of first op-amp is reduced as 51% and the capacitance area of first integrator is reduced as 48%. Therefore, the proposed method can optimize the power and the area. The proposed architecture in this paper is simulated under conditions which are supply voltage of 1.8V, input signal 1Vpp/1KHz, signal bandwidth of 24KHz and sampling frequency of 2.8224MHz in the 0.18um CMOS process. The simulation results are SNR(Signal to Noise Ratio) of 88.9dB and ENOB(Effective Number of Bits) of 14-bits. The total power consumption of the proposed SDM is $180{\mu}W$.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.322-327
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• 2000

This paper investigates the time-dependent crack growth in X20CrMoV 12 1 steel weld joints. Crack growth test are carried out $545^{\circ}C$ on side-grooved 1/2T CT specimens under static loads. A simulated material is produced for the intercritical HAZ, where fracture normally occurs. Constitutive properties are obtained for the simulated HAZ material as well as for the base metal and weld metal. Finite element analyses of crack growth are performed on the models with and without a HAZ layer, using the experimental crack length-time history. The inclusion of HAZ layer increase the load line velocities significantly. The crack growth rates are correlated reasonably well with $C^*$. The smallest crack size for the validity of $C^*$ is found much smaller than the ASTM crack initiation size for 1T CT specimen of creep ductile materials.

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.706-713
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• 1994

Isothermal vapor-Liquid equilibrium data have been measured for binary systems MTBE-methanol, MTBE-n-heptane, and methanol-n-heptane at $45^{\circ}C$ and $65^{\circ}C$ by using head space gas chromato-graphy (H.S.G.C). Among these systems a minimum azeotrope was observed in both of MTBE-methanol system and n-heptane-methanol system. Particularly n-heptane-methanol system has a heterogeneous minimum azotrope since it has an immisible region. These equilibrium data were correlated with the excess Gibbs energy model, and the thermodynamic consistency test was also carried out by using Redlich-Kister equation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1193-1202
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• 1989

본 논문에서는 발전소의 소재로 많이 쓰이고 있는 304 스테인리스강(앞으로는 304SS로 표기함)과 316스테인리스강(앞으로는 316SS로 표기함)의 크립 균열 발생 거동 을 각각 600.deg. C와 625.deg. C에서 조사한다. 이 온도는 발전소의 반응기(reactor)에 사용 되는 304SS와 316SS이 받는 온도이다. 즉 304SS와 316SS의 크립 균열 발생을 지배 하는 파괴 매개변수가 무엇인지가 크립 파괴 실험을 통하여 조사된다. 실험 결과는 이미 제안되어 있는 크립 균열 발생 모델에서 예측된 결과와 비교된다. 특히 304SS 와 316SS은 고온에서의 연성도가 변형률 속도에 따라 변하는 것으로 알려져 있다. 본 연구에서는 '변형률 속도에 따른 재료의 연성도의 변화에 근거한 균열 발생 모델' 을 제안하고, 그 모델에서 예측된 크립 발생 거동을 실험 결과와 비교한다.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.34C no.4
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• pp.26-35
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• 1997

This paper proposes a multi-bit $\Sigma\Delta$ modulator arcitecture which eliminates signal clipping problem. To avoid signal clipping, the output values of intgrators are monitored and modified by a reference value. This oepration is recorded as a digital code to restore actual signal value. Due to the digital code, the substraction of feedback value from the multi-bit quantizer can be calculated by a digital adder and this simplifies dAC operation making the accurate DAC of conventional multi-bit $\Sigma\Delta$ modulator scheme unnecessary. These features make N-th modulator can be implemented by sharing an integrator among N stages to decrease the required chip area. As an experimental example, a 4th order .sum..DELTA. modulator with oversampling ratio of 64 was simulated to show over 130 DB SNR at rail-to-rail input sinusoidal signal.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.98-111
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• 1995

High temperature low cycle fatigue shows that cycle-dependent crack growth owing to cyclic plastic deformation occurred simultaneosly with time-dependent crack growth owing to intergranular deformation. Consequently, to estimate crack growth rate uniquely, many to investigators have proposed various kinds of parameters and theories but these could not produce satisfactory results. Therefore the goal of this study is focused on prediction of crack growth rate using predominant damage rule, linear cumulative damage rule and transitional parameter ${\Delta}J_c/{\Delta}J_f$. On the basis of these sinusoidal loading waveform at 600$^{\circ}C$ and 700$^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1719-1730
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• 1993

This paper presents the theoretical natural frequencies of out-of-plane deformable ring based on the variables such as out-of-plane deflection, torsional rotation and shear rotation. Based on the same variables, a finite element eigen analysis is carried out by using the $C^0$-continuous, isoparametric element which has three nodes per element and three degrees-of-freedom at each node. Numerical experiments are peformed to find the integration scheme which produces accurate natural frequencies, natural modes and correct rigid body motion. The uniformly reduced integration and the selective reduced integration give more accurate numerical frequencies than the uniformly full integration, but the uniformly reduced integration produces incorrect rigid body motion while selective reduced integration does correct one. Therefore, the ring element based on the three variables which employes selective reduced integration is recommended to avoid spurious modes, to alleviate the error due to shear locking and to produce correct rigid body motion, simultaneously.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2331-2338
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• 1994

Experimental conditions of the optical shadow methods of caustics for measurement of the stress intensity factor and the J-integral in various materials(polycarbonate, PMMA, Al 5586D) are investigated. The necessary experimental requirements toe determine accurate values of the stress intensity factors and the J-integrals are described. The ratio of $r_o$ (radius of initial curve) to $r_p$ (plastic zone size) is selected as a parameter to verify the experimental limitation of the method of caustics in determination of fracture parameters. In this study, transmission caustics method was used for compact tension specimens made of polycarbonate and PMMA. while reflection caustics method was applied to c-shaped tension specimen made of Al 5586D. The appropriate ranges of $r_o/r_p$ tp determine accurate values of stress intensity factors were found to be 1.5~1.8. Existing experimental results have been obtained mainly by changing $r_p$ with different loads in $r_o/r_p$. However, in this study we could obtain varying $K_{caus}/K_{th}$ over the wide range of $r_o/r_p$ at fixed load conditions with newly designed optical arrangement. Thus, we could find the range in which theoretical and experimental results agree well each other by changing $r_o$ values only. In Al 5586D specimen, experimental caustics were located inside of the plastic zone, and $K_{caus}/K_{th}$ were found to be not unity in this range. It is found that $J_{caus}/J_{th}=1{\;}with{\;}r_o/t{\geq}0.8$ and the experimental plastic zone includes the contours of caustics.

• Radiation Oncology Journal
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• v.19 no.2
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• pp.199-204
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• 2001

Purpoe : To find the optimal values of total arc degree to protect the normal brain tissue from high dose radiation in stereotactic radiotherapy planning. Methods and Materials : With Xknife-3 planning system & 4 MV linear accelerator, the authors planned under various values of parameters. One isocenter, 12, 20, 30, 40, 50, and 60 mm of collimator diameters, $100^{\circ},\;200^{\circ},\;300^{\circ},\;400^{\circ}C,\;500^{\circ},\;600^{\circ}$ or total arc degrees, and $30^{\circ}\;or\;45^{\circ}$ or arc intervals were used. After the completion of planning, the plans were compared each other using $V_{50}$ (the volume of normal brain that is delivered high dose radiation) and integral biologically effective dose. Results : At $30^{\circ}$ of arc interval, the values of $V_{50}$ had the decreased pattern with the increase of total arc degree in any collimator diameter. At 45 arc interval, up to $400^{\circ}$ of total arc degree, the values of $ V_{50}$ decreased with the increase of total arc degree, but at $500^{\circ}\;and\;600^{\circ}$ of total arc degrees, the values increased. At $30^{\circ}$ of arc interval, integral biologically effective dose showed the decreased pattern with the increase of total arc degree in any collimator diameter. At $45^{\circ}$ arc interval with less than 40 mm collimator diameter, the integral biologically effective dose decreased with the increase of total arc degree, but with n and n mm or collimator diameters, up to $400^{\circ}$ or total arc degree, integral biologically effective dose decreased with the increase of total arc degree, but at $500^{\circ}\;and\;600^{\circ}$ of total arc degrees, the values increased. Conclusion : In the stereotactic radiotherapy planning for brain lesions, planning with $400^{\circ}$ of total arc degree is optimal. Especially, when the larger collimator more than 50 mm diameter should be used, the uses of $500^{\circ}\;and\;600^{\circ}$ of total arc degrees make the increase of$V_{50}$ and integral biologically effective dose. Therefore stereotactic radiotherapy planning using $400^{\circ}$ of total arc degree can increase the therapeutic ratio and produce the effective outcome in the management of personal and mechanical sources in radiotherapy department.