• 설비공학논문집
• /
• 제13권12호
• /
• pp.1255-1265
• /
• 2001

A numerical study has been conducted to characterize the transient flow in a utility gas turbine burning natural gas. The solution domain encompasses the supply gas pressure regulator to the combustor of the gas turbine that employs multi-nozzle fuel injectors. Some results produced for verification in the present study agree suite well with the experimental ones. It is found that the total gas flow may decrease noticeably during its combustion mode change, which would be the reason of momentary combustion upset, when a reference case of opening ratios of control valves in the system is applied. Several parameters are then varied in order to make the total gas flow stable over that period of time. Results of this study may be useful to understand the unsteady behavior of combustion system burning natural gas.

• 한국해양공학회지
• /
• 제4권1호
• /
• pp.101-109
• /
• 1990

The friction welding has more technical and economic advantages than the other welding processes. As this welding process has the characteristics such as curtailment of production time, materials, cost reduction, etc., it has been widely used in production of various mechanical components which have complex shapes. So, this paper deals with optimizing the friction welding conditions and analyzing various mechanical properties of the friction welded joints of torsion bar material SUP9A bar to bar. The results obtained are summarized as follows; 1) The quantitative relation between heating time($t_{1}$, sec) and total upset(U, mm)can be obtained. The empirical formula obtained is ; U = 3.29$t_{1}$ + 1.6 2) The tensile strength($\sigma_{t}$, kgf/$mm^{2}$) of friction welding joints as post weld heat treated(PWHT) depends upon heating time($t_{1}$, sec) quantitatively and the empirical formula obtained is ; $\sigma$= -5.1$t_{1}\;^{2}$+44.90$t_{1}$+45.2 3) It is certain that the optimum condition for friction welded joints of SUP9A steel bars of diameter 14.5mm is, considering on various properties such as tensile strength, torsional strength, impact energy and strain of the joints after PWTH ; n = 2000rpm, $P_{1}$=8kgf/$mm^{2}$, $P_{2}$=20kgf/$mm^{2}$, $t_{1}$=4sec, $t_{2}$=3sec 4) The tensile strength, torsional strength and hardness were increased with the increased with the increasing carbon equivalent, but toughness was decreased.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2005년도 한국우주과학회보 제14권1호
• /
• pp.143-147
• /
• 2005

우주시스템 연구실에서 개발 중인 HAUSAT-2의 우주방사능 환경은 포획된 양자와 전자, 태양양성자이다. 본 논문에서는 우주방사능 환경에 대해 임무기간동안의 총 피폭량을 계산하였고, 총 피폭량에 대해 HAUSAT-2에서 사용하는 부품들의 부품의 우주방사능 허용레벨 분류과정을 통해 사용가능성을 검증하였다. 또한 단일사건 발생확률을 계산하여 단일사건 발생에 대비하는 시스템을 설계에 반영하였다.

• 한국해양공학회지
• /
• 제1권1호
• /
• pp.138-143
• /
• 1987

Friction welding has emerged as a reliable process for high-production commercial applications with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristcs of the pulse echo effects according to various change in welding conditions. This paper presents an attempt to determine the relationship between the varios welding conditions and the coefficients of reflection using the ultrasonic pulse echo method in dissibilar metals friction weld. The new approach of calculating the coefficients of reflection based on measured amplitudes of the echoes is applied in this paper. These coefficients provides a single quantitative measurement which involves both acoustic energy reflected at the welded interface as well as transmitted across the interface. As a result, it was known that the quantitave relationship between welding conditions and the coefficients of reflection using the ultrasonic pulse echo exists in dissimilar metals friction weld.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 1993년도 한국우주과학회보 제2권2호
• /
• pp.10-10
• /
• 1993

The cosmic ray experiment (CRE) on board the KITSAT-1 has been operating normally since the launch of the satellite. CRE is composed of two parts : the cosmic particle experiment (CPE) and the total dose experiment (TDE). Of these, we will discuss on the CPE results obtained the last several months. The data show much larger high energy Particle flux than the Previous UOSAT-3 data. The 550(single event upset) rate is also an order of magnitude higher than the UOSAT-3result. We will compare these results with the Bredictions of the CREME codel. ReferTncesAdams, J. H., Jr., 1987, NRL Memorandun Report 5901

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
• /
• pp.205-208
• /
• 2006

Similar friction welding were produced using 15 mm diameter solid bar in Ni-base superalloy(alloy718) to investigate their mechanical properties. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, AE total counts and ultrasonic attenuation coefficient. The specimens were tested as welded, not heat-treated. The tensile strength of the friction welded joints was increased up to 90% of the alloy718 base metal under the condition of all heating time. Optimal welding conditions were n=2,000 (rpm), $P_1=200$ (MFa), $P_2=200$ (MFa), $t_1=8$ (s), $t_2=5$ (s) when the total upset length is 4.4(mm). The weld interface of similar friction welded steel bars was mixed strongly.

• Journal of Advanced Marine Engineering and Technology
• /
• 제17권4호
• /
• pp.100-106
• /
• 1993

A study on optimizing the friction welding of copper(C1100) to aluminium(A1050) for developing the electrical sleeve was experimentally carried out and also on real-time nondestructive evaluation of the friction weld quality (strength) was accomplished by acoustic emission technique. The results obtained are summarized as the following ; 1) The heating upset $U_1$(mm) or total upset U(mm) tends to increase according to the increase of heating time $t_1$(sec). The relations between $U_1$ and $t_1$ or U and $t_1$are computed as follows when n=2000rpm, $P_1$=4, $P_2$=8kgf/$mm^2$, and $t_2$=6sec. U=1.6$e^{0.39t_1}$ $U_1$=3.65$e^{0.25t_1}$. 2) It was notified that the proper welding conditions by considering on both strength with more than 100% joint effieciency and toughness are heating time of 1.5-2.25 sec under n=200rpm, $P_1$=4, $P_2$=8kgf/$mm^2$, $t_2$=6sec. 3) It was confirmed that both AE total counts(N, counts) and the weld tensile strength (${\sigma}$, kgf/$mm^2$) of the welded joints increase as the increase of heating time, respectively, the relations between N and $t_1$, ${\sigma}$ and $t_1$ are computed from data points by regression analysis using the least square method as follows in case of the above proper condition ; N=50108+23917(ln $t_1$)${\sigma}$$=11.85+2.06(ln $t_1$). 4) Both empirical and calcularated equations of relationship between .sigma. and N are very coincident with a high reliability, as the following in case of the above proper welding condition ; Calculated : ${\sigma}$=0.00008N+7.5 Empirical :${\sigma}$= $8.17e^{0.0000072N}$. 5) It was confirmed that the real-time nondestructive weld strength evaluation for friction welding of copper(C1100) to aluminium(A1050) could be possible by acoustic emission technique.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.331-336
• /
• 2004

Dissimilar friction welding were produced using 10mm and 11mm diameter solid bar in Inconel ally(IN X-750) to Stainless steel(STS316L) to investigate their mechanical properties. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Virkers hardness surveys of the bond of area and HAZ and macro-structure investigations. The specimens were tested as welded, not heat-treated. The tensile strength of the friction welded steel bars was increased up to $95\%$ of the STS316L base metal under the condition of all heating time. Optimal welding conditions were n=2,000(rpm), $P_1=220(MPa),\;P_2=260(MPa),\;t_1=4(s),\;t_2=4(s)$ when the total upset length is 7(mm).

• 대한기계학회논문집A
• /
• 제30권4호
• /
• pp.402-408
• /
• 2006

Dissimilar friction welding were produced using 15(mm) diameter solid bar in chrome molybedenum steel(KS SCM440) to carbon steel(KS S45C) to investigate their mechanical properties. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and H.A.Z and microstructure investigations. The specimens were tested as-welded and post-weld heat treated(PWHT). The tensile strength of the friction welded steel bars was increased up to 100% of the S45C base metal under the condition of all heating time. Optimal welding conditions were n=2,000(rpm), $P_1=60(MPa),\;P_2=100(MPa),\;t_1=4(s),\;t_2=5(s)$ when the total upset length is 5.4 and 5.7(mm), respectively. The peak of hardness distribution of the friction welded joints can be eliminated by PWHT. Two different kinds of materials are strongly mixed to show a well-combined structure of macro-particles without any molten material and particle growth or any defects.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2003년도 추계학술대회 논문집
• /
• pp.158-162
• /
• 2003

A study on friction welding of chrome molybedenum steel(SCM440) to carbon steel(S45C) is examined experimentally through tensile test, hardness test. So, this paper deals with optimizing the welding conditions and analyzing various mechanical properties about friction welds of SCM440 to S45C steel. The tensile strength of the friction welded joint was increased up to 100% of the S45C base matal under the condition of all heating time. Optimal welding conditions were n=2,000(rpm), $P_{1}=60(MPa)$, $P_{2}=100(MPa)$, $t_{1}=4(s)$, $t_{2}=5(s)$ when the total upset length is 5.7(mm).