• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.123-128
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• 2001

The creep constants which are used to the reference stress equations of creep damage were obtained to type 316LN stainless steel, and their determining methods were described in detail. Typical Kachanov and Rabotnov(K-R) creep damage model was modified into the damage equations with reference stress concepts, and the modified equations were applied practically to type 316LN stainless steel. In order to determine the reference stress value, a series of high-temperature tensile tests and creep tests were accomplished at $550^{\circ}C$ and $600^{\circ}C$. By using the experimental creep data, the creep constants used in reference stress equations could be obtained to type 316LN stainless steel, and a creep curve on rupture strain was predicted. The reference stress concept on creep damage can be utilized easily as a design tool to predict creep life because the process, which is quantified by the measurement of voids or micro cracks during creep, is omitted.

• 한국해양공학회지
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• 제16권3호
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• pp.59-64
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• 2002

In the present study, we examined the influence of prestrain on creep strength of Class M alloy(STS310S) and Class A(STS310J1TB) alloys containing precipitates. Prestrain was given by prior creep at a higher stress than the following creep stresses. Creep behaviour before and after stress change and creep rate of pre-strained specimens were compared with that of virgin specimens. Pre-straining produced the strain region where the strain rate was lower than that of a virgin specimen both for STS310J1TB and STS310S steels. The reason for this phenomenon was ascribable to the viscous motion of dislocations, the interaction between dislocations and precipitates in a STS310J1TB steel, and the interaction of dislocations with sub-boundaries in a STS310S steen which has the higher dislocation density and smaller subgrain size resulted from pre-straining at higher stress.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.47-52
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• 2000

F.R.P specimens were made by mixture CM(chopped mat) 450-104 matrix & RC(roving clothes)570-100 Roving, the mixture ratio Resin: hardener (92:8) for tensile test. It was also made of plates by hand lay-up method and was been cured for 24 hours and then was cut tensile specimens in accordance with ASTM D638 Type 3. Knowing exact behavior of bonded area's stress and strain when the tensile test was going on, the test specimens were made of 2 plies laminae of F.R.P in each for supporting cut part in middle of specimen length. And in middle part also were covered of F.R.P plies of 1/2, 2/3 length of specimen in each as well. Also we consider shear stress in adhered area. This study reveals that as plys length is more longer, rupture stress grows remarkably larger.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.194-199
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• 2000

The creep rate is affected by the temperature and in fact. if the temperature above $T_M/2(T_M:melting\;point)$. The aim of the present investigation is to study the relationship of static creep and cyclic creep behavior of pure copper and the formulation of these phenomena with the special attention to the instantaneous strain. strain rate from time and number of cycles have the same inclination Steady state creep rate depend upon maximum stress and can be expressed as linear function according to Power law creep equations Creep rupture time has relation with creep rate. and it make a group represented as the same direct line regardless of max stress, stress ratio and the temperature. Initial strain effect on continuous creep deformation. and have guantitative relationship between elastic and Plastic strain. LMP have similar tendency than OSDP and MHP according to temperature

• 한국자동차공학회논문집
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• 제14권2호
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• pp.16-22
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• 2006

Stainless steel has widely been used in various industrial fields because it has high corrosion resistance. But, we have little design data about the creep life prediction of SUS316L stainless steel. Therefore, in this study, a series of creep tests and study on them under 16 constant stress and temperature combined conditions have been performed to get the creep design data and life prediction of SUS316L stainless steels and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 10. And last, the creep rupture fractographs show the intergranular ductile fracture with many dimples.

• 한국정밀공학회지
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• 제27권7호
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• pp.101-108
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• 2010

Domestic three-way catalyst satisfies exhaust gas conversion efficiency or pressure drop etc. but doesn't satisfy thermal durability. Thermal stress analysis for three-way catalyst was performed based on experimental temperature distribution. Thermal safety of three-way catalyst was estimated by safety factor. Aspect ratio variable had the most significant effect on thermal stress. Thickness variable had the least significant effect on thermal stress. Optimal conditions for premature failure prevention of three-way catalyst were as follows : (1) aspect ratio of three-way catalyst : 0.6:1 (2) 2.84mm thick (3) silicon nitride. The safety of Taguchi-optimized three-way catalyst were 4.7 times higher than that of existent three-way catalyst.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2953-2959
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• 2021

A new practical modeling of the Norton's power law creep is proposed and implemented to analyze the high temperature behaviors of Alloy 690 SG tube material. In the model, both the stress exponent n and the rate constant B are simply treated as the temperature dependent parameters. Based on the two-step optimization procedure, the temperature function of the rate constant B(T) was determined for the data set of each B value after fixing the stress exponent n value by using the prior optimized function at each temperature. This procedure could significantly reduce the numerical errors when using the power law creep equations. Based on the better description of the steady-state creep rates, the experimental rupture times could also be well predicted by using the Monkman-Grant relationship. Furthermore, the difference in tensile strengths at high temperatures could be very well estimated by assuming the imaginary creep stress related to the given strain rate after correcting the temperature effects on the elastic modulus.

• 한국안전학회지
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• 제20권3호
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• pp.34-41
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• 2005

For assessing residual lift of the steam pipe in fossil power plants, inspections and analysis are usually focused on the critical locations such as butt welds, elbows, Y-piece and T-piece of the steam pipes. In predicting the residual life of T-piece, determination of local stress near welds considering system load as well as internal pressure is not a simple problem. In this study, stress analysis of a T-piece pipe was conducted using a three-dimensional model which represents the T-piece of a domestic fossil power station. Elastic and elastic-creep analysis showed the maximum stress level and its location. Residual creep rupture life was also calculated using the stress analysis results. It was argued that the calculated life is reasonably same as the measured one. The stress analysis results also support life prediction methodology based on in-field replication technique.

• 한국재료학회지
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• 제2권4호
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• pp.270-278
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• 1992

W-0.4wt% Ni, W-0.8wt% Ni 활성 소결체의 Ni rich상의 양이 응력 파단 성질에 미치는 영향을 조사하기 위하여, direct load creep tester를 사용, 100$0^{\circ}C$~120$0^{\circ}C$, 수소 분위기에서 응력 파단시험을 하였다. 100시간 응력 파단 강도는 니켈 함량이 0.4wt%, 0.8wt%로 증가 함에 따라, W-0.2wt% Ni의 경우와 비교하여 100$0^{\circ}C$에서 43%, 90%, $1100^{\circ}C에서$ 35%, 60% 높았으며, 이는 초기 결정립 조대화, 비이론밀도의 상승과 시험 중 결정립 성장 때문으로 생각된다. W-0.4wt% Ni의 크리프변형 활성화 에너지는 81.3kca1/mol으로, 변형기구는 Ni rich 상을 통한 W 확산과 결정립 내부 변형이다. 응력 파단 시험 후, 파단면은 입계 파괴 양상을 나타내었다. 소결시 생성된 고립 기공이 결정입계에 있는 Ni rich상을 따라 전파하였기 때문이다.

• 대한기계학회논문집A
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• 제31권12호
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• pp.1157-1164
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• 2007

Ceramic honeycomb structures have performed successfully as catalyst supports for meeting hydrocarbon, carbon monoxide and nitrous emissions standards for gasoline-powered vehicles. Three-way catalyst converter has to withstand high temperature and thermal stress due to pressure fluctuations and vibrations. Thermal stress constitutes a major portion of the total stress which the ceramic catalyst support experiences in service. In this study, temperature distribution was measured at ceramic catalyst supports. Thermal durability was evaluated by power series dynamic fatigue damage model. Radial temperature gradient was higher than axial temperature gradient. Thermal stresses depended on direction of elastic modulus. Axial stresses are higher than tangential stresses. Tangential and axial stresses remained below thermal fatigue threshold in all engine operation ranges.