• Journal of Magnetics
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• 제6권1호
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• pp.27-30
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• 2001

We present a new procedure to evaluate the residual life of 1Cr-1Mo-0.25V steel from reversible magnetic permeability. The method is based on the existence of first harmonics in the differential magnetization around the coercive force. The apparatus is based on the detection of the voltage induced in a coil using a lock-in amplifier tuned to the frequency of the exciting coil. Results obtained for the first harmonics and Vickers hardness on aged samples show that the peak interval of reversible permeability and Vickers hardness decrease as aging time increases. The correlation between Vickers hardness and the peak interval of the reversible permeability may be used to evaluate the residual life of 1Cr-lMo-0.25V steel, nondestructively.

• 한국철도학회논문집
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• 제7권2호
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• pp.125-129
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• 2004

This study investigates the fatigue lift estimation of butt weld specimen for the railway vehicle by examining butt weld bead profiles. The butt weld beads, which are welded by semi-robot method, have non-uniform bead profiles described by $\theta$, p and h. The stress concentration factors, K$\_$t/, are changed by different $\theta$, p and h from 1.395 to 2.863. Hence, the sensitivity of K$\_$k/ is changed by each $\theta$, p and h. As $\theta$ becomes lower and p and h become higher, K$\_$t/ increases. The fatigue life can be estimated very closely for the AAY specimens without residual stress using only butt weld bead profiles. But, for the AAN specimens with residual stress, the fatigue life must be estimated by considering both the weld bead profiles and the residual stress data.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권4호
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• pp.177-183
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• 2002

A pulsed tracer gas technique is applied to measure the distributions of local mean age and local mean residual-life-time of air in a half-scale experimental chamber, The airflow patterns in the chamber are visualized by a Helium bubble generator for three different exhaust locations. A supply slot is located at the top of a right wall, and an exhaust slot is at either bottom-left (Case 1), bottom-right (Case 2), or top-left (Case 3) location. Results show that the distributions of local mean age and local mean residual-life-time are different from each other, but both of them are closely related to the airflow pattern in the space. Included are discussions on explaining the variations of overall room ventilation effectiveness depending upon airflow rates for three different supply-exhaust configurations.

• 대한수학회지
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• 제58권1호
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• pp.237-264
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• 2021

In this work the stationary bootstrap of Politis and Romano [27] is applied to the empirical distribution function of stationary and associated random variables. A weak convergence theorem for the stationary bootstrap empirical processes of associated sequences is established with its limiting to a Gaussian process almost surely, conditionally on the stationary observations. The weak convergence result is proved by means of a random central limit theorem on geometrically distributed random block size of the stationary bootstrap procedure. As its statistical applications, stationary bootstrap quantiles and stationary bootstrap mean residual life process are discussed. Our results extend the existing ones of Peligrad [25] who dealt with the weak convergence of non-random blockwise empirical processes of associated sequences as well as of Shao and Yu [35] who obtained the weak convergence of the mean residual life process in reliability theory as an application of the association.

• 한국가스학회지
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• 제25권5호
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• pp.30-36
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• 2021

정유 및 석유화학산업의 개질로 튜브에 사용되는 mod HP강에 대한 잔여수명의 예측법을 튜브의 표면 금속조직에 석출된 탄화물의 면적분율에 대한 정량적인 평가를 통해 연구하였다. 표면복제법을 활용한 미세조직 분석을 통하여 탄화물의 면적분율과 잔여수명 사이의 관계를 실험적으로 구하였다. 신재(Virgin)와 950 ℃의 개질로에서 1.8, 6.0, 7.2, 8.5, 9.7 및 16.2년 실제 사용한 튜브들을 광학현미경(OM)을 사용하여 관찰하였으며, 석출물의 면적분율을 Image J 프로그램을 이용한 정량적 이미지 분석에 의해 측정하였다. 석출물의 면적분율이 증가함에 따라 잔여수명이 감소하여 서로 반비례하는 결과를 보여주었다. 이 관계를 사용온도와 수명을 결합한 파라미터인 LMP로 나타내면, 신재에서 LMP 값이 가장 높게 나타났고, 사용시간이 증가할수록 LMP가 감소하여 잔여수명이 줄어 듦을 나타내었다. LMP와 탄화물의 면적분율과의 상관관계를 나타내는 관계식을 도출하였다. 도출한 관계식은 현장에서 잔여수명 평가를 위해 표면복제법 적용으로 면적분율을 측정하여 잔여수명을 평가하는데 사용될 수 있다.

• Journal of Welding and Joining
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• 제15권4호
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• pp.187-193
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• 1997

In the weldmentsm the crack propagation rate is changed due to the residual stress. The crack propagation rate is high in the region with the residual stress. However it shows rhw same behavior with the base metal in the region that does not include the residual stress. The fatigue crack growth rate for the material with residual stresses can be predicted more precisely by using the effective stress ratio. The difference between experimental results and prediction results in the initial stage seems to be due to the redistribution of residual stresses and microstructural change.

• 한국정밀공학회지
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• 제20권5호
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• pp.148-155
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• 2003

Most manufacturing processes such as welding, cutting and molding generate residual stresses on the surface of manufactured parts. Between compressive and tensile residual stresses, the tensile residual stress is harmful to the surface integrity, which results in reduced fatigue life and causes other structural failures when the service stresses are superimposed on the residual stresses. In the research, the residual stresses in the hardened tool steel (SKD11) were measured using hole-drilling method. The specimens were prepared through hard turning. Most of residual stresses in the machined surface were compressive.

• 한국환경농학회지
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• 제40권2호
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• pp.92-98
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• 2021

BACKGROUND: Unintentional residual pesticide in soil derived from preceding crops and the transfer to succeeding crops was considered a critical barrier for positive list system (PLS). Thus, an uncertain risk is predicted for ethoprophos applied at cultivation of preceding crop (Korean cabbage) to succeeding crop (spinach). METHODS AND RESULTS: Ethoprophos was treated on soil following the recommended dose and 5 times dose according to the safe use guidelines for Korean cabbage after seeding. On the 4 days after harvesting of preceding crop, spinach was sowed. The initial residual amounts of ethoprophos on soil (7.081-19.493 mg/kg) were decreased to 3.832-7.218 mg/kg until the harvest of Korean cabbage, and then finally decreased to 0.011-0.079 mg/kg after spinach cultivation. The uptake rates of ethoprophos from soil by Korean cabbage were 0.01-0.03% and distributed to root (0.150-0.903 mg/kg) and shoot (0.021-0.151 mg/kg), respectively. The residual amounts of uptake and translocation from preceding crop cultivated soil to spinach edible part were found to be below LOQ. CONCLUSION: The plant back internal (PBI) for ethoprophos is not recommended during sequential cultivation of leafy vegetables, since the residual amounts of ethoprophos in spinach were less than MRL (0.02 mg/kg).

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.341-346
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• 2002

In this study, an effect that compressive residual stress formed by shot-peening the surface of spring steel(JISG SUP-9) at each shot velocity(1800, 2200, 2600, 3000rpm) on the fatigue crack growth property and threshold stress intensity factor, ${\Delta}K_{th}$, was examined. Followings are the result (1) Compressive residual stress on surface of specimen was determined at each -601 MPa(1800rpm), -638 MPa(2200rpm), -587 MPa (2600rpm), -550 MPa(3000rpm) by shot velocity of shot peening and threshold stress intensity factor, ${\Delta}K_{th}$, fatigue crack growth rate, da/dN, on fatigue crack growth is obstructed by the compressive residual stress was determined at each $5.619\;MPa\sqrt{m}$(Un-peening), $8.319\;MPa\sqrt{m}$(1800rpm), $8.797\;MPa\sqrt{m}$(2200rpm), $7.835\;MPa\sqrt{m}$(2600rpm), $7.352\;MPa\sqrt{m}$(3000rpm) (2) Existing compressive residual stress by effect of shot velocity of shot-peening on relation of crack length. a, and number of cycle, N, was 2 times progressed in case of 2200rpm than specimen of Un-peening on fatigue life. And fatigue life was 1.6 times progressed incase of 3000rpm by Over peening. (3) Fatigue life of Material on Paris' law, $da/dN=C({\Delta}K)^m$, that effect of material constant, C, and fatigue crack growth exponent, m, was influenced by effect of. C and m.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2383-2389
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• 2002

This paper describes an experimental study on fatigue life extension by using cold working process in fastener hole of aircraft structure. Cold working process was applied for A12024-7351 specimens by considering the effect of edge margin on fatigue life. It is generally recognized that cold working process offers a protective zone around fastener hole of aluminum aircraft structure due to the residual compressive stresses which lead to retardation of crack growth. Thus this process provides the beneficial effect of increasing the fatigue life of the component. there by decreasing maintenance costs. It has also been successfully incorporated into damage tolerance and structural integrity programs. Cold working specimens were tested at constant amplitude peak cyclic stresses. Fatigue life of cold working specimen compared with that of specimen fabricated with base material. The increase of fatigue life for cold working specimen is discussed by both considering the effect of residual compressive stresses measured by X-ray diffraction technique and quantitative effect of edge margin.