• Journal of Welding and Joining
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• 제32권2호
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• Steel and Composite Structures
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• 제34권2호
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• pp.189-213
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• 2020

Stainless-clad (SC) bimetallic steels that are manufactured by metallurgically bonding stainless steels as cladding metal and conventional mild steels as substrate metal, are kind of advanced steel plate products. Such advanced composite steels are gaining increasingly widespread usage in a range of engineering structures and have great potential to be used extensively for large civil and building infrastructures. Unfortunately, research work on the SC bimetallic steels from material level to structural design level for the applications in structural engineering field is very limited. Therefore, the aim of this paper is to investigate the material behaviour of the SC bimetallic steels under the cyclic loading which structural steels usually could encounter in seismic scenario. A number of SC bimetallic steel coupon specimens are tested under monotonic and cyclic loadings. The experimental monotonic and cyclic stress-strain curves of the SC bimetallic steels are obtained and analysed. The effects of the clad ratio that is defined as the ratio of the thickness of cladding layer to the total thickness of SC bimetallic steel plate on the monotonic and cyclic behaviour of the SC bimetallic steels are studied. Based on the experimental observations, a cyclic constitutive model with combined hardening criterion is recommended for numerical simulation of the cyclic behaviour of the SC bimetallic steels. The parameters of the constitutive model for the SC bimetallic steels with various clad ratios are calibrated. The research outcome presented in this paper may provide essential reference for further seismic analysis of structures fabricated from the SC bimetallic steels.

• Nuclear Engineering and Technology
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• 제20권2호
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• pp.88-104
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• 1988

이차원의 유한요소법을 이용하여 axisymmetric R-$\theta$system으로 나누어서 정상과 부하추종 운전시에 핵연료 페렛트와 피복관의 열역학적 거동을 분석하기 위해서 FURA전산코드를 개발하였다. 온도분포와 내부압력을 정확히 계산하기 위해서 페렛트와 피복관의 변형과 핵분열의 기체방출을 전체 핵연료봉 길이로 고려하였다. 열역학적 평 형방정식을 얻기 위해서 Galerkin's Technique과 가상일의 원리를 사용하였고 역학적 해석을 위해서 탄성-소성, 크리프뿐만아니라 스엘링, 재배열, 고밀화 현상등을 고려하였다. 기하학적 모델에서는 4-결점 요소라 페레트 길이의 1/2만을 택하였다. 비선형식을 안정하게 해석하기 위해서 음해법을 도입하여 뉴튼-랩손 반복법을 적용하였다 이 코드의 검증은 해석해와 실험데이타로 비교하였다. 핵연료봉의 일반적인 거동은 axisymmetry system으로 계산하였고 균열된 페레트에 접촉하는 피복관의 거동은 R-$\theta$system을 사용하였다. 부하추종에 의한 피복관의 변형시효의 민감도는 출력율, 진동수, 진폭등으로 비교하였다.

• Nuclear Engineering and Technology
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• 제41권2호
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• pp.179-186
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• 2009

This paper presents a thermal creep test under internal pressure and post-test characterization performed on high burnup (68 MWd/kgU) ZIRLO. This research has been done by the CSN, ENRESA, and ENUSA in order to investigate the behavior of advanced cladding materials in contemporary PWRs at higher burnup under dry cask storage conditions. Also, to investigate the hydride reorientation, the cool-down of the samples after the test has been done in a coordinated manner with the internal pressure. The creep results obtained are consistent with the expected behavior from reference CWSR material, Zr-4. During the test, the material retained significant ductility: one specimen leaked during the test at an engineering strain of the tube section of 17%; remarkably, the crack closed due to de-pressurization. Although significant hydride reorientation occurred during the cool-down under pressure, no specimen failed during the cool-down.

• Nuclear Engineering and Technology
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• 제30권3호
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• pp.202-211
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• 1998

Interfacial stresses at two-material interfaces and initial displacement field over the entire domain are obtained by modifying the potential energy functional with a penalty function, which enforces continuity of the stresses at the interface of two materials. Based on the initial displacement field and interfacial stresses, a new methodology to generate a continuous stress field over the entire domain has been proposed by combining the modified projection method of stress-smoothing and Loubignac's iterative method of improving the displacement field. Stress analysis is carried out on two examples made of dissimilar materials : one is a two-material cantilever composed of highly dissimilar materials and the other is a zirconium-lined cladding tube made of slightly dissimilar materials. Results of the analysis show that the proposed method provides an improved continuous stress field over the entire domain, and accurately predicts the nodal stresses at the interface, while the conventional displacement-based finite element method produces significant stress discontinuities at the interface. In addition, the total strain energy evaluated from the improved continuous stress field converges to the exact value in a few iterations.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1541-1550
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• 2001

This paper describes experimental investigations in the direct extrusion of copper clad aluminum rods through conical dies. Composite materials consist of two or more different material layers. Copper clad aluminum composite materials are being used fur economic and structural purposes and the development of an efficient production method of copper clad aluminum composite material rods by extrusion is very important, It is necessary to know the conditions in which successful uniform extrusion ,and sound cladding may be carried out without any defects in the direct extrusion. There are several variables that have an influence on determining a sound clad extrusion. In order to investigate the influence of these parameters on the hot direct extrudability of the copper clad aluminum composite material rods, the experimental study have been performed with various extrusion temperatures, extrusion ratios and semi-cone angles of die. Subsequently, the microscopic inspection of interface bonding is carried out for extruded products. By measuring hardness, along extrusion way of products, a variation of hardness has been discussed. Proportional flow state has been considered by measuring radius ratio of Cu sleeve and Al core before and after extrusion.

• 자원리싸이클링
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• 제21권5호
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• pp.18-30
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• 2012

Zr은 고온에서의 높은 치수안정성, 내식성은 물론 낮은 중성자 흡수단면적을 지녀 원자력산업용 소재 중 1차 방사능 차폐재인 핵연료 피복관으로 사용되며 현재까지 다른 소재로 대체 불가능하다. 하지만 Hf을 정제한 Zr sponge 제조기술은 미국, 프랑스, 러시아만 가지고 있어 원자력의존도가 높은 한국에서는 국가전략물자로 분류 철저히 관리되고 있다. 국내 유통되는 Zr의 대부분은 원자력산업에 사용되어 지며 유통구조는 정제된 Zr합금을 국외로부터 수입하여 tube로 가공 후 핵연료집합체로 제조되고, 그 외 소량이 합금첨가원소 및 폭약재 등 고부가가치 일반산업에 사용된다. 본 논문에서는 Zr 제조기술에 대한 현재산업현황 및 정련기술을 살펴보고, 최근 연구되고 있는 Electrolytic reduction process와 Molten oxide electrolysis와 같은 신 제련기술에 대한 소개 및 Zr recycling의 전반적인 기술소개도 포함하였다.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1333-1344
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• 2019

An integrated approach of model simplification for high burnup spent nuclear fuel is proposed based on material calibration using optimization. The spent fuel rods are simplified into a beam with a homogenous isotropic material. The proposed approach of model simplification is applied to fuel rods with two kinds of interfacial configurations between the fuel pellets and cladding. The differences among the generated models and the effects of interfacial bonding efficiency are discussed. The strategy of model simplification adopted in this work is to force the simplified beam model of spent fuel rods to possess the same compliance and failure characteristics under critical loads as those that result in the failure of detailed fuel rod models. It is envisioned that the simplified model would enable the assessment of fuel rod failure through an assembly-level analysis, without resorting to a refined model for an individual fuel rod. The effective material properties of the simplified beam model were successfully identified using the integrated optimization process. The feasibility of using the developed simplified beam models in dynamic impact simulations for a horizontal drop condition is examined, and discussions are provided.

• Nuclear Engineering and Technology
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• 제20권3호
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• pp.189-196
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• 1988

핵연료소결체의 편심이 정상상태에서 핵연료봉 열적 성능에 미치는 영향을 조사하였다. 지배방정식은 핵연료소결체와 피복관영역에 대해 2차원 원통좌표계 (r, $\theta$)로 각각 세우고 유한요소법으로 풀었다. 갭(gap)영역에서 방위각 의존적인 열전달계수를 사용하여 동심구조는 그대로 두는 반면 갭크기의 비대칭성을 고려하였다. 재료물성치는 온도의 함수로 사용되었으며 체적 열발생은 반경의 함수로 고려하였다. 핵연료 소결체의 편심으로 인해 피복관 외부 표면에서 최대국부열속은 증가하였고, 핵연료 소결체의 최대온도와 핵연료 평균온도는 감소하였다. 전자는 최소 DNBR계산시 불확실도에 영향을 미칠 것으로 생각되며, 후자의 두현상은 핵연료 소결체의 용융 가능성과 사고시 핵연료 잠재에너지를 줄어들게 할 것으로 예상된다. 또한, 핵연료 소결체의 편심으로 인해 핵연료 소결체의 온도분포는 비대칭을 이루고 최대온도의 위치는 변동되었다.

• Nuclear Engineering and Technology
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• 제48권4호
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• pp.1009-1014
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• 2016

SiC-based ceramic composites are currently being considered for use in fuel cladding tubes in light-water reactors. The joining of SiC ceramics in a hermetic seal is required for the development of ceramic-based fuel cladding tubes. In this study, SiC monoliths were diffusion bonded using a Ti foil interlayer and additional Si powder. In the joining process, a very low uniaxial pressure of ~0.1 MPa was applied, so the process is applicable for joining thin-walled long tubes. The joining strength depended strongly on the type of SiC material. Reaction-bonded SiC (RB-SiC) showed a higher joining strength than sintered SiC because the diffusion reaction of Si was promoted in the former. The joining strength of sintered SiC was increased by the addition of Si at the Ti interlayer to play the role of the free Si in RB-SiC. The maximum joint strength obtained under torsional stress was ~100 MPa. The joint interface consisted of $TiSi_2$, $Ti_3SiC_2$, and SiC phases formed by a diffusion reaction of Ti and Si.