The seismic separation joint is an important device that absorbs vibration displacement from earthquake shock and protects fire extinguishing pipes and various utility pipes. In this study, the mechanical behavior occurring in U-typed and V-typed seismic separation joint was analyzed according to the length of the bellows, the length of the elbow straight pipe, and the open angle. As a result, as the length of the bellows increased, the stress and natural frequency decreased. In addition, as the length of the elbow straight pipe increased, the stress tended to decrease in the case of forced displacement in the vertical direction. As the open angle increased, the stress in the case of forced displacement in the left and right directions increased.

For the performance analysis of deep geological repository systems, numerical simulation with multi-physics is required, which specifically covers Thermal (T), Hydraulic (H), and Mechanical (M) behaviors in the disposal environment. Numerous simulation models have been developed so far, each of which varies in the approach and methodology for solving THM problems. Fully-coupled THM simulation codes such as ROCMAS, THAMES, and CODE_BRIGHT were mainly developed in the initial stage of DEvelopment of COupled models and their VALidation against EXperiments (DECOVALEX), with the advantage of thorough calculations consisting of correlated several variables on different physics. Due to the difficulty of solving the complex Jacobian Matrix and the following burden for the computational calculation, weakly-coupled THM models have been suggested in recent researches: TOUGH2-MP with FLAC3D, TOUGH2 with UDEC and OpenGeoSys with FLAC3D. This methodology of loose coupling allows the practical use of computational code optimized for each physics, thereby increasing the efficiency in simulation. However, these suggested models require two different numerical codes to calculate THM behaviors, which leads to several inherent issues: compatibility during maintenance, updating and dependency between two codes. In this study, therefore, the authors build a unified code for simulating THM behaviors in the deep geological repository. The concept involves the iterative sequential coupling between TH and M for calculation efficiency. As having developed the simulation code, High-level rAdiowaste Disposal Evaluation System (HADES), to describe TH behavior based on Multi-physics Object-Oriented Simulation Environment (MOOSE) software, the authors make a milestone to develop and couple the MOOSE-based new code for M behavior as Sub-app, with the previous HADES set to be Main-app. New model for M behavior will be verified with the benchmark case of DECOVALEX-THMC Task D, comparing the mechanical simulation results: stress evolution over time, profiles of stress and vertical displacement. The existing simulation results from HADES will also be updated with the coupled calculations, with regard to temperature and saturation. Additionally, the effective stress evolution can be assessed in terms of repository’s stability with Spalling Strength and Mohr-Coulomb failure criterion. This concept for new simulation model has its meaning in that it aims to demonstrate the specific methodology of loosely coupling multi-physics in unified simulation code and analyze THM complex interactions with considering mutual influence on various physics. It is expected that HADES can be renewed as an integral simulation model for deep geological repository systems by possessing the capacity for analyzing and assessing mechanical behavior.

Research on the safety of nuclear spent fuel has been heavily experimented and modelled from a mechanical perspective. The issues of corrosion, irradiation creep, hydride and hydrogen embrittlement have been addressed more than two decades since the early 2000s. Among these degradation behavior, hydrogen embrittlement and hydride reorientation have been the most important topics for establishing the integrity of nuclear spent fuel and have been studied in depth. In order to assess the safety of spent nuclear fuel, firstly, it is necessary to establish the safety criteria in all nuclear cycle, i.e., the failure criteria guidelines for nuclear fuel assemblies and nuclear fuel rods, and then examine the safety analysis. The contents of U.S.NRC Regulations, Title 10 General, Chapter 1 Code of Federal Regulation (CFR), Part 50, 71 and 72, describe the safety criteria for the safety assessment of nuclear fuel assemblies and nuclear fuel rods. In this study, technically important points in safety analysis on nuclear fuel are checked through the reference of those NRC regulation. As result, we confirmed that the safety assessment of nuclear fuel after 20 years of interim storage is now being tested by ORNL and PNNL. There are not quantitative criteria related to material safety. However qualitative criteria which is dependent on environmentally condition describe the safety analysis. There is some literature study about DBTT, yield stress, ultimate tensile strength, flexural rigidity data. In FRAPCON code Modelling of yield strength and creep had been established, but radial hydride or hydride reorientation has not considered.

In recent years, the importance of the thermo-hydraulic-mechanical-chemical coupled processes is increasing in the performance assessment (PA) of the high-level radioactive waste repository. In the case of mechanical behavior, it is very important because it can affect fluid flow and radionuclide transport by changing the porosity and permeability of the medium. In particular, Excavation Damaged Zone (EDZ) should be considered essential in PA because the migration of radionuclide is affected by the enhanced hydraulic transmissivity and altered geomechanical behavior of EDZ. Furthermore, due to various thermo-hydraulic behaviors such as decay heat generated from radioactive waste, pore water pressure increase, and swelling pressure of bentonite buffer material, mechanical evolution is occurred which may change the size and physical properties of EDZ. Therefore, to solve this problem, analysis of coupled thermal-hydraulic-mechanical (THM) processes with the effect of long-term evolution of EDZ due to the mechanical behavior should be accompanied. In this study, numerical model for the long-term evolution due to mechanical behavior considering EDZ using the Adaptive Process-based total system performance analysis framework for a geological disposal system (APro) proposed by the Korea Atomic Energy Research Institute (KAERI). In the case of EDZ, the concept of Mazars’ damage evolution model was applied to simulate the behavior using the continuum model, and the change in hydraulic properties according to the degree of damage was considered. To investigate the importance of mechanical behavior in PA, the results were compared by performing numerical analysis according to the presence or absence of mechanical analysis. Finally, numerical analysis considering the mechanical evolution of EDZ was conducted using the model developed in this study to investigate the effect of EDZ.

Transition metal carbides (TMCs) are used to process difficult-to-cut materials due to the trend of requiring superior wear and corrosion properties compared to those of cemented carbides used in the cutting industry. In this study, TMC (TiC, TaC, Mo2C, and NbC)-based cermets were consolidated by spark plasma sintering at 1,300 oC (60 oCmin) with a pressure of 60 MPa with Co addition. The sintering behavior of TMCs depended exponentially on the function of the sintering exponent. The Mo2C-6Co cermet was fully densified, with a relative density of 100.0 %. The Co-binder penetrated the hard phase (carbides) by dissolving and re-precipitating, which completely densified the material. The mechanical properties of the TMCs were determined according to their grain size and elastic modulus: TiC-6Co showed the highest hardness of 1,872.9 MPa, while NbC-6Co showed the highest fracture toughness of 10.6 MPa*m1/2. The strengthened grain boundaries due to high interfacial energy could cause a high elastic modules; therefore, TiC-6Co showed a value of 452 ± 12 GPa.

Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 μm. The hardness of STS 440C alloy is improved by austenitization at 1,100 oC with sub-zero treatment and tempering at 200 oC. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.

Abdominal organs are the most vulnerable body parts under vehicle trauma, and there is high mortality from acute injuries in accidents. There are various ways to reduce this high mortality; one method is Resuscitative Endovascular Balloon Occlusion of the Aorta, which has recently become very popular as a minimally invasive alternative in the emergent management of patients with non-compressible hemorrhages below the diaphragm. However, high safety factor for patients is applied in actual clinical practice because there is no exact standard for the operating time. Therefore, in this study, the effects of the mechanical behavior of organ tissues for the duodenum, kidney, and liver on the operating time of Resuscitative Endovascular Balloon Occlusion of the Aorta is investigated in order to obtain data needed to establish standards of operating time. In characteristic analysis of organ tissues, uniaxial tensile test and compression test are conducted according to the operating time.

Titanium aluminides have attracted special interest as light-weight/high-temperature materials for structural applications. The major problem limiting practical use of these compounds is their poor ductility and formability. The powder metallurgy processing route has been an attractive alternative for such materials. A mixture of Ti and Al elemental powders was fabricated to a mechanical alloying process. The processed powder was hot pressed in a vacuum, and a fully densified compact with ultra-fine grain structure consisting of Ti3Al intermetallic compound was obtained. During the compressive deformation of the compact at 1173 K, typical dynamic recrystallization (DR), which introduces a certain extent of grain refinement, was observed. The compact had high density and consisted of an ultra-fine equiaxial grain structure. Average grain diameter was 1.5 μm. Typical TEM micrographs depicting the internal structure of the specimen deformed to 0.09 true strain are provided, in which it can be seen that many small recrystallized grains having no apparent dislocation structure are generated at grain boundaries where well-developed dislocations with high density are observed in the neighboring grains. The compact showed a large m-value such as 0.44 at 1173 K. Moreover, the grain structure remained equiaxed during deformation at this temperature. Therefore, the compressive deformation of the compact was presumed to progress by superplastic flow, primarily controlled by DR.

유한요소법(finite element method)은 다양한 분야에서 재료의 역학적 거동을 더욱더 현실적으로 해석하고 예측하는 방법으로 다양한 분야의 제품 개발에 적용되고 있다. 하지만 섬유배향과 변형률 속도가 역학적 특성에 영향을 미치는 유리섬유 강화 플라스틱 복합재료에 관한 수치해석을 이용한 접근 방법은 현재까지 다소 어려움이 있다. 본 연구의 목적은 고분자, 고무, 금속 등과 같은 다양한 복합재료를 위한 선형, 비선형 다중스케일 재료 모델링 프로그램인 Digimat의 수치해석 재료 모델을 활용하여 유리섬유 강화 플라스틱 복합재료의 역학적 특성을 정의하고 검증하는 것에 있다. 또한 이를 통해 좀더 현실 적으로 고분자 복합재료의 거동을 예측하고자 한다. 이를 위해 다양한 고분자 중 30wt%의 단섬유 질량 비율을 갖는 폴리부 틸렌 텔레프탈레이트(polybutylene terephthalate, PBT)의 섬유배향과 변형률 속도에 따른 인장 특성을 참고문헌을 통해 조사하였다. 또한 Moldflow 프로그램을 사용한 사출해석을 통해 유리섬유 배향 정보를 계산하였으며 이를 매핑(mapping) 과 정을 통해 유한요소 인장 시편 모델에 전달하였다. 대표적인 유한요소 상용 프로그램 중 하나인 LS-DYNA는 유리섬유 배향과 변형률 속도에 따른 복합재료의 인장 특성을 연구하기 위해 Digimat과의 연성해석(coupled analysis)에 활용되었다. 그리고 유리섬유 강화 플라스틱 복합재료를 해석하기 위한 LS-DYNA의 다양한 비등방성(anisotropic) 재료 모델들의 장단점을 서로 비교하고 평가하였다.

고준위방사성폐기물의 처분터널 및 처분공 간격을 결정하고 처분시스템의 성능을 평가하기 위해서는 열-수리-역학적인 복합 거동 변화에 대한 이해가 반드시 필요하고 이를 반영하여 해석해야만 한다. 하지만 한국형 기준 처분시스템에서의 처분 터널 및 처분공 간격을 결정하기 위해 수행된 기존의 연구들은 이러한 복합거동 특성을 반영하지 않고 열 해석 결과만을 근거로 처분시스템을 설계하였다. 따라서 본 연구에서는 열-수리-역학적인 복합거동 특성을 반영하여 한국형 기준 처분시스템의 성능을 TOUGH2-MP/FLAC3D를 이용하여 평가하였다. 고준위방사성폐기물이 처분된 이후 방사성 붕괴열에 의해 처분 시스템의 온도는 급격히 증가하다가 붕괴열의 감소로 온도는 서서히 감소하였으며, 해석 기간 1,000년 동안 벤토나이트 완충재의 최고 온도는 설계 기준인 100℃ 이하로 유지되는 것으로 나타났다. 처분용기와 벤토나이트 완충재의 계면에서의 최고 온도는 약 3.21년이 지난 시점에 용기의 중간 지점에서 약 96.2℃로 나타났으며, 암반에서의 최고 온도는 폐쇄 후 약 17년 이 지난 시점에서 약 68.2℃로 계산되었다. 처분용기 부근 벤토나이트 완충재는 처분 초기에 온도 변화에 따른 건조현상이 발생하여 포화도가 감소하지만, 시간이 지남에 따라 주변 암반으로부터의 지하수 유입에 의해 포화도가 증가하는 것으로 계 산되었다. 이후, 벤토나이트 완충재 및 뒷채움재 모두 약 266년 이후 완전히 포화되는 것으로 계산되었다. 처분시스템에서의 온도 변화에 따른 열응력 그리고 벤토나이트 완충재 및 뒷채움재의 팽윤압으로 인한 응력 변화가 처분장 주변 암반에 미치는 영향을 평가하고자 수치해석에서 계산된 응력을 스폴링 강도(spalling strength)와 Mohr-coulomb 파괴 기준식과 비교 하였다. 계산 결과 일축압축강도와 스폴링 강도에 도달하지 않는 것으로 나타나 처분시스템이 스폴링에 의한 파괴는 나타나지 않을 것으로 판단되며, Mohr-coulomb 파괴 기준 역시 충족하는 것으로 나타났다. 본 연구에서 사용된 수치해석 코드와 방법론은 다양한 조건에서의 한국형 기준 처분시스템에 대한 성능평가뿐만 아니라, 복층 처분시스템에 대한 설계와 성능평가에 활용될 수 있을 것으로 판단된다.

고준위방사성폐기물 처분시스템에서는 방사성 핵종의 붕괴열과 암반으로부터의 지하수 유입으로 열응력 및 팽윤압의 발생으로 열-수리-역학적 복합거동(coupled thermo-hydro-mechanical behavior)이 예상되기 때문에 한국원자력연구원은 처분시스템 및 근계암반에서의 열-수리-역학적인 복합거동 특성을 평가하기 위해서 지하처분연구시설(KAERI Underground Research Tunnel, KURT)에서 2016년부터 현장시험(In-situ Demonstration of Engineered Barrier System, In-DEBS)을 수행 중에 있다. 본 연구에서는 In-DEBS 현장시험 데이터 분석하고 벤토나이트 완충재와 화강암반에서의 열-수리-역학적 복합거동 특성을 평가하기 위해 TOUGH2-MP/FLAC3D을 이용하여 수치해석을 수행하였다. 또한 벤토나이트 블록과 KURT 화강암의 열-수리-역학적 복합거동 특성을 평가하기 위해 사용된 각각의 열, 수리, 그리고 역학적 모델의 적합성을 평가하고 자 현장시험에서 계측된 온도, 상대습도, 그리고 변위의 결과와 수치해석으로 계산된 결과를 비교하였다. 온도와 상대습도의 계산 결과를 현장 데이터와 비교·분석한 결과, 전체적으로 유사한 경향을 보일 뿐만 아니라 시간에 따라 변화하는 정량적인 값 역시 유사하게 나타났다. 역학적 해석 결과를 살펴보면, 계산된 변위의 전반적인 경향은 유사하지만 해석 결과가 계측 값에 비해 상대적으로 작게 나타났다. 축대칭 모델을 이용하여 In-DEBS 현장시험에서 관측된 열-수리-역학적 복합거동 특성을 전반적으로 평가할 수 있었지만, 벤토나이트 블록 및 KURT 암반에서의 열-수리-역학적 복합거동을 면밀히 살펴보기 위해서는 추후 터널의 형상과 주변 KURT 터널의 영향을 반영한 3차원 해석이 필요할 것으로 판단된다. 본 연구에서 사용된 입력 물성과 열-수리-역학적 모델은 추후 In-DEBS 장기 거동 및 처분시스템에서의 열-수리-역학적 복합거동 특성을 평가하고 예측하는데 활용될 수 있을 것으로 기대된다.

In this study, we investigate the deformation behavior of Hf44.5Cu27Ni13.5Nb5Al10 metallic glass powder under repeated compressive strain during mechanical milling. High-density (11.0 g/cc) Hf-based metallic glass powders are prepared using a gas atomization process. The relationship between the mechanical alloying time and microstructural change under phase transformation is evaluated for crystallization of the amorphous phase. Planetary mechanical milling is performed for 0, 40, or 90 h at 100 rpm. The amorphous structure of the Hf-based metallic glass powders during mechanical milling is analyzed using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Microstructural analysis of the Hf-based metallic glass powder deformed using mechanical milling reveals a layered structure with vein patterns at the fracture surface, which is observed in the fracture of bulk metallic glasses. We also study the crystallization behavior and the phase and microstructure transformations under isothermal heat treatment of the Hf-based metallic glass.

This study investigates the oxidation properties of Fe-14Cr ferritic oxide-dispersion-strengthened (ODS) steel at various high temperatures (900, 1000, and 1100°C for 24 h). The initial microstructure shows that no clear structural change occurs even under high-temperature heat treatment, and the average measured grain size is 0.4 and 1.1 μm for the as-fabricated and heat-treated specimens, respectively. Y–Ti–O nanoclusters 10–50 nm in size are observed. High-temperature oxidation results show that the weight increases by 0.27 and 0.29 mg/cm2 for the asfabricated and heat-treated (900°C) specimens, and by 0.47 and 0.50 mg/cm2 for the as-fabricated and heat-treated (1000°C) specimens, respectively. Further, after 24 h oxidation tests, the weight increases by 56.50 and 100.60 mg/cm2 for the as-fabricated and heat-treated (1100°C) specimens, respectively; the latter increase is approximately 100 times higher than that at 1000°C. Observation of the surface after the oxidation test shows that Cr2O3 is the main oxide on a specimen tested at 1000°C, whereas Fe2O3 and Fe3O4 phases also form on a specimen tested at 1100°C, where the weight increases rapidly. The high-temperature oxidation behavior of Fe-14Cr ODS steel is confirmed to be dominated by changes in the Cr2O3 layer and generation of Fe-based oxides through evaporation.

This study investigates changes in the mechanical behaviors, especially hardness and indentation load-displacement curves, of thermal barrier coatings (TBCs) brought about by thermal shock. The TBCs on the Nickel-based bondcoat/superalloy was prepared with diameters of 25.4 mm and 600 μm thickness. The results of thermal shock cycling test from 1100 oC of the highest temperature indicate that the thermal shock do not influence on the mechanical behavior, but a continuous decrease in porosity and increase in hardness were observed after 1200 thermal shock cycles; these changes are believed to be due to sintering of thermal barrier coating materials. The results that no degradation in the indentation load-displacement curves indicate that the coating shows good thermal shock resistance up to 1200 cycles at 1100 oC in air.