• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.129.2-129.2
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• 2005

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2004년도 추계학술발표회 발표논문집
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• pp.911-912
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• 2004

1. Cathodic hydrogen charging considerably reduced the tensile ductility of ODS steels and a 9Cr-2W RMS. The hydrogen embrittlement of ODS steels was strongly affected by specimen sampling orientation, showing significant embrittlement in the T-direction. This comes from the microstructural anisotropy caused by elongated grains of ODS steels in L-direction. 2. The ODS steels contained a higher concentration of hydrogen than 9Cr-2W RMS at the same cathodic charging condition, and the critical hydrogen concentration required to transition from ductile to brittle fracture was in the range of $10{\sim}12$ wppm, which approximately 10 times larger than that of a 9Cr-2W martensitic steel. 3. The ODS steels showed a typical ductile to brittle transition behavior and it strongly depended on the specimen sampling direction, namely L- and T-direction. In T-direction, the SP-DBTT was about 170 L, irrespective of the ODS materials, and L-direction showed a lower SP-DBTT than that of T-direction.

• Journal of Welding and Joining
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• 제7권4호
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• pp.56-67
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• 1989

In this study, the possibility of evaluating the peculiar fracture strength of weldment in high strength steels was investigated by means of a small punch(SP) test. In order to obtain the ductile-brittle transition temperature(DBTT) of SP energy by which the fracture strength of weldment in structural steels such as SS41 and SM53B steels had been evaluated in our preceding publication, the effects of notches and loading rates on SP energy were discussed. It was found that the correspondence of SP energy to critical COD at test temperature -196.deg. C showed a linear relation with some deviation. The empirical correlation with scatter band, Esp/(Esp)p = 1.67[.delta./(.delta./sub c//(.delta./sub c/)/sub p/]-0.55, was developed between the SP energy ratio and critical COD ratio of each weld structure compared with parent material at test temperature -196.deg. C. In addition, there did not appear to be a significant effect of test materials and specimen size etc. on the correlation.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1161-1162
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• 2006

In order to overcome the recrystallization embrittlement and irradiation embrittlement of Mo, which are major problems for its fusion applications, internally nitrided Mo alloys were prepared by a novel multi-step internal nitriding. Neutron irradiation was performed in the Japan Material Testing Reactor (JMTR). After irradiation, nitrided Mo alloys exhibited $\iota$ ower ductile-brittle transition temperature than irradiated TZM. These results suggested that multi-step internal nitriding was effective to the improvement in the embrittlement by irradiation. Transmission electron microscope observation revealed that TiN particles precipitated by nitriding acted as a sink for irradiation-induced defects.

• 한국생산제조학회지
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• 제20권4호
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• pp.382-385
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• 2011

There is an immense need to obtain nanometric surface finish on optical glass owing to the advantage of improved performance of the components. But owing to brittleness and hardness, optical glass is one of the materials that is difficult to ultra-precision turning. According to the hypothesis of ductile mode machining, regardless of their hardness and brittleness, will undergo a transition from brittle to ductile machining region below a critical undeformed chip thickness. Below this threshold, it is suggested that the energy required for plastic formation. Thus, plastic deformation is the predominant mechanism of material removal in machining these materials in this mode. An experimental study is conducted diamond cutting for machining BK7 glass. The investigation presents the feasibility of achieving nanometric surface and the understanding the mechanism of cutting glass, proving the cutting edge radius effect.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1398-1407
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• 2000

The structural steels of power plant show the decrease of mechanical properties due to degradation such as temper embrittlement, creep damage and softening during long-term operation at high temper ature. The typical causes of material degradation damage are the creation and coarsening of carbides(M23C6, M6C) and the segregation of impurities(P, Sb and Sn) to grain boundary. It is also well known that material degradation induces the cleavage fracture and increases the ductile-brittle transition temperature of steels. So, it is very important to evaluate degradation damage to secure the reliable and efficient service condition and to prevent brittle failure in service. However, it would not be appropriate to sample a large test piece from in-service components. Therefore, it is necessary to develop a couple of new approaches to the non-destructive estimation technique which may be applicable to assessing the material degradation of the components with not to influence their essential strength. The purpose of this study is to propose and establish a new electrochemical technique for non-destructive evaluation of material degradation damage for Cr-Mo steels which is widely used in the high temperature structural components. And the electrochemical anodic polarization test results are compared with those of semi-nondestructive SP test.

• Nuclear Engineering and Technology
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• 제38권5호
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• pp.405-410
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• 2006

Microstructural features and their related mechanical property changes in the 309L cladding and the heat affected zone (HAZ) of SA508 cl.3 steel were investigated through the use of TEM, tensile and small punch (SP) tests. The specimens were irradiated at 563 K up to the neutron fluences of $5.79{\times}10^{19}n/cm^2$ (>1MeV). The microstructure of the clad was mainly composed of a fcc ${\gamma}-phase$, a low percentage of bcc ${\delta}-ferrite$, and a brittle ${\sigma}-phase$. Along the weld fusion line there formed a heavy carbide precipitation with a width of $20{\sim}40{\mu}m$, showing preferential cracking during plastic deformation. The yield stress and ductile-to-brittle transition temperature (DBTT) of the irradiated clads increased. The origin of the hardening and the shift of the DBTT are discussed in terms of the irradiation-produced defect clusters of a fine size and brittle ${\sigma}-phase$.

• 한국가스학회지
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• 제2권4호
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• pp.42-46
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• 1998

소형 시험편 기술은 최소량의 재료를 사용하여 그 재료의 물리적인 거동을 특성화할 수 있기 때문에 산업설비로부터 많은 재료를 수집할 수 없는 경우에 유용한 방법이다. 본 연구에서 사용한 재료는 화력발전소 터빈로터 소재로 많이 사용되고 있는 1Cr-1Mo-0.25V강이었으며, $^630{\circ}C$에서 등온열화처리하여 5종류의 가속 열화 모사재를 만들었다. 충격시험에는 표준 시험편과 소형 시험편이 사용되었으며, 일부 소형 시험편에 소성 구속을 증가시키기 위해 측면흠을 만들어 넣었다. 표준 시험편과 소형 시험편의 충격특성을 비교하였으며 크기효과를 고찰하였고, 소형 시험편의 연성취성천이온도와 표준 시험편의 연성취성천이온도와의 상관관계를 만들었다. 따라서 소형 시험편의 충격시험결과로부터 표준 시험편의 충격특성을 추정하는 것이 가능하게 되었다.

• Geomechanics and Engineering
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• 제22권3호
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• pp.219-226
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• 2020

Unconfined compression test (UCT) is widely conducted in laboratories to evaluate the mechanical behavior of frozen soils. However, its results are sensitive to the initial conditions of sample creation by freezing as well as the end-surface conditions during loading of the specimen into the apparatus for testing. This work compared ice samples prepared by three-dimensional and one-dimensional freezing. The latter created more-homogenous ice samples containing fewer entrapped air bubbles or air nuclei, leading to relatively stable UCT results. Three end-surface conditions were compared for UCT on ice specimens made by one-dimensional freezing. Steel disc cap with embedded rubber was found most appropriate for UCT. Three frozen materials (ice, frozen sand, and frozen silt) showed different failure patterns, which were classified as brittle failure and ductile failure. Ice and frozen sand showed strain-softening, while frozen silt showed strain-hardening. Subsequent investigation considered the influence of fines content on the unconfined compression behavior of frozen soil mixtures with fines contents of 0-100%. The mixtures showed a brittle-to-ductile transition of failure patterns at 10%-20% fines content.

• 한국재료학회지
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• 제4권5호
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• pp.590-599
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• 1994

취성재료의 균열첨단에서 전위의 이동에 대한 거동을 이해하기 위하여 단결정의 알루미나에 대한 취성-연성 전이(BDT)에 대한 한 연구가 진행되었다. 여러 온도에서, 예비균열된 시편으로 4점 굽힘시험을 이용하여 임계응력확대계수와 항복강도가 측정되었다. 그 결과로, BDT온도는 변형속도와 시편 방향에 따라 달랐다.:(1120)파단면에 대하여 $4.2 \times 10^{-6}$와 $4.2 \times 10^{-7}s^{-1}$에서 BDT온도는 각각$1034^{\circ}C$, $1150^{\circ}C$이었다. 또한 4점굽힘 시험을 이용하여 연성영역에서 균열첨단으로 부터 방출된 전위의 이동거리과 방향은 에칭 피트법에 의해서 측정되었다. 이중 에칭법을 이용하여 즉정된 사파이어에서 전위의 이동속도는 모델링 연구에 응용되었다.