• 열처리공학회지
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• 제6권1호
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• pp.1-8
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• 1993

In this paper, the surface roughness influenced by Sm45C hardness in high frequency induction hardening and mechanical characteristics for the changed Hv 598 part and the unchanged hardness Hv 223 part by use of cermet and ceramic cutting tools was experimentally examined. Finally, we could be had some important results by processing surface roughness on cutting conditions such as cutting speed, feed rate, depth of cut and changes of tool nose radius. The results are summarized as follows. 1. In case of the same cutting condition, the hardness of workpiece was high and acquired the best processing surface roughness when the radius of the tool nose had 0.8 mm and feed rate was 0.04 mm/rev. 2. In case of the hardness of workpiece, though the cutting speed didn't have an effect on processing surface roughness, the less feed rate and the more processing surface roughness improved. On the other hand, the low inside the hardness of workpiece, the more cutting speed and the more feed rate increase, the processing surface of roughness improved. 3. Regardless of the hardness of workpiece, the change of the cutting depth didn't have great effect on the surface roughness. 4. On cutting the high surface hardness part with cutting tools of cermet and ceramic, it can be acquired the higher processing surface roughness because it hadn't been taken effect on cutting speed, In case of the cutting process of the low inside hardness part the two cutting tools have acquired the similar processing surface roughness.

• 한국방사선학회논문지
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• 제12권3호
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• pp.389-395
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• 2018

본 연구는 두부 인체모형 팬텀을 컴퓨터 단층촬영 장치를 이용하여 스캔 후 영상에서 발생한 선속경화현상을 고 관전압 적용 방법과 본 연구에서 적용한 금속인공물감소 알고리즘 적용 영상을 비교하여 금속인공물감소 알고리즘 적용의 유용성을 알아보고자 하였다. 그 결과 관전압을 140 kVp로 높여 스캔 시 CT value가 0.02~0.05 % 감소하여 선속경화현상 감소 효과가 상대적으로 낮았으며(P>0.05), 금속인공물감소 알고리즘 적용 시 CT value가 12.4~26.9 % 감소하여 선속경화현상 감소 효과에 상대적으로 의미가 있는 것으로 분석되었다(p<0.05). 또한 임상영상평가표에 의한 정성적 평가에서도 인공물의 경우 MAR알고리즘 적용 후 1.8점으로 평가 되었고, 해상도 및 대조도 평가에서 MAR알고리즘 후 7.2점으로 평가되어 선속경화현상 감소에 있어 금속인공물감소 알고리즘 적용이 의미가 있는 것으로 평가되었다. 따라서 불가항력적으로 발생하는 선속경화 현상에 의한 인공물의 경우 기존연구에서 도출한 다양한 방법과 더불어 본 실험을 통해 제시한 금속인공물 감소 알고리즘을 적용하여 스캔한다면 선속경화현상에 의해 발생한 인공물 감소에 유용할 것으로 사료된다.

• Tribology and Lubricants
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• 제32권1호
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• pp.18-23
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• 2016

The effective case depth for case-hardened rolling bearing has been discussed. For this purpose, rolling contact fatigue tests for ball bearings built with inner race of various hardness values were conducted until L₁₀ calculating rating life using a bearing life test machine under radial loading. Then, the distribution of residual stress below the inner raceway, which depended on the hardness value, was measured by X-ray diffraction. As a result, the linear relationship was established between the hardness value of the inner race and the theoretical shear stress evaluated at the depth where the residual stress disappeared below the inner raceway. Based on the relationship, it could be found that the factor of safety in bearing manufacturer’s rules for the effective case depth of case hardened rolling bearings was set higher. However, it could be also found that the hardness values at the depth where the maximum shearing stress acted below the raceway surface in a tapered roller bearing hardened by the carburizing process, were not sufficient for preventing plastic deformation under the basic dynamic load rating. Consequently, further efforts were still required to reduce or to disperse the contact load on the material design of a rolling bearing in order to prolong its life.

• 보존과학연구
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• 통권7호
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• pp.278-291
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• 1986

In this report the practical case of Viking ship's conservation in Denmarke specially among the Eurpoean nations is introduced. The contents of it are summarized as follows :From 1957 to 1962 the Danish National Museum Salvaged five Viking ships from the bottom of Roskilde Fjord, Which were composed of the pieces of timber whose surface was soft because they had lain on the sea bed for about a thousand years. Excavation had been carried out in the same way as in the field by driving down a sheet piling around the wrecks and pumping the water out. These pieces of the wreck ships were packed in airtight plastic bags one by one to be transported for Brede and then immidiately had to go through the treatment for conservation. The conservation treatment process for the pieces includes three steps ; the preliminary process prior to the hardening treatment, the hardening and the assemble of the ships. In the first step ; the preliminary process, all remains of mud and shells from the fjord bed are washed off, and measuring followed ; every single piece of wreckage was drawn so that the form and size of the piece, nail holes, and breaks were registered before conservation. In the second ; the hardening treatment step, the pieces of the woreckage were filled with P.E.G. This Polyethylene Glycol method was the best to handle in the subsequent mounting of the ships in the museum. In the final, the Glycol-treated pieces were pieced together to spips with support of a system of reinforcements. They were to fit in place after corrections of the form were made several times.

• 전산구조공학
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• 제5권1호
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• pp.119-132
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• 1992

반복하중을 받는 짧은 I보(Beam)의 횡-비틀림 좌굴(Lateral-Torsional Buckling)에 대한 광범위한 Parametric Study를 수행하여 보의 좌굴현상을 좀 더 깊이 고찰하고자 한다. 유한한 비틀림변형의 뒤틀림(Warping)이외에 미소한 절단변형의 뒤틀림도 고려한 기하학적(완전) 비선형의 일차원 보를 해석적 모델로 사용하고, 또한 금속의 주기적소성(Cyclic Plasticity)거동을 보다 잘 나타내기 위해 다축 주기적소성모델을 Consistent Return Mapping Algorithm과 결합시켜 적용한다. 기준치 근방에서 아래와 같은 여러가지 Parameter Study를 수행하므로써 반복하중을 받는 짧은 I보의 횡-비틀림 좌굴의 일반적 응답을 고찰한다 : 재료의 강복강도, 강복플래토(Yield Plateau), 변형율경화, 이동경화(Kinematic Hardening), 잔류응력, 작용하중의 절단중심에 대한 편심률, 작용하중의 보 단면에 대한 높이, 작용하중의 보 길이방향의 위치, 보 단면의 치수, 작용하중으로부터 멀리 떨어진 지지단의 고정도.

• 대한토목학회논문집
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• 제2권4호
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• pp.23-32
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• 1982

강구조물(鋼構造物)의 안전유지(安全維持) 및 보수보강(補修補强)에 필요한 자료(資料)를 얻기 위해, 공용이역(供用履歷)을 갖는 강재(鋼材)와 갖지 않는 강재(鋼材)의 기계적(機械的) 성능(性能) 및 인성변화(靭性變化)를 실험적(實驗的) 방법(方法)을 통(通)해 비교검토 하였다. 본(本) 연구(硏究)에서는, 공용중(供用中)에 받은 피로누적(疲勞累積)에 의한 경화(硬化) 및 취화인성저하(脆化靭性低下)등을 검토하였으며, 파악된 사항이 강구조물(鋼構造物) 연결방법(連結方法)에 사용되고 있는 용접(鎔接)에 미치는 영향을 고찰하였다. 그 결과(結果), 경화(硬化) 및 취화(脆化)의 영향은 강도증가(强度增加) 보다 인성저하(靭性低下)에 더 많은 작용을 하였으며, 강구조물(鋼構造物) 연결방법(連結方法)으로 채택한 용접(鎔接)에서도 같은 경향을 보였다. 또한 공용이역(供用履歷)을 갖는 강재(鋼材)와 갖지 않는 강재(鋼材)를 용접(鎔接)하였을 경우에는 상온(常溫)에서도 취성(脆性)을 나타내고 있음을 알 수 있었다.

• 열처리공학회지
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• 제13권4호
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• pp.224-230
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• 2000

Garbon steel(SM35C) was gas nitrocarburized at $580^{\circ}C$ in $55%N_2-40%NH_3-5%CO_2$ mixed gas atmosphere, and then the steel was induction hardened at $850^{\circ}C$. The microstructure of gas nitrocarburized surface layer was observed by optical microscope and SEM. The phase analysis was carried out by X-ray diffraction method. The mechanical properties of gas nitrocarburized SM35C steel was evaluated by hardness, wear and fatigue test. The thickness of compound and diffusion layer were increased with increasing the gas nitrocarburizing time and the densest compound layer was obtained at 3 hours gas nitrocarburizing time. In case of 15sec induction hardening after gas nitrocarburizing, the surface hardness was decreased from 800Hv to 630Hv owing to the decomposition of compound layer, but wear resistance was increased because of increased hardness of diffusion layer. The fatigue strength of induction hardened steel after gas nitrocarburizing, $58kgf/mm^2$, was higher than $41.5kg/mm^2$ of gas nitrocarburized steel and $45kg/mm^2$ of induction hardened steel, respectively.

• 한국산학기술학회논문지
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• 제17권4호
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• pp.718-725
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• 2016

본 논문에서는 대형 선박의 판형 열교환기 등에 널리 이용되고 있는 순 티타늄 판재의 소성변형을 유한요소해석하기 위한 기초 데이터로서 순 티타늄 판재의 유동곡선을 평가하였다. 순 티타늄 판재의 프레스 가공 시에 판재에는 국부적으로 큰 소성변형이 발생하고 있다. 그러나 기존의 단축 인장실험에서 얻을 수 있는 소성변형률이 낮아서 티타늄 판재의 가공공정 설계를 위한 유한요소해석의 정밀도를 떨어뜨리는 경우가 있다. 본 연구에서는 큰 소성변형률 까지 안정적으로 성형이 가능한 유압벌지실험을 수행하여 재료의 소성변형에서 가공경화특성을 나타내는 유동곡선으로써 진응력-진변형률 선도를 구하였고 그 결과를 인장실험 결과와 비교하였다. 순 티타늄 판재의 유압벌지실험에서 재료의 변형률은 3D 디지털 영상상관법을 이용한 ARAMIS 시스템으로 실시간 측정된다. 이 유압벌지실험으로부터는 소성 변형률이 0.65 이상 까지도 안정적으로 재료의 소성유동곡선을 얻을 수 있었으며 그 결과는 Kim-Tuan 이 문헌 17[Y.S. Kim, J.H. In, Korean Acadmia-Ind. Coop. Soc.,(be in print), 2016] 의 연구에서 제안한 가공경화식으로 잘 핏팅됨을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1970-1977
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• 2019

Understanding the irradiation hardening effect of structural steels under various irradiation conditions plays an important role in developing advanced nuclear systems. Such being the case, a crystal plasticity model for body-centered cubic (BCC) crystal based on the density of dislocations and irradiation defects is summarized and numerically implemented in this paper. Based on this model, nano-indentation hardness of Chinese A508-3 steels with ion irradiation is calculated. Very good agreement is observed between simulation and experimental data of several different irradiation doses subjected to various operating temperatures, from which, it can be concluded that indentation hardness increases with increasing irradiation dose at both room temperature and high temperature. Consequently, the validity of this model has been proved properly, and furthermore, the model established in this paper could guide the study of irradiation hardening effect and temperature effect to some extent.

• Computers and Concrete
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• 제22권2호
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• pp.227-237
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• 2018

Today, the modeling of concrete as a material within finite element simulations is predominantly done through nonlinear material models of concrete. In current sophisticated computational systems, there are a number of complex concrete material models which are based on theory of plasticity, damage mechanics, linear or nonlinear fracture mechanics or combinations of those theories. These models often include very complex constitutive relations which are suitable for the modeling of practically any continuum mechanics tasks. However, the usability of these models is very often limited by their parameters, whose values must be defined for the proper realization of appropriate constitutive relations. Determination of the material parameter values is very complicated in most material models. This is mainly due to the non-physical nature of most parameters, and also the large number of them that are frequently involved. In such cases, the designer cannot make practical use of the models without having to employ the complex inverse parameter identification process. In continuum mechanics, however, there are also constitutive relations that require the definition of a relatively small number of parameters which are predominantly of a physical nature and which describe the behavior of concrete very well within a particular task. This paper presents an example of such constitutive relations which have the potential for implementation and application in finite element systems. Specifically, constitutive relations for modeling the plane stress state of concrete are presented and subsequently tested and evaluated in this paper. The relations are based on the incremental theory of elastic strain-hardening plasticity in which a non-associated flow rule is used. The calculation result for the case of concrete under uniaxial compression is compared with the experimental data for the purpose of the validation of the constitutive relations used.