• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.106-110
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• 1997

A split Hopkinson bar has been used for obtaining material properties in high strain rate state, In this paper, the apparatus was modified to obtain the high strain rate properties of sheet metal for an autobody. From the experiments with the new apparatus, the material properties of SPCEN in the high strain rate state have been acquired and compared with quasi-static experimental results.

• Computers and Concrete
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• 제11권6호
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• pp.515-529
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• 2013

The moment-curvature relation for simple bending is a well-studied subject and the classical moment-curvature diagram is commonly found in literature. The influence of axial forces has generally been considered as compression onto symmetrically reinforced cross-sections, thus strain at the reference fiber never has been an issue. However, when dealing with integral structures, which are usually statically indeterminate in different degrees, these concepts are not sufficient. Their horizontal elements are often completely restrained, which, under imposed deformations, leads to moderate compressive or tensile axial forces. The authors propose to analyze conventional beam cross-sections with moment-curvature diagrams considering asymmetrically reinforced cross-sections under combined influence of bending and moderate axial force. In addition a new diagram is introduced that expands the common moment-curvature relation onto the strain variation at the reference fiber. A parametric study presented in this article reveals the significant influence of selected cross-section parameters.

• Mycobiology
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• 제47권2호
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• pp.173-179
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• 2019

Cladophialophora is characterized by simple hyphomycetes with brown hyphae that give rise to branched chains of pale brown conidia and shows affinities with the Herpotrichiellaceae. A fungal strain belonging to the genus Cladophialophora was isolated from soil in Daegu, Korea. This strain produces numerous greenish to dark black lanose aerial mycelia with hair like structures. It is morphological similar to C. chaetospira, C. inabaensis, and C. multiseptata; however, the conidiophores and conidia sizes of the newly isolated strain (KNU16-032) are clearly different from them. The novelty of the strain was also confirmed based on phylogenetic analysis using the data sets of the internal transcribed spacer region of and the partial sequence of 28S ribosomal DNA region along with the cultural characteristics. Because morphological observations and phylogenetic analysis indicated that the strain is distinct from previously known Cladophialophora species, we propose this species as a new species Cladophialophora lanosa sp. nov., and provide the detailed descriptions in this study.

• Journal of Microbiology and Biotechnology
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• 제13권1호
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• pp.90-98
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• 2003

In vivo $^31p$ Nuclear Magnetic Resonance ($^31p$NMR) and metabolic studies were carried out on an acetic acid tolerant mutant, Zymomonas mobilis $ZM4/Ac^R$, and compared to those of the parent strain, Z. mobilis ZM4, to evaluate possible mechanisms of acetic acid resistance. This investigation was initiated to determine whether or not the mutant strain might be used as a suitable recombinant host far ethanol production from lignocellulose hydrolysates containing various inhibitory compounds. $ZM4/Ac^R$ showed multiple resistance to other lignocellulosic toxic compounds such as syringaldehyde, furfural, hydroxymethyl furfural, vanillin, and vanillic acid. The mutant strain was resistant to higher concentrations of ethanol or lower pH in the presence of sodium acetate, compared to ZM4 which showed more additive inhibition. in vivo $^31p$ NMR studies revealed that intracellular acidification and de-energization were two mechanisms by which acetic acid exerted its inhibitory effect. For $ZM4/Ac^R$, the internal pH and the energy status were less affected by sodium acetate compared to the parent strain. This resistance to pH change and de-energization caused by acetic acid is a possible explanation for the development of resistance by this strain.

• 소성∙가공
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• 제27권2호
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• pp.115-122
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• 2018

Most domestic and international standards on the forming limit diagram (FLD) including ISO 12004-2, use a 'position-dependent method,' which determines the forming limit from a strain distribution measured on the specimen after necking or fracture. However, the position-dependent method has inherent problems such as the incidence of asymmetry of a strain distribution, the estimation of missing data near fracture, the termination time of test, and the deformation due to the new stress equilibrium after a fracture, which is blamed for causing sometimes a significant lab-to-lab variation. The 'time-dependent method,' which is anticipated to be a new international standard for evaluating the forming limit, is expected to greatly improve these intrinsic disadvantages of the position-dependent method. It is because the time-dependent method makes it possible to identify and accurately determine the forming limit, just before the necking point from the strain data as continuously measured in a short time interval. In this study, we propose a new time-dependent method based on a Gaussian fitting of strain acceleration with the introduction of 'normalized correlation coefficient.' It has been shown in this study that this method can determine the forming limit very stably and gives a higher value, which is in comparison with the results of the previously studied position-dependent and time-dependent methods.

• Journal of Preventive Medicine and Public Health
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• 제36권1호
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• pp.71-76
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• 2003

Objectives : New organizational work systems, and their impact on the mental health of employees, are considered to beone of the most important topics in the area of industrial health. This study was conducted to compare job characteristics (job demand and decision latitude) levels, and psychosocial distress of workers in acompany introducing to new organizational work systems, to those of workers managed by traditional work systems. Methods ; A study sample of 627 shipbuilding workers (446the new work organizational system and 181 the traditional system) were recruited for this study. A structured-questionnaire was used to assess general characteristics, job characteristics(work demand, decision latitude), and psychosocial distress. Results : The decision latitude was not significantly higher in the new work system compared to the traditional system. However, the job demand was significantly higher in the new work system than in the traditional system. The psychosocial distress was higher within the new work system than the traditional system, but no significant relationships were found. The proportion of increased strain was significantly greater with the new system than the traditional system. Conclusion : These results suggest that increases in the decision latitude did not sufficiently compensate for higher job strain or increased work intensity. If the increase in the decision latitude was temporary, with the typical job demand remaining high, such work can be still be considered to have a job strain Futureresearch should consider psychosocial distress and fatigue as importantproblems caused by new work organizational systems, and should be performed to assess their impact through out industry.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2003년도 생물공학의 동향(XIII)
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• pp.434-437
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• 2003

A new bacterial strain, was isolated from activated sludge, identified and named P. aeruginosa EMS1. The new strain produced surface-active rhamnolipids by batch cultivation in mineral salts medium with waste flying oils. The mutant strain KH7, designated P. aeruginosa EMS1, derived by random mutagenesis with N-methyl-N-nitro-N-nitrosogoanidine treatment producing high levels of the biosurfactants was selected by an ion-pair plate assay. The mutant strain KH7 showed 4-5 times more hydrocarbon emulsification as compared to the parent when grown on waste frying oils and various hydrocarbons. Furthermore, P. aeruginosa EMS1 and mutant strain KH7 was also able to use whey as a co-substrate for growth and biosurfactant production. As results of this study, mutant strain KH7 is a very efficient biosurfactant producer, and its culture conditions are relatively inexpensive and economical. Rhamnolipid is synthesized by the rhlAB-encoded rhamnosyltransferase. To be convinced of these genes, we performed PCR based on P. aeruginosa PAO1 whole-genome database. rhl gene cluster nucleotide and amino acid sequences were compared for both parent and mutant. Comparison of nucleotide sequence of rhlAB, there were usually terminal's codons exchange.

• Steel and Composite Structures
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• 제21권4호
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• pp.921-947
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• 2016

Concrete Filled Fibre Reinforced Polymer Tube (CFFT) for new columns construction has attracted significant research attention in recent years. The CFFT acts as a formwork for new columns and a barrier to corrosion accelerating agents. It significantly increases both the strength capacity (Strength enhancement ratio) and the ductility (Strain enhancement ratio) of reinforced concrete columns. In this study, based on predefined selection criteria, experimental investigation results of 134 circular CFFT columns under axial compression have been compiled and analysed from 599 CFFT specimens available in the literature. It has been observed that actual confinement ratio (expressed as a function of material properties of fibres, diameter of CFFT and compressive strength of concrete) has significant influence on the strength and ductility of circular CFFT columns. Design oriented models have been proposed to compute the strength and strain enhancement ratios of circular CFFT columns. The proposed strength and strain enhancement ratio models have significantly reduced Average Absolute Error (AAE), Mean Square Error (MSE), Relative Standard Error of Estimate (RSEE) and Standard Deviation (SD) as compared to other available strength and strain enhancement ratios of circular CFFT column models. The predictions of the proposed strength and strain enhancement ratio models match well with the experimental strength and strain enhancement ratios investigation results in the compiled database.

• 대한기계학회논문집A
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• 제26권3호
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• pp.521-527
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• 2002

In this paper, tensile behavior and low cycle fatigue behavior of 316L stainless steel which is currently favored structural material for several high temperature components such as the liquid metal cooled fast breeder reactor (LMFBR) were investigated. Research was performed at 55$0^{\circ}C$, $600^{\circ}C$ and $650^{\circ}C$ since working temperature of 316L stainless steel in a real field is from 40$0^{\circ}C$ to $650^{\circ}C$. From tensile tests performed by strain controls with $1{\times}10^{-3}/s,\; l{\times}10^{ -4}/s \;and\; 1{\times}10/^{ -5}/ s $ strain rates at each temperature, negative strain rate response (that is, strain hardening decreases as strain rate increases) and negative temperature response were observed. Strain rate effect was relatively small compared with temperature effect. LCF tests with a constant total strain amplitude were performed by strain control with a high temperature extensometer at R.T, 55$0^{\circ}C$, $600^{\circ}C$, $650^{\circ}C$ and total strain amplitudes of 0.3%~0.8% were used and test strain rates were $1{times}10^{-2} /s,\; 1{times}10^{-3} /s\; and\; 1{times}10^{-4} /s$. A new energy based LCF life prediction model which can explain the effects of temperature, strain amplitude and strain rate on fatigue life was proposed and its excellency was verified by comparing with currently used models.

• 한국지반공학회논문집
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• 제28권12호
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• pp.17-25
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• 2012

유한요소해석 등에 의한 수치해석에서는 정식화된 응력-변형률 관계가 필요하다. 그러나 현재까지 여러 연구자들에 의해 발표된 응력-변형률 관계의 정식화는 미소변형률 수준에서부터 피크에 이르기까지 전체를 모두 만족하지 못하게 표현하였다. Tatsuoka and Shibuya(1991)는 하나의 식으로 연약 점성토에서 연암에 이르는 광범위한 지반재료에 대해 적용 가능하며, 넓은 범위의 변형률 수준($10^{-6}{\sim}10^{-2}$)에 대해 적용할 수 있는 새로운 제안식을 발표하였다. 본 연구는 세계 각국의 주요 연구기관에서 사용되고 있는 7종류의 연구용 표준사 공시체 및 2종류의 유리 구슬(Glass beads) 공시체를 이용하여 평면변형률압축시험을 실시하였다. 최대주응력방향(${\sigma}_1$)의 변형률과 최소주응력방향(${\sigma}_3$)의 변형률을 각각 $10^{-6}$에서 $10^{-2}$까지 상세히 측정하였고, 얻어진 시험 결과를 새롭게 제안된 식에 적용하였다. 그 결과 미소변형률 수준에서 피크에 이르는 응력-변형률 관계의 실측된 데이터와 매우 잘 일치하는 결과를 얻었다.