• 한국표면공학회지
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• 제43권6호
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• pp.260-265
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• 2010

STD 61 steel has been widely used for tools, metallic mold and die for press working because of its favorable mechanical properties such as high toughness, and creep strength as well as excellent oxidation resistance. The STD 61 tool steel coated with TiN and ZrN by sputtering results in improvement of wear and corrosion resistance. In this study, surface characteristics of TiN and ZrN film coated STD 61 by sputtering were studied by using FE-SEM, EDS, XRD, and XRR and nanoindentation tests. From the results of surface characteristics of coated specimen, the ZrN coated surface showed finer granular than that of TiN coated surface. The coated layer structures of ZrN and TiN were grown to (111) and (200) preferred orientation. From the results of XRR test for surface roughness, density and growth rate of coating film, surface roughness and growth rate of ZrN coated film revealed lower values those of TiN coated film, whereas density of ZrN coated film showed higher values than that of TiN coated film. From the nanohardness and elastic modulus test, nanohardness value and elastic modulus of ZrN coated film became higher than those of TiN coated film.

• Computers and Concrete
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• 제7권4호
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• pp.317-329
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• 2010

The paper describes localization of deformation in a bar under tensile loading. The material of the bar is considered as non-linear viscous elastic and the bar consists of two symmetric halves. It is assumed that the model represents behavior of the quasi-brittle viscous material under uniaxial tension with different loading rates. Besides that, the bar could represent uniaxial stress-strain law on a single plane of a microplane material model. Non-linear material property is taken from the microplane material model and it is coupled with the viscous damper producing non-linear Maxwell material model. Mathematically, the problem is described with a system of two partial differential equations with a non-linear algebraic constraint. In order to obtain solution, the system of differential algebraic equations is transformed into a system of three partial differential equations. System is subjected to loadings of different rate and it is shown that localization occurs only for high loading rates. Mathematically, in such a case two solutions are possible: one without the localization (unstable) and one with the localization (stable one). Furthermore, mass is added to the bar and in that case the problem is described with a system of four differential equations. It is demonstrated that for high enough loading rates, it is the added mass that dominates the response, in contrast to the viscous and elastic material parameters that dominated in the case without mass. This is demonstrated by several numerical examples.

• Journal of Welding and Joining
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• 제21권3호
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• pp.68-77
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• 2003

It is important to understand the characteristics of material strength and fracture under the dynamic loading like as earthquakes to assure the integrity of welded structures. The characteristics of dynamic strength and fracture in structural steels and their welded joints should be evaluated based on the effects of the strain rate and the service temperature. It is difficult to predict or measure temperature rise history with the corresponding stress-strain behavior. In particular, material behaviors beyond the uniform elongation can not be precisely evaluated, though the behavior at large strain region after the maximum loading point is much important for the evaluation of fracture. In this paper, the coupling phenomena of temperature and stress-strain fields under the dynamic loading was simulated by using the finite element method. The modified rate-temperature parameter was defined by accounting for the effect of temperature rise under the dynamic deformation, and it was applied to the fully-coupled analysis between heat conduction and thermal elastic-plastic behavior. Temperature rise and stress-strain behavior including complicated phenomena were studies after the maximum loading point in structural steels and their undermatched joints and compared with the measured values.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.611-620
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• 2017

A new theory of weightless sagging planer elasto-flexible cables under point loads is developed earlier by the authors and used for predicting the nonlinear dynamic response of cable-suspended linear elastic beams. However, this theory is not valid for nonlinear elastic cracked concrete beams possessing different positive and negative flexural rigidity. In the present paper, the flexural response of simply supported cracked concrete beams suspended from cables by two hangers is presented. Following a procedure established earlier, rate-type constitutive equations and third order nonlinear differential equations of motion for the structures undergoing small elastic displacements are derived. Upon general quasi-static loading, negative nodal forces, moments and support reactions may be introduced in the cable-suspended concrete beams and linear modal frequencies may abruptly change. Subharmonic resonances are predicted under harmonic loading. Uncoupling of the nodal response is proposed as a more general criterion of crossover phenomenon. Significance of the bilinearity ratio of the concrete beam and elasto-configurational displacements of the cable for the structural response is brought out. The relevance of the proposed theory for the analysis and the design of the cable-suspended bridges is critically evaluated.

• 한국농공학회논문집
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• 제52권3호
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• pp.73-79
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• 2010

In the present study, the loading frequency dependencies of cyclic shear strength and elastic shear modulus of reconstituted clay were examined by performing undrained cyclic triaxial tests and undrained cyclic triaxial tests to determine deformation properties. The result of undrained cyclic triaxial test of reconstituted and saturated clay shows that a faster frequency leads to higher stress amplitude ratio, but when the frequency becomes fast up to a certain point, the stress amplitude ratio will reach its maximum limit and the frequency dependence becomes insignificant. And also, the result of undrained cyclic triaxial deformation test shows a fact that a faster loading frequency leads to higher equivalent shear modules and smaller hysteresis damping ratio, and confirms the frequency dependence of cohesive soil. Meanwhile, the result of the creep test shows that continuing creep is created in the undrained cyclic triaxial test with slow loading frequency rate, and since loading rate becomes slower at the vicinity of the maximum and the minimum deviator stress due to sine wave loading, the vicinity of the maximum and the minimum deviator stress shall be more influenced by creep.

• Journal of Welding and Joining
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• 제7권1호
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• pp.42-50
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• 1989

The application of fracture mechanics is being increased gradually to assess the safety of welded structures containing crack. Fatigue crack propagation behavior and elastic-plastic fracture toughness J$_{IC}$ of home made flux cored wire(1.22mm) CO$_{2}$ weldments was discussed. Especially fatigue crack propagation test was carried out by .DELTA.K control instead of load control and elastic-plastic fracture toughness J$_{IC}$ was obtained by ASTM-R curve method on C.T.specimen in transverse direction of weldments. The results obtained are as follows; (1) Weld metal presented an almost complete similarity to base metal on fatigue crack propagation rate in transverse direction. (2) Weld metal was more than base metal on J$_{IC}$ value in transverse direction. (3) F.C.W. CO$_{2}$ weldments had an excellent characteristic of fatigue crack propagation rate and J$_{IC}$ in less than 50kg/mm$^{2}$ steel grade, this would result from that weld metal had good static strength.trength.

• Computers and Concrete
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• 제31권6호
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• pp.469-484
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• 2023

The response mechanism of simply supported two-way reinforced concrete (RC) slabs under fire was numerically studied from the view of stress redistribution using the finite element software ABAQUS. Results show that: (1) Simply supported two-way RC slabs undergo intense stress redistribution, and their responses show four stages, namely elastic, elastic-plastic, plastic and tensile membrane stages. There is no cracking in the fire area of the slabs until the tensile membrane stage. (2) The inverted arch effect and tensile membrane effect improve the fire resistance of the two-way slabs. When the deflection is L/20, the slab is in an inverted arch effect state, and the slab still has a good deflection reserve. The deformation rate of the slab in the tensile membrane stage is smaller than that in the elastic-plastic and plastic stages. (3) Fire resistance of square slabs is better than that of rectangular slabs. Besides, increasing the reinforcement ratio or slab thickness improves the fire resistance of the slabs. However, an increase of cover thickness has little effect on the fire resistance of two-way slabs. (4) Compared with one-way slabs, the time for two-way slabs to enter the plastic and tensile cracking stage is postponed, and the deformation rate in the plastic and tensile cracking stage is also slowed down. (5) The simply supported two-way RC slabs can satisfy with the requirements of a class I fire resistance rating of 90 min without additional fire protection.

• Safety and Health at Work
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• 제8권2호
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• pp.189-197
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• 2017

Background: Despite the recent efforts to prevent industrial accidents in the Republic of Korea, the industrial accident rate has not improved much. Industrial safety policies and safety management are also known to be inefficient. This study focused on dynamic characteristics of industrial safety systems and their effects on safety performance in the Republic of Korea. Such dynamic characteristics are particularly important for restructuring of the industrial safety system. Methods: The effects of damping and elastic characteristics of the industrial safety system model on safety performance were examined and feedback control performance was explained in view of cost and benefit. The implications on safety policies of restructuring the industrial safety system were also explored. Results: A strong correlation between the safety budget and the industrial accident rate enabled modeling of an industrial safety system with these variables as the input and the output, respectively. A more effective and efficient industrial safety system could be realized by having weaker elastic characteristics and stronger damping characteristics in it. A substantial decrease in total social cost is expected as the industrial safety system is restructured accordingly. Conclusion: A simple feedback control with proportional-integral action is effective in prevention of industrial accidents. Securing a lower level of elastic industrial accident-driving energy appears to have dominant effects on the control performance compared with the damping effort to dissipate such energy. More attention needs to be directed towards physical and social feedbacks that have prolonged cumulative effects. Suggestions for further improvement of the safety system including physical and social feedbacks are also made.

• Korea-Australia Rheology Journal
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• 제21권2호
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• pp.109-117
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• 2009

Absorption rate of carbon dioxide was measured in the aqueous xanthan gum (XG) solution in the range of 0~0.15 wt% containing diisopropanolamine (DIPA) of $0{\sim}2\;kmol/m^3$ in a flat-stirred vessel with an impeller of 0.05 m and agitation speed of 50 rpm at $25^{\circ}C$ and 101.3 kPa. The volumetric liquid-side mass transfer coefficient ($k_La$) of $CO_2$, which was obtained by the measured physical absorption rate, was correlated with the viscosity and the elastic behavior of XG solution such as Deborah number as an empirical formula. The chemical absorption rate of $CO_2$ ($R_A$), which was estimated by the film theory using the measured $k_La$ and the known kinetics of reaction between $CO_2$ and DIPA, was compared with the measured rate. The aqueous XG solution with elastic property of non-Newtonian liquid made $k_La$ and $R_A$ increased compared with Newtonian liquid based on the same viscosity of the solution.

• 대한치과교정학회지
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• 제33권5호
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• pp.371-380
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• 2003

본 연구는 체인형 합성고무탄성재의 시간에 따른 탄성력 감쇄의 양상을 평가하여, 이들 재료의 임상적용시 적절한 교정력의 적용을 위해 참고가 될 만한 기준을 구해보려는 목적으로 시행되었다. 공간폐쇄시 사용되는 체인형 합성고무탄성재의 탄성감쇄정도를 알아보기 위하여, 임상에 널리 사용되는 두 가지의 체인형 합성고무탄성재를 구강내 상태와 유사한 조건하에서 4주간 신장시켜 관찰한 결과 다음과 같이 요약할 수 있었다. 1. 시간에 따른 탄성력 감쇄양상은 전형적인 log함수의 형태를 보이며, 4주후 잔존탄성력은 원래의 $41.2\~64.6\%$이며 제품에 따라 차이가 있었다. 2. 신장후 초기 10분 동안 탄성력의 급격한 감소를 보여서, 초기힘의 $20\~25\%$를 상실하였으며, 이후 감소량이 줄어들어 1주이후부터 4주까지의 평균감소량은 $1.5\%$정도로 거의 일정한 힘의 크기를 보여주었다. 3. 동일한 재료를 사용하더라도, 탄성재의 신장량이 증가할수록 잔존탄성력이 감소하여 탄성감쇄율이 증가하였다