• International Journal of Concrete Structures and Materials
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• v.19 no.1E
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• pp.41-48
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• 2007

Addition of latex to concrete is known to increase its durability and permeability. The purpose of this study is to analyze air void systems in latex-modified concretes using a reasonable and objective method of image analysis with such experimental variables as water-cement (w/c) ratios, latex contents (0%, 15%) and cement types (ordinary portland cement (OPC), high-early strength (HES) cement and very-early strength (VES) cement). The results are analyzed by spacing factor, air volume (content) after hardening, air void distribution and structure. Additionally, air void systems and permeability of latex-modified concrete (LMC) are compared by a correlation analysis. The results are as follows. The LMC of the same w/c ratio showed better air entraining (AE) effect than OPC with AE water reducer. The VES-LMC showed that the quantity of entrained air below $100{\mu}m$ increased more than four times. For the case of HES-LMC, microscopic entrained air between the range of 50 to $500{\mu}m$ increased greater than 7 times even in the absence of anti-foamer. Although spacing factor was measured rather low, the permeability of latex-modified concrete was good. It is construed that air void system does not have a considerable effect on the property of latex-modified concrete, but latex film (membrane) has a definite influence on the durability of LMC.

• Computers and Concrete
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• v.19 no.3
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• pp.315-323
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• 2017

Within the context of continuum mechanics, inelastic behaviours of constitutive responses are usually modelled by using phenomenological approaches. Elasto-plastic damage modelling is extensively used for concrete material in the case of progressive strength and stiffness deterioration. In this paper, a review of the main features of elasto-plastic damage modelling is presented for uniaxial stress-strain relationship. It has been reported in literature that the influence of Alkali-Silica Reaction (ASR) can lead to severe degradations in the modulus of elasticity and compression strength of the concrete material. In order to incorporate the effects of ASR related degradation, in this paper the constitutive model of concrete is based on the coupled damage-plasticity approach where degradation in concrete properties can be captured by adjusting the yield and damage criteria as well as the hardening moduli related parameters within the model. These parameters are adjusted according to results of concrete behaviour from the literature. The effect of ASR on the dynamic behaviour of a beam and a column are illustrated under moving load and cyclic load cases.

• Transactions of Materials Processing
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• v.10 no.2
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• pp.101-110
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• 2001

The thermal problem of press work is classified into two cases. First, the temperature of forming die passively rises due to the heating effect of plastic deformation. The warm forming is the second case in which the external heating is applied to the die and blank holder. So, the purpose of this study is to provide database for the forming characteristics at various temperature conditions. In this study, the tensile test was carried out for the commercial steel sheets such as SCPI and SCP3C with the thickness of 0.7mm and 1.4mm respectively. The tensile strength, total elongation, Lankford value and the flow curve have been obtained at the temperature of $25^{\circ}C$, $50^{\circ}C$, $100^{\circ}C$, $150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$ and $300^{\circ}C$, respectively. From the results, we can see that both the tensile strength and total elongation decrease as the temperature increases. In the light of anisotropy, the effect of thickness is dominant than the material specs. For the temperature dependency of flow curves, there are only small differences for the work-hardening exponent, and the strength intensity decreases monotonically as temperature increases. The present results we useful as input data for the analysis of sheet metal forming processes with the various temperature conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.239-242
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• 2005

In the roll forming, a flat strip is progressively deformed by feeding it through a series of rotating rolls. There are various layouts for the tube toll-forming stages. The process sequences are as follows: leveling, roll-forming, welding, bead removing, seam annealing, cooling, sizing and cutting. Electric resistance welded(ERW) tubes have been widely used for the machinery parts, especially for hydroformed automotive parts. However conventional ERW tubes do not have a high formability because of hardening of welded portion by rapid cooling. Moreover the decrease in thickness of the welded portion during the grinding of the inner and outer bead may reduce the formability of the tube. In case of applying the tubular parts without grinding the bead, the flow of the fluid can be prevented due to the turbulent flow induced by the inner bead. In attempt to determine the optimal bead grinding amount in the roll forming process, in the present paper, the effects of the removal depth and width of the inner beads on the hydroformability are analyzed by the finite element simulation.

• Korean Journal of Materials Research
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• v.14 no.6
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• pp.436-442
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• 2004

Elastic and plastic deformation behaviors of the high purity aluminum and the silica glass were studied using nanoindentation and finite element analysis(FEA) techniques. Berkovich- and cone-type indenters were used for the nanoindentation test. Deformation behaviors and nanoindent profiles of elastic, elastic-plastic or plastic materials were clearly visualized by FEA simulation. Effects of the penetration depth and strain hardening on the deformation behavior were examined. Pile-up and sink-in behaviors were studied by using FEA technique. Degree of pile-up or sink-in was found to be a function of the ratio of elastic modulus to yield strength of materials. FEA was found to be an effective method to study deformation behaviors of materials under nanoindentation, especially in the case when pile-up or sink-in phenomena occurred.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.1
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• pp.159-165
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• 2005

Shot peening can be defined as the process of work hardening of the surface of components by means of propelled stream of spherical shot. Benefits due to shot peening are increase in resistance to fatigue, stress corrosion cracking, fretting, galling, erosion and closing of pores. In this study, the influence of shot peening on the corrosion was investigated on spring steel immersed in $3.5\%\;NaCl$. The immersion test was performed on the two kinds of specimens. Corrosion potential, polarization curve, residual stress and etc. were investigated from experimental results. From test results, the effect of shot peening on the corrosion was evaluated. The important results of the experimental study on the effects of shot peened spring steels on the environment corrosion are as follows; In case of corrosion potential, shot peened specimen shows more activated negative direction as compared with parent metal. Surface of specimen, which is treated with the shot peened, is placed as more activated state against inner base metal. It can cause the anti-corrosion effect on the base metal.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.568-573
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• 2013

The deformation properties of a TiC-Mo eutectic composite were investigated in a compression test at temperatures ranging from room temperature to 2053 K and at strain rates ranging from $3.9{\times}10^{-5}s^{-1}$ to $4.9{\times}10^{-3}s^{-1}$. It was found that this material shows excellent high-temperature strength as well as appreciable room-temperature toughness, suggesting that the material is a good candidate for high-temperature application as a structure material. At a low-temperature, high strength is observed. The deformation behavior is different among the three temperature ranges tested here, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurs, and from the beginning the work hardening level is high. At a high temperature, a yield drop occurs again, after which deformation proceeds with nearly constant stress. The temperature- and yield-stress-dependence of the strain is the strongest in this case among the three temperature ranges. The observed high-temperature deformation behavior suggests that the excellent high-temperature strength is due to the constraining of the deformation in the Mo phase by the thin TiC components, which is considerably stronger than bulk TiC. It is also concluded that the appreciable room-temperature toughness is ascribed to the frequent branching of crack paths as well as to the plastic deformation of the Mo phase.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.4
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• pp.235-241
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• 2005

Thermal creep properties of the advanced zirconium fuel claddings named by HANA alloys which were developed for high burn-up application were evaluated. The creep test of HANA cladding tubes was carried out by the internal pressurization method in temperature range from 350 to $400^{\circ}C$ and in the hoop stress range from 100 to 150 MPa. Creep tests were lasted up to 800 days, which showed the steady-state secondary creep rate. The creep resistance of HANA fuel claddings was affected by final annealing temperature and various factors, such as alloying element, applied stress and testing temperature. From the results the microstructure observation of the samples before and after creep test by using TEM, the dislocation density was increased in the sample of after creep test. The Sn as an alloying element was more effective in the creep resistance than other elements such as Nb, Fe, Cr and Cu due to solute hardening effect of Sn. In case of HANA fuel claddings, the improved creep resistance was obtained by the control of final heat treatment temperature as well as alloying element.

• Structural Engineering and Mechanics
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• v.10 no.4
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• pp.405-426
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• 2000

Two approximate methods based on mechanism analysis suitable for seismic assessment/design of structural concrete are reviewed. The methods involve use of equal energy concept or equal displacement concept along with appropriate patterns of inelastic deformations to relate structure's maximum lateral displacement to member and plastic deformations. One of these methods (Clough's method), defined here as a ductility-based approach, is examined in detail and a modification for its improvement is suggested. The modification is based on estimation of maximum inelastic displacement using inelastic design response spectra (IDRS) as an alternative to using equal energy concept. The IDRS for demand displacement ductilities are developed for a single degree of freedom model subjected to several accelerograms as functions of response modification factor (R), damping ratios, and strain hardening. The suggested revised methodology involves estimation of R as the ratio of elastic strength demand to code level demand, and determination of design base shear using $R_{design}{\leq}R$ and maximum displacement, determination of plastic displacement using IDRS and subsequent local plastic deformations. The methodology is demonstrated for the case of a 10-story precast wall panel building.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.141-152
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• 2018

The heating process such as line heating, triangular heating and so on is widely used in plate forming of shell plates found in bow and stern area of outer shell in a ship. Local shrinkage during heating process is main physical phenomenon used in plate forming process. As it is well appreciated, the heated plate undergoes the change in material and mechanical properties around heated area due to the harsh thermal process. It is, therefore, important to investigate the changes of physical and mechanical properties due to heating process in order to use them plate the design stage of shell plates. This study is concerned with the development of formula of plastic hardening constitutive equation for steel plate on which line heating is applied. In this study the stress correction formula for the heated plate has been developed based on the numerical simulation of tension test with varying plate thickness and heating speed through the regression analysis of multiple variable case. It has been seen the developed formula shows very good agreement with results of numerical simulation. This paper ends with usefulness of the present formula in examining the structural characteristic of ship's hull.