• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.909-912
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• 2008

Fiber is an important ingredient in strain-hardening cementitious composite (SHCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of SHCC. But SHCC has serious problem as drying shrinkage because silica powder is used to make SHCC in order to improve bond strength between reinforcing fibers and cement matrix. Therefore, curing method (period and temperature) is very important for SHCC to show high tensile performance. a variety of experiments have being performed to access the performance of SHCC recently. This research emphasis is on the mechanical properties of SHCC made in Polyvinyl alcohol (PVA), Polyethylene (PE) fibers and steel cord (SC), and how curing method affects the composite property, and ultimately its strain-hardening performance.

• Corrosion Science and Technology
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• v.5 no.2
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• pp.69-76
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• 2006

Premature cracking of the epoxy coatings applied on ship's ballast tanks(BT) can lead to damage of ship's hulls. To avoid this, it's important to have clear understanding of the underlying mechanism and primary factors of the coating crack. In this study, the efforts were made to clarify the integrated effects of main factors, i.e., initial coating shrinkage, thermally induced strain, steel-structural strain and the intrinsic coating flexibility at the initial and after aging, to the early cracking phenomena of epoxy coating in the ship's ballast tank. The coating crack is caused by combination of thermal stress, structural stress, and internal stresses which is closely related to chemical structures of the coatings. On the other hand, thermal stresses and dimensional stabilities would rarely play a major role in coating crack for ballast tank coatings with rather large flexibility. Crack resistance of the coatings at early stages can be estimated roughly by measuring internal stress, FT-IR and $T_g$ value of the coatings. A new screening test method was also proposed in this study, which can be possibly related to the long-term resistance of epoxy-based paints to cracking.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.85-98
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• 1993

A method of analysis for the material and geometric nonlinear analysis of planar prestressed concrete cable-stayed bridges including the time-dependent effects due to load history, creep, shrinkage, aging of concrete and relaxation of prestress is described. The analysis procedure, based on the finite element method, is capable of predicting the response of these structures through elastic, cracking, inelastic and ultimate ranges. The nonlinear formulation for the description of motion is based on the updated Lagrangian approach. To account for the material nonlinearity, nonlinear stress-strain relationship and cracking of concrete, nonlinear stress-strain relationships of reinforcing steel, prestressing steel, and cable, including load reversal are given. Results from a numerical examples on ultimate analyses of cable-stayed bridges are presented to illustrate the analysis method.

• Composites Research
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• v.25 no.2
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• pp.34-39
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• 2012

A thermo-poro-elastic constitutive model of unidirectionally fiber-reinforced composite materials is suggested by extending the unmixing-mixing scheme which is based upon composite micromechanics. The strain components of thermal expansion due to a temperature change, gas pressure in pores, and chemical shrinkage are included in the constitutive model. On purpose to verify the derived constitutive relations, the representative volume element of two-dimensional lamina subject to various loading conditions is analyzed by the finite element method. The overall stress and strain responses are obtained, and compared with the predicted values by the unmixing-mixing scheme. The numerical results show the usefulness of the proposed model to predict the thermoelastic behavior of porous composites.

• Journal of the Korean Society of Clothing and Textiles
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• v.17 no.1
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• pp.63-75
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• 1993

Partially oriented polyester yarn (PET POY) was treated in the unrestrained state using various solvents at different temperatures. Interactions between PET POY & solvents were estimated by the changes of microstructure, morphology and mechanical properties. The correlation between the changes of microstructure & morphology and the changes of mechanical properties was also studied. TCE, Dioxane, O-DCB, DMF, and BA were found to be active solvents, while Iso-AA and water were found to be weak solvents. PET POY was affected mainly by the solvents when treated with active solvents and affected mainly by heat when treated with weak solvents. Changes by the solvent treatment in microstructure and morphology were : an increase in crystallinity, a change in birefringence, a shrinkage in length, and a change in DSC curve. As for the changes in mechanical properties, findings in the PET POY when treated with solvents were : a decrease in stress-at-break, a change in yield stress, an increase in strain-at-break & yield strain, and a decrease in initial modulus. Changes in microstructure and morphology directly affected the mechanical properties.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.109-116
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• 2006

An incremental approach to predict the time dependent flexural behavior of composite girder is presented in the framework of incremental finite element method. Age dependent nature of creep, shrinkage, and maturing of elastic modulus of concrete is prescribed in the incremental tangent description of constitutive relation derived based on the first order Taylor series expansion applying to the total from of stress-strain relation. The loop phenomenon in which age dependent nature of concrete causes stress redistribution and it causes creep in turn is taken into account in the formulation through the incremental representation of constitutive relation. The developed algorithm predicts the time dependent deflections of 4.8m long two span double composite box girder subjected to shrinkage, maturing of elastic modulus, and creep initially induced by self weight. Comparison shows a good agreement between the predicted and measured results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.452-459
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• 2017

In recent years, to reduce self-weight of structural elements, the use of SCP (Steel Concrete Plate) instead of prestressed concrete is increasing. Because SCP has a complicated sectional shape and includes a large number of studs, the use of high-fluidity concrete is required. Therefore, in this study, to prevent the restrained shrinkage behavior by the stud, the effects of using an expansive agent (EA) and shrinkage reducing agent (SRA) were investigated, and the optimal mixture proportions to maximize the filling capacity were determined based on the fine aggregate ratio. The test results indicated that the combined use of EA and SRA exhibited the smallest shrinkage. The ratio of the crushed sand and washed sea sand was determined to be 5:5, and the proper fine aggregate ratio was found to be 55.6%, because when the ratio was too high, a decrease in strength and an increase in shrinkage strain were expected. The high-fluidity concrete effectively filled the large-sized SCP module.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.521-529
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• 2002

A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.109-113
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• 2002

Interfacial and electrical properties for the carbon fiber reinforced epoxy-amine terminated (AT) PEI composites were performed using microdroplet test and electrical resistance measurements. As AT PEI content increased, the fracture toughness of epoxy-AT PEI matrix increased, and IFSS was improved due to the improved toughness and energy absorption mechanisms of AT PEI. The microdroplet in the carbon fiber/neat epoxy composite showed brittle microfailure mode. At 15 wt% AT PEI content, ductile microfailure mode appeared because of improved fracture toughness. After curing, the changes of electrical resistance (ΔR) with increasing AT PEI content increased gradually because of thermal shrinkage. The matrix fracture toughness was correlated to IFSS, TEC and electrical resistance. In cyclic strain test, the maximum stress and their slope of the neat epoxy case were higher than those of 15 wt% AT PEI. The results obtained from electrical resistance measurements under curing process and reversible stress and strain were consistent well with matrix toughness properties.

• Textile Coloration and Finishing
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• v.15 no.6
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• pp.33-38
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• 2003

This study surveys the effects of POY physical properties and processing conditions of belt texturing machine to the textured yarns. The various textured yarns are made with the variations of 1st heater temperature, draw ratio, velocity ratio, and the physical properties of these specimens such as yam linear density, tenacity, breaking strain, and wet and dry thermal shrinkages are measured and analysed with the various processing conditions of texturing machine. Especially, the thermal characteristics of the textured yarns, which are affected at the fabric hands and the determination of the processing conditions in the dyeing and finishing processes, are investigated through the thermal stress analyser and DSC experiments.