• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.41-48
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• 1991

A set of constitutive equations is formulated to predict elastic-plastic strain hardening response of sintered porous iron under combined tension and torsion. The proposed constitutive equations were capable of predicting characteristic behaviors of porous metals. Agreement between theoretical curves and experimental data for elastic-plastic response of sintered porous iron was very good for various initial porosities.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.718-725
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• 2016

In this study, the plastic flow curve of commercially pure titanium sheet (CP Ti) actively used in the plate heat exchanger etc., was evaluated. The plastic flow curve known as hardening curve is a key factor needed in conducting finite element analyses (FEA) for the forming process of a sheet material. A hydraulic bulge test was performed on the CP Ti sheet and the strain in this test was measured using the DIC method and ARAMIS system. The measured true stress-true strain curve from the hydraulic bulge test (HBT) was compared with that from the tensile test. The measured true stress-true strain curve from the hydraulic bulge test showed stable plastic flow curve over the strain range of 0.7 which cannot be obtained in the case of the uniaxial tensile test. The measured true stress-true strain curve from the hydraulic bulge test can be fitted well by the hardening equation known as the Kim-Tuan model.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.371-379
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• 2013

This paper investigates the cracking and tension-stiffening behavior of 100 MPa shrinkage-compensated strain-hardening cement composite (SHCC) and conventional concrete tie elements in monotonic and cyclic tension. Strain and surface crack formation of tension ties were monitored with two strain displacement transducers and a photo microscope with a lens of magnification 50 times. Three different cement composites such as conventional concrete, shrinkage-compensated SHCC, and normal SHCC were used in the tie specimens to investigate the influence of the cement composite type on the tension stiffening and cracking behavior. Test results indicated that initial shrinkage of the ultra high-strength cement composites is greatly reduced as the 10% replacement of cement by the shrinkage-compensating admixture based on calcium sulfo-aluminate (CSA). The test results on the SHCC tension ties showed that the first cracking load decreases proportionally to the initial shrinkage strain. Reinforced ultra high-strength SHCC ties with the initial shrinkage compensation exhibited improved tension stiffening and smaller crack spacings, i.e. the reduction in crack width. Cyclic loading did not have a significant effect on tension stiffening and cracking behavior of tension ties with normal concrete and SHCC materials.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.21-28
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• 2006

This paper presents both experimental and analytical studies for the development of an ECC(Engineered Cementitious Composites) using ground granulated blast furnace slag(slag). This material has been focused on achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, micromechanics was adopted to properly select optimized range of the composition based on steady-state cracking theory and experimental studies on matrix, and interfacial properties. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties of the fiber in a matrix and the fracture toughness of mortar matrix. The addition of the slag resulted in slight increases in the frictional bond strength and the fracture toughness. Subsequent direct tensile tests demonstrate that the fiber reinforced mortar exhibited high ductile uniaxial tension behavior with a maximum strain capacity of 3.6%. Both ductility and tensile strength(~5.3 MPa) of the composite produced with slag were measured to be significantly higher than those of the composite without slag. The slag particles contribute to improving matrix strength and fiber dispersion, which is incorporated with enhanced workability attributed to the oxidized grain surface. This result suggests that, within the limited slag dosage employed in the present study, the contribution of slag particles to the workability overwhelms the side-effect of decreased potential of saturated multiple cracking.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.135-148
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• 2001

In this study, an assessment method was proposed to evaluate the pullout resistance between geosynthetic and backill soil by using a stress-strain relationship of the orthotropic composite material subjected to both longitudinal and vertical loadings. For this analysis friction characteristics of geosynthetic-soil and stress-strain relationships subjected to soil confined pressure were investigated by performing the laboratory pullout tests for three types of geosynthetics and performing the confined extension tests far seven types of geosynthetics having geotextiles, composite geosynthetics and geogrids. A comparison was made between unconfined an confined moduli far each geosynthetic material to quantify the soil confinement effect on stress-strain properties. A comparison was also made between the relative increase of moduli at the same strain level among the seven geosynthetic materials to demonstrate the different responses of these geosynthetic materials under soil confinement. Based on the proposed procedure, it was shown that values of the increased tensile force are applicable fur the evaluation of friction strengths between five types of geosynthetics and sands in light of the soil confinement effect.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.27-34
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• 2017

We investigated the feasibility of parylene F usage as an intermediate layer between a polydimethylsiloxane (PDMS) substrate and an Au thin-film interconnect as well as the swelling effect of PDMS substrate on the stretchable deformability of an Au thin film. The 150-nm-thick Au film, which was sputtered on a PDMS substrate without a parylene F layer, exhibited an initial resistance of $11.7{\Omega}$ and an overflow of its resistance at a tensile strain of 12.5%. On the other hand, the Au film, which was formed with a 150-nm-thick parylene F layer, revealed an much improved resistance characteristics: $1.21{\Omega}$ as its initial resistance and $246{\Omega}$ at its 30% elongation state. With swelling of PDMS substrate, the resistance of an Au film substantially decreased to $14.4{\Omega}$ at 30% tensile strain.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.353-354
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• 2009

Tensile deformation behavior with different strain rate was investigated. $Zr_{56.2}Ti_{13.8}Nb_{5.0}Cu_{6.9}Ni_{5.6}Be_{12.5}$ (bulk metallic glass alloy possessed crystal phase which was called $\beta$-phase of dendrite shape, mean size of $20{\sim}30{\mu}m$ and occupied 25% of the total volume) was used in this study. Maximum tensile strength was obtained as 1.74Gpa at strain rate of $10^2/s$ and minimum strength was found to be 1.6GPa at $10^{-1}/s$. And then, maximum plastic deformation occurred at the strain rate of $5{\times}10^{-2}/s$ and represented 1.75%, though minimum plastic deformation showed 0%. In the specific range of strain rate, relatively higher plastic deformation and lower ultimate tensile strength were found with lots of shear bands. The fractographical observation after tensile test indicated that vein like pattern on the fracture surface was well developed especially in the above range of strain rate.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.59-68
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• 2010

In the present study, the deformation capacity of slender shear walls with thin web subject to inelastic deformation after flexural yielding was studied. Web-crushing and rebar-fracture were considered as the governing failure mechanisms of walls. To address the effect of the longitudinal elongation on web-crushing and rebar-fracture, the longitudinal elongation was predicted by using truss model analysis. The failure criteria by web-crushing and rebar-fracture were defined as a function of the longitudinal elongation. The proposed method was applied to 17 shear wall specimens with boundary columns, and the prediction results were compared with the test results. The results showed that proposed method predicted the maximum deformations and failure modes of the wall specimens with reasonable precision.

• Journal of the Korean Geosynthetics Society
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• v.4 no.3
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• pp.11-19
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• 2005

Long-term stability of two type geogrids were evaluated. Membrane drawn type geogrid showed the exponential type tensile property and textile type geogrid showed the rapid increase of tensile property closer toward the break point. Short term accelerated creep test was done for textile type geogrid but done for membrane drawn type geogrid at ambient temperature because of its thermal property. Creep strain for membrane drawn type geogrid was larger than the ultimate tensile strain by tensile test. Reduction factor by creep deformation of textile type geogrid was smaller than that of membrane type geogrid. From this result, it was seen that the textile type geogrid is more stable than membrane type geogrid by creep deformation.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.933-936
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• 2008

An engineered cementitious composite (Engineered Cementitious Composite) had been developed in previous study. Theoretical prediction of the tensile stress-strain relation of ECC is important in providing the material constitutive relation necessary for designing structural members. But, few studies have been reported with regard to predicting the tensile stress-strain relation of ECC. Prediction of the tensile stress-strain relation of ECC accounting for actual bridging curve, such as fiber dispersion is needed. The present study extends the work as developed by Kanda et al., by modeling the bridging curve, accounting for fiber dispersion, the degree of matrix spalling, and fiber rupture to predict the tensile stress-strain relation of ECC. The role of material variation in the bridging curve, such as number of effective fiber actually involved in the bridging capacity and how it affects the multiple cracking process is discussed. The approach for formulating the tensile stress-strain relation is discussed next, where the procedure for obtaining the necessary parameters, such as the crack spacing, is presented. Finally, the predicted stress-strain relation will be validated with experimental tests results.