• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.491-496
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• 2013

Finite element simulations of tensile tests were performed to determine the equivalent stress - equivalent plastic strain curves, critical equivalent stresses, and critical equivalent plastic strains. Then, the curves were used as inputs to finite element simulations of fracture toughness tests to determine the plane strain fracture toughness. The critical COD was taken as the COD when the equivalent plastic strain at the crack tip reached a critical value, and it was used as a crack growth criterion. The relationship between the critical COD and the critical equivalent plastic strain or the reduction of area was found. The relationship between the plane strain fracture toughness and the product of the critical equivalent stress and the critical equivalent plastic strain was also found.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.1
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• pp.23-31
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• 2016

In this study, we modified the conventional tensile split Hopkinson bar(TSHB) apparatus typically used for the high strength steel to evaluate the tensile deformation behavior of soft metallic sheet materials under high strain rates. Stress-strain curves of high purity single and multi-crystalline materials were obtained using this experimental procedure. Grain morphology and initial crystallographic orientation were characterized by EBSD(Electron Backscattered Diffraction) method measured in a FE-SEM(Field emission-scanning electron microscopy). The fractured surfaces were observed by using optical microscopy. The relationship between plastic deformation of aluminum crystalline materials under high-strain rates and the initial microstructure and the crystallographic orientations has been addressed.

• KCI Concrete Journal
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• v.13 no.1
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• pp.19-25
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• 2001

Based on the orthotropic hypoelasticity formulation, a constitutive material model of concrete taking account of triaxial stress state is presented. In this model, the ultimate strength surface of concrete in triaxial stress space is described by the Hsieh's four-parameter surface. On the other hand, the different ultimate strength surface of concrete in strain space is proposed in order to account for increasing ductility in high confinement pressure. Compressive ascending and descending behavior of concrete is considered. Concrete cracking behavior is considered as a smeared crack model, and after cracking, the tensile strain-softening behavior and the shear mechanism of cracked concrete are considered. The proposed constitutive model of concrete is compared with some results obtained from tests under the states of uniaxial, biaxial, and triaxial stresses. In triaxial compressive tests, the peak compressive stress from the predicted results agrees well with the experimental results, and ductility response under high confining pressure matches well the experimental result. The reinforcing bars embedded in concrete are considered as an isoparametric line element which could be easily incorporated into the isoparametric solid element of concrete, and the average stress - average strain relationship of the bar embedded in concrete is considered. From numerical examples for a reinforced concrete simple beam and a structural beam type member, the stress state of concrete in the vicinity of talc critical region is investigated.

• 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 Korea Concrete Institute
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• v.14 no.5
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• pp.766-773
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• 2002

The failure phenomenon of overlaid concrete structures, such as surface crack, and peel-off failure, shear bond failure in the end contact zone, was investigated due to humidity changes. To investigate this failure phenomenon, the surface tensile stress, and the shear stress, the vertical tensile stress in the contact zone were analysed using the non-linear stress-strain relationship of material such as strain-hardening- and strain-softening diagrams. Overlay thickness and overlay material were the main variables in the analyses. It is assumed that the initial surface humidity of overlaid concrete structures was 100％ r.H. With a atmospheric humidity of 55％ r.H. and two load cases for drying(LCI), curing and drying(LC2), the stress states of overlaid concrete structures were calculated. The result shows that only fictitious cracks occurred in the overlay surface of CM2O, ECM25, and no shear bond failure occurred in the contact zone without CM2O. The peel-off failure was proved to be the main cause of the damage in the overlaid concrete structures. Only for overlay thickness of 1cm occurred no peel-off failure in the case of drying after a long-term public use(LC1). In the case of curing and drying during overlay work(LC2) occurred the peel-off failure within 1.5days for all the overlaid concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.25-33
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• 2020

To investigate the relationship between strain distribution and tensile properties of brittle material, five types of tensile coupon of carbon fiber reinforced polymer (CFRP) modified the tab portion in order to have a strain distribution including S0, SD1, SD2, SV1, SV2 were tested. The ultimate stress and strain of SD2 and SV2 which was intended to have larger strain distribution were smaller than those of SD1 and SV1, that was more clearly shown in the test results of the symmetric coupons (SV series) than the asymmetric coupons (SD series). In addition, the ultimate stress and strain of most coupons with strain distribution in this study were decreased when compared to the control group with uniform strain. These results were analyzed in various ways through 1) the average of the strain values directly measured by the strain gages, 2) the converted strain calculated by dividing the total deformation by the effective length, and 3) the ultimate effective strain derived from both the elastic modulus and the ultimate load. The values measured by strain gage indicates response of the local region precisely, but it does not represent the response from whole section. However, the converted strain and effective strain can supplement disadvantage of gage because they represent the average response of whole section. In particular, the effective strain can provide rupture strain conservatively, which can be utilized in practice, when the value obtained by strain gage was not effective due to gage damage or abnormal gage readings near ultimate load. This value provides a value that can be used even when partial rupture has occurred and is reasonably useful for specimens with strain distribution.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.273-279
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• 2017

In sheet metal forming numerical analysis, the strain hardening equation has a significant effect on calculation results, especially in the field of spring-back. This study introduces the Kim-Tuan strain hardening model. This model represents sheet material behavior over the entire strain hardening range. The proposed model is compared to other well known strain hardening models using a series of uniaxial tensile tests. These tests are performed to determine the stress-strain relationship for Al6016-T4, DP980, and CP Ti sheets. In addition, the Kim-Tuan model is used to integrate the CP Ti sheet strain hardening equation in ABAQUS analysis to predict spring-back amount in a bending test. These tests highlight the improved accuracy of the proposed equation in the numerical field. Bending tests to evaluate prediction accuracy are also performed and compared with numerical analysis results.

• Journal of the Semiconductor & Display Technology
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• v.3 no.2
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• pp.35-40
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• 2004

The total relaxed stress in annealing and the thermal strain/stress were obtained from the identification of the residual stress-free state using electronic speckle pattern interferometry (ESPI). The residual stress fields in case of both single and film / substrate systems were modeled using the thermo-elastic theory and the relationship between relaxed stresses and displacements. We mapped the surface residual stress fields on the indented bulk Cu and the 0.5 $\mu\textrm{m}$ Au film by ESPI. In indented Cu, the normal and shear residual stress are distributed over -1.7 GPa to 700 MPa and -800 GPa to 600 MPa respectively around the indented point and in deposited Au film on Si wafer, the tensile residual stress is uniformly distributed on the Au film from 500 MPa to 800 MPa. Also we measured the residual stress by the x-ray diffractometer (XRD) for the verification of above residual stress results by ESPI...

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.267-279
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• 2009

A numerical model that can simulate the nonlinear behavior of ultra high strength fiber reinforced concrete (UHSFRC) structures subjected to monotonic loading is introduced. The material properties of UHSFRC, such as compressive and tensile strength or elastic modulus, are different from normal strength reinforced concrete. The uniaxial compressive stress-strain relationship of UHSFRC is designed on the basis of experimental result, and the equivalent uniaxial stress-strain relationship is introduced for proper estimation of UHSFRC structures. The steel is uniformly distributed over the concrete matrix with particular orientation angle. In advance, this paper introduces a numerical model that can simulate the tension-stiffening behavior of tension part of the axial member on the basis of the bond-slip relationship. The reaction of steel fiber is considered for the numerical model after cracks of the concrete matrix with steel fibers are formed. Finally, the introduced numerical model is validated by comparison with test results for idealized UHSFRC beams.

• Geomechanics and Engineering
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• v.6 no.3
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• pp.277-292
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• 2014

Soil nailing, as an effective stabilizing method for slopes and excavations, has been widely used worldwide. However, the interaction mechanism of a soil nail and the surrounding soil and its influential factors are not well understood. A pullout model using a hyperbolic shear stress-shear strain relationship is proposed to describe the load-deformation behavior of a cement grouted soil nail. Numerical analysis has been conducted to solve the governing equation and the distribution of tensile force along the nail length is investigated through a parametric study. The simulation results are highly consistent with laboratory soil nail pullout test results in the literature, indicating that the proposed model is efficient and accurate. Furthermore, the effects of key parameters, including normal stress, degree of saturation of soil, and surface roughness of soil nail, on the model parameters are studied in detail.