• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.447-456
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• 2001

Many investigators have tried to represent the nonlinear behavior of stress-strain relationship of concrete using mathematical curves. Most of empirical expressions for stress-strain relationship, however, have focused on old age concrete, and were not able to represent well the behavior of concrete at an early age. Where wide understanding on the behavior of concrete from early age to old age is very important in evaluating the durability and service life of concrete structures. In this paper, effect of 5 different strength levels and ages of from 12 hours to 28 days on compressive stress-strain relationship was observed experimentally and analytically. Tests were carried out on $\phi$100${\times}$200mm cylindrical specimens water-cured at 20${\pm}$3$^{\circ}C$. An analytical expression of stress-stain relationship with strength and age was developed using regression analyses on experimental results. For the verification of the proposed model, the model was compared with present and existing experimental data and some existing models. The analysis shows that the proposed model predicts well experimental data and describes well effect of strength and age on stress-strain relationship.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.34-41
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• 2003

A Green's function approach is adopted for analyzing the thermoelastic deformation and stress analysis of a plate made of functionally graded materials (FGMs). The solution to the 3-dimensional steady temperature is obtained by using the laminate theory. The fundamental equations for thermoelastic problems are derived in terms of out-plane deformation and in-plane force, separately. The thermoelastic deformation and the stress distributions due to the bending and in-plane forces are analyzed by using a Green’Às function based on the Galerkin method. The eigenfunctions of the Galerkin Green's function for the thermoelastic deformation and the stress distributions are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the rectangular plate. Numerical examples are carried out and effects of material properties on thermoelastic behaviors are discussed.

• Geotechnical Engineering
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• v.14 no.4
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• pp.33-46
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• 1998

Anisotropy of stiffness, from extremely small strains to post-failure strains, of isotropically consolidated air-pluviated sands in plane strain compression was studied by using the newly developed instrumentation for small strain measurements. Seven types of sand of the world-wide origins were tested, which have been extensively used for research purposes. Stress-strain at the specimen boundaries. It was found that the maximum Young's modulus $E_{max}$ was irrespective of the angle $\delta$ of the $\delta_1$ direction relative to the bedding plane. However, the normalized$ E_{max}$ was varied with the types of sand. Furthermore, the dependency of the strain and stress level on the stiffness was increased as $\delta$ decreased.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.105-114
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• 1994

초경합금은 기계적 성질이 다른 WC의 분상상과 Co의 결합상으로 구성되어 있다. 만일 이합금이 거시적으로 균일하게 변형을 하면, 각 상들은 이들의 응력상태에 따라 다르게 변형될 것이다. 따라서 WC-Co 합금의 변형특성과 강화기구를 명확히 알기 위해서는 각상의 미시적 변형과 파괴기구를 검토할 필요가 있다. 본 연구에서는 시편에 굽힘하중을 가하여, X선 회절로 분산상인 WC상 및 결합상인 Co상의 X선적 탄성정수와 응력정수를 측정하였다. WC-Co합금중의 WC상과 Co상의 상응력은 WC(112)면과 CO(311)면의 회절로서 결정하였다. 그리고 이 상응력들을 복합법칙의 적용가능성에 대하여 검토하였다.

• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.291-301
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• 2007

The overlay model is a certain kinds of numerical analysis method to present the material non-lineariy which is represented the baushinger effect and the strain hardening. This model simulates the complex behavior of material by controlling the properties of the layers which like the hardening ratio, the section area and the yield stress. In this paper, the constitutive equation and plastic flow rule of each layer which are laid in the plane stress field are obtained by using the thermodynamics. Two numerical examples were tested for the validity of proposed method in uniaxial stress and plane stress field with comparable experimental results. The only parameter for the test is the yield stress distribution of each layers.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.216-223
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• 2019

The objective of this study is to propose a reliable stress-strain model in compression for lightweight concrete using bottom ash aggregates and air foam(LWC-BF). The slopes of the ascending and descending branches in the fundamental equation form generalized by Yang et al. were determined from the regression analyses of different data sets(including the modulus of elasticity and strains at the peak stress and 50% peak stress at the post-peak performance) obtained from 9 LWC-BF mixtures. The proposed model exhibits a good agreement with test results, revealing that the initial slope decreases whereas the decreasing rate in the stress at the descending branch increases with the increase in foam content. The mean and standard deviation of the normalized root-square mean errors calculated from the comparisons of experimental and predicted stress-strain curves are 0.19 and 0.08, respectively, for the proposed model, which indicates significant lower values when compared with those(1.23 and 0.47, respectively) calculated using fib 2010 model.

• Polymer(Korea)
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• v.38 no.5
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• pp.645-649
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• 2014

The causes of residual stress in an injection molded part are high temperature variation and shear stress during molding process. Chemical cracking test is one of the methods of measuring residual stress and cracks are developed according to the degree of residual stress. In this study, the relationship between chemical cracking and exerted stress have been investigated. Deformation jig was designed and used to give a stress through deformation in a specimen. Specimens were molded by a hot press using polycarbonate (PC) and annealed to remove residual stresses in the specimens. Specimens were fixed in the deformation jig and immersed into the solvent to create cracks in the specimens. Solvents were prepared by using tetrahydrofuran and methyl alcohol. As stress accordance with the deformation in the specimen increased, the frequency and density of cracks in the specimen also increased. The results of this study can be used for the measurement of residual stress quantitatively in an injection molded PC product using a chemical cracking method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.20-20
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• 1997

고강도 알루미늄 대형 링롤재를 급냉할 때 발생하는 잔류응력을 2차원 및 3차원 유한 요소 해석하였고, 3단계 절단법에 의해 측정된 변형율과 ABAQUS의 요소제거 기능을 이용한 해석 값을 직접 비교하였다. 급냉후 잔류응력 해석결과는 2단과시효 후 측정값과 비슷한 경향을 보였으나 그 절대값의 차이가 크게 나타났다 이는 시편 링의 높이가 작아 실험 값이 부정확하였기 때문이며 링의 높이를 증가시켜 높이방향으로 균일한 응력분포를 갖도록 하면 그 차이가 감소될 것으로 판단된다. 잔류응력을 측정하는 3단계 절단 과정을 모사한 3차원 해석결과와 측정된 변형율을 직접 비교함으로써 실험과 해석의 정확성을 향상시킬 수 있도록 하였다. 이로부터 잔류응력이 존재하는 일반적인 알루미늄 구조물의 기계가공에 의한 변형을 정확히 예측할 수 있는 기반을 마련하였으며 구조해석 시 잔류응력의 영향을 고려할 수 있게 되었다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.12
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• pp.220-225
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• 1998

압축성 초탄성 평판의 순수굽힘에 대한 비선형 변형해석의 수학적 정해가 본 논문에 구해져 있다. 이차원 평면 변형도 상태가 해석을 위하여 가정되었으며, 비선형 순수굽힘 변형해석결과는 고전적인 선형 순수굽힘 변형해석결과와 비교되었다. 고전적인 선형굽힘 결과와는 다르게 비선형 순수굽힘 상태에서는 반경방향응력은 영이 아니며 또한 각방향응력도 선형 상태가 아닌 것으로 규명되었다.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.95-105
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• 2000

Anisotropy of stiffiness, from extremely small strains to post-failure strains, of isotropically consolidated air-pulviated sands in plane strain compression was studied by using the newly developed instrumentation for small strain measurements. Seven types of sand of the world-wide origins were tested, which have been extensively used for research purposes. Stress-strain relationships for a wide range of strain from about 0.0001% to 10% were obtained with measuring axial and lateral strains locally free from the effects of bedding and membrane penetration errors at the specimen boundaries. It was found that the maximum shear modulus Gmax was irrespective of the angle $\delta$of the $\sigma$1 direction relative to the bedding plane. However, the normalized Gmax was varied with the types of sand. Furthermore, the dependency of the strain and stress level on the stiffness increased as decreased.