• Polymer(Korea)
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• v.24 no.5
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• pp.690-700
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• 2000

In this study, an elastomer-assistered compression molding process was investigated by experiments as well as modeling for the long-fiber reinforced thermoset composites. The consolidation pressure generated by fixed-volume and variable-volume conditions was thermodynamically derived for both elastomer and curing prepregs, and was compared with the pressure measured during curing of epoxy matrix. Exhibiting non-linear viscoelastic characteristics in the compressive stress-strain tests, the measured stress was well compared with a modifed KWW (Kohlrausch-Williame-Watts) equation, which is based on the Maxwell viscoelastic model. Using the developed model equations, the consolidation pressure generated by the elastomer was successfully predicted for the compression molding process of thermoset composite materials in tile closed mold system.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.215-228
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• 2002

In a companion paper. (Oh, 2002), the constitutive model, called GUX model, was implemented as a user subroutine in ABAQUS code, where the GUX model could describe the behavior of overall strain range. An accuracy analysis verified that the implicit stress integration maintained the accuracy of solutions successfully. Since the GUX model is an anistropic hardening elasto-plastic constitutive model based on total stress concept, geotechnical problems under fully drained or undrained condition can be analyzed after acquisition of stress-strain relationships from drained or undrained triaxial tests. This study includes the analyses of the stability of embankments on soft clays and weathered soils and the example of axially loaded soil-pile system. In the large deformation analyses, geometric nonlinearity was considered and the result of analyses with GUX model was compared with that of Mises model for the overall strain range behavior.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.161-171
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• 1993

The aim of this study is to provide the stress-strain behavior of hardening geological materials such as rock or concrete on three dimensional spaces by using Desai model based on plastic theory. To validate proposed model, truly triaxial tests with high pressure under variety of stress paths in which three principal stresses were controlled independently using concrete materials were performed. The main results are summerized as follows: 1. Various stress paths for hardening materials used are satisfactorily explained by performing the truly triaxial test with high pressure. This is very important to investigate constitutive equations for materials like rock or concrete. 2. Since the proposed yield function is continuous, it avoids the singularity point at the intersection of two function in the previous models, thus, reducing the difficulties for computer implementation. 3. Analytic predictions for yielding behavior on $J_1-{\sqrt{J_{2D}}}$ octahedral and triaxial plane, as well as volumetric strain and stress-strain behavior agree well with experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.272-278
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• 2011

In the present work, FEM analyses are carried out to investigate the fractures occurred within the structural part in the course of combustion experiment. The loss of structural integrity stems from the localized deformation and the damage induced due to a severe change in the thermal load. Moreover, the two-back stress evolution model is proposed using the Armstrong-Frederick and the Phillips' rules to depict the plastic deformation, and the continuum damage mechanics is also incorporated into the present model. It is noted that the present model is able to formulate a wide range of constitutive description with ease. The numerical results depicts that a severe strain localization and damage evolution can be obtained depending on the dominant back stress.

• Geotechnical Engineering
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• v.12 no.2
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• pp.9-18
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• 1996

The results of a series of triaxial compression tests on remolded normally consolidated clay are compared with the predictions .by the isotropic single -hardening constitutive model, which incorporates eleven parameters. The parameters can be determined from undrained triaxial compression tests on isotropically consolidated specimens of remolded clay. The model with the determined parameters is applied to predict the stress-strain and pore pressure behaviors for untrained triaxial compresion tests on anisotropically consolidated specimens. Also the model is utilized to predict the stress strain and voltmetric strain behavior for drained triaxial compression tests on both isotropic and anisotropic specimens. The predicted response agrees well with the measured behavior for undrained triaxial compression tests on not only isotropically but also anisotroically but also anisotropically consolidated specimens. The initial volumetric strain is, however, predicted to be less than the measured value from drained triaxial compression tests, while the predicted volumetric strain close to failure is greater than the measured value. Nevertheless, it may be stated generally that overall acceptable predictions are produced. Therefore, the results of this study indicate that the applicability of the model on prediction of the behavior of normally consolidated clay is achieved sufficiently.

• Composites Research
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• v.36 no.5
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• pp.315-320
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• 2023

In the manufacturing process of thermosetting carbon fiber composite materials using an autoclave, the internal temperature changes according to the set temperature cycle. This temperature change causes the resin in the composite material to cure. Heat is generated through the chemical reaction of the resin, which can result in a difference between the temperature inside the autoclave and the temperature of the composite material. Previous research assumed that the temperatures of the composite material and the autoclave were the same and analyzed to predict the residual stress and thermal deformation after manufacturing. However, these stresses and deformations depend on the temperature and degree of cure of the composite material. Therefore, this study verifies a thermal-chemical model analysis technique that takes into account the heat generated by the chemical reaction of the resin to accurately calculate the temperature and degree of cure. Additionally, case studies were conducted for different thicknesses to investigate whether this model exhibits similar trends across varying thicknesses.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.528-535
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• 2011

In the present, the formation of shear band under a simple shear deformation is investigated using a rate-independent elastic-plastic constitutive relations. Moreover, the strain gradient terms are incorporated to obtain a non-local plastic constitutive relation, which in turn represented using combined two-back stress hardening model. Then, the continuum damage model is also included to the proposed model. The post-localization behavior are studied by introducing a small imperfection in a work piece. The strain gradient affects the shear localization significantly such that the intensity of shear band decreases as the strain gradient coefficient increases when the J2 flow theory is employed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.309-317
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• 1999

이 논문에서는, 섬유가 보강된 직교 이방성 복합재료의 제작 과정에서 발생하는 잔류 응력을 조사하였다. 직교 이방성 복합 재료의 제작 과정은 경화 과정과 냉각 과정으로 나누어 지며 이 과정에서 발생하는 잔류 응력을 3차원 경계요소법을 이용하여 해석하였다. 모재는 선형 점탄성 거동을 한다고 가정하고, 종속 영역법을 도입하여 해석 모델을 섬유 영역과 모재 영역으로 나누었다. PATRAN을 사용하여 모재에서의 잔류 응력 분포를 도시하였으며 해석 결과를 검토하여 잔류 응력이 국부적으로 모재의 항복을 야기시킬 수 있음을 제시하였다.

• Composites Research
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• v.16 no.1
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• pp.34-41
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• 2003

A cure process control model was proposed to optimize the curing process of thick filament wound structure. There are two types of smart cure, one is that the boundary conditions of the hollow cylinder are same between inner surface and outer surface, and the other is that inner surface temperature is slightly higher than outer surface to initiate cure reaction from the inner side to the outer side to reduce residual stress.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.195-204
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• 2012

In the construction of high-rise buildings, bent re-bars are manually straightened to connect slabs to core-walls, which are usually cast before floor structures. During cold bending and straightening of re-bars, plastic deformation causing work hardening, Bauschinger effect and aging hardening is unavoidable. Tensile tests of coldly bent and straightened re-bars were conducted with test parameters of grade, diameter, and bend radius of re-bars as well as age between bending and straightening. Test results showed that proportional limits were lower and strain hardening occurred without yield plateaus. Inside and outside of re-bars with compression and tension deformations, respectively, during bending showed lower yield points due to Bauschinger effect and no yield plateaus due to work hardening, respectively. When re-bar grade was higher, yield point became significantly lower where Grade 400 re-bars had yield strengths lower than specified yield strength of 400 MPa. Because the surface of re-bar has higher strength than the core of re-bar, Bauschinger effect was more obvious for higher-grade re-bars. When age between bending and straightening was greater, yield strength increased and elongation decreased (i.e. embrittlement occurs). Using measured data, stress-strain relationship for straightened re-bars was developed based on Ramberg-Osgood model, which can be used to evaluate stiffness of joints when straightened re-bars are applied.