• Journal of Ocean Engineering and Technology
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• v.10 no.2
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• pp.106-119
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• 1996

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low speciffic weight, low thermal expansibillity, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductillity in order to compensate the weakness of ceramic.The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strngth of joint to a large amount by forming a singular stress field. In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined. In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.

• Geotechnical Engineering
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• v.10 no.3
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• pp.17-32
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• 1994

To model the anisotropic behavior of soils in the case of reverse loading, an anisotropic hardening description is proposed on the basis of generalized isotropic hardening(GIH) rule. There is a core of the GIH rule in the allowance of the concept that the center of homology of isotropic hardening can be any proper stress states inside a yield surface. The plastic deformations could be represented for the condition of reverse loading, and an explicit constitutive relationship was formulated by utilizing a simple hardening function. The proposed hardening description has been compared with other anisotropic hardening models. For verification three sets of triaxial test results have been predicted for the drained and undrained behavior of overconsolidated clays and Ko consolidated clays.

• Geotechnical Engineering
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• v.11 no.4
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• pp.49-62
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• 1995

Soil nailing has been widely rosed during the last two decades to stabilize sheep excavated slopes in several countries. In thin study, the discrete element method has been applied to evaluate the stability of the reiuorced slope. This method is capable of not only estimat ins tensile and sheer stresses mobilized in nails but also providing individual safety factors of soil and nails, It has been assumed that the nailed slope be comprised of slices connected with elastoplastic twinkler springs. A reasonable mechanism is applied for representing the behavior between nails and adj scent soils. Taking into account for the bequence of construction the developed method well predicts the measured tensile forces developed in nails so that it is possible to appropriately evaluate the overall safety factor.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.108-109
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• 2012

DLC 박막은 고경도 및 저마찰의 우수한 물리적 특성을 갖는 것으로 널리 알려져 다양한 산업분야에 적용이 되고 있다. 또한, 그 응용 분야 확대를 위해 DLC 박막의 후막화, 대면적 균일처리, 경제성 확보 등의 연구 노력이 지속되고 있다. 특히, DLC 박막은 높은 내부응력에 의해 후막화가 어렵고, 탄소와 수소의 화학적 결합에 의한 고형 물질로 내열성이 다른 경질코팅 물질 보다 취약하다는 단점을 갖고 있다. 본 연구는 DLC 박막의 내부응력 완화를 위해 실리콘 및 질소 원소를 함유하여 박막을 제작하고, 제작 공정 조건이 박막의 물성에 미치는 영향을 연구하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.257-262
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• 2009

Elastic-Plastic structural analysis was performed to evaluate structural characteristic and integrity for rocket motor case of solid propulsion system. The structural analyses were compared and evaluated using the simplified 2-D axisymmetric model and 3-D full model for rocket motor case with torispherical dome type. And pre-tension load for bolt model was considered in structural analysis. The results of displacement and stress for the simplified 2-D axisymmetric model and 3-D full model were in an good agreement with each other. Therefore, the simplified 2-D axisymmetric model for rocket motor case was recommended to verify quickly the structural integrity and save the modeling and calculating time in initial design stage. Also, the structural characteristic and integrity for rocket motor case according to 5 dome types was evaluated to select the optimal dome shape.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.41-49
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• 1993

This paper presents a geometrically non-linear and elastoplastic F.E. formulation using a total Lagrangian approach for the two dimensional isoparametric curved beam elements. The beam element is derived by using plane stress elements. The basic element geometry is constructed using the coordinates of the nodes on the element center line and the nodal point normals. The element displacement field is described using two translations of the node on the center line and a rotation about the axes normal to the plane containing the center line of the element. The layered approach is used for the elastoplastic analysis of the plane framed structure with the arbitrary cross section. The iterative load or displacement incremental method for non-linear finite element analysis of the frame structure is used. Numerical examples are presented to demonstrate the behavior and the accuracy of the proposed beam element for geometric and elastoplastic non-linear applications. Comparisons made with present theory and other published data show that tilt' beam element products accurate results with good convergence characteristics.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.241-250
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• 2003

This study, investigated the characteristics of residual stress in weldis composed of similar or dissimilar steels, are investigated byusing 3three-dimensional thermal elasto-plastic FEM analysis. The results showed that for the groove welding of the similar steels, increasedthetensile strength of the steels (POSTEN60

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.423-430
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• 2013

In this research, a paramteric study to account for the effect of interfacial strength and nanotube agglomeration on the elastoplastic behavior of carbon nanotube reinforced polypropylene composites is performed. At first, the elastoplastic behavior of nanocomposites is predicted from molecular dynamics(MD) simulations. By combining the MD simulation results with the nonlinear micromechanics model based on the Mori-Tanaka model, a two-step domain decomposition method is applied to inversely identify the elastoplastic behavior of adsorption interphase zone inside nanocomposites. In nonlinear micromechanics model, the secant moduli method combined with field fluctuation method is used to predict the elastoplastic behavior of nanocomposites. To account for the imperfect material interface between nanotube and matrix polymer, displacement discontinuity condition is applied to the micromechanics model. Using the elastoplastic behavior of the adsorption interphase zone obtained from the present study, stress-strain relation of nanocomposites at various interfacial bonding condition and local nanotube agglomeration is predicted from nonlinear micromechanics model with and without the adsorption interphase zone. As a result, it has been found that local nanotube agglomeration is the most important design factor to maximize reinforcing effect of nanotube in elastic and plastic behavior.

• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.61-70
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• 1988

In order to consider the concept of the fitness for purpose'in fatigue design of offshore structure, fracture mechanics is applied to evaluate initial or weld defects. Generally, linear elastic fracture mechanics has been applied to tstimate initial fatigue crack propagation rate as well as long fatigue crack propagation rate. But, initial fatigue crack propagation rate in elasto-plastic notch field may not be characterized by application of stress intensity factor range .DELTA. K, because plastic effect due to stress concentration of notch may contribute to initial crack propagation. Therefore, to introduce the plastic effect into fatigue crack driving force, in this studty, the evaluating method of J-integral range .DELTA. J, was developed by willson was modified for application to notch field. In calculation of .DELTA. J obtained from the modified J-integral, stress gradient and crack closure behavior in the notch field were considered. The initial crack propagation rates in the notch fields of mild steels and high tensile strength steels were correlated to .DELTA. J. As the result, it was cleared that the present .DELTA. J is applicable to charachterize the fatigue crack propagation rates in both the elastic and elasto-plastic notch fields.

• Geotechnical Engineering
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• v.8 no.2
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• pp.45-58
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• 1992

An elasto-plastic constitutive model for geological materials, which satisfies the flezibility and stability at the same time, can be used in a number of geotechnical problems. Using the spacing ratio of critical state, a flexible model is proposed based on the stability of modified Camflay model. The spacing ratio of critical state can be simply evaluated, and practically used in describing the undrained shearing behavior of clay. The proposed model has precisely predicted the stress paths and stress -strain relationships, compared with the modified Camflay model, with respect to undrained triaxial test results. Besides, the effects of strain rate, creep, and relaxation can also be considered. Using the quasi-state boundary surface, the constitutive relations are well predicted. Therefore, it is found that the assumption of associative flow rule is well posed for undrained behavior of normally consolidated clay.