• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.44-47
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• 2009

In this paper, limitation of rigid-plastic finite element method caused from rigid-plasticity assumption and numerical problem is investigated in detail and a useful scheme is proposed to get rid of the plastic deformation in rigid or elastic region. A typical example of a possible long bar extrusion process is given, which may be impossible to simulate without using the proposed scheme. The scheme is successfully applied to simulating the long bolt forging processes.

• Structural Engineering and Mechanics
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• v.3 no.2
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• pp.185-192
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• 1995

A numerical algorithm for plane stress and shell elasto-plasticity is presented in this paper. The proposed strain decomposition (SD) algorithm is an elastic predictor/plastic corrector algorithm, and in the context of operator splitting, is a return mapping algorithm. However, it differs significantly from other return mapping algorithms in that only the necessary response functions are used without invoking their gradients, and the stress increment is updated only at the end of the time step. This makes the proposed SD algorithm more suitable for materials with complex yield surfaces and will guard against error accumulation during the time step. Comparative analyses of structural systems using the proposed strain decomposition (SD) algorithm and the iterative radial return (IRR) algorithm are presented. The results demonstrate the accuracy and usefulness of the proposed algorithm.

• Computers and Concrete
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• v.16 no.2
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• pp.329-342
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• 2015

The present paper aims at developing a method to accommodate multi-surface concrete plasticity from the point of view of a consistency concept applied to general tangent operators. The idea is based on a Taylor series expansion of the actual effective stress at the stress point corresponding to the previous accumulated true stresses plus the current increment values, initially taken to be elastic. The proposed algorithm can be generalized for any multi-surface criteria combination and has been tested here for typical cement-based materials. A few examples of application are presented to demonstrate the effectiveness of the multi-surface technique as used to a combination of Rankine and Drucker-Prager yield criteria.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.113.1-113.1
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• 2007

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.4
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• pp.1-8
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• 1983

This paper describes the application of the finite element method to the large deflection elastic plastic analysis and ultimate load calculation of axisymmetric shell of revolution with initial imperfection subjected to external pressure. The nonlinear equilibrium equations are linearized by the successive incremental method and are solved by the combination of load increment and iteration scheme with considering plastic deformation theory. To get the more realistic effect of large deflection, corrected coordinats and directions of applied load ar every load increment steps are used. The effects of the plasticity, initial imperfection and the shape of shells on the ultimate load of clamped circular cap under external pressure are investigated. Consequently, the following conclusions are obtained; (1) At same geometric parameter $\lambda$, each shape of clamped circular caps yield same elastic ultimate loads in both cases, i.e. with and without initial imperfections, whereas, in the case of elastic-plastic state the shell becomes thicker, the ultimate loads are getting smaller. (2) The effects of initial imperfection to ultimate load are most significant in the elastic case and are more senstive in the elastic-plastic state with the thinner shells.

• Steel and Composite Structures
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• v.32 no.5
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• pp.657-670
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• 2019

This paper proposes a one-dimensional fiber beam element model taking account of materially non-linear behavior, benefiting the highly efficient elastic-plastic analysis of girders with shear-lag effects. Based on the displacement-based fiber beam-column element, two additional degrees of freedom (DOFs) are added into the proposed model to consider the shear-lag warping deformations of the slabs. The new finite element (FE) formulations of the tangent stiffness matrix and resisting force vector are deduced with the variational principle of the minimum potential energy. Then the proposed element is implemented in the OpenSees computational framework as a newly developed element, and the full Newton iteration method is adopted for an iterative solution. The typical materially non-linear behaviors, including the cracking and crushing of concrete, as well as the plasticity of the reinforcement and steel girder, are all considered in the model. The proposed model is applied to several test cases under elastic or plastic loading states and compared with the solutions of theoretical models, tests, and shell/solid refined FE models. The results of these comparisons indicate the accuracy and applicability of the proposed model for the analysis of both concrete box girders and steel-concrete composite girders, under either elastic or plastic states.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.315-318
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• 2003

Recently, condenser tube which is used for a cooling system of automobiles is mainly manufactured by the conform extrusion but this method is inferior as compared with direct extrusion in productivity per the unit time and in the equipment investment. Therefore, it is essential for the conversion of direct extrusion with porthole die. The direct extrusion with porthole die can produce condenser tube which has the competitive power in costs and qualities compared with the existing conform extrusion. This study is designed to evaluate metal flow, welding pressure, extrusion load tendency of mandrel deflection that is affected by variation of porthole shape in porthole die. Estimation is carried out using finite element method under the non-steady state. Also this study was examined into the cause of mandrel fracture through investigating elastic deformation of mandrel during the extrusion.

• Structural Engineering and Mechanics
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• v.51 no.6
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• pp.909-922
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• 2014

In this paper, we present an alternative seismic design strategy for cable stayed bridges with concrete pylons when subjected to strong ground motions. The comparison of conventional seismic design using supplemental dampers (strategy A) and the new strategy using nonlinear seismic design of pylon columns (strategy B) is exemplified by one typical medium span cable stayed bridge subjected to strong ground motions from 1999 Taiwan Chi-Chi earthquake and 2008 China Wenchuan earthquake. We first conducted the optimization of damper parameters according to strategy A in response to the distinct features that strong ground motions contain. And then we adopted strategy B to carry out seismic analysis by introducing the elastic-plastic elements that allowing plasticity development in the pylon columns. The numerical results show that via strategy A, the earthquake induced structural responses can be kept in the desired range provided with the proper damping parameters, however, the extra cost of unusual dampers will be inevitable. For strategy B, the pylon columns may not remain elastic and certain plasticity developed, but the seismic responses of the foundation will be greatly decreased, meanwhile, the displacement at the top of pylon seems to be not affected much by the yielding of pylon columns, which indicates the pylon nonlinear design can be an alternative design strategy when strong ground motions have to be considered for the bridge.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.73-79
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• 2003

Recently many kinds of gears have been produced by forging in order to enhance the mechanical properties of the gears and the productivity of the process. Developments in forging technology are the reason for the increased usage. However, a critical problem of the forged gears is the dimensional change or distortion caused by elastic recovery after forging, and relief of the residual stresses during subsequent heat treatments. Distortion is of great concern to the manufacturers of precision parts, because it influences directly the dimensional accuracy and the grade of carburized bevel gears. In the present paper, distortion due to cold forging and heat treatment of bevel gears is investigated. Distortions of forged gears, machined gears and die are measured and compared. Numerical analysis is used to simulate the complete cold forging process and heat treatment process for the machined gears and shows good agreement with the experimental measurements.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.94-97
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• 1999

The study has been performed for the relation between die and product in closed die upsetting by the experiment. the strain of die has been given by the simple experiment using the strain gauge located at the outer surface of die and the deformation history of die and product has been given by the experiment and Lame's formula. the product with accurate dimension and shape can be obtained by analysing elastic deformation of die during upsetting process. The deformation of die during metal forming process has been given by the experiment and lame's formula. The product with accurate dimension and shape can be obtained by analysing elastic deformation of die during upsetting process. The deformation of die during metal forming process has been usually predicted by the experience of industrial engineers of finite element analysis. But it is difficult to predict the dimension of product at unloading and ejected states. The study has given useful result for the deformation history of die and product through the experiment and Lame's formula at closed die upsetting and can be applied in the die design for product with accurate dimension.