• Structural Engineering and Mechanics
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• v.61 no.2
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• pp.275-282
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• 2017

The Fleck-Hutchinson theory on strain gradient plasticity (SGP), proposed in Adv. Appl Mech 33 (1997) 295, has recently been reformulated by adopting the strategy of decomposing the second order strain presented by Lam et al. in J Mech Pays Solids 51 (2003) 1477. The newly built SGP satisfies the non negativity of plastic dissipation, which is still an outstanding issue in other SGP theories. Furthermore, it explicitly shows how elastic strain gradients and corresponding elastic characteristic length scales come into play in general elastic-plastic loading histories. In this study, the relation between elastic length scales and plastic length scales is investigated by taking wire torsion as an example. It is concluded that the size effects arising when two sets of length scales are of the same order are essentially elastic instead of plastic.

• Structural Engineering and Mechanics
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• v.11 no.4
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• pp.423-442
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• 2001

This paper presents a method of elastic-plastic analysis for planar steel frames that provides the accuracy of distributed plasticity methods with the computational efficiency that is greater than that of distributed plasticity methods but less than that of plastic-hinge based methods. This method accounts for the effect of spread of plasticity accurately without discretization through the cross-section of a beam-column element, which is achieved by the following procedures. First, nonlinear equations describing the relationships between generalized stresses and strains of the cross-section are derived analytically. Next, nonlinear force-deformation relationships for the beam-column element are obtained through lengthwise integration of the generalized strains. Elastic-plastic flexibility coefficients are then calculated by differentiating the above element force-deformation relationships. Finally, an elastic-plastic stiffness matrix is obtained by making use of the flexibility-stiffness transformation. Adding the conventional geometric stiffness matrix to the elastic-plastic stiffness matrix results in the tangent stiffness matrix, which can readily be used to evaluate the load carrying capacity of steel frames following standard nonlinear analysis procedures. The accuracy of the proposed method is verified by several examples that are sensitive to the effect of spread of plasticity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.06a
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• pp.12-12
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• 2006

• Proceedings of the KWS Conference
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• 2003.05a
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• pp.210-212
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• 2003

Finite element analysis of welding processes, which entail phase evolution, heat transfer and deformation, is considered in this paper. Attention focuses on numerical implementation of the thermo-elastic-plastic constitutive equation proposed by Leblond et al in consideration of the transformation plasticity. Based upon the multiplicative decomposition of deformation gradient, hyperelastic formulation is employed for efficient numerical integration, and the algorithmic consistent moduli for elastic-plastic deformations including transformation plasticity are obtained in the closed form. The convergence behavior of the present implementation is demonstrated via a couple of numerical example.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.108-111
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• 1999

Elastic deformation of die has been investigated to improve the accuracy of cold forged parts. In order to improve the accuracy of forged parts we have investigated the elastic deformation of forging die by analysis with commercial. F. E. M code DEFORM and experiments using he strain gages. In the F. E. M analysis two types are used for elastic deformation of die. the one considers die as elastic body and the other considers the die as rigid body. The latter relatively takes a lot of time. The results from the two types are very similar with each other. Considering the results of analysis and experiments it is likely that the elastic strain of forging die is very small.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.334-336
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• 2009

An elastic-plasticity model during the austenitic decomposition was derived and implemented to incorporate the two important deformation behaviors observed during the phase transformations: the volumetric strain and transformation induced plasticity due to the temperature change and phase transformation. To obtain transformed phase volume fractions during cooling, the fourth order Runge-Kutta method was used to solve the Kirkaldy's phase kinetics model which is function of temperature, austenitic grain size and chemical composition. The volumetric strain was calculated by considering the densities of constituent phases, while the transformation induced plasticity was based on the micro-plasticity due to the volume mismatch between soft austenitic phase and other harder phases. The constitutive equations were implemented into the implicit finite element software and a simple boundary value problem was chosen as a model problem to validate the effect of transformation plasticity on the deformation behavior of steel under cooling from high temperature. It was preliminary concluded that the transformation plasticity plays a critical role in relaxing the developed stress during forming and thus reducing the magnitude of springback.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.498-498
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.112-116
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• 2002

In cold forging, the elastic behavior of the die has a direct influence on the accuracy of the forging part. And the die dimension is continuously changed during the loading, unloading, and ejecting stage. In this paper, we evaluated the elastic deflections of cold forging die during loading, unloading, and ejecting stage. Uni-axial strain gauges are used to measure elastic strain of die during each forging stage. Strain gauges are attached on the surface of die. A commercial F.E.M code, DEFORM-2D$\^$TM/ is used to predict elastic strain of die. Two method of F.E.M. analysis are used to compare with measured and calculated elastic strain. One is to regard the die as rigid body over forging cycle. And then, the die sass is analyzed by loading the die with pressure from the forging part. The other is to regard the die as elastic body from forging cycle. The elastic strain of die is calculated and the die is elastically deformed at each strop. The calculated results under the elastic die assumption are well agreed with experimental data using strain gauges.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.333-338
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• 1998

Mechanical properties of polycrystalline{{{{ {Ti }_{3 }{SiC}_{2 } }} were investigated. Hertzian indentation test using a spher-ical indenter was used to study elastic and plastic behavior in{{{{ {Ti }_{3 }{SiC}_{2 } }} A high ratio of hardness to elastic mo-dulus indicated that mechanical properties of{{{{ {Ti }_{3 }{SiC}_{2 } }} are somehow similar to those of metals. Indentation stress-strain curve deviated from an ideal elastic limit indicating exceptional plasticity in this material. De-formation zones were formed below the contact as well as around the contact area. Intragrain slip would ac-count for high plasticity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.34-37
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• 2003

Cold forging has several advantages as compared with conventional forming by cutting process. In this study, the elastic deformations of straight bevel gear and die induced by cold forging process are investigated to use 3D-Scanner. So we could estimate the total elastic deformation as comparing between forged bevel gears and die. And finite element analysis has been performed to predict the elastic deformation, each of cold forged bevel gear and die. The predicted values are compared with the experimental values and as a result they are well agreed with experimental data.