• Geotechnical Engineering
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• v.12 no.4
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• pp.145-156
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• 1996

An implicit stress integration algorithm was formulated for implementing an aiusotorpic hardening constitutive model which has been based op the generalized isotropic hardening rule in nonlinear finite element analysis technique. the rate form of stress tensor was implicitly integrated using the generalized trapezoidal rule and the tangent stress-strain modulus was evaluated consistently with the nonlinear solution technique. As a result, it has been found that the nonlinear analysis with the anisotropic hardening constitutive model might be performed accurately and efficiently.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.135-140
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• 2004

Wear mechanisms may be briefly classified by mechanical, chemical and thermal wear. A plane strain finite element method is used with a new material stress and temperature fields to simulate orthogonal machining with continuous chip formation. Deformation of the workpiece material is healed as elastic-viscoplastic with isotropic strain hardening and the numerical solution accounts for coupling between plastic deformation and the temperature field, including treatment of temperature-dependent material properties. Effect of the uncertainty in the constitutive model on the distributions of strait stress and temperature around the shear zone are presented, and the model is validated by comparing average values of the predicted stress, strain, and temperature at the shear zone with experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1390-1393
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• 2005

The hardening model based on the dislocation mechanics is employed to study the experimentally observed high tensile elongations of NiAl along the [110] orientation at intermediate temperatures. In the hardening model proposed, a mobility of dislocation is assumed to be restricted to glide through the slip plane by forest dislocation and thermally activated cross-slip event. Overall deformation behavior of NiAl was greatly influenced by temperature-dependent dislocation mobility that both experimental and simulated yield stresses decreased as temperature increased. The results of simulation showed anomalous hardening behaviors analogous to those of experiment at certain circumstances. This behavior occurred due to the hardening contributions generated by cross-slip events that disable the dislocation motion in the primary slip systems. By comparing simulation results with experiments, it is confirmed that the proposed hardening model can represent anomalous tensile elongations due to the hardening by forest dislocations and cross-slip events.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.2
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• pp.67-74
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• 2017

Recently there have been many concerns on structural integrity of nuclear piping under seismic loadings. In terms of failure of nuclear piping due to seismic loadings, an important failure mechanism is low cycle fatigue with large cyclic displacements. To investigate the effects of seismic loading on low cycle fatigue behavior of nuclear piping, the cyclic behavior of materials and nuclear piping needs to be accurately estimated. In this paper, the non-linear finite element (FE) analyses have been carried out to evaluate the effects of three different cyclic hardening models on cyclic behavior of materials and nuclear piping, such as isotropic hardening, kinematic hardening and combined hardening.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.361-370
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• 2006

The results of previous tests by many researchers have been compiled to evaluate the flexural strength of steel-fiber reinforced concrete beams. Existing prediction equations for flexural strength of such beams were examined, and a new equation based on mechanical and empirical observations, was proposed. In other words, the constitutive models for steel fiber reinforced concrete(SFRC) were proposed, which incorporate compressive and tensile strength. A steel model might also exhibit stain-hardening characteristics. Predictions based on the model are compared with the experimental data. For the collection of tests, a variation of the Henager equations, modified to apply to fiber-reinforced concrete beams, provided reliable estimates of flexural strength. The proposed equations accounted for the influence of fiber-volume fraction, fiber aspect ratio, concrete compressive strength and flexural steel reinforcement ratio. The proposed equations gave a good estimation for 129 flexural specimens evaluated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.492-497
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• 2005

In this study, we propose an advanced nanoindentaion test, Nano Pillar Compression Test (NPCT) to measure a stress-strain relation for micro scale polymer structures. Firstly, FEM analysis is performed to research behavior of micro polymer pillars in several specimen aspect ratios and different friction conditions between specimen and tip. Based on the FEM results, micro scale UV-curable polymer pillars are fabricated on a substrate by Nano Stereo Lithography (NSL). To measure their mechanical properties, uniaxial compression test is performed using nanoindentation apparatus with flat-ended diamond tip. In addition, the dependency of compression properties on loading condition and specimen size are discussed.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.2
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• pp.59-68
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• 2018

This study compares true stress-true strain curves obtained by tensile tests of various piping materials with bi-linear stress-strain approximation suggested in the JSME Code Case(CC) Draft, a guideline for piping seismic inelastic response analysis. Based on the comparisons, the reliability of the bi-linear approximation is evaluated. It is found that bi-linear stress-strain curve of TP316 stainless steel is in good agreement with its true stress-true strain curve. However, Bi-linear stress-strain curves of TP304 stainless steel and carbon steels determined by the approximation cannot appropriately estimate their stress-strain behavior. Accordingly new bi-linear approximations for carbon steels and low-alloy steels are proposed. The proposed bi-linear approximations for carbon and low-alloy steels, which include the temperature effect on strength and hardening of material, estimate their stress-strain behavior reasonably well.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.77-86
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• 1997

The advanced development in many fields of engineering and science has caused much interests and demands for crashworthiness and non-linear dynamic transient analysis of structure response. Crash and impact problems have a dominant characteristic of large deformation with material plasticity for short time scales. The structural material shows strain rate-dependent behaviors in those cases. Conventional rate-independent constitutive equations used in the general purposed finite analysis programs are inadequate for dynamic finite strain problems. In this paper, a rate-dependent constitutive equation for elastic-plastic material is developed. The plastic stretch rate is modeled based on slip model with dislocation velocity and its density so that there is neither yielding condition, nor loading conditions. Non-linear hardening rule is also introduced for finite strain. Material constants of present constitutive equation are determined by experimental data of mild steel, and the constitutive equation is applied to uniaxile tension loading.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.4
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• pp.383-390
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• 2015

This study conducted tensile tests on SA508 Gr.1a low alloy steel and SA312 TP316 stainless steel piping materials under various strain rates at room temperature (RT) and $316^{\circ}C$ to investigate the effects of loading rate on the deformation behavior of nuclear piping materials. At RT, the deformation behavior for both pipe materials showed a typical loading rate dependence, i.e., the strength increased and the ductility decreased as the loading rate increased. At $316^{\circ}C$, however, the strength and elongation of SA508 Gr.1a low alloy steel decreased as the loading rate increased, and its reduction of area non-linearly varied with the loading rate. For SA312 TP316 stainless steel, the strength, elongation, and reduction of area at $316^{\circ}C$ were almost the same regardless of the loading rate. At both temperatures, the strain hardening capacity was nearly independent of the loading rate for SA508 Gr.1a low alloy steel, while it decreased with increasing loading rate for SA312 TP316 stainless steel.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.21-28
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• 2006

This paper presents both experimental and analytical studies for the development of an ECC(Engineered Cementitious Composites) using ground granulated blast furnace slag(slag). This material has been focused on achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, micromechanics was adopted to properly select optimized range of the composition based on steady-state cracking theory and experimental studies on matrix, and interfacial properties. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties of the fiber in a matrix and the fracture toughness of mortar matrix. The addition of the slag resulted in slight increases in the frictional bond strength and the fracture toughness. Subsequent direct tensile tests demonstrate that the fiber reinforced mortar exhibited high ductile uniaxial tension behavior with a maximum strain capacity of 3.6%. Both ductility and tensile strength(~5.3 MPa) of the composite produced with slag were measured to be significantly higher than those of the composite without slag. The slag particles contribute to improving matrix strength and fiber dispersion, which is incorporated with enhanced workability attributed to the oxidized grain surface. This result suggests that, within the limited slag dosage employed in the present study, the contribution of slag particles to the workability overwhelms the side-effect of decreased potential of saturated multiple cracking.