• Tribology and Lubricants
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• v.32 no.5
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• pp.160-165
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• 2016

AISI 4140 steel is widely used in various mechanical components owing to its superior mechanical properties. Surface hardening techniques are often used to further improve the properties, particularly for applications with moving components. The aim of this research is to understand the effect of heat treatment process on surface properties and tribological characteristics of AISI 4140 steel. In this work, we prepare two different AISI 4140 steel specimens- one cooled by air and one by oil- and determine surface properties such as surface topography and roughness using a confocal microscope. We also observe the cross-sections of the specimens using a scanning electron microscope to understand the difference in the material structure. In addition, we assess the hardness with respect to the distance from the surface using a micro-Vickers hardness tester. After characterizing the surfaces of the specimens, we investigate the wear characteristics of the specimens under hydrodynamic lubrication. The results show the presence of grooves on the surface of the oil-cooled specimens. It is likely that such grooves are formed during the cooling process using the oil. However, we observe no other significant differences in the surface properties of the specimens. The wear test results show the occurrence of severe wear on the oil-cooled specimens, which may be due to the groove formed on the surface. The results of this work may be helpful to improve surface properties using surface hardening techniques from a tribological perspective.

• Nuclear Engineering and Technology
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• v.10 no.2
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• pp.73-78
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• 1978

The effect of temperature and strain rate on the deformation behavior of $\alpha$-uranium was investigated in the temperature ranged 300$^{\circ}$ to 55$0^{\circ}C$ by strain, rate change test. Strain rate sensitivity, activation volume, strain rate sensitivity exponent and dislocation velocity exponent were determined. The strain rate sensitivity exponent and dislocation velocity exponent were determined. The strain rate sensitivity exponent increases with strain below 40$0^{\circ}C$, while the exponent decreases with strain above 50$0^{\circ}C$. It is believed that the increase of strain rate sensitivity exponent with strain below 40$0^{\circ}C$ can be attributed to an increase in internal stress as a result of work hardening while decrease of the exponent with strain above 50$0^{\circ}C$ is due to predominance of thermal softening over work hardening because more slip, system are active in deformation above about 50$0^{\circ}C$.

• Computational Structural Engineering
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• v.10 no.4
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• pp.217-228
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• 1997

The high precision analysis by the p-version of the finite element method are fairly well established as highly efficient method for linear elastic problems, especially in the presence of stress singularity. It has been noted that the merits of the p-version are accuracy, modeling simplicity, robustness, and savings in user's and CPU time. However, little has been done to exploit their benefits in elasto-plastic analysis. In this paper, the p-version finite element model is proposed for the materially nonlinear analysis that is based on the incremental theory of plasticity using the constitutive equation for work-hardening materials, and the associated flow rule. To obtain the solution of nonlinear equation, the Newton-Raphson method and initial stiffness method, etc are used. Several numerical examples are tested with the help of the square plates with cutout, the thick-walled cylinder under internal pressure, and the circular plate with uniformly distributed load. Those results are compared with the theoretical solutions and the numerical solutions of ADINA

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.413-423
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• 1991

Multiaxial loading by combinations of tension-torsion-internal pressure have been applied to the thins-walled tubular specimens prepared from cold drawn tubes of SAE 1020 steel. Prior to the multiaxial loading, each specimen has been twisted to different shear strains. Uniaxial tensile yield stresses measured at different angles to the tube axis clearly show that the initial orthotropic symmetry is maintained during twisting. The orthotropy axes are observed to rotate with shear strains. The plane stress yield locus measured for each twisted specimens show that yield surface shape does not remain similar during twisting and thus anisotropic work hardening is not a function of only plastic work.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1992.03a
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• pp.159-176
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• 1992

Limit analysis has been rendered versatile in many problems such as structural problems and metal forming problems. In metal forming analysis, a slip-line method and an upper bound method approach to limit solutions is considered as the most challenging areas. In the present work, a general algorithm for limit solutions of plastic flow is developed with the use of finite element limit analysis. The algorithm deals with a generalized Holder inequality, a duality theorem, and a combined smoothing and successive approximation in addition to a general procedure for finite element analysis. The algorithm is robust such that from any initial trial solution, the first iteration falls into a convex set which contains the exact solution(s) of the problem. The idea of the algorithm for limit solution is extended from rigid/perfectly-plastic materials to work-hardening materials by the nature of the limit formulation, which is also robust with numerically stable convergence and highly efficient computing time.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.19-28
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• 1997

This study was made of the effect of cold working on the stress corrosion cracking(SCC) of austenitlc 304 stainless steel in boiling 42% $MgCl_2$ solution. For this experiment, specimens cold-worked of 0%, 10%, 20%, 30%, 40% were fabricated respectively, and then experiments of mechanical properties and stress corrosion cracking(SCC) of these specimens were carried out. The results of these experiments indicate that the maximum resistance to SCC showed at 20% of cold working degree and that the SCC susceptibility depended on the volume fraction of deformation-induced martensite by cold working and the work hardening of matrix. On the other hand, the fracture mode was changed. This phenomenon was considered that deformation-induced martensite was grown from transgranular fracture mode to intergranular fracture mode and caused by increased of dislocation density along the slip planes.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.315-323
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• 1998

This study has been conducted to develope the combined heat treating technique of gas carburising - gas nitriding and gas carburising to improve the hot working performance of type H3 hot work tool steel. Case depth and carbrides coarsening were increased with increasing carburising temperature and time, respectively. Surface hardness showed decreasing tendency with increasing 2nd tempering temperature after carburising treatment. After carburising, 2nd treatment at 500 to 600 was chosen according to a hardness demand of final product. High temperature tempering resistance showed more excellent quality during such carburising-nitriding or carburising than complex treatment as after conventional hardening.

• Coupled systems mechanics
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• v.11 no.6
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• pp.525-542
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• 2022

In this work we present an advanced approach to the design of small wind turbine support steel structures. To this end we use an improved version of previously developed geometrically exact beam models. Namely, three different geometrically exact beam models are used, the first two are the Reissner and the Kirchhoff beam models implementing bi-linear hardening response and the third is the Reissner beam capable of also representing connections response. All models were validated in our previous research for a static response, and in this work they are extended to dynamic response. With these advanced models, we can perform analysis of four practical solutions for the installation of small wind turbines in new or existing buildings including effects of elastoplastic response to vibration problems. The numerical simulations confirm the robustness of numerical models in analyzing vibration problems and the crucial effects of elastoplastic response in avoiding resonance phenomena.

• Journal of the Korean Geosynthetics Society
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• v.11 no.2
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• pp.1-9
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• 2012

In order to review the utility of Lade's single hardening constitutive model, a series of isotropic compression-expansion tests and consolidated drained triaxial tests including as CTC, TC, RTC, and OSP were performed by Baekma river sand with various of stress path. Parameters required in model were determined using these tests. The accuracy of analysis was reviewed by back analysis of test results used to determine the 11 parameters of soil property through the test of each stress path. Also. for verifying the accuracy of prediction for the stress-strain behavior using failure criterion related 9 parameters with correlational equation and constant and yield criterion related parameters h, ${\alpha}$ and ${\eta}_1$, when stress path is different with each other, it has been obtained in the review result of stress path dependent characteristics of the constitutional model through the analyzing results of CTC, TC, RTC, OSP, and fine silica sand tests.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.29-39
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• 2010

By understanding the construction process of sea dikes and the current state of the thickness and speed of fluid in the bottom layer protection work of final closure gaps, a construction method applicable for the blocking of bottom layer work will be selected. The three construction methods selected will be tested in site through various methods, and the reinforcement of bottom layer protection and impervious effect will be verified. The verification results are as follows: 1) The overall riprap layer were 0.5~1.0m thicker than planned so that the grouting depth and grout input amount increased 2) The applied construction methods permeability of riprap layers were improved from $\alpha{\times}10^{-2}cm/s$ before the construction to $\alpha{\times}10^{-4}cm/s$ after construction. 3) The results of core extraction in order to grossly verify the hardening time and durability allowed the identification of grout injection effect. The amount of filling of the injection was difficult to judge because the slime in many areas made the reading of borehole photography difficult.