• Journal of the Korea Concrete Institute
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• 제13권6호
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• pp.602-609
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• 2001

A strut-and-tie model was proposed to predict the shear strength of RS beam which is a hybrid steel beam with reinforced concrete ends. The proposed model is capable of considering the concrete softening effects due to diagonal shear cracks at the embedded area of steel in concrete. It can predict tile failure strength of RS beam from the mathematical formulations which are based on equilibrium, compatibility, and the constitutive laws of cracked reinforced concrete. The previous experimental results of 15 RS beams were analyzed with the proposed model and the analytical results were also compared with formulas currently available. The comparison revealed that the proposed model can predict the strength of RS beam better than the others. The average ratio of experimental strengths to analytical results was 1.02 and the standard deviation was 0.126.

• Journal of the Korean Geotechnical Society
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• 제19권5호
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• pp.223-232
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• 2003

In this study, a constitutive model called the disturbed state concept (DSC) was modified to be applied to the interface shear stress-displacement relationship between geosynthetics. The DSC model is comprised of two reference states, namely the relative intact (RI) and the fully adjusted (FA) state, and one function, namely the disturbance function. This model is a unified approach and can allow for various models as an RI state such as elastic-perfectly plastic model, hierarchical model, and so on. In addition, by using this model, the elastic and plastic displacements can be considered simultaneously. Comparisons between the measured data and predicted results through the parameters determined from four sets of large direct shear tests showed good agreements with each other, especially for the smooth geomembrane-involved interface. Although there are slight differences at peak shear strength for textured geomembrane-involved interface, this model can still be useful to predict the position of displacement at peak strength and the large displacement (or residual) shear strength.

• Transactions of Materials Processing
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• 제17권7호
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• pp.466-472
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• 2008

In this paper, tension tests and formability tests are performed to construct a database related to mechanical properties and the formability of the AZ31B Mg alloy sheet. A forming test with a hemi-spherical punch is conducted at varying temperatures to establish a forming limit diagram. In order to verify the applicability of the analysis using the conventional flow hardening model, a finite element analysis is performed on the hemi-spherical punch forming process and the results are compared with experimental ones. The study investigates problems involving a computational analysis that does not consider flow softening of the magnesium alloy at elevated temperatures.

• Transactions of Materials Processing
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• 제12권4호
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• pp.408-413
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• 2003

Dies may have to be replaced for a number of reasons, such as changes in dimensions due to die wear or plastic deformation, deterioration of the surface finish, break down of lubrication and cracking or breakage. In this paper, die cooling methods have been suggested to improve die service life considering die wear and plastic deformation in hot forging process. The yield strength of die decreases at higher temperatures and is dependent on hardness. Also, to evaluate die life due to wear, modified Archard's wear model has been proposed by considering the thermal softening of die expressed in terms of the main tempering curve. It was found that the use of die with cooling hole was more effective than that of direct cooling method to increase the die service life for spindle component.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.135-139
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• 1999

The static softening behavior of AISI 4140 could be characterized by the hot torsion test in the temperature ranges of 10$0^{\circ}C$~120$0^{\circ}C$ and strain rate ranges of 0.05/sec~5/sec. Deformation efficiency which was based on dynamic materials model was calculated from flow stress curves obtained continuous deformation. Interrupted deformation was performed with 2 pass deformation in the pass strain ranges of 0.25{{{{ epsilon _p}}}} ~3{{{{ epsilon _p}}}} and interrupted time ranges of 0.5~100sec. The dependences of process variables pass strain ({{{{ epsilon _i}}}}) stain rate ({{{{ {. } atop {$\varepsilon$ } }}}}) temperature (T) and interpass time ({{{{ {t }_{i } }}}}) on static recrystallization (SRX) and metadynamic recrystallization .(MDRX) could be indicidually predicted from the modified Avrami's equations. Comparison of the softening kinetics between MDRX and SRX showed that the rate of MDRX was more rapid than that of SRX for the same deformation variables. Controlled multipass deformations were performed using deformation efficiency static and metadynamic recrystallization of AISI 4140.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제25권6호
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• pp.458-461
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• 2016

In this study, a finite element analysis for high-speed blanking of mild steel is performed. A thermomechanically coupled simulation model of a blanking process was developed using ABAQUS/Explicit. Through a simulation of the high-speed blanking process of mild steel, the influence of the punch speed, tool edge radius, and work material thickness on the development of the plastic heat and punch load were studied. The results of the study revealed that a higher punch speed caused thermal softening of the work material and decreased the punch load. Decreasing tool edge radius could help reduce the punch load. In addition, the results of the study revealed that the thermal softening effect was more dominant in the blanking of a mild steel sheet with a greater thickness as compared to that in the blanking of a mild steel sheet with a lower thickness.

• Transactions of Materials Processing
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• 제20권6호
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• pp.427-431
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• 2011

In general, hot stamped component is trimmed by costly and time consuming laser cutting when the material strength is over 1,500MPa. The aim of this work was to demonstrate that the trimming die life is improved and the trimming load is decreased by lowering the strength of the region to be trimmed. The model employed in this study was a hat shape, similar to the cross section of many hot stamped products. FE-analysis of hot stamping process was performed to evaluate the effect of tool shape on cooling rate at the area to be trimmed. The best tool shape was thus identified, which created slower cooling and lower hardness at the region to be trimmed. The wear at the cutting tool edge was also reduced.

• Structural Engineering and Mechanics
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• 제12권3호
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• pp.231-248
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• 2001

The three-dimensional behavior of confined concrete was investigated, including strength enhancement due to triaxial compressive stresses, lateral expansion, compression softening, cover spalling and post-peak ductility. A finite element program based on a nonlinear elasticity methodology was employed to evaluate the ability to model triaxial behavior of reinforced concrete (RC) by combining constitutive models proposed by several researchers. The capability of compression field based models to reproduce the softening behavior of lightly cracked confined concrete was also investigated. Data from tested specimens were used to evaluate the validity of the formulations. Good agreement with the experimental results was obtained.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.366-369
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• 2008

In this paper, tension tests and formability tests are performed to construct a database related to mechanical properties and the formability of the AZ31B Mg alloy sheet. A forming test with a hemi-spherical punch is conducted at varying temperatures to establish a forming limit diagram. In order to verify the applicability of the analysis using the conventional flow hardening model, a finite element analysis is performed on the hemi-spherical punch forming process and the results are compared with experimental ones. The study investigates problems involving a computational analysis that does not consider flow softening of the magnesium alloy at elevated temperatures.

• Structural Engineering and Mechanics
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• 제10권2호
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• pp.165-180
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• 2000

An analytical model with tension softening for the prediction of the capacity of prestressed concrete beams under pure torsion and under torsion combined with shear and flexure is introduced. The proposed approach employs bilinear stress-strain relationship with post cracking tension softening branch for the concrete in tension and special failure criteria for biaxial stress states. Further, for the solution of the governing equations a special numerical scheme is adopted which can be applied to elements with practically any cross-section since it utilizes a numerical mapping. The proposed method is mainly applied to plain prestressed concrete elements, but is also applicable to prestressed concrete beams with light transverse reinforcement. The aim of the present work is twofold; first, the validation of the approach by comparison between experimental results and analytical predictions and second, a parametrical study of the influence of concentric and eccentric prestressing on the torsional capacity of concrete elements and the interaction between torsion and shear for various levels of prestressing. The results of this investigation presented in the form of interaction curves, are compared to experimental results and code provisions.