• Journal of the Korean institute of surface engineering
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• v.26 no.2
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• pp.63-70
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• 1993

The mechanical properties of ferrite-martensited dual phases steels are affected by the microstructural factors, such as martensited volume fractions, ferrite grain size, strength ratio, connectivity, etc. Two phase alloys are technologically important. However, there is a lack of understanding as to stress-strain behavior of dual phase alloy in terms of stress-strain behavior of each component phases. The lack of the understanding stems from the complex deformation behavior of two phase alloys. The aim of this study is to rationalize stress-strain behavior of dual phase alloy in terms of the stress-strain behavior of component phase by systematically considering all the factors listed above. It was found that for a given martensite volume fraction, the calculated stress-strain curve was higher for a finer particles size than for a coarse particle sized within the range of the strains considered, and this behavior was seen for all the different volume fraction alloys considered. The calculated stress-strain curves were compared with corresponding experimental curves, and in general, good agreement was found. The maximum difference in flow stress between the calculated and the experimental results occurs at the nearly beginning of the plastic deformation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.160-163
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• 2004

The hub hole in a wheel of vehicles usually formed with hole expansion process. Formability of material, especially the hole expansion ratio, is important to produce a fine hub hole. The hub hole expansion process is different from general forming process or bore expansion process in the viewpoint of forming a thick plate. In the hole expansion process of the plate with a hole, as the hole being expanded, the crack is occurred to outward direction at the boundary of a hole. Therefore, it is need to apply the fracture criterion in the hub hole expansion process. In this paper, the hub hole expansion process is simulated with commercial elasto-plastic finite element code, LS-DYNA3D considering some ductile fracture criteria. Fracture mode and hole expansion ratio is compared with respect to the fracture criteria. Analysis results demonstrate that only the effective plastic strain is not adequate to predict the fracture mode in the hub hole. And the analysis results also indicate that the ductile fracture criteria properly predict the fracture mode but hole expansion ratio is different with the result of each other because of their different characteristics.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.241-247
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• 2015

In order to prevent shape defects such as fluting and stretcher strains during press forming of aged low carbon steel sheets, roller leveling conditions for reducing yield point elongation were studied. Yield point elongations of leveled sheets were determined as a function of leveling, which is defined as the plastic fraction or the ratio of plastically deformed part in sheet thickness section to the whole thickness of the sheet. By adjusting this plastic fraction during leveling to more than 78%, yield point elongation in the leveled sheets was reduced so no fluting occurred during subsequent tangential bending. Stretcher strains can be avoided by leveling the sheet to an 84% plastic fraction condition.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.505-511
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• 2003

Experimental investigation was conducted into the flexure/shear-critical behavior of earthquake-damaged reinforced concrete columns with lap splicing of longitudinal reinforcement in the plastic hinge region. Six test specimens in the aspect ratio of 2,5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes of which magnitude could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under a constant axial load, P=$0.1f_{ck}A_g. Residual seismic performance of damaged columns was evaluated and compared to that of the corresponding original columns. Test results show that RC bridge piers with lap-spliced longitudinal steels in the plastic hinge region appeared to fail at low ductility. This was due to the debonding of the lap splice, which resulted from insufficient development of the longitudinal steels. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region indicated significant improvement both in flexural strength and displacement ductility, and strain energy ductility.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.3
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• pp.259-266
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• 2004

Detailed two-dimensional and three-dimensional finite element (FE) analyses of double-edge cracked tension (DE(T)) specimens are carried out to investigate the effect of the relative crack length and the thickness on experimental J testing schemes. Finite element analyses involve systematic variations of relevant parameters, such as the relative crack depth and plate width-to-thickness ratio. Furthermore, the strain hardening index of material is systematically varied, including perfectly plastic (non-hardening) cases. Based on FE results, a robust experimental J estimation scheme is proposed.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.04a
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• pp.233-240
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• 1997

Seven kinds of hysteric model were used and classified three groups considering the absorbing capacities of strain energy for each model. Four kids of each model. Four kinds of strong motion earthquake record (two of them were recorded in Japan and the others in U.S.A) are used. The yield strength of building was set in the ratio to the maximum input acceleration (Yield Strength / Maximum Acceleration = 0.5~3.0). Natural periods of structures were varied 0.1~3.0 second with an interval of 0.1 second. First group : Elastic-Plastic model, Ramberg-Osgood model Second group : Degrading Tri-liner model, Takeda model Third group : Slip model, Origin model, Max-D model Elastic-plastic response spectra were calculated for response velocities, displacement, energy input, ductility factors, accumulated ductility factors. The equivalent response values of M.D.O.F systems against S.D.O.F system were calculated to compare the relationship of two systems.

• Steel and Composite Structures
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• v.30 no.2
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• pp.123-140
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• 2019

This paper presents experimental study on effects of width-to-thickness ratio and loading history on cyclic rotational capacity of H-shaped steel beams subjected to pure bending. Eight Class 3 and 4 H-shaped beams with large width-to-thickness ratios were tested under four different loading histories. The coupling effect of local buckling and cracking on cyclic rotational capacity of the specimens was investigated. It was found that loss of the load-carrying capacity was mainly induced by local buckling, and ductile cracking was a secondary factor. The width-to-thickness ratio plays a dominant effect on the cyclic rotational capacity, and the loading history also plays an important role. The cyclic rotational capacity can decrease significantly due to premature elasto-plastic local buckling induced by a number of preceding plastic reversals with relative small strain amplitudes. This result is mainly correlated with the decreasing tangent modulus of the structural steel under cyclic plastic loading. In addition, a theoretical approach to evaluate the cyclic rotational capacity of H-shaped beams with different width-to-thickness ratios was also proposed, which compares well with the experimental results.

• Journal of Ocean Engineering and Technology
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• v.13 no.4 s.35
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• pp.55-62
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• 1999

Cold rolled steel has much plastic strain in the material surface produced by manufacturing process. The strain causes the variation of surface residual stress, in which influences the fatigue behavior under repeated loading. As experimental results, it was confirmed that the behavior of residual stress ${\sigma}_r$, with cycle N consisted of three stages except stress amplitude near fatigue limit in SPCC steel. On the first stage compressive residual stress decreased rapidly, on the second stage gradually, and on the last stage slightly. The relation between ${\sigma}_r$, and log N appeared linear behavior except the early part of cycle ratio $N/N_f$. The average gradient of ${\sigma}_r$, with respect to log N seemed to take a constant value without initial cycle ratio. On the other hand, the $N_f$ line was regressed by the first-order polynomial equation on ${\sigma}_r-log\;N_f$ diagram. Therefore, this study showed that both the gradient of ${\sigma}_r$, with respect to log N and the $N_f$ line was useful in predicting the cycle ratio $N/N_f$.

• Geomechanics and Engineering
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• v.3 no.4
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• pp.323-337
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• 2011

Israel's coastal region consists, mainly, of Pleistocene and Holocene sands with varying degrees of calcareous cementation, known locally as "kurkar". Previous studies of these materials emphasized the difficulty in their geotechnical characterization, due to their extreme variability. Consequently, it is difficult to estimate construction stability, displacements and deformations on, or within these soils. It is suggested that SPT and Menard pressuremeter tests may be used to characterize the properties of these materials. Values of elastic modulus obtained from pressuremeter tests may be used for displacement analyses at different strain levels, while accounting for the geometric dimensions (length/diameter ratio) of the test probe. A relationship was obtained between pressuremeter modulus and SPT blow count, consistent with published data for footing settlements on granular soils. Cohesion values, for a known friction angle, are estimated, by comparing field pressuremeter curves to curves from numerical (finite element or finite difference) analyses. The material analyzed in the paper is shown to be strain-softening, with the initial cohesion degrading to zero on development of plastic shear strains.

• Computers and Concrete
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• v.1 no.2
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• pp.189-209
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• 2004

Several extensions to the Thelandersson phenomenological model for concrete under transient high temperatures are explored. These include novel expressions for the temperature degradation of the elastic modulus and the temperature dependency of the coefficient of the free thermal strain. Furthermore, a coefficient of thermo mechanical strain is proposed as a bi-linear function of temperature. Good qualitative agreement with various test results taken from the literature is demonstrated. Further extensions include the effects of plastic straining and temperature dependent Poisson's ratio. The models performance is illustrated on several simple benchmark problems under uniaxial and biaxial stress states.