• Journal of Welding and Joining
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• v.16 no.6
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• pp.44-51
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• 1998

It is well known that the fine bainitic microstructure obtained by TMCP(thermo-mechanical control process) secures the high toughness of base metal. Besides, TMCP steel is very suitable for high heat input in welding as it has low carbon equivalent. In HAZ, however, the accelerated cooling effect imparted on the matrix by the weld thermal cycles is relieved and thus the weldment of TMCP steel has softening zone which shows low fracture toughness compared with base metal. Therefore, PHWT of weldment is carried out to improve the fracture toughness in weldment of TMCP steel which has softening zone. In this study, the effects of PWHT on the weldment of AH36-TMCP steel are investigated by the small punch (SP) test. From the several results such as SP energy and displacement at room temperature, the behavior of transition curves, the fracture strength at -196$^{\circ}C$, distribution of (DBTT)sp and (DBTT)sp, the PWHT condition of A.C. after 85$0^{\circ}C$-1 sec W.C. was suitable condition for recovering a softening zone of HAZ as welded.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.304-307
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• 2008

In order to evaluate the effect of permanent softening behavior on springback prediction, 2D-draw bending simulations were compared with experiments for friction stir welded DP590 steel sheets. To account fur the nonlinear hardening behavior, the combined isotropic-kinematic hardening law was utilized with and without considering the permanent softening behavior during reverse loading. Also, the non-quadratic orthotropic yield function, Yld2000-2d, was used to describe the anisotropic initial-yielding behavior of the base sheet while anisotropic properties of the weld zone were ignored for simplicity.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.28-34
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• 1988

The fatigue test was carried out to evaluate the fatigue characteristics of the accelerated cooled (ACC) TMCP steel and its welded joint. From this study, it was confirmed that ACC TMCP steel has higher fatigue strength than conventional steels. After welding, however, the fatigue strength of ACC TMCP steel was deteriorated associated with HAZ softening when weld reinforcement was removed. On the other hand, with weld reinforcement, there is no effect of HAZ softening on the fatigue strength of welded joint because it is strongly dependant on the detail weld geometry i.e., stress concentration factor. Accordingly the fatigue strength of actual welded joint increases with decreasing the stress concentration factor of welded joint, regardless of HAZ softening.

• Computers and Concrete
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• v.1 no.4
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• pp.433-455
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• 2004

The paper presents results of FE-calculations on shear localizations in quasi-brittle materials during both an uniaxial plane strain compression and uniaxial plane strain extension. An elasto-plastic model with a linear Drucker-Prager type criterion using isotropic hardening and softening and non-associated flow rule was used. A non-local extension was applied in a softening regime to capture realistically shear localization and to obtain a well-posed boundary value problem. A characteristic length was incorporated via a weighting function. Attention was focused on the effect of mesh size, mesh alignment, non-local parameter and imperfections on the thickness and inclination of shear localization. Different methods to calculate plastic strain rates were carefully discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.861-864
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• 2008

This study was performanced to investigate the fractural and fatigue behavior of ultra-strength steel fiber reinforcement concrete. The tension softening diagram can describe the post-cracking behavior of concrete in tension. In this paper, Three points bending tests with a notch have been carried out to investigate tensile properties of the steel fiber reinforced concrete(SFRC) according to variation of the height. Poly-linear approximation method combined with FEM analysis is applied to the steel fiber reinforced concrete to determine the tension softening diagrams and also to certify the validity of the method. The simulated load-CMOD curves using the determined softening diagrams though the poly-linear approximation method completely agree with the measured ones.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1201-1216
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• 2015

This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-${\delta}$ tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.

• Journal of the Korean Ceramic Society
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• v.32 no.5
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• pp.601-607
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• 1995

The bond strength between the low-firing-substrate and Cu conductor depended on the softening point and the amount of frit added to the metal paste. The addition of 3 wt% frit (softening point: 68$0^{\circ}C$) to the metal paste resulted in the improvement of bond strength, which was approximately 3 times higher (3kg/$\textrm{mm}^2$) than that of non frit condition. It was also found that fracture surface shifted to the ceramic substrate in the interface region. These phenomena were attributed to the frit migration into the metal-ceramic interface. It was thought that the migration of glass frit occurred extensively when the softening point of glass firt was 68$0^{\circ}C$. The sheet resistance of Cu conductor remained constant by the addition of 4 wt% frit regardless of softening point of frit. For all samples with more than 4 wt% frit, the sheet resistance increased abruptly.

• Transactions of Materials Processing
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• v.4 no.2
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• pp.169-179
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• 1995

Static restoration mechanism during hot interrupted deformation of Cu-Zn alloy was studied in the temperature range from $550^{\circ}C$ to $750^{\circ}C$ and at a constant strain rate of 0.1/sec. At a given temperature, the hot interrupted deformations were performed with variation of interrupted time $t_i$ form 1 to 50 sec and of interrupted strain ${\varepsilon}_i$ from 0.15 to 0.90. From the analysis of the values of the critical strain of ${\varepsilon}_c$ for tje initiation of dynamic recrystallization and the peak strain of${\varepsilon}_p$, the relationship ${\varepsilon}_c{\fallingdotseq}0.7{\varepsilon}_p$ was obtained. It was clarified that the softening of the interrupted deformation was mainly the static recrystallization and the fractional softening(FS) which was over 30% mostly confirmed this result. The fractional softening of the interrupted time $t_i$ especially and pre-strain. The FS increased with increasing strain rate, interrupted time and pre-strain. The change of microstructures after hot deformation could be predicted by the FS. when the FS was 30~100%, static recrystallization was happened and grain growth was observed at the condition which was $750^{\circ}C$ deformation temperature, 0.45 prestrain and this condition's FS value was over 100%.

• Journal of the Korean Geosynthetics Society
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• v.2 no.1
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• pp.57-68
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• 2003

Strain-softening model is developed to characterize the interface behavior of geomembrane with geotextile and geosynthetic clay liner(GCL). The model proposed in this research is calibrated by using data from direct shear tests conducted on smooth and textured geomembrane. The research is divided into two regions, pre-peak and post-peak, to take into account of strain-softening effect. Although slight difference between measured and back calculated data is observed under high normal stress, good agreements, in general, are found from back calculations. Especially, good consistency is observed in the case of low normal stress. Based on the results, it can be concluded that the proposed model can be a reasonable constitutive law to figure out the behavior of strain-softening between interfaces of geomembrane. In addition, DSC(Disturbed State Concept) model is also presented for further application in geosynthetic interfaces.

• Korean Journal of Medicinal Crop Science
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• v.6 no.3
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• pp.210-215
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• 1998

Solomon's seal (Polygonatum odoratum) was traditionally propagated by its rhizomes but seed propagation has not been practiced due to their dormancy and high price. To improve the seedling production through seed pretreatments, the experiment was conducted to determine the effect of seedcoat softening and seed prechilling on seed germination and bulbil formation of the seal. The prechilling was done for 4 to 16 weeks at $3^{\circ}C$ and the softening was forced with 10% KOH for 40 minutes. Seed germination, bulbil formation and length, no. of root and root length were measured at 6 and 12 weeks after sowing. Seed germination and bulbil formation were greater at 8 to 12 week prechilling than at shorter or longer treatment when only the prechilling was enforced. Prechilling had greater effect compared to seed coat softening. In addition, the softening treatment before prechilling showed higher germination and bulbil formation compared to single treatment of them. The softening treatment prior to prechilling was better than the reverse treatment in number of root except the above two characters. Duration of prechilling treatment was able to be shortened below 8 weeks when the softening treatment was applied before prechilling.