• Structural Engineering and Mechanics
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• v.24 no.2
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• pp.269-273
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• 2006

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.677-687
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• 2006

Kriging interpolation is one of the generally used interpolation techniques in Geostatistics field. This technique includes the experimental and theoretical variograms and the formulation of kriging interpolation. In contrast to the conventional least square method for stress recovery, kriging interpolation is based on the weighted least square method to obtain the estimated exact solution from the stress data at the Gauss points. The weight factor is determined by variogram modeling for interpolation of stress data apart from the conventional interpolation methods that use an equal weight factor. In addition to this, the p-level is increased non-uniformly or selectively through a posteriori error estimation based on SPR (superconvergent patch recovery) technique, proposed by Zienkiewicz and Zhu, by auto mesh p-refinement. The cut-out plate problem under tension has been tested to validate this approach. It also provides validity of kriging interpolation through comparing to existing least square method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.533-541
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• 2007

The Zienkiewicz-Zhu(Z/Z) error estimate is slightly modified for the hierarchical p-refinement, and is then applied to L-shaped plates subjected to bending to demonstrate its effectiveness. An adaptive procedure in finite element analysis is presented by p-refinement of meshes in conjunction with a posteriori error estimator that is based on the superconvergent patch recovery(SPR) technique. The modified Z/Z error estimate p-refinement is different from the conventional approach because the high order shape functions based on integrals of Legendre polynomials are used to interpolate displacements within an element, on the other hand, the same order of basis function based on Pascal's triangle tree is also used to interpolate recovered stresses. The least-square method is used to fit a polynomial to the stresses computed at the sampling points. The strategy of finding a nearly optimal distribution of polynomial degrees on a fixed finite element mesh is discussed such that a particular element has to be refined automatically to obtain an acceptable level of accuracy by increasing p-levels non-uniformly or selectively. It is noted that the error decreases rapidly with an increase in the number of degrees of freedom and the sequences of p-distributions obtained by the proposed error indicator closely follow the optimal trajectory.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.619-624
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• 2009

Titanium alloys have been attractive due to a high ratio of strength to weight as well as good corrosion resistance. However, strengthening causes a decrease in ductility in Ti alloys, as is usual in other alloys. For enhanced strength without ductility reduction, grain refinement and tensile properties were investigated as functions of thickness reduction of cold rolling and annealing condition in Ti-15V-3Cr-3Sn-3Al alloy with a ${\beta}$ single phase. The average grain size of the specimen, which was cold-rolled by 90% and annealed at 700$^{\circ}C$ for 5 min, was decreased to approximately 19 ${\mu}m$. The grain refinement of 63 μm to 19 ${\mu}m$ increased yield stress by 90 MPa without a significant decrease in total elongation. The Ti-15-3 alloy exhibited very low work hardening during tensile test at a crosshead speed of 2 mm/min. This result was discussed based on dynamic recovery associated with dislocation annihilation in grain boundaries.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.89-92
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• 2000

In this paper, an effective procedure is presented for the local recovery of displacements and stresses in multilayered composite panels, which incorporate the local refinement using mesh superposition. The mesh superposition method is used to refine the global coarse mesh by superimposing refined mesh to the localized zone of interest without transition zones. The finite element model used is a solid element based on the Hellinger-Reissner variational principle. The a posteriori computation of the through-the-thickness distributions of displacements and stresses is achieved using a predictor-corrector procedure. The procedure utilizes the superconvergent stresses and nodal displacements of the finite element patch. The element patch is generated by locally superimposing a refined local mesh to the coarse global mesh.

• Structural Engineering and Mechanics
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• v.3 no.4
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• pp.325-340
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• 1995

The iterative procedure to use the nonconforming elements in elasto-plastic problems is established and applied to the variable node transition solid element developed for the automated three-dimensional local mesh refinement. Through numerical tests, the validity and performance of the element are examined. As the nonlinear iterative procedure presented in this paper is accomplished for the general three-dimensional case, it can also be easily applied to the two-dimensional elements such as membranes, plates and shells.

• Journal of Korea Society of Industrial Information Systems
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• v.13 no.5
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• pp.44-54
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• 2008

The objective of this research is to develop a measurement instrument for service recovery quality in the Internet commerce setting. To this same end, Parasuraman et al.(2005) have devised a scale called E-RecS-QUAL, which we revised and supplemented to develop another instrument named eSR-Q. To guarantee its reliability and validity, this instrument went through the refinement and validation processes for internal consistency and construct validity in terms of convergent, discriminant, and nomological validity. Our final scale consists of four dimensions including responsiveness, compensation, contact, and apologies altogether with fourteen measures. Overall, this research deals with the related research background, the scale development and validation processes, its limitations, and future research directions.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.3
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• pp.187-197
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• 1996

In this study, the properties of coil spring made by Cu-Zn-Al and B added shape memory alloys are investigated. The measurement of recovery displacement and energy with increasing weight, and thermocycling properties have been studied using displacement measuring device. Transformation temperature and phase change by thermocycling have been also investigated by DSC and X-ray diffractometer. Grain size of the alloy is refined from 1.2mm to $400{\mu}m$ by 0.06wt% of B addition. The maximum recovery energy of the coil spring for B added alloy is larger than that of no B added alloy, it is because of grain refinement. And shape memory ability of the coil spring by thermocycling decrease with increasing thermocycling after thermocycle under load. The degradation of shape memory properties of coil spring by thermocycling is improved by B addition.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.718-719
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• 2006

Two different commercial aluminium powder grades have been densified by direct hot extrusion. The extrusion temperature was $425^{\circ}C$, with an extrusion ratio of 1:16. Prior to extrusion, some green compacts were pre-sintered ($500^{\circ}C$). The evolution of the extrusion load during the process and the hardness of the final products have been investigated. Additionally, microstructural characterization by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD) was carried out. The obtained results evidence grain refinement. Additionally, inter-metallic precipitation, dynamic recovery and geometric dynamic recrystallization take place depending on some process variables, powder composition, heat treatment, strain $\ldots$

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.265-272
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• 2007

The finite element linear buckling analysis of folded plate structures using adaptive h-refinement methods is presented in this paper. The variable-node flat shell element used in this study possesses the drilling D.O.F. which, in addition to improvement of the element behavior, permits an easy connection to other elements with six degrees of freedom per node. The Box-typed structures can be analyzed using these developed flat shell elements. By introducing the variable-node elements some difficulties associated with connecting the different layer patterns, which are common in the adaptive h-refinement on quadrilateral mesh, can be overcome. To obtain better stress field for the error estimation, the super-convergent patch recovery is used. The convergent buckling modes and the critical loads associated with these modes can be obtained.