• Journal of the Korean Society for Heat Treatment
• /
• v.25 no.3
• /
• pp.115-120
• /
• 2012

It has been known that the ferritic stainless steel can be changed to martensitic stainless steel when nitrogen is added. However the high hardness of martensitic stainless steel prevents the plastic deformation. In this study, instead of martensite, the surface microstructure was changed into nitrogen pearlite to increase the plastic deformation easily by isothermal heat treatment after high temperature gas nitriding (HTGN) the AISI 430 ferritic stainless steel. The isothermal treatment was carried out at $780^{\circ}C$ for 4, 6, and 10 hrs, respectively, after HTGN treatment at $1100^{\circ}C$ for 10 hrs. The surface layer of isothermal-treated steel appeared nitrogen pearlite composed with fine chromium nitride and ferrite. Hence, the interior region that was not affected by nitrogen permeation exhibited ferrite phase. When quenching the isothermal treated steel at 1100oC, martensitic phase formed at the surface layer. The hardness of surface layer of isothermal-treated steel and quenched steel measured the value of 150~240 Hv and 630 Hv, respectively.

• Journal of the Korean GEO-environmental Society
• /
• v.8 no.6
• /
• pp.29-36
• /
• 2007

The control and prediction of surface settlement, gradient and ground displacement are the main factors in urban tunnel construction. This paper carried out the estimation and prediction of ground behavior around tunnel due to excavation using computational method and case study in detail for the analysis of deformation behavior in urban NATM tunnel. Computational method was performed by FLAC-2D with strain softening model and elastic plastic model. Field measurements of surface subsidence and ground displacement were adopted to monitor the ground behavior resulting from the tunneling and these values were applied to modify tunnel design parameters on construction.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.28 no.3
• /
• pp.302-308
• /
• 2008

Composite materials are widely used as structural materials for aerospace engineering because of its excellent mechanical properties such as light weight, high stiffness, and low thermal expansion. In driving, impact damage is one of the common but dangerous damages, caused by internal failure of the laminas interface which is not detected by in the surface. Many techniques to detect defects or delaminate between laminates have been reported. Shearography is a kind of laser speckle pattern interferometry with the advantages of non-destructive, non-contact, high resolution and displacement slope measurement. In this paper, the shearography is used to evaluate non-destructively impact damaged surface of the composite material and a measuring method using shearography for the thermal deformation of a impact damaged composite material is discussed. The basic principles of the technique are also described briefly.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.30 no.2 s.150
• /
• pp.296-305
• /
• 2006

This study evaluate the effect of laundering on the deformation of knitted spandex/cotton fabrics compared with that of knitted cotton fabrics. Commercial knitted spandex/cotton and knitted cotton fabrics for T-shits were laundered in a drum-type washing machine and dried in a tumble dryer. Wale spirality, shrinkage, elastic recovery and surface contour of knitted fabrics were investigated under different laundering conditions: washing temperature, presoaking time and washing cycles. Knitted spandex/cotton fabrics had a lower angle of spirality than knitted cotton fabrics. After the first washing cycle, the angles of spirality of all the fabrics had decreased greatly. Knitted cotton fabric of low density deformed more than that of higher density. Knitted spandex/cotton. fabric of low density shrank less, because of the greater extension given during heat-set. Permanent elongation length at the 80$\%$ extension was longer than at the 50$\%$ extension, and the knitted spandex/cotton fabric which was expanded greatly during heat-set had a lower elastic recovery rate. The surface appearance of the knitted spandex/cotton fabrics was worsl~ than that of the knitted cotton fabrics before laundering and after repeated laundering, because of the much protruded cotton fibers from the yarns.

• Tribology and Lubricants
• /
• v.17 no.3
• /
• pp.236-243
• /
• 2001

In this study, flow factors are evaluated in terms of kurtosis using random rough surface generated numerically. As h/$\sigma$become large ø$\sub$x/, ø$\sub$y/, ø$\sub$fp/, approach to 1 and ø$\sub$s/, ø$\sub$fs/ to 0 asymptotically regardless of kurtosis. ø$\sub$x/, ø$\sub$y/, ø$\sub$fp/ increase with increasing kurtosis in the mixed lubrication regime. ø$\sub$s/, ø$\sub$fs/ is associated with an additional flow transport due to the combined effect of sliding and roughness. As h/$\sigma$ decreases ø$\sub$s/, ø$\sub$fs/ increase up to a certain point, and then decrease toward zero. This behavior can be attributed to the increasing number of contacts in the mixed lubrication regime. ø$\sub$x/ in the presence of elastic deformation on the surface is larger than ø$\sub$x/ in the absence of it because local film thickness(h$\sub$T/) increases by elastic deformation.

• Structural Engineering and Mechanics
• /
• v.51 no.3
• /
• pp.413-431
• /
• 2014

By carrying out the experiment of eight pieces of brick masonry walls with pilaster strengthened by Glass fiber reinforced polymer (GFRP) and one piece of normal masonry wall with pilaster under low reversed cyclic loading, the failure characteristic of every wall is explained; Seismic performances such as hysteresis, stiffness and its degeneration, deformation, energy consumption and influence of some measures including strengthening means, reinforcement area proportion between GFRP and wall surface, "through-wall" anchor on reinforcement effects are studied. The test results showed that strengthening modes have little influence on stiffness, stiffness degeneration and deformation of the wall, but it is another thing for energy consumption of the wall; The ultimate load, deformation and energy consumption of the walls reinforced by glass fiber sheets was increased remarkably, rigidity and its degeneration was slower; Seismic performance of the wall which considers strengthening means, reinforcement area proportion between GFRP and wall surface, "through-wall" anchor at the same time is better than under the other conditions.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.14 no.2
• /
• pp.57-66
• /
• 2006

AA5182-polypropylene sandwich sheet was manufactured, and the mechanical properties evaluation was executed in order to identify $L{\ddot{u}}ders$ band that causes fabrication process problem and especially surface roughness. To identify formability, deformation behavior, plastic strain ratio (R-value) and pole figure were measured, and texture analysis was performed. In the case of sandwich sheet, the unstable deformation behavior has decreased. As well, for sandwich sheet, A1 skin could manage the most of load, and the elongation has improved about 45% more than that of A1 skin. The plastic strain ratio of A1 skin and sandwich panel, which indicates serration behavior, was obtained from instantaneous plastic strain ratio evaluation. Also, the planar anisotropy of sandwich sheet has decreased more than that of A1 skin. According to these results, the sandwich sheet produced lightening effect and could control unstable deformation characteristic, that is, surface roughness caused by $L{\ddot{u}}ders$ band. Furthermore, it was proved that the texture control of the rolling attachment of A1 skin is necessary to improve the formability of the sandwich panel.

• Earthquakes and Structures
• /
• v.10 no.6
• /
• pp.1429-1449
• /
• 2016

The effect of porosity on bending and free vibration behavior of simply supported functionally graded plate reposed on the Winkler-Pasternak foundation is investigated analytically in the present paper. The modified rule of mixture covering porosity phases is used to describe and approximate material properties of the FGM plates with porosity phases. The effect due to transverse shear is included by using a new refined shear deformation theory. The number of unknown functions involved in the present theory is only four as against five or more in case of other shear deformation theories. The Poisson ratio is held constant. Based on the sinusoidal shear deformation theory, the position of neutral surface is determined and the equation of motion for FG rectangular plates resting on elastic foundation based on neutral surface is obtained through the minimum total potential energy and Hamilton's principle. The convergence of the method is demonstrated and to validate the results, comparisons are made with the available solutions for both isotropic and functionally graded material (FGM). The effect of porosity volume fraction on Al/Al2O3 and Ti-6Al-4V/Aluminum oxide plates are presented in graphical forms. The roles played by the constituent volume fraction index, the foundation stiffness parameters and the geometry of the plate is also studied.

• Journal of the Korean institute of surface engineering
• /
• v.29 no.5
• /
• pp.379-385
• /
• 1996

Adhesion of Cu/Cr and Cu/$Cu_xCr_{1-x}$ thin films onto polyimide substrates has been studied. For an adhesion layer, Cr or Cu-Cr alloy films were deposited onto polyimide using DC magnetron sputtering machine. Then Cu was sputter-deposited and finally, Cu was electroplated. Adhesion was evaluated using $90^{\circ}C$ peel test or T-peel test. Plastic deformation of the peeled metal layer was qualitatively measured using XRD technique. It is confirmed that high interfacial fracture energy and large plastic deformation are important to enhance the peel adhesion strength. High peel strength is obtained when the interface is strongly bonded. More ductile film has higher peel strength. In Cu-Cr alloy films, opposite effects of the Cr addition in the alloy film on the peel strength are operative: a beneficial effect of strong interfacial bonding and a negative effect of smaller plastic deformation.

• International Journal of Precision Engineering and Manufacturing-Green Technology
• /
• v.5 no.5
• /
• pp.651-658
• /
• 2018

We comprehensively investigated the wrinkles of a stiff layer covering a spherical void embedded in a rubber matrix after the void experienced inflation or contraction. We developed an easy experimental way to realize the inflation and contraction of the voids. The inflation took place in a void right beneath the surface of the matrix and the contraction happened in a void at the bottom of the rubber matrix. In the inflation, the wrinkle at the center of the deformation was random, and the pattern propagated into rabyrinthine, herringbone, and then oriented parallel lines as the position was away from the center of the inflation to the edge. The cracks were concentric, which were perpendicular to the parallel wrinkled pattern. In the contraction, the wrinkle was simply concentric around the surface of the void without any crack. The cracks were found only near the center of the deformation. The strain distribution in the stiff layer after the inflation and contraction was theoretically analyzed with simulations that were in excellent agreement with the experimental results.