• Steel and Composite Structures
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• 제38권5호
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• pp.583-597
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• 2021

This article develops a nonclassical model to analyze bending response of squared perforated microbeams considering the coupled effect of microstructure and surface stress under different loading and boundary conditions, those are not be studied before. The corresponding material and geometrical characteristics of regularly squared perforated beams relative to fully filled beam are obtained analytically. The modified couple stress and the modified Gurtin-Murdoch surface elasticity models are adopted to incorporate the microstructure as well as the surface energy effects. The differential equations of equilibrium including the Poisson's effect are derived based on minimum potential energy. Exact closed form solution is obtained for bending behavior of the proposed model considering the classical and nonclassical boundary conditions for both uniformly distributed and concentrated loads. The proposed model is verified with results available in the literature. Influences of the microstructure length scale parameter, surface energy, beam thickness, boundary and loading conditions on the bending behavior of perforated microbeams are investigated. It is observed that microstructure and surface parameters are vital in investigation of the bending behavior of perforated microbeams. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams that commonly used in nanoactuators, nanoswitches, MEMS and NEMS systems.

• 한국압력기기공학회 논문집
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• 제20권1호
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• pp.16-24
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• 2024

Denting of steam generator (SG) tube is defined as the reduction in tube diameter due to the stresses exerted by the corrosion products formed on the outer diameter surface. This phenomenon is mostly observed in the crevices between SG tube and the top-of tubesheet or tube support plate. Despite the replacement of SG tube with Alloy 690, which has better corrosion resistance than Alloy 600, the denting of SG tube still remains a potential problem that could decrease the SG integrity. Deformation of SG tube by denting phenomenon can affect the surface properties and microstructure of SG tube. In this study, the effects of plastic deformation on surface properties and microstructure of Alloy 690 thermally treated (TT) tube was investigated by using the various analysis techniques. The plastic deformation of Alloy 690 increased the surface roughness and area. Many surface defects such as ripped surface and micro-cracks were observed on the deformed Alloy 690TT specimen. Based on the electron backscatter diffraction analysis, the dislocation density of deformed SG tube increased compared to non-deformed SG tube. In addition, the effects of changes in surface properties and microstructure of SG tube on general corrosion behavior were discussed.

• Structural Engineering and Mechanics
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• 제53권1호
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• pp.105-130
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• 2015

In this paper, the classical continuum mechanics is adopted and modified to be consistent with the unique behavior of micro/nano solids. At first, some kinematical principles are discussed to illustrate the effect of the discrete nature of the microstructure of micro/nano solids. The fundamental equations and relations of the modified couple stress theory are derived to illustrate the microstructural effects on nanostructures. Moreover, the effect of the material surface energy is incorporated into the modified continuum theory. Due to the reduced coordination of the surface atoms a residual stress field, namely surface pretension, is generated in the bulk structure of the continuum. The essential kinematical and kinetically relations of nano-continuums are derived and discussed. These essential relations are used to derive a size-dependent model for Mindlin functionally graded (FG) nano-plates. An analytical solution is derived to show the feasibility of the proposed size-dependent model. A parametric study is provided to express the effect of surface parameters and the effect of the microstructure couple stress on the bending behavior of a simply supported FG nano plate.

• 한국표면공학회지
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• 제30권1호
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• pp.13-22
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• 1997

In order to investigate the effects of microstructure Oil film on the welding spatter in Zn electroplated steel, Zn electroplated surface and layer structure with USS-Paddition was observed using XRD, XPS and optical microscopy. Wettability of water drop on the Zn electroplated steel surface was measured using Z.Mei model. Oil absorption test was carried out using Oil pen. Morphology of spot welding and spatter with USS-P addition, applied current, and oil-spray or oil-without was observed using SEM and optical microscopy. Surface morphology of Zn electroplated steel showed finer structure as USS-P content increased. Wettabiliy on the Zn electroplated surface decreased with increasing USS-P content. Size of welding trace increased and spatter occured arround the welding part as applied current increased, whereas spatter disappeared as USS-P content increased and disappeared in case of oil spraying on the Zn electroplated surface.

• 한국주조공학회지
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• 제20권5호
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• pp.316-322
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• 2000

Effect of surface roughness and microstructure of the specimen on tensile properties of Ni-Al bronze casting has been investigated. surface roughnesses of the tensile test specimen of interest are in range of 0.1 to 2.0 ${\mu}m$ in Ra obtained by changing machining conditions. Fracture of the Ni-Al bronze casting initiated at the surface and propagated in a brittle manner during tensile tests. Tensile elongation value of the casting was strongly dependent on the surface roughness range studied, while tensile and yield strengths were almost independent on it. The elongation value was almost constant up to the surface roughness of 1.0 ${\mu}m$ in Ra, and then decreased in a linear manner with an increase in Ra value up to 2.0 ${\mu}m$. However, tensile strength and hardness were strongly dependent on the microstructure, especially ${\alpha}$ phase fraction, and were decreased with increasing ${\alpha}$ phase fraction in microstructure. It is, therefore, recommended that decrease of surface roughness up to 1.0 ${\mu}m$ in Ra, shrinkage porosity and ${\alpha}$ phase are required in order to obtain good tensile properties for Ni-Al bronze casting.

• 대한기계학회논문집A
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• 제21권12호
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• pp.2019-2028
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• 1997

It has been well established that resistant force and wear that occur during rolling motion depend on several factors such as material type, hardness, subsurface microstructure, applied load, and speed. The purpose of this work is to investigate the effect of microstructure and the state of deformed layer on the rolling contact characteristics in dry and lubricated rolling contacts. The results of this work show that the rolling resistance behavior depends on the state of the deformed layer. Also, lubrication can reduce the plastic flow at the surface but may still have an effect on the subsurface strain. The cross-sectional view of the microstructure shows that surface traction has a difinite effect on the morphology of the surface region. That is, significant slip seems to have taken place between the ball than those of the dry rolling case. The surface generation effects were significantly less compared to the case of dry rolling contact.

• 열처리공학회지
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• 제33권2호
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• pp.57-64
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• 2020

In the present study, we investigated whether the surface oxidation of C-bearing TWIP steel ℃curs in the air during specimen delivery from an annealing furnace to a water bath and how the microstructure and tensile properties are influenced by surface oxidation. A cold-rolled Fe-18Mn-0.6 (wt%) steel was exposed in the air for 5 s after annealing at various temperatures (750℃, 850℃ and 1000℃) for 10 min in a vacuum, and then water-quenched. For comparison, another specimen, which had been quartz-sealed in a vacuum, was annealed at 1000℃ for 10 min and immediately water-quenched without exposure to air. The 750℃ and 850℃-annealed specimens and the quartz-sealed specimen showed a γ-austenite single phase in the entire specimen due to negligible surface oxidation. However, the 1000℃-annealed specimen exhibited a dual-phase microstructure consisting of ε-martensite and γ-austenite at the sub-surface due to decarburization. Whereas the specimens without decarburization revealed high elongations of 70-80%, the decarburized specimen exhibited a low elongation of ~40%, indicating premature failure due to cracking inside the decarburized layer with ε-martensite and γ-austenite.

• 한국주조공학회지
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• 제22권3호
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• pp.114-120
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• 2002

A new titanium based alloy, Ti-10Ta-10Nb, has designed to examine the improved mechanical properties and biocompatibility. A specimen of titanium alloy was melted in a consumable vacuum arc furnace and homogenized at $1050^{\circ}C$ for 24 h. The effect of hot rolling on microstructure was estimated after rolling at $400^{\circ}C$ and $800^{\circ}C$ respectively. Surface of melted alloy by consumable vacuum arc melting was consisted of rough surface and it was changed to sound surface by coating of $ZrO_2$ slurry on copper mold surface. The hardness of Ti-10Ta-10Nb alloy increased with the amount of${\alpha}+{\beta}$ phase. Ti-10Ta-10Nb alloy showed $Widmanst{\"{a}}ten$ structure by hot rolling at $800^{\circ}C$ and in the rolling ${\beta}-region$ was negligible effects on microstructure refining.

• 한국표면공학회지
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• 제49권4호
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• pp.376-381
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• 2016

The effects of ICP (Inductively Coupled Plasma) power, ranging from 0 to 200 W, on the crystal structure, microstructure, surface roughness and mechanical properties of magnetron sputtered VN coatings were systematically investigated with FE-SEM, AFM, XRD and nanoindentation. The results show that ICP power has a significant influence on coating microstructure and mechanical properties of VN coatings. With the increasing of ICP power, coating microstructure evolves from a porous columnar structure to a highly dense one. Average crystal grain size of single phase cubic fcc VN coatings was decreased from 10.1 nm to 4.0 nm with increase of ICP power. The maximum hardness of 28.2 GPa was obtained for the coatings deposited at ICP power of 200 W. The smoothest surface morphology with Ra roughness of 1.7 nm was obtained from the VN coating sputtered at ICP power of 200 W.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 1999년도 춘계학술발표회 초록집
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• pp.86-87
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• 1999