• Advances in materials Research
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• v.11 no.4
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• pp.279-298
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• 2022

In this paper, the important novelty and the defining a physical phenomenon of the resent research is the development of nonlocal stress and strain parameters on the porous sandwich beam with functionally graded materials in the top and bottom face sheets.Also, various beam models including Euler-Bernoulli, Reddy and the generalized formulation of two-variable beam theories are obtained in this research. According to a nonlocal strain elasticity theory, the strain at a reference point in the body is dependent not only on the stress state at that point, but also on the stress state at all of the points throughout the body. Thus, the nonlocal stress-strain elasticity theory is defined that can be actual at micro/nano scales. It can be seen that the critical buckling load and transverse deflection of sandwich beam by considering both nonlocal stress-strain parameters is higher than the nonlocal stress parameter. On the other hands, it is noted that by considering the nonlocal stress-strain parameters simultaneously becomes the actual case.

• Computers and Concrete
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• v.4 no.5
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• pp.377-402
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• 2007

The paper presents quasi-static plane strain FE-simulations of strain localization in reinforced concrete beams without stirrups. The material was modeled with two different isotropic continuum crack models: an elasto-plastic and a damage one. In case of elasto-plasticity, linear Drucker-Prager criterion with a non-associated flow rule was defined in the compressive regime and a Rankine criterion with an associated flow rule was adopted in the tensile regime. In the case of a damage model, the degradation of the material due to micro-cracking was described with a single scalar damage parameter. To ensure the mesh-independence and to capture size effects, both criteria were enhanced in a softening regime by nonlocal terms. Thus, a characteristic length of micro-structure was included. The effect of a characteristic length, reinforcement ratio, bond-slip stiffness, fracture energy and beam size on strain localization was investigated. The numerical results with reinforced concrete beams were quantitatively compared with corresponding laboratory tests by Walraven (1978).

• Structural Engineering and Mechanics
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• v.65 no.5
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• pp.573-585
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• 2018

This article presents strain gradient elasticity-based procedures for static bending, free vibration and buckling analyses of functionally graded rectangular micro-plates. The developed method allows consideration of smooth spatial variations of length scale parameters of strain gradient elasticity. Governing partial differential equations and boundary conditions are derived by following the variational approach and applying Hamilton's principle. Displacement field is expressed in a unified way to produce numerical results in accordance with Kirchhoff, Mindlin, and third order shear deformation theories. All material properties, including the length scale parameters, are assumed to be functions of the plate thickness coordinate in the derivations. Developed equations are solved numerically by means of differential quadrature method. Proposed procedures are verified through comparisons made to the results available in the literature for certain limiting cases. Further numerical results are provided to illustrate the effects of material and geometric parameters on bending, free vibrations, and buckling. The results generated by Kirchhoff and third order shear deformation theories are in very good agreement, whereas Mindlin plate theory slightly overestimates static deflection and underestimates natural frequency. A rise in the length scale parameter ratio, which identifies the degree of spatial variations, leads to a drop in dimensionless maximum deflection, and increases in dimensionless vibration frequency and buckling load. Size effect is shown to play a more significant role as the plate thickness becomes smaller compared to the length scale parameter. Numerical results indicate that consideration of length scale parameter variation is required for accurate modelling of graded rectangular micro-plates.

• Journal of Microbiology
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• v.40 no.4
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• pp.282-288
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• 2002

Since culture of Helicobacter pylori is relatively insensitive and cumbersome, molecular detection and typing of H. pylori isolates are gaining importance for strain differentiation. In the present study genomic DNA of 42 gastric biopsies and H. pylori isolates from corresponding patients were analyzed and compared by PCR-based RFLP assay. The 1,132-bp product representing an internal portion of ureC gene of H. pylori was amplified by PCR and digested with restriction enzymes HindⅢ, AiuⅠ and PvuⅠ. The HindⅢ, AluⅠ and PvuⅠ digestion produced 4, 7, and 2 distinguishable RFLP patterns respectively from 42-H. pylori isolates. By combining all three restriction enzyme digestions, 15 RFLP patterns were observed. However, when PCR products from 42 gastric biopsy specimens were digested by restriction enzymes HindⅢ, AluⅠ and PvuⅠ, we observed 5, 8 and 2 RFLP patterns, respectively. Patterns from 34 of 42 gastric biopsy specimens matched those of corresponding H. pylori isolates from respective patients. Patterns from the remaining eight biopsy specimens differed and appeared to represent infection with two H. pylori strains. The patterns of one strain from each of these biopsies was identical to that of the isolate from corresponding patients and the second pattern presumably represented the co-infecting strain. From the study, it appears that PCR-based RFLP analysis is a useful primary tool to detect and is distinguish H. pylori strains from gastric biopsy specimens and is superior to culture techniques in the diagnosis of infection with multiple strains of H. pylori.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.109.1-109
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• 2002

This paper presents a macro/micro flip chip mounting head system for precise force control. In the proposed macro/ micro system, the macro actuator is conventional do servomotor with a ball screw mechanism and the micro actuator is a voice coil motor(VCM) that consists of four NdFeB magnets and a winded moving coil. For force control, a sensitive strain-gauge force sensor is mounted in the micro actuator. Through harmonic motion between macro and micro actuator, we would like to get precise contact force control when small sized flip chip is mounted on flexible substrate in high speed. In order to show the effectiveness of the proposed macro/micro flip chip mounting head system, we com...

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.64-72
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• 2014

In the past, prism patterns have been linear triangular shapeswith a $90^{\circ}$ angle; however, new micro prism patterns having acute angles or obtuse angles have recently been the subject of demandin the display, lighting and photovoltaic industries. Micro-cutting experiments for micro-prism patterns having $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ angles on an electroplated Ni mold were performed and it was found in this study that the specific cutting resistance increased with a decrease in the tool angles (prism pattern angles). The cause of this variation had been thought to be the increase of the ploughing force due to tip rounding and the friction force due to the edge effect. However, the depth of the cut was large enough that it was possible to neglect these effects. Therefore, this study introduced the concept of representative stress of indentation. The measured stress was varied according to the indentation depth eventhoughthetestedspecimenswereidentical ; the varied stress was termed the representative stress. According to indentation theory, the strain that the Ni mold experienced increased with a decrease in the tool angle. Based on the stress-strain relationship, higher strain means higher stress and higher specific cutting resistance. Therefore, the specific cutting resistance was higher at smaller tool angles that had higher strain and stress.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.387-390
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• 2009

This study was designed to fabricate the micro-electro-mechanical systems (MEMS) parts such as micro spur gears using hot extrusion of gas atomized Al-78Zn powders. For this purpose, it is important to develop new methods to fabricate micro-dies and choose suitable extrusion conditions for a micro-forming. Micro-dies with Ni were fabricated by LIGA technology. LIGA technology was capable to produce micro-extrusion dies with close tolerances, thick bearing length and adequate surface quality. Superplastic Al-78Zn powders have the great advantage in achieving deformation under low stresses and exhibiting good micro formability with average strain rates ranging from $10^{-3}$ to $10^{-2}\;s^{-1}$ and constant temperatures ranging from 503 to 563K. Al-78Zn powders were compacted into a cylindrical shape (${\Phi}3{\times}h10$) under compressive force of 10kN and, subsequently, the compacted powders were extruded at 563k in a hot furnace. Micro-extrusion has succeeded in forming micro-gear shafts.

• Transactions of Materials Processing
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• v.19 no.6
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• pp.352-356
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• 2010

This paper was designed to fabricate the micro-spur gear by the LIGA and hybrid powder extrusion process. It is important to manufacture a micro-die with a high aspect ratio and determine appropriate extrusion conditions for a microforming. Ni has been used to fabricate micro-dies. LIGA process was capable to produce micro-extrusion dies with close tolerance, longer bearing length and adequate surface quality. Superplastic Al-78Zn powders have the great advantage in achieving deformation under low stresses and exhibiting good micro-formability with average strain rate raging from $10^{-3}$ to $10^{-2} s^{-1}$ and constant temperature ranging from 503 to 563K. Al-78Zn powders were compacted into a cylindrical shape ($\Phi3\times$h10mm) under compressive force of 10kN and, subsequently, the compacted powders were extruded by the hybrid powder extrusion process controlling of the temperature holing time for a improvement on formability of Al-22Zn powder. Micro-extrusion has succeeded in forming micro-gear shafts.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.323-324
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• 2012

Flammability limits of opposed flow diffusion flame in a narrow channel was investigated experimentally and theoretically. There were three different extinction modes corresponding to high strain rate (HSR), low strain rate (LSR) and dilution ratio (DR) limits. To investigate these limits, a theoretical study was followed by focusing on flow and heat transfer characteristics. Consequently, a dead space concept that has been used for premixed flames was important to reveal the heat loss mechanism in a narrow channel especially for LSR conditions even in the case of diffusion flames.

• Journal of Welding and Joining
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• v.7 no.4
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• pp.38-45
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• 1989

In this study, in order to evaluate the shape and the size of the plastic zone at the notch tip before stable crack growth, a newly developed technique for plastic strain measurement, that is, the recrystallization-etching technique was applied to observe the intense strain zone at the notch tip of weld HAZ. 1) The recrystallized specimens showed that the amount of the intense strain zone, more than 20% plastic zone, was quantitatively observed as the plane strain state during the growth of the plastic zone. 2) The behavior of plastic deformation at midsection are different for parent and weld HAZ. In addition, the micro crack initiation occurs at midsection, parent and weld HAZ when the crack opening displacement(COD) value is .delta.$_{t}$=0.4mm. 3) The plastic zone for parent proceeds in the forward direction at notch tip and for weld HAZ in the right and left direction at the notch tip. 4) The relation between plastic strain energy(Wp) and COD(.delta.$_{t}$) depended on yield stress, gradient and plastic strain size.ize.