• Steel and Composite Structures
• /
• 제42권5호
• /
• pp.699-710
• /
• 2022

This work presents a comprehensive study on the surface energy effect on the axial frequency analyses of AFGM nanorods in cylindrical coordinates. The AFGM nanorods are considered to be thin, relatively thick, and thick. In thin nanorods, effects of the inertia of lateral motions and the shear stiffness are ignored; in relatively thick nanorods, only the first one is considered; and in thick nanorods, both of them are considered in the kinetic energy and the strain energy of the nanorod, respectively. The surface elasticity theory which includes three surface parameters called surface density, surface stress, and surface Lame constants, is implemented to consider the size effect. The power-law form is considered for variation of the material properties through the axial direction. Hamilton's principle is used to derive the governing equations and boundary conditions. Due to considering the surface stress, the governing equation and boundary condition become inhomogeneous. After homogenization of them using an appropriate change of variable, axial natural frequencies are calculated implementing harmonic differential quadrature (HDQ) method. Comprehensive results including effects of geometric parameters and various material properties are presented for a wide range of boundary condition types. It is believed that this study is a comprehensive one that can help posterities for design and manufacturing of nano-electro-mechanical systems.

• Steel and Composite Structures
• /
• 제41권6호
• /
• pp.805-820
• /
• 2021

In this research, the buckling and free vibration of three-phase carbon nanotubes/ fiber/ polymer piezoelectric nanocomposite face sheet sandwich microbeam with microsensor and micro-actuator surrounded in elastic foundation based on modified couple stress theory (MCST) is investigated. Three types of porous materials are considered for sandwich core. Higher order (Reddy) and sinusoidal shear deformation beam theories are employed for the displacement fields. Sinusoidal surface stress effects are extracted for sinusoidal shear deformation beam theory. The equations of motion are derived by Hamilton's principle and then the natural frequency and critical buckling load are obtained by Navier's type solution. The determined results are in good agreement with other literatures. The detailed numerical investigation for various parameters is performed for this microsensor-microactuator. The results reveal that the microsensor-microactuator enhanced by increasing of Skempton coefficient, carbon nanotubes diameter length to thickness ratio, small scale factor, elastic foundation, surface stress constants and reduction in porous coefficient, micro-actuator voltage and CNT weight fraction. The valuable results can be expedient for micro-electro-mechanical (MEMS) and nano-electro-mechanical (NEMS) systems.

• 대한기계학회논문집A
• /
• 제35권5호
• /
• pp.543-547
• /
• 2011

원자력발전소의 이종용접부에서 일차응력부식균열이 발생하고 있으며 용접부의 잔류응력이 균열발생 및 성장에 기여할 수 있다. 용접부의 잔류응력은 기본적으로 용접에 의해 형성되지만 기계가공에 의해 표면잔류 응력상태가 변화할 수 있다. 본 논문에서는 기계가공이 원전재료인 SA508과 오스테나이트 스테인리스강에 표면잔류응력에 미치는 영향을 평가하였다. 이를 위해 SA508, TP304, F316L 재료를 연마, 연삭, 방전가공으로 가공한 후 표면에 형성되는 잔류응력을 측정하였다. 측정방법은 구멍뚫기법과 엑스선회절법을 사용하였다. 기계가공방법에 따라 각 재료에 미치는 잔류응력의 크기 및 방향, 잔류응력이 형성되는 깊이 등의 특성을 확인하였다.

• 한국군사과학기술학회지
• /
• 제20권5호
• /
• pp.608-619
• /
• 2017

In this paper, the effects of parameters related to the residual stress induced due to laser shock peening process to determine mitigation of the initial tensile residual stresses are discussed, such as the maximum pressure, pressure pulse duration, laser spot size and number of laser shots. In order to estimate the influence of the initial tensile residual stresses, which is generated by welding in 35CD4 50HRC steel alloy, the initial condition option was employed in the finite element code. It is found that $2{\times}HEL$ maximum pressure and a certain range of the pressure pulse duration time can produce maximum mitigation effects near the surface and depth, regardless of the magnitudes of tensile residual stess. But plastically affected depth increase with increasing maximum pressure and pressure pulse duration time. For the laser spot size, maximum compressive residual stresses have almost constant values. But LSP is more effective with increasing the magnitudes of tensile residual stress. For the multiple LSP, magnitudes of compressive residual stresses and plastically affected depths are found to increase with increasing number of laser shots, but the effect is less pronounced for more laser shots. And to conclude, even though the initial tensile residual stresses such as weld residual stress field are existed, LSP is enough to make the surface and depth reinforcement effects.

• Restorative Dentistry and Endodontics
• /
• 제18권2호
• /
• pp.483-496
• /
• 1993

Dentin hypersensitivity medicaments such as Gluma, Scotchbond 2, All-Bond 2, which are resin adhesives, were used to compare the sealing effects of dentinal tubule under mechanical stress. Topical application of above medicaments on the dentin surfaces of extracted teeth followed by artificial tooth brushing for 6 weeks was performed for the comparison. The following conclusions on the degree of dentinal tubule exposure versus time by were reached by using polyvinyl siloxane impression material for taking the impression, epoxy resin for the duplication and SEM for observing the surface. 1. SEM was used to compare the accuracy of the duplicated surface, but no differences were found when teeth samples and the duplicated surfaces were observed. 2. After comparing the degree of dentinal tubules exposure with varnish applied contrast group, resin adhesive materials showed much less exposure as time went by. 3. The results indicated that AU-Bond 2 adhesive, under mechanical stress, showed lesser exposure of dentinal tubules comparing with Gluma and Scotchbond 2 adhesives After the results were put together, it was demonstrated that resin replica method is an useful way to evaluate the treatment effects of the dentinal tubule hypersensitivity medicaments. Also, it was noticed that under mechanical stress, All-Bond 2, classified as fourth generation, illustrated the best dentinal tubules sealing effects.

• 대한기계학회논문집A
• /
• 제23권11호
• /
• pp.2022-2032
• /
• 1999

In recent years, the subject of remaining life assessment has drawn considerable attention in the power generation industry. In power generation systems a variety of structural components, such as steam pipes, turbine rotors, and superheater headers, typically operate at high temperatures and high pressures. Thus a life prediction methodology accounting for fracture and rupture is increasingly needed for these components. For accurate failure assessment, in addition to the single parameter such as K or J-integral used in traditional fracture mechanics, the second parameter like T-stress describing the constraint is needed. The most critical defects in such structures are generally found in the form of semi-elliptical surface cracks in the welded piping-joints. In this work, selecting the structures of surface-cracked plate and straight pipe, we first perform line-spring finite element modeling, and accompanying elastic-plastic finite element analyses. We then present a framework for including constraint effects (T-stress effects) in the R6 failure assessment diagram approach for fracture assessment.

• Steel and Composite Structures
• /
• 제21권2호
• /
• pp.429-442
• /
• 2016

The aim of this paper is to determine temperature and stress distributions in a ceramic based on Partially Stabilized Zirconia coated steel piston crown by using plasma spraying for improving performance of a marine diesel engine. Effects of coating constituent and thickness on temperature and stress distributions were investigated including comparisons with results from an uncoated piston by means of finite element method namely ANSYS. Temperature developed at the coated surface is significantly higher than that of the uncoated piston. The maximum stress components occur between bond coat and adjacent ceramic layer. Provided that coating thickness is constant as 0.5 mm, when numbers of layers increase, magnitude of the normal stress decrease about 34.1% on the base metal surface according to uncoated piston, but the base metal surface temperature of the steel piston increase about 13.1%.

• Composites Research
• /
• 제28권5호
• /
• pp.297-310
• /
• 2015

This study aims to develop efficient composite laminates for buckling load enhancement, interlaminar shear stress minimization, and weight reduction. This goal is achieved through cover-skin lay-ups around skins and stiffeners, which amplify bending stiffness and defer delamination by means of effective stress distribution. The design problem is formulated as multi-objective optimization that maximizes buckling load capability while minimizing both maximum out-of-plane shear stress and panel weight. For efficient optimization, response surface methodology is employed for buckling load, two out-of-plane shear stresses, and panel weight with respect to one ply thickness, six fiber orientations of a skin, and four stiffener heights. Numerical results show that skin-covered composite stiffened panels can be devised for maximum buckling load and minimum interlaminar shear stresses under compressive load. In addition, the effects of different material properties are investigated and compared. The obtained results reveal that the composite stiffened panel with Kevlar material is the most effective design.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 추계학술대회 논문집
• /
• pp.418-422
• /
• 2005

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire has been investigated. Test pieces were fabricated using die series with different mean and final reduction ratio. Surface residual stresses in the axial direction were measured by X-ray diffraction, Broker's 2-dimensional GADDS system. Results were compared with stress profiles which were calculated by 3D and 2D finite element simulation, Hibbitt's ABAQUS 6.4 program in Finite Element Analysis. By means of FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.

• 소성∙가공
• /
• 제15권2호
• /
• pp.153-157
• /
• 2006

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire have been investigated. Test pieces were fabricated using die series with different mean and final reduction ratios. Surface residual stresses in the axial direction were measured by X-ray diffraction, Bruker's 2-dimensional GADDS system. The results were compared with stress profiles that were calculated by 3D and 2D finite element simulations, ABAQUS 6.4 program in finite element analysis(FEA). By means of the FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.