• Smart Structures and Systems
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• v.21 no.1
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• pp.65-74
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• 2018

In this article, an analytic non-classical model for the free vibrations of nanobeams accounting for surface stress effects is developed. The classical continuum mechanics fails to capture the surface energy effects and hence is not directly applicable at nanoscale. A general beam model based on Gurtin-Murdoch continuum surface elasticity theory is developed for the analysis of thin and thick beams. Thus, surface energy has a significant effect on the response of nanoscale structures, and is associated with their size-dependent behavior. To check the validity of the present analytic solution, the numerical results are compared with those obtained in the scientific literature. The influences of beam thickness, surface density, surface residual stress and surface elastic constants on the natural frequencies of nanobeams are also investigated. It is indicated that the effect of surface stress on the vibrational response of a nanobeam is dependent on its aspect ratio and thickness.

• Journal of the Korean Society of Safety
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• v.14 no.3
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• pp.25-32
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• 1999

This study has been performed to investigate the stress distribution around defects that behave as stress concentrators. Besides, the effect of stress interaction effects on the initiation of primary cracks were also investigated by rotary bending fatigue tests which were performed with specimens drilled micro surface defects and the stress distribution was analyzed using Finite Element Method. In addition, the stress interaction effects around defects and cracks were investigated by comparing the results of experiments and F.E.M. The results obtained are summarized as follows ; 1) Area which slip and micro cracks initiated at micro surface defects is between the maximum shear stress points and this area is over than ${\pm}30^{\circ}$ from the maximum stress point along the defect edge. 2) The stress interaction effect for the small size defect is larger than that of large size defect when the interval between them is near 3) Interval which there is no shear stress interaction effect analyzed by F.E.M. is larger than that of experimental results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.8
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• pp.678-686
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• 2002

This paper presents the effects of accumulation of surface charges on hydrophobic level and the changes of surface potential decay with various artificial environment treatments on high temperature vulcanized (HTV) silicone rubber used for outdoor insulating material. For this study, the charging apparatus by corona discharge, in which grid electrode was installed between the main corona and ground electrode, was used. From this study, it was found that the accumulation of surface charges above a critical surface potential on silicone insulating materials could lead to the temporary loss of surface hydrophobicity. In addition, corona stress and water absorption stress increase the decay rate of surface charges of HTV silicone rubber, while ultraviolet (UV) stress causes longer decay time. We could conclude that the effects of surface charges on hydrophobicity level and the changes of surface state by various artificial treatments were found through a trend of surface potential decay.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.154-158
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• 2007

For the application of flexible printed circuit board (FPCB), electroplated copper is required to have low surface roughness and residual stress. In the paper, the effects of surface roughness and residual stress of electroplated copper as thick as $8{\mu}m$ were studied on organic additives such as inhibitor, leveler and accelerator. Polyimide film coated with sputtered copper was used as a substrate. Surface roughness and surface morphology were measured by 3D-laser surface analysis and FESEM, respectively. Residual stress was calculated by Stoney's equation after measuring radius curvature of specimen. The addition of additives except high concentration of accelerator in the electrolyte decreased surface roughness of electroplated copper film. Such a tendency was explained by the function of additives among which the inhibitor and the leveler inhibit electroplating on a whole surface and prolusions, respectively. The accelerator plays a role in accelerating the electroplating in valley parts. The inhibitors and the leveler increased residual stress, whereas the accelerator decreased it. It was thought to be related with entrapped additives on electroplated copper film rather than the preferred orientation of electroplated copper film. The reason why additives lead to residual stress remains for the future work.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.134-137
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• 2008

The effects of residual stress and surface defects on the mechanical properties of the high carbon steel filament used for the automotive tire have been experimentally investigated. The samples were fabricated with annealing temperature. The residual stress was measured by focused ion beam and strain mapping software which has advantages, such as data with high accuracy and fast data acquisition time. Mechanical properties, such as tensile strength and fatigue resistance, were gradually increased up to $200^{\circ}C$ and then slightly decreased. From the measurement of residual stress and level of surface defect, it was revealed that the critical factor was varied with different temperature region. That is, the fatigue resistance increased due to decreasing the residual stress and decreased due to increasing the size and distribution of surface defect.

• Computers and Concrete
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• v.32 no.5
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• pp.439-454
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• 2023

In this article, the surface stress effects on the buckling analysis of the annular sandwich plate is developed. The proposed plate is composed of two face layers made of carbon nanotubes (CNT) reinforced composite with assuming of fully bonded to functionally graded porous core. The generalized rule of the mixture is employed to predict the mechanical properties of the microcomposite sandwich plate. The derived potentials energy based on higher order shear deformation theory (HSDT) and modified couple stress theory (MCST) is solved by employing the Ritz method. An exact analytical solution is presented to calculate the critical buckling loads of the annular sandwich plate. The predicted results are validated by carrying out the comparison studies for the buckling analysis of annular plates with those obtained by other analytical and finite element methods. The effects of various parameters such as material length scale parameter, core thickness to total thickness ratio (hc/h), surface elastic constants based on surface stress effect, various boundary condition and porosity distributions, size of the internal pores (e0), Skempton coefficient and elastic foundation on the critical buckling load have been studied. The results can be served as benchmark data for future works and also in the design of materials science, injunction high-pressure micropipe connections, nanotechnology, and smart systems.

• Wind and Structures
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• v.27 no.6
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• pp.431-438
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• 2018

This paper presents a free vibration analysis of size-dependent functionally graded (FG) nanobeams with all surface effects considerations on the basis of modified couple stress theory. The material properties of FG nanobeam are assumed to vary according to power law distribution. Based on the Euler-Bernoulli beam theory, the modeled nanobeam and its equations of motion are derived using Hamilton's principle. An analytical method is used to discretize the model and the equation of motion. The model is validated by comparing the benchmark results with the obtained results. Results show that the vibration behavior of a nanobeam is significantly influenced by surface density, surface tension and surface elasticity. Also, it is shown that by increasing the beam size, influence of surface effect reduces to zero, and the natural frequency tends to its classical value.

• Structural Engineering and Mechanics
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• v.53 no.1
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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.

• Steel and Composite Structures
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• v.36 no.2
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• pp.143-161
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• 2020

In nanosized structures as the surface area to the bulk volume ratio increases the classical continuum mechanics approaches fails to investigate the mechanical behavior of such structures. In perforated nanobeam structures, more decrease in the bulk volume is obtained due to perforation process thus nonclassical continuum approaches should be employed for reliable investigation of the mechanical behavior these structures. This article introduces an analytical methodology to investigate the size dependent, surface energy, and perforation impacts on the nonclassical bending behavior of regularly squared cutout nanobeam structures for the first time. To do this, geometrical model for both bulk and surface characteristics is developed for regularly squared perforated nanobeams. Based on the proposed geometrical model, the nonclassical Gurtin-Murdoch surface elasticity model is adopted and modified to incorporate the surface energy effects in perforated nanobeams. To investigate the effect of shear deformation associated with cutout process, both Euler-Bernoulli and Timoshenko beams theories are developed. Mathematical model for perforated nanobeam structure including surface energy effects are derived in comprehensive procedure and nonclassical boundary conditions are presented. Closed forms for the nonclassical bending and rotational displacements are derived for both theories considering all classical and nonclassical kinematics and kinetics boundary conditions. Additionally, both uniformly distributed and concentrated loads are considered. The developed methodology is verified and compared with the available results and an excellent agreement is noticed. Both classical and nonclassical bending profiles for both thin and thick perforated nanobeams are investigated. Numerical results are obtained to illustrate effects of beam filling ratio, the number of hole rows through the cross section, surface material characteristics, beam slenderness ratio as well as the boundary and loading conditions on the non-classical bending behavior of perforated nanobeams in the presence of surface effects. It is found that, the surface residual stress has more significant effect on the bending deflection compared with the corresponding effect of the surface elasticity, Es. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams.

• Tribology and Lubricants
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• v.27 no.1
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• pp.34-39
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• 2011

In this study, finite element analysis of particle-surface collision using 2-dimensional elements was performed to observe the effects of abrasive size and impact angle. The result of the simulation on the change in abrasive size revealed that larger abrasive particle induced larger contact stress due to force transfer through slurry fluid as the particle moved and pushed the fluid. This observation brought an important finding that the slurry fluid could make the workpiece surface soften and then change the mechanical properties of the surface layer such as elastic modulus and yield strength. As for the impact angle, it was found that the contact stress increased with the angle of impact and jumped up at a specific angle. Such result would be attributed to the complex effects of the impact velocity and angle.