• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.226-231
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• 2012

Characteristics of carburized surface layers in 0.18C-3.5Ni-1.5Cr-0.2Mo steels for main shaft bearings of wind turbines have been analyzed and evaluated before and after rolling contact fatigue tests. Mixed microstructure consisting of retained austenite and tempered martensite has been formed with compressive residual stresses in the surface hardened layers of the specimens showing uniform hardness distribution with value about Hv700 after vacuum carburizing and tempering. It has been found on the raceway of the layers of the specimens after rolling contact fatigue tests that the amount of retained austenite decreased and compressive residual stresses increased, resulting from cyclic contact stresses applied during the tests. It has been also revealed that higher durability of the bearings can be obtained through controlling the amount of the retained austenite in the surface of the bearing steels to be lower in this study.

• Journal of the Korean Society of Safety
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• v.23 no.3
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• pp.8-11
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• 2008

In the present work, the measurement method of residual stresses in thermal barrier coatings(TBCs) which are received the thermal shock is performed numerically. For this, the internal residual stresses are predicted by commercial FEM software ABAQUS because the hole drilling strain gage method measures residual stresses only near the surface of a material. As the results of this study, the residual stresses are linearly increased when the surface temperatures are over $1,200^{\circ}C$. It is also found that the values of residual stress are increased as the coating thickness is thin.

• Tribology and Lubricants
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• v.19 no.1
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• pp.26-30
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• 2003

The stresses of surface and substrate under the rough surface contact are irregular. Using rainflow counting method for irregular stresses, the fatigue surface crack initiation lift was calculated. With the surface generated by computer, this paper figures out the random load generated by contacting to the rough surface, analyzes the stress of its subsurface, and calculates the fatigue crack initiation life of the rough surface fatigue theory.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.4
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• pp.160-166
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• 2001

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.417-420
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• 2000

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Steel and Composite Structures
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• v.37 no.2
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• pp.229-251
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• 2020

In this paper, dynamic buckling of a smart sandwich nanotube is studied. The nanostructure is composed of a carbon-nanotube with inner and outer surfaces coated with ZnO piezoelectric layers, which play the role of sensor and actuator. Nanotube is under magnetic field and ZnO layers are under electric field. The nanostructure is located in a viscoelastic environment, which is assumed to obey Visco-Pasternak model. Non-local piezo-elasticity theory is used to consider the small-scale effect, and Kelvin model is used to describe the structural damping effects. Surface stresses are taken into account based on Gurtin-Murdoch theory. Hamilton principle in conjunction with zigzag shear-deformation theory is used to obtain the governing equations. The governing equations are then solved using the differential quadrature method, to determine dynamic stability region of the nanostructure. To validate the analysis, the results for simpler case studies are compared with others reported in the literature. Then, the effect of various parameters such as small-scale, surface stresses, Visco-Pasternak environment and electric and magnetic fields on the dynamic stability region is investigated. The results show that considering the surface stresses leads to an increase in the excitation frequency and the dynamic stability region happens at higher frequencies.

• Structural Engineering and Mechanics
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• v.60 no.2
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• pp.175-191
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• 2016

The present article is aimed at an investigation of stresses produced in a microstretch elastic half-space due to a moving load. The expressions of normal stress, shear stress and tangential couple stress produced in this case have been obtained in closed form. To find the displacement fields the perturbation method is applied. Significant effect of moving load on variation of stresses developed at different depths below the surface due to the depth of substrate and frictional coefficient of the rough surface of the medium has been observed. The effects of different shapes of irregularity and depth of irregularity on normal, shear and tangential couple stresses have been discussed. Some particular cases have also been deduced from the present investigation. Finally, the analytical developments have been illustrated numerically for aluminium-epoxy-like material substrate under the action of moving load.

• Computers and Concrete
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• v.1 no.1
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• pp.31-46
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• 2004

A methodology is presented for computing stresses in structural concrete members exposed to fire. Coupled heat and moisture migration simulations are used to establish temperature, pore pressure, and liquid-saturation state variables within near-surface zones of heated concrete members. Particular attention is placed on the use of coupled heat and multiphase fluid flow simulations to study phenomena such as moisture-clogging. Once the state variables are determined, a procedure for combining the effects of thermal dilation, mechanical loads, pore pressure, and boundary conditions is proposed and demonstrated. Combined stresses are computed for varying displacement boundary conditions using data obtained from coupled heat and moisture flow simulations. These stresses are then compared to stresses computed from thermal analyses in which moisture effects are omitted. The results demonstrate that moisture migration has a significant influence on the development of thermal stresses.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.129-145
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• 1991

The purpose of this study was to analyze the stresses and displacements of various esthetic restorations and abutment teeth. The finite element models of central incisor were divided into four groups according to the types of restoration. Three load cases were applied; 1) 45 degrees on the incisal edge, 2) horizontal force on the labial surface, and 3) 26 degrees diagonally on the lingual surface. Material property, geometry, and load conditions of each model were inputed to the two dimensional finite element program and stresses and displacements were analyzed. Results were as follows; 1. In the cases of porcelain fused gold ann and porcelain laminate venner, stresses were equally distributed in supporting abutment tooth. 2. The metal coping of porcelain fused gold u and collarless porcelain fused gold crown functioned as a good stress distributor. 3. When the horizontal load applied, the highest tensile and compressive stresses were seen in the cervical margin of restoration and the dentin of the abutment tooth. 4. The highest displacement of restoration was seen when load was applied at an mee of 26 degrees diagonally in lingual surface of tooth in centric occlusion. 5. The influence of loading direction on the stresses and displacements in the restoration was greater than that of various design. 6. The possibility of fracture was highest in porcelain jacket crown.

• Steel and Composite Structures
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• v.22 no.4
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• pp.837-853
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• 2016

This paper presents the experimental and numerical study on the distribution of transverse and longitudinal residual stresses in cold-formed thick-walled structural steel rectangular hollow sections manufactured by indirect technique. Hole-drilling method is employed to measure the magnitude of the transverse and longitudinal surface residual stress distribution, and the effects of the residual stresses are evaluated qualitatively by sectioning method. It is shown that compared to normal cold-formed thin-walled structural hollow sections (SHS), the cold-formed thick-walled SHS has similar level of residual stress in the flat area but higher residual stresses in the corner and welding areas. Both the transverse and longitudinal residual stresses tend to open the section. In order to predict the surface residual stresses in the corners of the cold-formed thick-walled SHS, an analytical model is developed. 2D finite element simulation of the cold bending process is conducted to validate the analytical approach. It is shown that in analyzing bending for thick-walled sections, shifting of neutral axis must be considered, since it would lead to nonlinear and non-symmetrical distribution of stresses through the thickness. This phenomenon leads to the fact that cold-formed thick-walled SHSs has different distribution and magnitude of the residual stresses from the cold-formed thin-walled SHSs.