• Steel and Composite Structures
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• 제22권4호
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.622-627
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• 2001

The object of this paper is to compare stress intensity factor that be calculated by Raju-Newman's equation, finite element method, and Vessel INTegrity analysis inner flaws(VINTIN) program for longitudinal semi-elliptical cracks in cylindrical vessel under inner pressure. For this, three-dimensional finite-element analyses were performed to obtain the stress intensity factors for various surface cracks with t/R = 0.1. The finite element meshes were designed for various crack shapes with t/R of 0.1. The crack depth to thickness ratio, a/t, was set to 0.2 and 0.5 matching Raju-Newman's equation. The crack depth to length ratio, a/c, was set to 0.2 and 0.4 in the same way and 0.33 was added to extend the range of crack configuration. Finite Element Analyses(FEA) were performed using the commercial FEA program ABAQUS. The results showed that the Raiu-Newman solutions were about 4-10% lower than FEA's using symmetric model of one-eighth of a vessel and close to those of FEA using symmetric model or one-forth or a vessel. Ana VINTIN solutions were nearly equal to those or Raju-Newman.

• 한국정밀공학회지
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• 제16권2호통권95호
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• pp.138-144
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• 1999

Longitudinal wave and shear wave velocity changes of PMMA Polymer meterial under the the unidirection load were measured. The Third-order elastic modulus and acousto-elastic modulus of PMMA are obtained. The theoretical and experemental values of the velocity change of each wave by stress are compared each other and the validity of theoretical expression is examinated.

• Journal of Welding and Joining
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• 제21권5호
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• pp.561-567
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• 2003

For construction of I-beam steel structures, a fillet welding is one of the main manufacturing process. However, this welding process cause some problems associated with welding residual stress and welding deformation that are harmful to the safety of structures. Accordingly, this study clarified the creation mechanism of the welding deformation on I-beam steel structure from the experimental results given by the FEM method. To prevent or minimize the longitudinal bending deformation, first of all, a field supervision is necessary to observe the optimal groove design. Secondly, the welding order for cooling weld zone is needed.

• 한국정밀공학회지
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• 제8권1호
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• pp.41-49
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• 1991

A knowledge of the resdual stress distribution at circumferential weldments can normally increase the accuracy of a fracture assessment in pipe line. In this paper, we present the measurements about the residual stress distributions at three kinds of circumferential butt welded pipes using the holl drilling strain gage method. By this experiment, we have obtined the following characteristics. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed from compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self-restraint bending force in the pipe welding.

• Structural Engineering and Mechanics
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• 제87권2호
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• pp.107-116
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• 2023

The three-dimensional Hashin criterion and user subroutine VUMAT were used to simulate the damage in the composite layer, and the secondary stress criterion was used to simulate the interlayer failure of the cohesive element of the bonding layer and the propagation characteristics under the layer. The results showed that when the shear stress wave (shear wave) propagates on the surface of the laminate, the stress wave attenuation along the fiber strength direction is small, and thus producing a large stress profile. When the compressive stress wave (longitudinal wave) is transmitted between the layers, it is reflected immediately instead of being transmitted immediately. This phenomenon occurs only when the energy has accumulated to a certain degree between the layers. The transmission of longitudinal waves is related to the thickness and the layer orientation. Along the symmetry across the thickness direction, the greater is the stress amplitude along the layer direction. Based on the detailed investigation on the impact on various laminated composites carried out in this paper, the propagation characteristics of stress waves, the damage and the destruction of laminates can be explained from the perspective of stress waves and a reasonable layering sequence of the composite can be designed against damage and failure from low velocity impact.

• Human Ecology Research
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• 제59권2호
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• pp.233-243
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• 2021

This study examined the longitudinal effects of media usage by early school-age children and of maternal parenting stress on children's school adjustment. The study focused on the mediating effect of executive function difficulty. Longitudinal data to examine the hypothetical model were drawn from the eighth (2015) through tenth (2017) waves of the Panel Study of Korean Children (PSKC) collected by the Korea Institute of Child Care and Education (KICCE). A total of 581 children (293 boys and 288 girls) and their mothers were included. Confirmatory factor analysis, structural equation model, and bootstrapping analysis were applied using SPSS 25.0 and Amos 26.0. The results are as follows. First, no significant correlation was found between early school-age children's media usage and maternal parenting stress. Second, neither media usage by early school-age children nor maternal parenting stress were found to directly affect children's school adjustment. Third, media usage by early school-age children and maternal parenting stress were shown to indirectly affect children's school adjustment via executive function difficulties. In other words, higher levels of media usage by early school-age children and maternal parenting stress during the first grade lead to greater executive function difficulties after a year, which, in turn, lead to a lower level of school adjustment in the third grade. This study indicates the need to develop practical support for the psychological wellbeing of mothers while they are performing their role as a parent and for children in maintaining suitable levels of media usage during early childhood.

• 대한간호학회지
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• 제48권1호
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• pp.109-121
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• 2018

Purpose: This study was conducted to examine the longitudinal effects of parenting stress and parental control attitudes on problem behaviors in preschool children, using a latent growth model. Methods: Participants were 1,724 pairs of parents and 1,724 preschool children who had completed the panel survey on Korean children ($5^{th}{\sim}7^{th}$ survey panels). Results: An analysis of the multivariate latent growth model of parenting stress, parental control attitudes, and children's problem behaviors suggested that the parents' intercepts for parenting stress influenced their intercepts for parental control attitudes (father: ${\beta}=.21$, p<.001; mother: ${\beta}=.55$, p<.001). In addition, the slopes for fathers' parenting stress was the only aspect that affected the slopes for mothers' parental control attitudes (${\beta}=.77$, p<.001). Moreover, both the intercepts and slopes of parenting stress and parental control attitudes significantly affected the children's problem behaviors. Conclusion: This study is significant as it provides longitudinal evidence of the impact of parenting stress and parental control attitudes on children's problem behaviors. The findings suggest that accurately assessing changes in parenting stress and parental control attitudes and developing intervention programs to reduce them will be effective in reducing problem behaviors in children.

• 아동학회지
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• 제36권4호
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• pp.209-227
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• 2015

The present study investigated maternal parenting stress trajectories, using data gathered from the Korean Children Panel Survey. Four factors-monthly income, maternal depression levels, infants' negative emotionality, marital conflict-which were taken from reports made by the mothers' used in this study, were examined as predictors of maternal parenting stress trajectories. The effects of maternal parenting stress trajectories, parenting styles and toddlers' peer interruptive behaviors were also examined. The findings were as follows: First, maternal parenting stress trajectories somewhat increased from the 1st year period to the 4th year period. Second, infants' negative emotionality and marital conflict within the first year were observed to have a connection to the initial level and slope of maternal parenting stress trajectories. Third, maternal parenting stress trajectories predicted positive parenting styles, and parenting styles had a longitudinal impact on toddlers' peer interruptive behaviors at the 5th year period.

• Computers and Concrete
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• 제20권4호
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• pp.469-481
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• 2017

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.