• Advances in aircraft and spacecraft science
• /
• v.9 no.1
• /
• pp.69-93
• /
• 2022

Reduced graphene oxide (rGO) is one of the derivatives of graphene, which has drawn some experimental research interests in recent years however, numerical research studying the mechanical behaviors of composites made of rGO has not been taken into consideration yet. The objective of this research is to investigate the buckling, and free vibration of functionally graded reduced graphene oxide reinforced nanocomposite (FG rGORC) plates employing isogeometric analysis (IGA). The effective Young's modulus of rGORC is determined based onthe Halpin-Tsai model. Four different FG distribution types of rGO are considered varying across plate thickness. Besides, the refined plate theory is used based on Reddy's third-order function. To capture the size effect, modified couple stress theory (MCST) is employed. A comprehensive study is provided examining the effect of various parameters including rGO weight fraction, FG distribution types, boundary conditions, material length scale parameter, etc. Our obtained results show that the addition of only 1% of uniformly distributed rGO into epoxy plates leads to the fundamental frequency and critical buckling load 18% and 39% higher than those of pure epoxy plates, respectively.

• Geomechanics and Engineering
• /
• v.28 no.5
• /
• pp.477-491
• /
• 2022

In the present study, the effects of thermal loading on the buckling and resonance frequency of graphene platelets (GPL) reinforced nano-composites are examined. Functionally graded (FG) material properties are considered in thickness direction for the thermal responses of the composite. The equivalent material properties are obtained using Halphin-Tsai nano-mechanical model for composite layers. Moreover, the effects of nano-scale sizes are taken into account, employing functionally modified couple stress (FMCS) parameter. In this regard, for the first time, it is demonstrated that at certain values of GPL weight fraction, thermal buckling occurs. In obtaining results of vibrational behavior, both analytical solution and deep neural network (DNN) methods are used. The DNN method needs low computational costs to predict the resonance behavior. A comprehensive parametric study is conducted to indicate the effects of several geometrical, material, and loading conditions on the vibrational and buckling behavior of cylindrical shell structures made of GPL-nanocomposites. It is shown that the effect of temperature change on the occurrence of buckling is vital while it has a negligible impact on the resonance frequency of the structure. Moreover, the size-dependency of the results is demonstrated, and it cannot be neglected in nano-scales.

• Advances in nano research
• /
• v.13 no.4
• /
• pp.393-406
• /
• 2022

In the present article, functionally graded small-scaled plates based on modified strain gradient theory (MSGT) are studied for analyzing the nonlinear bending and post-buckling responses. Von-Karman's assumptions are applied to incorporate geometric nonlinearity and the first-order shear deformation theory is used to model the plates. Modified strain gradient theory includes three length scale parameters and is reduced to the modified couple stress theory (MCST) and the classical theory (CT) if two or all three length scale parameters become zero, respectively. The Ritz method with Legendre polynomials are used to approximate the unknown displacement fields. The solution is found by the minimization of the total potential energy and the well-known Newton-Raphson technique is used to solve the nonlinear system of equations. In addition, numerical results for the functionally graded small-scaled plates are obtained and the effects of different boundary conditions, material gradient index, thickness to length scale parameter and length to thickness ratio of the plates on nonlinear bending and post-buckling responses are investigated and discussed.

• Advances in nano research
• /
• v.8 no.4
• /
• pp.283-292
• /
• 2020

In the present research, differential quadrature (DQ) method has been utilized for investigating free vibrations of porous functionally graded (FG) micro/nano beams in thermal environments. The exact location of neutral axis in FG material has been assumed where the material properties are described via porosity-dependent power-law functions. A scale factor related to couple stresses has been employed for describing size effect. The formulation of scale-dependent beam has been presented based upon a refined beam theory needless of shear correction factors. The governing equations and the associated boundary conditions have been established via Hamilton's rule and then they are solved implementing DQ method. Several graphs are provided which emphasis on the role of porosity dispersion type, porosity volume, temperature variation, scale factor and FG material index on free vibrational behavior of small scale beams.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.110-114
• /
• 2008

Determination of weld-induced residual stress has been an important issue in nuclear power industry because several failures were reported in dissimilar metal weld parts due to primary water stress corrosion cracking. In this context, a couple of remarkable round robin analyses were conducted to quantify the welding simulation variables and to establish optimized numerical analysis process. The purpose of the present research is to introduce welding simulation results for a safety and relief nozzle, which has a dissimilar metal weld part as well as a similar metal weld part. First, finite element analyses are carried out to calculate residual stresses at the inside of nozzle considering only dissimilar metal welding. Subsequently, residual stresses taking into account both the dissimilar and similar metal welding are computed. The similar metal weld effect is evaluated by compa

• Geomechanics and Engineering
• /
• v.25 no.4
• /
• pp.283-294
• /
• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Korean Journal of Child Studies
• /
• v.33 no.1
• /
• pp.205-221
• /
• 2012

The purpose of this study was to examine effects of father involvement, marital happiness and conflicts, and meanings of parenthood on maternal parenting stress and compare the relative importance of those variables in three (low, middle, and upper) income groups. The subjects of this study were 654 nuclear families which consisted of 3 family members, couple and their infant children aged between 4 months and 10 months. Data was taken from the 2008 Panel Data of Korean Children. The results of this study were as follows : First, maternal parenting stress, father involvement, mother's marital satisfaction and conflicts were statistically significant according to income levels. Second, mother's marital satisfaction was the most significant variable in predicting father involvement, and mother's marital conflict was the most significant one in predicting maternal parenting stress. Third, the significance and numbers of variables which were impacted upon maternal parenting stress and father involvement varied according to income groups. Fourth, in all three income groups, the effects of father involvement on maternal parenting stress was not significant when marital relationship and meanings of parenthood underwent in regression analysis. However, father involvement was impacted upon maternal parenting stress by itself.

• Journal of the Korean Home Economics Association
• /
• v.37 no.6
• /
• pp.59-76
• /
• 1999

This study was to investigate casual relation of psychological well-being and quality of life of married couples. For the data set 434 married couples living in Pusan, Korea were chosen. The data were analyzed using M, SD, t-test, Pearson's correlation, multiple regression, and path analysis. The findings of this study are as follows; First, marital satisfaction and the level of quality of life are higher for husbands than wives. Whereas psychological distress is higher for wives than husbands. Second, for husbands, husband's level of education, job satisfaction, husband's housework participation, and job stress have significant effect on marital satisfaction. For wives, wife's level of education, husband's housework participation, and husband's job stress have significant effect on marital satisfaction. Third, for husbands, job satisfaction and job stress have significant effect on psychological distress. For wives, husband's job stress have significant effect on psychological distress. Fourth, for husbands, job stress, marital satisfaction and psychological distress have significant direct effect on quality of life. Besides, husband's age, husband's level of education, job satisfaction, job stress, husband's housework participation, and marital satisfaction are indirectly associated with quality of life. For wives, marital satisfaction and psychological distress have significant direct effect on quality of life. Besides, wife's level of education, husband's job stress, husband's housework participation, and marital satisfaction are indirectly associated with quality of life.

• Structural Engineering and Mechanics
• /
• v.30 no.5
• /
• pp.577-592
• /
• 2008

Laplace-Fourier transform techniques are used to investigate the interaction caused by mechanical, thermal and microstress sources in a generalized thermomicrostretch elastic medium with temperature-dependent mechanical properties. The modulus of elasticity is taken as a linear function of reference temperature. The integral transforms are inverted using a numerical technique to obtain the normal stress, tangential stress, tangential couple stress, microstress and temperature distribution. Effect of temperature dependent modulus of elasticity and thermal relaxation times have been depicted graphically on the resulting quantities. Comparisons are made with the results predicted by the theories of generalized thermoelasticity. Some particular cases are also deduced from the present investigation.

• Korean Parent-Child Health Journal
• /
• v.8 no.1
• /
• pp.3-16
• /
• 2005

Purpose: This study was to investigate the stress of parents while they were rearing their children. Method: This study reviewed the preceding research related to parents' stress and breeding stress with consideration of modem society, family system and parents' role. Results: In the parent-child relationship, parents feel stressed when they found it difficult to come up with an expectation to the parents' role of rearing child. Therefore, considering the health of parents and children, it is important to mediate parents who are under stress. Moreover, since parents cannot handle this problem all alone, it should be discussed and solved not only by individual but also by family, and further by social context. The parent-child relationship in early infancy is a core element to the development of an individual. Parents have influence on a child's development the most and play a big role. In particular, many parents these days believe that parent-child relationship is changing in a democratic way and a couple breeds their child together. However, in reality, the relationship has not been changed and is even regarded as more difficult situation than it was in the traditional society. Parents are oppressed with not being adapted to social changes and advance, and child also feels the same. Conclusion: Parents need education and support for child rearing without having any stresses. Health care provider consider this issues and to build a healthy parent-child relationship by helping parents.