• Journal of the Korean Wood Science and Technology
• /
• v.44 no.1
• /
• pp.75-84
• /
• 2016

Thermal performance of wooden houses used by building materials effectively contributing to building energy saving has been improved. However, the performance was decreased to the condensation and mould growth from exterior wall because the moisture control was difficult to high insulation and airtightness. Therefore, the hygrothermal performance of exterior wall, that selected 5 types of wooden houses, evaluated using the hygrothermal simulation program: heat and moisture behavior, condensation and mould growth risk. Wooden houses were selected Rural houses standard plans '10 and '14, $2^{{\prime}{\prime}}{\times}6^{{\prime}{\prime}}$ type, EIFS and wood-based passive house. And the wall A, B, C, D and E were determined by layer component of each wall. The U-value of exterior wall are 0.171, 0.172, 0.221, 0.150, $0.079W/m^2K$. The OSB absolute water content of the wall A and C was exceeds the reference value of 20%, and it was confirmed that condensation occur at insulation material inner surface through the condensation evaluation in the winter. The wall D and E showed excellent results with condensation and water content evaluation compared to others. However, mould growth risk assessment in all five types of wall had have risk. We were determined that hygrothermal performance difference of exterior wall occur the difference in the layer structure rather than in thermal performance.

• Journal of Conservation Science
• /
• v.37 no.5
• /
• pp.464-476
• /
• 2021

Various materials, depending on the personality of the artist, are required for contemporary art. Thus, it is necessary to decipher the expressive intentions of the artist and characteristics of the materials required for the conservation of such art. The purpose of this study is to analyze the causes underlying the deterioration of sculptures made from soap and to determine the ideal hygrothermal environment required to stably exhibit and store these artworks. Furthermore, we aim to maintain the long-term structures of the artworks in accordance with the changing expressions and intentions of the artist. Our analysis confirmed that the extracts of the soap sculptures were composed of glycerin and that the sculptures were sensitive to humidity. Moreover, we determined that a relative humidity (RH.) of approximately 60~65% made for an appropriate hygrothermal environment required to preserve the sculptures. We also preserved each work in various ways by applying appropriate preservation treatment, and found that the optimum preservation environment for soap sculptures was a temperature of 20±2℃ and a RH. of 60±5%.

• Structural Engineering and Mechanics
• /
• v.73 no.2
• /
• pp.191-207
• /
• 2020

This study aims at investigating the size-dependent free vibration of porous nanoplates when exposed to hygrothermal environment and rested on Kerr foundation. Based on the modified power-law model, material properties of porous functionally graded (FG) nanoplates are supposed to change continuously along the thickness direction. The generalized nonlocal strain gradient elasticity theory incorporating three scale factors (i.e. lower- and higher-order nonlocal parameters, strain gradient length scale parameter), is employed to expand the assumption of second shear deformation theory (SSDT) for considering the small size effect on plates. The governing equations are obtained based on Hamilton's principle and then the equations are solved using an analytical method. The elastic Kerr foundation, as a highly effected foundation type, is adopted to capture the foundation effects. Three different patterns of porosity (namely, even, uneven and logarithmic-uneven porosities) are also considered to fill some gaps of porosity impact. A comparative study is given by using various structural models to show the effect of material composition, porosity distribution, temperature and moisture differences, size dependency and elastic Kerr foundation on the size-dependent free vibration of porous nanoplates. Results show a significant change in higher-order frequencies due to small scale parameters, which could be due to the size effect mechanisms. Furthermore, Porosities inside of the material properties often present a stiffness softening effect on the vibration frequency of FG nanoplates.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.23 no.3
• /
• pp.243-249
• /
• 2014

Currently, CFRP composites are rapidly replacing steel plates, as they are lighter, stronger, and more elastic; however, they are poorly suited to hygrothermal and impact-collapsed environments because moisture can alter their molecule arrangement and chemical properties. In this study, environments are experimentally simulated in order to investigate changes in the moisture absorption inside a CFRP composite and to determine its weakest point. Moreover, changes in the moisture absorption ratio at temperatures of $60^{\circ}C$ and $80^{\circ}C$ are studied and compared in order to understand how changes in temperature affect moisture absorption inside CFRP composites. Results show that moisture absorption leads to a strength reduction of around 50%. In addition, the moisture absorption rate inside CFRP composites is shown to change rapidly with increasing temperature. Accordingly, it showed that the change in matrix also has a weak point.

• Structural Engineering and Mechanics
• /
• v.67 no.3
• /
• pp.219-232
• /
• 2018

This paper deals with the static bending of various types of FGM sandwich plates resting on two-parameter elastic foundations in hygrothermal environment. The elastic foundation is modeled as Pasternak's type, which can be either isotropic or orthotropic and as a special case, it converges to Winkler's foundation if the shear layer is neglected. The present FGM sandwich plate is assumed to be made of a fully ceramic core layer sandwiched by metal/ceramic FGM coats. The governing equations are derived from principle of virtual displacements based on a shear and normal deformations plate theory. The present theory takes into account both shear and normal strains effects, thus it predicts results more accurate than the shear deformation plate theories. The results obtained by the shear and normal deformation theory are compared with those available in the literature and also with those obtained by other shear deformation theories. It is concluded that the present results are slightly deviated from other results because the normal deformation effect is taken into account. Numerical results are presented to show the effects of the different parameters, such as side-to-thickness ratio, foundation parameters, aspect ratio, temperature, moisture, power law index and core thickness on the stresses and displacements of the FG sandwich plates.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.6
• /
• pp.782-789
• /
• 2010

It is important to satisfy the requirements and standards for the protections of passengers in a car accident. There are lots of studies on the crushing energy absorption of a structure member in automobiles. In this paper, we have studied to investigate collapse characteristics and moisture absorption movements of CFRP( carbon fiber reinforced plastics) structure members when CFRP laminates are under the hygrothermal environment. In particular, the absorbed energy, mean collapse load and deformation mode were analyzed for CFRP members which absorbed most of the collision energy. Also, variation of stacking angle is important to increase the energy absorption capability. The purpose of this study is to evaluate the strength reduction and moisture absorption behavior of CFRP hat shaped member. Therefore we have made a impact collapse experiment to research into the difference of absorbed energy and deformation mode between moisture absorbed specimen and non-moisture absorbed. As a result, the effect of moisture absorption and impact loads of approximately 50% reduction in strength are shown.

• Smart Structures and Systems
• /
• v.23 no.3
• /
• pp.215-225
• /
• 2019

In the present paper, the nonlocal strain gradient refined model is used to study the thermal stability of sandwich nanoplates integrated with piezoelectric layers for the first time. The influence of Kerr elastic foundation is also studied. The present model incorporates two small-scale coefficients to examine the size-dependent thermal stability response. Elastic properties of nanoplate made of functionally graded materials (FGMs) are supposed to vary through the thickness direction and are estimated employing a modified power-law rule in which the porosity with even type of distribution is approximated. The governing differential equations of embedded sandwich piezoelectric porous nanoplates under hygrothermal loading are derived through Hamilton's principle where the Galerkin method is applied to solve the stability problem of the nanoplates with simply-supported edges. It is indicated that the thermal stability characteristics of the porous nanoplates are obviously influenced by the porosity volume fraction and material variation, nonlocal parameter, strain gradient parameter, geometry of the nanoplate, external voltage, temperature and humidity variations, and elastic foundation parameters.

• Smart Structures and Systems
• /
• v.24 no.2
• /
• pp.267-292
• /
• 2019

The present article addresses the coupled free vibration problem of skew magneto-electro-elastic plates (SMEE) considering the temperature-moisture dependent material properties. The plate kinematics follows Reddy's higher order shear deformation theory. With the aid of finite element methods, the governing equations of motion are derived considering the Hamilton's principle and solved by adopting condensation technique. The influence of different temperature and moisture dependent empirical constants on the frequency response of SMEE plate has been assessed. In addition, the natural frequencies corresponding to various fields are evaluated and the effect of empirical constants on these coupled frequencies is determined. A detailed parametric study has been carried out to assess the individual effects of temperature and moisture dependent empirical constants along with their combined effect, aspect ratio, length-to-width ratio, stacking sequence and boundary conditions. The results reveal that the external environment as well as the geometrical skewness has a significant influence on the stiffness of the SMEE plates.

• Advances in nano research
• /
• v.6 no.4
• /
• pp.299-321
• /
• 2018

A layerwise shear deformation theory is applied in this paper for buckling analysis of piezoelectric truncated conical shell. The core is a multiphase nanocomposite reinforced by carbon nanotubes (CNTs) and carbon fibers. The top and bottom face sheets are piezoelectric subjected to 3D electric field and external voltage. The Halpin-Tsai model is used for obtaining the effective moisture and temperature dependent material properties of the core. The proposed layerwise theory is based on Mindlin's first-order shear deformation theory in each layer and results for a laminated truncated conical shell with three layers considering the continuity boundary condition. Applying energy method, the coupled motion equations are derived and analyzed using differential quadrature method (DQM) for different boundary conditions. The influences of some parameters such as boundary conditions, CNTs weight percent, cone semi vertex angle, geometrical parameters, moisture and temperature changes and external voltage are investigated on the buckling load of the smart structure. The results show that enhancing the CNTs weight percent, the buckling load increases. Furthermore, increasing the moisture and temperature changes decreases the buckling load.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.2
• /
• pp.119-128
• /
• 2010

The hygrothermal effect on the strength of composite single-lap bonded joints were investigated. The specimens were manufactured in four different manufacturing methods and tested in three different environmental conditions. An interesting result is that the strengths of the joints in the elevated temperature and wet (ETW) conditions were found to be 11 ~ 23% higher than those in the room temperature and dry (RTD) environment. In contrast, the strengths of the joints in the cold temperature and dry (CTD) condition decrease by 8 ~ 21% compared to those in the RTD environment except for cobonded joint. The difference in the strength by testing environments is mainly attributed to the change of the material properties of adhesive by temperature and moisture.