• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.273-281
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• 2015

In this paper, the performance of alkali-activated slag cement (AASC) is assessed in terms of compressive strength and drying shrinkage, using three different types of silica sand and river sand. The sand type has an important influence on the properties of AASC mortar. Three silica sands (SS1, SS2 and SS3) and river sand (RS) were considered. Three series of blended sands have been tested. A first series (S1) with RS and SS1, a second series (S2) with RS and SS2 and third series (S3) with RS and SS3 with a different blended ratios. The result shows a very significant influence of the blended sand on the AASC mortar properties. The compressive strength and drying shrinkage related with the particle sizes and blended ratios of sands are investigated considering blended sand properties like fineness modulus (FM) and relative specific surface. The type and blended ratio of sand seems to have very significant and important consequences for the mix design of the AASC mortar.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.2
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• pp.105-118
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• 2008

The newly developed analysis method for nanoindentation load-displacement curves are focused on not only obtaining elastic modulus and hardness values but also other mechanical properties, such as yield strength and strain hardening properties. Dao et al. developed a forward and reverse algorithm to extract the elasto-plastic properties of materials from the load-displacement curves obtained in nanoindentation test. These algorithms were only applicable for engineering metals (Poisson#s ratio 0.3) using the equivalent conical indenter of the Berkovich. However, the applicable metals are substantially limited because range of used in the finite element analysis is narrow. This study is designed to expand range of the applicable metals in the reverse algorithms established by Dao et al. and to improve the accuracy of that for extracting the elasto-plastic properties of materials. In this study, a representative strain was assumed to vary according to specific range of $E^*/{\sigma}_r$ and was defined as function of $E^*/{\sigma}_r$. Also, an initial unloading slope in reverse algorithms improved in this study was not considered as independent parameters of the load-displacement curves. The mechanical properties of materials for finite element analysis were modeled with the elastic modulus, E, the yield strength, ${\sigma}_y$, and the strain hardening exponents, n. We showed that the representative strain (0.033) suggested by Dao et al. was no longer applicable above the $E^*/{\sigma}_r$ of 400 and depended on values of $E^*/{\sigma}_r$. From these results, we constructed the dimensionless functions, in where the initial unloading slope was not included, for engineering metals up to $E^*/{\sigma}_r$ of 1500. These functions allow us to determine the mechanical properties with greater accuracy than Dao#s study.

• Imaging Science in Dentistry
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• v.38 no.2
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• pp.81-87
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• 2008

Purpose: To investigate the relationship between 3D bone architectural parameters and direction-related elastic moduli of cancellous bone of mandibular condyle. Materials and Methods: Two micro-pigs (Micro-$pig^R$, PWG Genetics Korea) were used. Each pig was about 12 months old and weighing around 44 kg. 31 cylindrical bone specimen were obtained from cancellous bone of condyles for 3D analysis and measured by micro-computed tomography. Six parameters were trabecular thickness (Tb. Th), bone specific surface (BS/BV), percent bone volume (BV/TV), structure model index (SMI), degree of anisotropy (DA) and 3-dimensional fractal dimension (3DFD). Elastic moduli of three orthogonal directions (superior-inferior (SI), medial-lateral (ML), andterior-posterior (AP) direction) were calculated through finite element analysis. Results: Elastic modulus of superior-inferior direction was higher than those of other directions. Elastic moduli of 3 orthogonal directions showed different correlation with 3D architectural parameters. Elastic moduli of SI and ML directions showed significant strong to moderate correlation with BV/TV, SMI and 3DFD. Conclusion: Elastic modulus of cancellous bone of pig mandibular condyle was highest in the SI direction and it was supposed that the change into plate-like structure of trabeculae was mainly affected by increase of trabeculae of SI and ML directions.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.96-100
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• 2009

The properties of recycled fine aggregates which had different source concrete were examined by mortar test. With higher strength of source concrete, specific gravity of recycled fine aggregate was higher and absorption of recycled fine aggregate was lower due to reduction of the volume of adhered cement paste. The compressive strength and flexible strength of mortar with recycled fine aggregate were affected by the interface boundary of new mortar and the strength of adhered mortar. Strength development of mortar with recycled fine aggregate reduced because recycled fine aggregate become a porous material with the smaller strength of source concrete. The drying shrinkage of mortar was about$800{\sim}2000{\mu}m/m$. It was about 1.5 times than that of mortar with natural fine aggregate. Relative dynamic modulus of elasticity was a similar level with that of mortar with natural fine aggregate.

• Korean Journal of Food Science and Technology
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• v.35 no.6
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• pp.1022-1027
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• 2003

The effect of ${\beta}$-glucan, prepared from waxy barley, on the dynamic viscoelasticity of nonwaxy and waxy barley starch during gelatinization and gelation was studied. Although no significant effect was observed on waxy starch, there were drastic changes in the dynamic viscoelasticity of nonwaxy starch. The gelatinization onset temperature of nonwaxy starch shifted to a higher temperature and showed a drastic increase in storage modulus and loss modulus at the range of $80{\sim}90^{\circ}C$. During the gelation of nonwaxy starch, ${\beta}$-glucan increased the rate of gel formation and weakened the network of starch and amylose by prohibiting their association. Therefore, we proved that there was no specific interaction between amylose and ${\beta}$-glucan. The addition of ${\beta}$-glucan to waxy starch seemed to have no effect of waxy starch.

• Steel and Composite Structures
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• v.29 no.4
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• pp.527-544
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• 2018

The paper presents the study on a change in modal parameters and structural stiffness of cable-stayed Fiberline Bridge made entirely of Glass Fiber Reinforced Polymer (GFRP) composite used for 20 years in the fjord area of Kolding, Denmark. Due to this specific location the bridge structure was subjected to natural aging in harsh environmental conditions. The flexural properties of the pultruded GFRP profiles acquired from the analyzed footbridge in 1997 and 2012 were determined through three-point bending tests. It was found that the Young's modulus increased by approximately 9%. Moreover, the influence of the temperature on the storage and loss modulus of GFRP material acquired from the Fiberline Bridge was studied by the dynamic mechanical analysis. The good thermal stability in potential real temperatures was found. The natural vibration frequencies and mode shapes of the bridge for its original state were evaluated through the application of the Finite Element (FE) method. The initial FE model was created using the real geometrical and material data obtained from both the design data and flexural test results performed in 1997 for the intact composite GFRP material. Full scale experimental investigations of the free-decay response under human jumping for the experimental state were carried out applying accelerometers. Seven natural frequencies, corresponding mode shapes and damping ratios were identified. The numerical and experimental results were compared. Based on the difference in the fundamental natural frequency it was again confirmed that the structural stiffness of the bridge increased by about 9% after 20 years of service life. Data collected from this study were used to validate the assumed FE model. It can be concluded that the updated FE model accurately reproduces the dynamic behavior of the bridge and can be used as a proper baseline model for the long-term monitoring to evaluate the overall structural response under service loads. The obtained results provided a relevant data for the structural health monitoring of all-GFRP bridge.

• Journal of Adhesion and Interface
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• v.8 no.4
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• pp.14-22
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• 2007

In the present study, the effect of milled glass powder and liquid-type nitrile rubber (NBR) on the thermal stability of phenolic resin and the dynamic mechanical properties of glass braid/phenolic composites has been investigated by means of thermogravimetric analysis and dynamical mechanical analysis. It was found that both milled glass power and NBR filled in the waterborne phenolic resin significantly influenced the thermal stability of phenolic resins and the storage modulus and tan delta of the composites. The presence of glass powder increased the thermal stability of the phenolic resin, whereas the presence of NBR resulted in the weight loss in the specific temperature range. The thermal stability of the phenolic resins without and with the fillers was dependent not only on the cure temperature but also on the cure time. The variation of the storage modulus and tan ${\delta}$ of strip-type glass braid/phenolic composites was also influenced with the introduction of glass powder and NBR to the phenolic matrix as well as by the cure conditions given.

• Journal of Forest and Environmental Science
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• v.39 no.1
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• pp.27-39
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• 2023

Twenty-five Eucalyptus clones (14 E. camaldulensis - EC and 11 interspecific eucalypt hybrid clones - EH) grown in three contrasting sites were evaluated for the growth and few wood traits at 4 years of age. The stability, genotype-site interaction and suitability of these clones for pulp and solid wood industry sectors were studied. Growth of eucalypt clones was significantly higher at site 1 with higher rainfall, but wood density did not differ significantly from lower rainfall sites. Kraft pulp yield (KPY) decreased from sites 1 to 3 based on moisture availability, but not between two groups of clones. Volumetric shrinkage (VS) was significantly higher in EC clones at site 3 with lowest rainfall, but there was no specific trend at other two sites with maximum (site 1) and intermediate (site 2) rainfall. The mechanical traits modulus of rupture (MOR) and modulus of elasticity (MOE) were at par in sites 1 and 2, but significantly lower at the driest site 3. The growth rate had a significant positive correlation with KPY, MOR and MOE and a negative correlation with VS, but no significant impact on wood density in both groups of clones. Genotype×environment interaction (G×E) was evident in most traits due to the difference in response of clones to moisture availability. Since wood density was negatively correlated to KPY, it has to be kept at an optimum level for the profitability of pulp industry. There was no significant difference between EC and EH clones for most traits except VS at site 3. Stability of clones varied across sites in different traits, and hence clones may be selected for deployment at each site by screening for growth, followed by wood density, considering the relationship of growth and density with other traits required by pulp and solid wood industry sectors.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.487-501
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• 2023

Nanoparticles have lower size and larger specific surface area, good stability and less toxic and side effects. In recent years, with the development of nanotechnology, its application range has become wider and wider, especially in the field of biomedicine, which has received more and more attention. Bone defect repair materials with high strength, high elasticity and high tissue affinity can be prepared by nanotechnology. The purpose of this paper was to study how to analyze and study the composite materials for sports bone injury based on multifunctional nanomaterials, and described the electrospinning method. In this paper, nano-sized zirconia (ZrO₂) filled micro-sized hydroxyapatite (HAP) composites were prepared according to the mechanical properties of bone substitute materials in the process of human rehabilitation. Through material tensile and compression experiments, the performance parameters of ZrO₂/HAP composites with different mass fraction ratios were analyzed, the influence of filling ZrO₂ particles on the mechanical properties of HAP matrix materials was clarified, and the effect of ZrO₂ mass fraction on the mechanical properties of matrix materials was analyzed. From the analysis of the compressive elastic modulus, when the mass fraction of ZrO₂ was 15%, the compressive elastic modulus of the material was 1222 MPa, and when 45% was 1672 MPa. From the analysis of compression ratio stiffness, when the mass fraction of ZrO₂ was 15%, the compression ratio stiffness was 658.07 MPa·cm³/g, and when it was 45%, the compression ratio stiffness is 943.51MPa·cm³/g. It can be seen that by increasing the mass fraction of ZrO₂, the stiffness of the composite material can be effectively increased, and the ability of the material to resist deformation would be increased. Typically, the more stressed the bone substitute material, the greater the stiffness of the compression ratio. Different mass fractions of ZrO₂/HAP filling materials can be selected to meet the mechanical performance requirements of sports bone injury, and it can also provide a reference for the selection of bone substitute materials for different patients.

• Journal of Adhesion and Interface
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• v.17 no.4
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• pp.131-135
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• 2016

We investigated the specific gravity and mechanical property changes of solid-state extruded polypropylene (PP)/talc composites before and after orientation. The specific gravity of the composites increases with increasing the filler contents. The specific gravity of the oriented specimen containing filler in PP matrix is found to be much smaller than that of pre-specimen due to the formation of more micro-voids. It was found that the tensile properties of the composites are increased up to the talc content of 10 wt%, but after the contents exceeding 10 wt%, the tensile properties are decreased. For oriented specimens, the tensile strength of the composites showed monotonously decrease with increasing talc contents. When the contents of talc is 10 wt%, the theoretical values according to Halpin-Tsai equation are close to the experimental values but over 20 wt% of talc contents, the deviation of the experimental values from the theoretical prediction becomes higher. The maximum flexural strength and modulus were observed for PP/talc composites when the talc contents was 10 wt% for both pre-specimen and oriented specimen.