• Journal of The Korean Society of Agricultural Engineers
• /
• v.61 no.2
• /
• pp.41-50
• /
• 2019

Stiffness characteristic of subgrade is one of the most important aspects for the design and evaluation of pavement and railway. However, adequate field testing methods for evaluating the stiffness characteristics of the subgrade have not been developed yet. In this study, an in-situ dynamic stiffness analyzer (IDSA) is developed to evaluate the characteristics of subgrade stiffness along the depth, and its performance is evaluated in elastic materials and a compacted soil. The IDSA consists of a falling hammer system, a connecting rod, and a tip module. Four strain gauges and an accelerometer are installed at the tip of the rod to analyze the dynamic response of the tip generated by the drop of hammer. Based on the Boussinesq's method, the stiffness and Young's modulus of the specimens can be calculated. The performance of IDSA was tested on three elastic materials with different hardness and a compacted soil. For the repeatability of test performance, the dynamic signals for force and displacement of the tip are averaged from the hammer impact tests performed five times at the same drop height. The experimental results show that the peak force, peak displacement, and the duration depend on the hardness of the elastic materials. After calculating the stiffness and elastic modulus, it is revealed that as the drop height of hammer increases, the stiffness and elastic moduli of MC nylon and the compacted soil rapidly increase, while those of urethanes less increase.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.04a
• /
• pp.842-848
• /
• 2013

Developments of Solid-State Gyroscopy during last decades are impressive and were based on thin-walled shell resonators like HRG or CRG made from fused quartz or leuko-sapphire. However, a number of design choices for inertial-grade gyroscopes, which can be used for high-g applications and for mass- or middle-scale production, is still very limited. So, considerations of fundamental physical effects in solids that can be used for development of a miniature, completely solid-state, and lower-cost sensor look urgent. There is a variety of different types of bulk acoustic (elastic) waves (BAW) in anisotropic solids. Shear waves with different variants of their polarization have to be studied especially carefully, because shear sounds in glasses and crystals are sensitive to a turn of the solid as a whole, and, so, they can be used for development of gyroscopic sensors. For an isotropic medium (for a glass or a fine polycrystalline body), classic Lame's theorem (so-called, a general solution of Elasticity Theory or Green-Lame's representation) has been modified for enough general case: an elastic medium rotated about an arbitrary set of axes. Travelling, standing, and mixed shear waves propagating in an infinite isotopic medium (or between a pair of parallel reflecting surfaces) have been considered too. An analogy with classic Foucault's pendulum has been underlined for the effect of a turn of a polarizational plane (i.e., an integration effect for an input angular rate) due to a medium's turn about the axis of the wave propagation. These cases demonstrate a whole-angle regime of gyroscopic operation. Single-crystals are anisotropic media, and, therefore, to reflect influence of the crystal's rotation, classic Christoffel-Green's tensors have been modified. Cases of acoustic axes corresponding to equal velocities for a pair of the pure-transverse (shear) waves have of an evident applied interest. For such a special direction in a crystal, different polarizations of waves are possible, and the gyroscopic effect of "polarizational precession" can be observed like for a glass. Naturally, formation of a wave pattern in a massive elastic body is much more complex due to reflections from its boundaries. Some of these complexities can be eliminated. However, a non-homogeneity has a fundamental nature for any amorphous medium due to its thermodynamically-unstable micro-structure, having fluctuations of the rapidly-frozen liquid. For single-crystalline structures, blockness (walls of dislocations) plays a similar role. Physical nature and kinematic particularities of several typical "drifts" in polarizational BAW gyros (P-BAW) have been considered briefly too. They include irregular precessions ("polarizational beats") due to: non-homogeneity of mass density and elastic moduli, dissymmetry of intrinsic losses, and an angular mismatch between propagation and acoustic axes.

• Food Engineering Progress
• /
• v.21 no.2
• /
• pp.167-173
• /
• 2017

Purple-fleshed potato powder (PFPP) was investigated to determine optimal mixing ratio with milk powder and dextrin to produce a ready-to-eat mashed potato powder. The rheological characteristics, color, and anthocyanin contents were studied at a different concentration of ingredients. The power-law model was applied to explain the mechanical spectra of mashed potatoes which represented the change in structure induced by different mixing ratios. Mixture design was used to obtain the experimental points used to establish the empirical models to describe the effects of each ingredient on the characteristic of the mashed potato. The results of mechanical spectra showed that both storage and loss moduli (G' and G'') were significantly influenced by PFPP and milk powder concentration. The power law parameters n' and n'' showed higher values for the mashed potato with a lower concentration of PFPP and a higher concentration of milk powder, which showed that the gel networks involved in the mashed potato were weaker. The optimum mixing ratio with the highest redness and anthocyanin content, while maintaining the rheological properties similar to the commercial mashed potato, was determined as PFPP:milk powder:dextrin = 90.49:4.86:4.65 (w/w). The proportions of PFPP and milk powder in the formulation significantly changed the characteristics of mashed potato, whereas no significant effect of dextrin was observed in this formulation.

• The Korean Journal of Physiology
• /
• v.7 no.2
• /
• pp.49-58
• /
• 1973

The distensibility of the major arteries has been investigated extensively, but the value expressed as Young Modulus varies widely by the different schools of the investigators, the major reason undoubtedly being the difficulties encountered in the measurement. In the present study, an attempt was made to elucidate the distensibility of the external carotid artery of the rabbit, which was placed in saline immediately after removing from the apparently healthy, normal rabbit without anesthesia. The circular section strip and longitudinal section strip were made from the whole artery, and Young Modulus of the whole artery, circular section and longitudinal section strips was calculated from the length-tension curve of each sample. Also, the similar samples of the artery seperately obtained were placed in ATP solution in the concentration of 0.15 mM and 0.30 mM, and Young Modulus was similary calculated. Experiments were performed at 15,45 and 75 min after the artery was removed from the rabbit, and the results thus obtained are summarized as follows. 1) Young Modulus of the whole external carotid artery of the rabbit in saline was $4.74{\times}10^7dyne/cm^2$ at 15 min, but lower values were obtained at 45 and 75 min, Young Modulus being $4.62{\times}10^7dyne/cm^2\;and\;4.13{\times}10^7dyne/cm^2$, respectively. When the arterial samples were placed in ATP solutions, Young Modulus did not change much throughout the experiment, and lower Young Moduli were obtained in 0.30 mM ATP solution than in 0. 15 mM ATP solution. 2) Young Modulus Of the Circular Section Strip in Saline was $4.11{\times}10^7dyne/Cm^2,\;3.75{\times}10^7dyne/cm^2\;and\;3.90{\times}10^7dyne/cm^2,$ respectively, at 15, 45 and 75 min, the value at 15 min being the highest. However, when the strip was placed in ATP solutions, no appreciable change was observed throughout the experiment, and Young Moduli were lower in 0.30 mM ATP solution than in 0.15 mM ATP solution. 3) Young Modulus of the longitudinal section strip in saline was $2.12{\times}10^7dyne/cm^2,\;2.48{\times}10^7dyne/cm^2\;and\;2.46{\times}10^7dyne/cm^2$, respectively, at 15, 45 and 75 min, Young Modulus being slightly elevated in the latter part of the experiment. A similar tendency was observed when the strip was placed in ATP solutions.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.32 no.1
• /
• pp.24-31
• /
• 2016

Purpose: Many studies have shown that airborne-particle abrasion of fiber post can improve the bonding strength to resin cement. But, airborne-particle abrasion may influence the property of fiber post. The purpose of this study is to evaluate the influence of airborne-particle abrasion on flexural strength of fiber post. Materials and Methods: Two fiber-reinforced posts; DT Light Post Size 2 (1.8 mm diameter, Bisco Inc) and RelyX Fiber Post Size 3 (1.9 mm diameter, 3M ESPE); were used in this study. Each group was divided into 3 subgroups according to different surface treatments; without pretreatment: $50{\mu}m$ aluminum oxide (Cobra$^{(R)}$, Renfert): and $30{\mu}m$ aluminum oxide modified with silica (Rocatec Soft$^{(R)}$, 3M ESPE). After airborne-particle abrasion procedure, three-point bending test was done to determine the flexural strength and flexural modulus. The diameter of each posts was measured to an accuracy of 0.01 mm using a digital micrometer. There was no diameter change before and after airborneparticle abrasion. The mean flexural moduli and flexural strengths calculated using the appropriate equations. The results were statistically analyzed using One-way ANOVA and Scheffe's post-hoc test at 95% confidencial level. Results: There was no significant difference on flexural strength between groups. Conclusion: In the limitation of this study, flexural strength and flexural modulus of fiber post are not affected by airborne-particle abrasion.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.1
• /
• pp.141-152
• /
• 2015

The objective of this study is to estimate shear wave velocity of rockfill materials by making practical use of the micro-earthquake records which are ordinarily obtained at a domestic rockfill dam and to verify its applicability. Micro-earthquake records were obtained at the site of Heongseong dam and Soyanggang dam, which are the existing multi-purpose dams in Korea. In the previous study, the fundamental periods of each dam were already evaluated by analyzing the response spectrum of the observed records. In this study, numerical analyses varying shear moduli of rockfill zone were carried out using the acceleration histories measured at the abutment as input ground motions. From comparison between the fundamental periods calculated by numerical analyses and measured records, the shear wave velocities with depth were estimated. It is found that the effect of different earthquake events on shear wave velocity estimation for the target dam materials is negligible and the shear wave velocity can be consistently evaluated. Furthermore, comparing the shear wave velocity with the previous researchers' empirical relationships and field test results, applicability of suggested method is verified. Therefore, in case that it is impossible to conduct field tests and estimation is preliminary, the suggested method can be practically used.

• Journal of Adhesion and Interface
• /
• v.11 no.4
• /
• pp.155-161
• /
• 2010

A series of ethylene vinyl acetate (EVA) based hot melt adhesives containing different types and compositions of tackifier resins were prepared to investigate their rheological behavior and T-peel adhesion strength on polyurethane (PU) elastomeric sheets. C5 aliphatic hydrocarbon resin (C5 resin), C9 aromatic hydrocarbon resin (C9 resin), hydrogenated dicyclopentadiene resin ($H_2$-DCPD resin), and dicyclopentadiene and acrylic monomer copolymer resin (DCPD-acrylic resin) were used as the tackifiers for the hot melt adhesives. To determine the polarity of the tackifiers, their oxygen contents were analyzed, and the DCPDacrylic resin was found to contain an oxygen content higher than the other tackifiers. Only the DCPD-acrylic resin showed complete miscibility with EVA and the homogeneous phase of the hot melt adhesive blends at all compositions. The T-peel adhesion strength between the hot melt adhesives and polyurethane elastomeric sheets was mainly affected by the polarity of the tackifier resins in the hot melt adhesives, rather than by the storage moduli, G', of the hot melt adhesives themselves.

• Journal of the Microelectronics and Packaging Society
• /
• v.22 no.4
• /
• pp.91-98
• /
• 2015

In order to apply to stretchable electronics packaging, locally stiffness-variant stretchable substrates consisting of island structure were fabricated by combining two polydimethylsiloxane elastomers of different stiffnesses and their elastic moduli were characterized as a function of the width of the high-stiffness island. The low-stiffness substrate matrix and the embedded high-stiffness island of the stretchable substrate were formed by using Dragon Skin 10 of the elastic modulus of 0.09 MPa and Sylgard 184 of the elastic modulus of 2.15 MPa, respectively. A stretchable substrate was fabricated to be a configuration of 6.5-cm length, 0.4-cm thickness, and 2.5-cm width, in which a high-stiffness Sylgard 184 island, of 4-cm length, 0.2-cm thickness, and 0.5~1.5-cm width, was embedded. The elastic modulus of a stretchable substrate was increased from 0.09 MPa to 0.16 MPa by incorporating the Sylgard 184 island of 0.5-cm width to Dragon Skin 10 substrate matrix. The elastic modulus was further improved to 0.18 MPa and 0.2 MPa with increasing the Sylgard 184 island width to 1.0 cm and 1.5 cm, which were in good agreement with values estimated by combining the Voigt structure of isostrain and the Reuss structure of isostress.

• Korean Journal of Agricultural Science
• /
• v.12 no.2
• /
• pp.309-323
• /
• 1985

The Paper describes the observed behaviour in the undrained triaxial condition of marine clays remoulded at various different levels of factors, to find out the effects of restricted factors on the stress-strain characteristics. The conventional triaxial compression tests $({\sigma}1>{\sigma}2={\sigma}3)$ were carried out on the 50mm in diameter and 100mm long cylindrical specimens of Gun-san bay mud under controlled various moisture content, density, axial strain rate and passing on No. 200 sieve. Significant conclusions from this study are; 1. The compressible deviator stress at failure of pure marine clay was observed to increase with the decrease of moulding moisture content. 2. The compressible deviator stress at failure increased with the increasing of moulding dry density. 3. The interaction between moisture content and density on the stress-strain characteristics of marine clay was remarkedly significant, as the result of factorial experimental method. 4. The effect of axial strain rate on stress-strain behaviour was unsignificant in marine clay and but the secant moduli could be pronounced on a slight decreasing with increase of the strain rate. 5. With the increasing of the passing on No. 200 sieve, the deviator stress increased regularly. 6. The multiple regression equation could be modeled for the prediction of stress or strain and the comparison with experimental results relatively proved the accuracy.

• Journal of the Korea Concrete Institute
• /
• v.20 no.3
• /
• pp.405-412
• /
• 2008

Six alkali-activated (AA) concrete mixes were tested to explore the significance and limitations of developing an environmental friendly concrete. Ground granulated blast-furnace slag and powder typed sodium silicate were selected as source material and an alkaline activator, respectively. The main parameter investigated was the replacement level of lightweight fine aggregate to the natural sand. Workability and mechanical properties of lightweight AA concrete were measured: the variation of slump with time, the rate of compressive strength development, the splitting tensile strength, the moduli of rupture and elasticity, the stress-strain relationship, the bond resistance and shrinkage strain. Test results showed that the compressive strength of lightweight AA concrete sharply decreased when the replacement level of lightweight fine aggregate exceeded 30%. In particular, the increase in the discontinuous grading of lightweight aggregate resulted in the deterioration of the mechanical properties of concrete tested. The measured properties of lightweight AA concrete were also compared, wherever possible, with the results obtained from the design equations specified in ACI 318-05 or EC 2, depending on the relevance, and the results predicted from the empirical equations proposed by Slate et al. for lightweight ordinary Portland cement concrete. The stress-strain curves of different concrete were compared with predictions obtained from the mathematical model proposed by Tasnimi. The measured mechanical properties of lightweight AA concrete generally showed little agreement with the predictions obtained from these equations.