• Proceedings of the Korean Geotechical Society Conference
• /
• 1997.10a
• /
• pp.65-72
• /
• 1997

• Journal of Biosystems Engineering
• /
• v.20 no.2
• /
• pp.133-140
• /
• 1995

The model of Poisson's ratio of the fruits was developed on the basis that the cylindrical fruits specimen became the barrel shape when it was being compressed. The model of the corrected creep compliance of the fruits was developed under considering the developed model of Poisson's ratio. Both of the Poisson's ratio and the corrected creep compliance of the samples showed the nonlinear viscoelastic behavior. Those models were a similar form, but their coefficients of the model were different, and these behaviors of the samples were well described by the nonlinear model as a function of the initial stress and time. Effects of storage condition and period on the Poisson's ratio of the samples were investigated, and comparisons between the corrected and the uncorrected creep compliance of the samples were made.

• Korean Journal of Food Science and Technology
• /
• v.24 no.2
• /
• pp.165-170
• /
• 1992

The creep behavior of gels made with $30{\sim}45%$ gelatinized rice starch was measured over a wide range of temperature. Compressive creep curves of rice starch gels conformed to a six element mechanical model consisting of one Hookean, two Voigt and one Newtonian component. The creep compliance of gels decreased with increasing starch concentrations. Among viscoelastic constants of the mechanical model, elastic modulus was mainly influenced by the change of starch concentrations. The concentration-invariant compliance curve was obtained by reduction to 38% using reduction parameter $a_{c}$. The creep compliance curves of 45% starch gels increased with temperature, which indicated that rice starch gels became softer and less rigid with increasing temperature. When the compliance at $20^{\circ}C$ was set as a reference curve, creep compliance data for 45% gels at various temperature could be superimposed as a continuous smooth curve. The apparent activation energies of 45% rice starch gels calculated by the modified WLF equation were not intrinsic, but decreased as temperature increased.

• Journal of Biosystems Engineering
• /
• v.15 no.3
• /
• pp.219-229
• /
• 1990

The compression creep behavior of grains when loaded depends not only on load but also on duration of load application. The most common methods of studying the load-time characteristics of agricultural products is by employing rheological models such as Burger's model. However it is sometimes not sufficient to describe the viscoelastic behavior of grains to be Burger's model. For this reason, this study was conducted to develop the rheological model which represented the creep compliance response of the rough rice kernel and was a function of initial stress applied and time. The effects of the initial stress applied and the moisture content on the compression creep behavior of the rough rice kernel were analyzed. The results were obtained from the study as follows: 1. Since the viscoelastic behavior of the rough rice kernel was nonlinear, the transient and steady state creep compliance was satisfactorily modelled as follows: $$J({\sigma},t)=A{\sigma}^B[C+Dt-exp(-Ft)]$$ But, for the every stress applied, the compression creep behavior of the samples tested can be well described by Burger's model respectively. 2. The creep compliance, the instantaneous elastic strain, the retarded elastic strain and the viscous strain of the sample tested generally increased in magnitude with increasing the applied initial stress and the moisture content used in the tests. At low moisture content, the creep compliance for the Japonica-type rough rice kernel Was a little higher than those for Indica-type and at high moisture content, vice versa at high moisture content. 3. The retardation times of the samples had not an uniform tendency by the initial stress and the moisture content. The retardation times ranged from 0.66 to 6.76 seconds, and the creep progressed from transient to steady state at a relatively high rate. 4. The less viscous strain than the instantaneous elastic strain for the samples tested indicated that rough rice kernel behaved as a viscoelastic body characterized by elasticity than viscosity.

• Journal of the Korea Concrete Institute
• /
• v.17 no.1 s.85
• /
• pp.11-18
• /
• 2005

In order to accurately assess the stresses occurring in the early-age concrete, a compliance function which can consider the characteristics of early-age concrete is required. Existing compliance functions, however, have the limit that they have been deduced from the data of hardened concrete and therefore, do not take into account the fast development of material properties in early-age concrete. Furthermore, the distinction between instantaneous compliance and creep compliance is not clear in the existing experimental method. The purpose of present study is to propose a compliance function which can describe the rapid change of hardening processes in early-age concrete. To this end, a test method which can estimate the instantaneous compliance without creep effects in the early-age concrete was suggested first. Based on the suggested experimental method, tests on the instantaneous as well as creep compliance were performed using MTS automatic servo-loop test machine. The test results showed that both instantaneous and aging viscoelastic compliance, which are constants in B3 model, were functions in terms of age of concrete especially at early ages. Therefore, the modified compliance function based on B3 model was proposed to provide more realistic prediction on the behavior of early-age concrete. It is expected that the present model allows more realistic evaluation of varying stresses in concrete structures at early ages.

• Journal of the Korean Wood Science and Technology
• /
• v.34 no.2
• /
• pp.46-57
• /
• 2006

To estimate nondestructively strength performances of laminated woods, 3-ply parallel- and cross-laminated wood specimens exposed under atmosphere conditions after bending creep test were prepared for this study. The effects of density of species, arrangement of laminae and lamination types on dynamic MOE obtained by flexural vibration were investigated, and regression analyses were conducted in order to estimate static bending strength and bending creep performances. Dynamic MOE of parallel-laminated woods showed 1.0~1.2 times higher values than static bending MOE, and those of cross-laminated woods showed 1.0~1.4 times higher values than static bending MOE. The degree of anisotropy of dynamic MOE perpendicular to the grain of face laminae versus that parallel to the grain of face laminae was markedly decreased by cross-laminating. There were strong correlations between dynamic MOE by flexural vibration and static bending MOE (correlation coefficient r = 0.919~0.972) or bending MOR (correlation coefficient r = 0.811~0.947) of 3-ply laminated woods, and the correlation coefficient were higher in parallel-laminated woods than in cross-laminated woods. It indicated that static bending strength performances were able to be estimated from dynamic MOE by flexural vibration. Also, close correlations between the reciprocal of dynamic MOE by flexural vibration and initial compliance at 0.008 h of 3-ply laminated woods were found (correlation coefficient r = 0.873~0.991). However, the correlation coefficient between the reciprocal of dynamic MOE and creep compliance at 168 h of 3-ply laminated woods was considerably lower than those between dynamic MOE and initial compliance, and it was hard to estimate creep compliance with a high accuracy from dynamic MOE due to the variation of creep deformation.

• Korean Journal of Food Science and Technology
• /
• v.30 no.4
• /
• pp.803-810
• /
• 1998

The mechanical and thermal properties of solutions of acorn starch were investigated, to determine the effect of sucrose on the retrogradation. The contents of moisture and amylose of purified acorn starch was 9.35, 27% respectively. From the moecular weight distribution, Mw and Mn of acorn starch were 1,220,432 and 137,201 relatively and the polydispersity of acorn starch was 8.8952. The creep compliance of acorn starch with and without sucrose were decreased with increasing sucrose concentration in the short term. The temperatures of DSC curve of 15% acorn starch solution containg sucrose shifted slightly to higher temperatures with increasing sucrose content. The enthalpy change associated with the gelatinization was increased with increasing sucrose content. After 7 days storage, the creep compliance of acorn starch gel with sucrose were shown higher than acorn starch gel. Regelatinization enthalpy of acorn starch/sucrose/water system was decreased with increasing sucrose content and increased with storage time. In addition, the characteristic temperatures such as onset temperature, peak temperature and conclusion temperature was increased by sucrose addition. Retrogradation ratio decreased with increasing sucrose content, thus sucrose inhibit retrogradation in the long term. Sucrose acts as an antistaling reagents and retatards the retrogradation.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.10a
• /
• pp.605-612
• /
• 2002

The objective of this study is to investigate the behavior of Visco-Elasto-Plastic materials of Silicate Grouted Sands due to external load. Uniaxial compression strength of silicate grouted sands was increased accordingly with curing time, but it was almost unchanged after 7days. A series of uniaxial compression creep tests were peformed for $\sigma$/$\sigma$$\sub$f/ = 8%,16% and 24%. The tested Silicated Grouted Sands exhibits three types of strains : elastic, plastic, viscoelastic. It is seen that the magnitude of the instantaneous recoverable strains $\varepsilon$$\sub$r/(o) is approximately independent of the unloading time. In this tests, The total creep strains( elastic, plastic, viscoelastic) are proportional to the stress level. Based on the constant creep test results, relationships between the time and the creep compliance are developed.

• Advances in concrete construction
• /
• v.14 no.1
• /
• pp.71-77
• /
• 2022

Creep phenomenon affects the stability and integrity of concrete structures. An inaccurate prediction of these strains may lead to the appearance of cracks and excessive deflections which may cause in some cases the demolition of structures. In fact, the measured values of these uncontrolled strains appear often to be clearly different and larger than the expected ones. Therefore, an accurate prediction of concrete deformations is a necessity. As a matter of fact, the codified descriptions of this phenomenon are unreliable and don't consider the effect of admixtures. The physical nature of creep is not well understood and almost all creep models are mainly of empirical nature. To overcome this issue, a study of the correlation between different parameters affecting concrete creep is performed and a new model for predicting creep of concrete is elaborated. This new model considers the effect of admixtures, specifically the silica fume, in predicting concrete creep and allows an accurate prediction of this phenomenon. The proposed model is based on the observation of physical behavior of creep phenomenon. It targets at expressing creep compliance in terms of structural and environmental parameters. In fact, the experimental observations show that creep curves follow two kinetic regimes leading to a model called Phenomenological Creep Model. By adequate regressions and substitutions, and according to this model, we can express creep compliance in terms of structural, environmental parameters and admixture types and percentage. The proposed new Phenomenological Creep Model Silica Fume (PCM19SF) calculates accurately creep of concrete by considering the effect of silica fume.

• Journal of Biosystems Engineering
• /
• v.17 no.1
• /
• pp.79-90
• /
• 1992

Viscoelastic characteristics of agricultural products may be determined through three basic tests ; stress relaxation, creep, and dynamic test. Considering the changeability of living materials, dynamic test in which information is derived in a relatively short time appears to be highly desirable, in which either cyclic stress or cyclic strain is imposed and the remaining quantity (strain or stress) is measured. The periodically varying stress will also result in periodically varying strain which in a viscoelastic material should theoretically be out of phase with the stress, because part of the energy subjected to sample is stored in the material as potential energy and part is dissipated as heat. This behavior results in a complex frequency-dependent compliance denoted by J($i{\omega}$). The complex compliance and therefore the storage compliance, the loss compliance, the phase angle, and percent energy loss for the sample should be obtainable with a given static viscoelastic property of the material under static load. The complex compliance of the rough rice kernel were computed from the Burger's model describing creep behavior of the material which were obtained in the previous study. Also, the effects of cyclic load and moisture content of grain on the dynamic viscoelastic behavior of the samples were analyized. The results obtained from this study were summarized as follows ; 1. The storage compliance of the rough rice kernel slightly decreased with the frequency applied but at above the frequency of 0.1 Hz it was nearly constant with the frequency, and the loss compliance of the sample very rapidly decreased with increase in the frequency on those frequency ranges. 2. It was shown that the storage compliance and the loss compliance of the sample increased with increase in grain moisture content. Effect of grain moisture content on the storage compliance of the sample was highly significant than effect of the frequency applied, but effect of the frequency on the loss compliance of the sample was more significant than effect of grain moisture content. 3. In low moisture content, the percent energy loss of Japonica-type rough rice was much higher than that of Indica-type rough rice, but, in high moisture content, vice versa.