• 한국소음진동공학회논문집
• /
• 제16권4호
• /
• pp.372-379
• /
• 2006

Little attention has been paid to static-strain-dependence of dynamic complex modulus of viscolelastic materials in computational analysisso far. Current commercial Finite Element Method (FEM) codes do not take such characteristics into consideration in constitutive equations of viscoelastic materials. Recent experimental observations that static-strain-dependence of dynamic complex modulus of viscolelastic materials, especially filled rubbers, are significant, however, require that solutions somehow are necessary. In this study, a simple technique of using a commercial FEM code, ABAQUS, is introduced, which seems to be far more cost/time saving than development of a new software with such capabilities. A static-strain-dependent correction factor is used to reflect the influence of static-strains in Merman model, which is currently the base of the ABAQUS. The proposed technique is applied to viscoelastic components of rather complicated shape to predict the dynamic stiffness under static-strain and the predictions are compared with experimental results.

• Journal of Biosystems Engineering
• /
• 제16권3호
• /
• pp.263-271
• /
• 1991

When grains is subjected to oscillating load, the dynamic viscoelastic behavior of the material will be describe the complex modulus of the material. The complex modulus and therefore the storage modulus, the loss modulus, and the phase angle for the sample should be obtainable with a given static viscoelastic property of the material under static load. The complex relaxation moduli 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 analized. The storage modulus of the rough rice kernel slightly increased with the frequency applied but at above the frequency of 0.1 Hz it was nearly constant with the frequency, and the loss modulus of the sample very rapidly decreased with increase in the frequency on those frequency ranges. It was shown that the storage modulus and the loss modulus of the sample increased with decrease in grain moisture content. Effect of grain moisture content on the storage modulus of the sample was highly significant than effect of the frequency applied, but effect of the frequency on the loss modulus of the sample was more significant than effect of grain moisture content.

• 한국도로학회논문집
• /
• 제16권3호
• /
• pp.43-50
• /
• 2014

PURPOSES : The dynamic modulus can be determined by applying the various theories from the Impact Resonance Testing(IRT) Method. The objective of this paper is to determine the best theory to produce the dynamic modulus that has the lowest error as the dynamic modulus data obtained from these theories(Complex Wave equation Resonance Method related to either the transmissibility loss or not, Dynamic Stiffness Resonance Method) compared to the results for dynamic modulus determined by using the Universal Testing Machine. The ultimate object is to develop the predictive model for the dynamic modulus of a Linear Visco-Elastic specimen by using the Complex Wave equation Resonance Method(CWRM) came up for an existing study(S. O. Oyadiji; 1985) and the Optimization. METHODS : At the destructive test which uses the Universal Testing Machine, the dynamic modulus results along with the frequency can be used for determining the sigmoidal master curve function related to the reduced frequency by applying Time-Temperature Superposition Principle. RESULTS : The constant to be solved from Eq. (11) is a value of 14.13. The reduced dynamic modulus obtained from the IRT considering the loss factor related to the impact transmissibility has RMSE of 367.7MPa, MPE of 3.7%. When the predictive dynamic modulus model was applied to determine the master curve, the predictive model has RMSE of 583.5MPa, MPE of 3.5% compared to the destructive test results for the dynamic modulus. CONCLUSIONS : Because we considered that the results obtained from the destructive test had the most highest source credibility in this study, the dynamic modulus data obtained respectively from DSRM, CWRM were compared to the results obtained from the destructive test by using th IRT. At the result, the reduced dynamic modulus derived from DSRM has the most lowest error.

• Journal of Biosystems Engineering
• /
• 제37권1호
• /
• pp.28-35
• /
• 2012

Purpose: This study performed the oscillatory test using the texture analyzer to characterize the viscoelastic behavior of apples such as the storage modulus (E'), the loss modulus (E"), the complex modulus (${\mid}E^*{\mid}$) and the energy dissipated per cycle ($W_{diss}$). Methods: The sinusoidal deformation with the frequency of 1-10 Hz and the maximum displacement of 0.1 mm were applied to the flesh tissues of Fuji, Golden Delicious and Red Delicious apples. The Lissajous figure was used to measure the phase angle(${\delta}$) between stress and strain curve. Results: Trigger force was critical to the measurement of the phase angle. E', E", ${\mid}E^*{\mid}$ and Wdiss were measured using the Lissajous figure and the phase angle. The complex modulus of Golden Delicious apple was significantly lower than those of Fuji apple and Red Delicious apple. Conclusions: Apple flesh was exhibiting more elasticity at low frequency, and more viscosity at high frequency. Dynamic compressive properties of Fuji apple were similar to those of Red Delicious apple but significantly different from those of Golden Delicious apple.

• 한국소음진동공학회논문집
• /
• 제13권2호
• /
• pp.132-143
• /
• 2003

Viscoelastic components for vibration isolation or shock absorption in automobiles, machines and buildings are often subject to a high level of static deformation. From the dynamic design point of view, it is requisite to predict dynamic complex stiffness of viscoelastic components accurately and efficiently. To this end, a systematic procedure for complex modulus measurement of the viscoelastic material under large static deformation is often required in the industrial fields. In this paper, dynamic test conditions and procedures for the viscoelastic material under small oscillatory load superimposed on large static deformation are discussed. Various standard test methods are investigated in order to select an adequate test methodology. The influence of fixed boundary condition in the compression tests upon complex stiffness are investigated and an effective correction technique is proposed. Then the uniaxial tension and compression tests are performed and its results are compared with analysis results from conventional constitutive models.

• 한국도로학회논문집
• /
• 제9권2호
• /
• pp.89-99
• /
• 2007

복소수계수 $E^*$로 표현되는 아스팔트 콘크리트의 탄성계수는 아스팔트 포장설계에서 매우 중요한 입력변수다. 일반적으로 아스팔트 콘크리트의 탄성계수는 동탄성 계수시험 (Dynamic Modulus Test)을 사용하여 평가한다. 그러나 동탄성계수시험은 일상적인 시험법으로 적용하기에는 고가의 시험장비, 복잡한 시험장비, 많은 시험시간 등의 문제가 있다. 이에 반하여 충격공진시험(IR: Impact Resonance test)은 비파괴시험으로서 간편한 시험장치, 단순한 시험방법이며 반복성이 뛰어나다. 본 연구의 주요 목적은 충격하중의 타격위치 시편거치 방법 충격하중원의 특성, 신호획득 속도, 신호처리방법 등을 포함한 IR시험의 시험조건의 영향을 평가하는 것이다. 본 연구에서 적용한 모든 시험조건 범위에서 충격공진시험에서 측정된 결과의 변동은 ${\pm}2.7%$ 이내에 들었다.

• Restorative Dentistry and Endodontics
• /
• 제34권5호
• /
• pp.450-459
• /
• 2009

본 연구의 목적은 새로 개발한 점탄성 측정기를 사용하여 수종의 광중합 복합레진의 초기 동적 점탄성 변화를측정하는 것이다. 본 연구에 사용된 점탄성 측정기는 세 부분으로 구성되었다. 첫째, 시편이 놓여지는 parallel plates; 둘째, DC 모터와 크랭크로 이루어진 회전진동전단변형 (Oscillatory shear strain)을 발생시키는 부분; 셋째, 전자기적 토크센서를 이용한 응력 측정 부분으로 구성되었다. 본 점탄성 측정기는 최대 2 Ncm의 토크를 측정할 수 있으며, 광중합기의 스위치는 컴퓨터와 연동하여 데이터 획득을 시작할 때 동시에 켜지도록 하였다. 본 연구에서는 시판 중인 6종의 광중합 복합레진 [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), Clearfil AP-X (CF)]을 사용하였다. 점탄성 측정기를 사용하여 동적 회전전단실험을 시행하였다. 직경 3 mm인 유리막대로 구성된 parallel plates 사이에 $14.2\;mm^3$의 복합레진을 적용시켰으며, 6 Hz의 진동수와 0.00579 rad의 진폭으로 변형을 가하고 발생된 응력을 측정하였다. 광중합이 시작됨과 동시에 측정이 시작되었으며, 광중합 후 10초 동안 점탄성의 변화를 관찰하였다. 각 복합레진에 대해 5 회 반복하여 측정하였고, 실험은 $25{\pm}0.5^{\circ}C$에서 진행되었다. 측정된 변형-응력 곡선으로부터 복소전단탄성계수 G*, 저장전단탄성 계수 G', 손실전단탄성 계수 G"를 구하였고 G*가 10 MPa에 이르는 시간을 구하였다. 각 재료의 복소전단탄성계수 G*와 10 MPa에 이르는 시간에 대해 일원분산분석 (One-way ANOVA)과 사후검정 (Tukey 검정)을 시행하였다 (${\alpha}$= 0.05). 결과는 다음과 같다. 1.본 연구를 위해 제작한 점탄성 측정기는 광중합 복합레진의 중합 초기 10초 동안의 동적 점탄성 변화를 신뢰성 있게 측정 할 수 있었다. 2. 모든 복합레진은 광조사 개시 후 $1{\sim}2$초의 불응기를 지난 다음 급격한 전단탄성계수의 증가를 보였다. 3. 모든 복합레진은 광중합 10 초간 손실전단탄성계수보다 저장전단탄성계수의 높은 증가를 보였다. 4. 광중합 초기 10초 후 복소전단탄성계수 값은 $150.3{\sim}563.7\;MPa$로, Z-100이 가장 높았고, 그 다음 Clearfil, Z-250, Z-350, Tetric Ceram, DenFil의 순이었다. 5. 복소전단탄성계수가 10 MPa에 이르는 시간은 Z-100이 2.55초로 가장 빨랐고, DenFil이 4.06초로 가장 느렸다.

• 소음진동
• /
• 제1권2호
• /
• pp.121-128
• /
• 1991

In order to use viscoelastic materials efficiently for noise and vibration control, or th qualify newly developed materials, knowledge of the Young' s modulus and loss factor is essemtial. These material properties, the so-called complex Young' s modulus, are frequently treated as dynamic charicteristics because of their dependence upon the frequency. Many techniques have been developed and verified for measuring complex Young' s modulus of viscoelastic materials. Among them, the impedance method is preferable in order to obtain the frequency information in detail. In this method, a cylindrical or prismatic specimen is excited into longitudinal harmonic vibration at one end, the other being fixed, and the resulting force is measured at the driving or fixed end. The amplitude ratio of the two signals and phase angle between them are then used to compute the material properties using various mathematical models. In this paper, the impedance method is investigated theoretically and experimentally. A way to determine the specimen geometry which is most appropriate for the identification of complex Young' s modulus using the lumped mass model is presented and discussed. Then experimental results supporting the theoretical predictions are presented.

• 소음진동
• /
• 제8권5호
• /
• pp.900-907
• /
• 1998

Rubber materials are extensively used in various machine design application, mainly for vibration/shock/noise control devices. Over the years an enormous effort has been put into developing procedures to provide properties of rubber material for design function. However, there are still a lot of difficulties in the understanding of dynamic characteristics of the rubber components in compression. In this paper, the dynamic characteristics of rubber materials for anti-vibration under compression were investigated. Dynamic and static tests for rubber material with 3 different hardness were performed. In dynamic tests, non-resonance method, impedance method, was used to obtain the complex modulus(storage modulus and loss factor) and the effects of static pre-strain on the dynamic characteristics were investigated. Also, a relation equation between linear dynamic and nonlinear static behavior of rubber material was discussed and its usefulness to predict their combined effects was investigated.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
• /
• pp.602-607
• /
• 1998

Rubber materials are extensively used in various machine design application, mainly for vibration/shock/noise control devices. Over the years an enormous effort has been put into developing procedures to provide properties of rubber material for design function. However, there are still a lot of difficulties in the understanding of dynamic characteristics of the rubber components in compression. In this paper, the dynamic characteristics of rubber materials for anti-vibration under compression were investigated. Dynamic and static tests for rubber material with 3 different hardness were performed. In dynamic tests, non-resonance method, impedance method, was used to obtain the complex modulus (storage modulus and loss factor) and the effects of static pre-strain on the dynamic characteristics were investigated. Also, a relation equation between linear dynamic and nonlinear static behavior of rubber material was discussed and its usefulness to predict their combined effects was investigated.