대진폭 진동 전단 변형하에서 폴리아크릴아마이드 용액의 동적 점탄성 거동

송기원,장갑식,백종승 부산대학교 1995 生産技術硏究所論文集 Vol.48 No.-

Using a Rheometrics Fluids Spectrometer, the nonlinear viscoelastic behavior of polyacrylamide(PAAM) solutions with large amplitude oscillatory shear deformation has been investigated by analyzing the strain amplitude dependence of the storage modulus and dynamic viscosity. In this paper, the strain limits of linear viscoelastic response were determined and the effect of angular frequency on these values was examined. The behavior of the storage modulus and dynamic viscosity with increasing strain amplitude was also compared in nonlinear viscoelastic region. Further, the influence of higher harmonic terms of the Fourier series of stress wave on nonlinear viscoelastic behavior was discussed. Main results obtained from this study can be summarized as follows : (1) The storage modulus shows a much stronger dependence on the strain amplitude and demonstrates a nonlinear behavior at a lower strain amplitude than does the dynamic viscosity. (2) The nonlinear viscoelastic behavior is slightly dependent on the angular frequency but has a remarkable dependence on the strain amplitude. (3) The strain limits of linear response of the storage modulus and dynamic viscosity are γ_(EL) = 40% and γ_(VL) = 80%, respectively. These values are independent of the measured angular frequencies. (4) The third harmonic term of the Fourier series has a large effect in the initial region of nonlinear viscoelastic behavior. Rheometrics Fluids Spectrometer를 사용하여 대진폭 진동 전단변형하에서 발생되는 폴리아크릴아마이드(PAAM) 용액의 비선형 점탄성 거동을 저장탄성율 및 동적점도의 변형량 의존성으로부터 고찰하였다. 본 논문에서는 동적 점탄성의 감소비가 5% 이내의 범위를 선형 점탄성으로 인정하여 저장탄성율 및 동적점도의 선형 응답한계를 결정하고 이들에 미치는 각주파수의 영향을 조사하였다. 그리고 비선형 영역에 있어서 변형량 증가에 따른 저장탄성율 및 동적점도의 감소거동을 비교하였다. 나아가서 응력파형의 Fourier 급수로부터 비선형 거동을 발생시키는 고차항의 영향을 검토하였다. 이상의 연구를 통해 대변형하에서의 비선형 거동은 저장탄성율이 동적점도에 비해 더욱 현저한 변형량 의존성을 나타내며 보다 작은 스트레인 영역에서 비선형 거동이 발생함을 알았다. 또한 비선형 점탄성 거동은 각주파수보다 변형량의 크기에 더욱 의존함이 확인되었다. 그리고 저장탄성율 및 동적점도의 선형 응답한계는 측정된 각주파수에 무관하게 각각 γ_(EL) = 40%, γ_(VL) = 80% 정도의 값을 나타내었다. 나아가서 Fourier 급수의 3차항의 영향이 비선형 거동의 초기영역에서도 크게 작용함이 밝혀졌다.

A Time-Strain Separable K-BKZ Constitutive Equation to Describe the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

안혜진,장갑식,송기원,Ahn, Hye-Jin,Chang, Gap-Shik,Song, Ki-Won The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.4

The present study has been designed to describe the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields using a time-strain separable K-BKZ constitutive equation (i.e., Wagner model). Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly(ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated with a various combination of several fixed strain amplitudes and constant angular frequencies. The linear dynamic data (storage modulus and loss modulus) over a wide range of angular frequencies were obtained to determine the relaxation spectrum parameters and the stress relaxation moduli at various deformation magnitudes were measured to determine the damping function. The effects of the number of relaxation spectrum parameters and damping functions on the prediction results of the Wagner model were examined in depth. The nonlinear viscoelastic functions were analyzed by the aid of 3D plots and predicted over a wide range of strain amplitudes to evaluate the overall predictability of the Wagner model. The main findings obtained from this study are summarized as follows : (1) The Lissajous patterns predicted by the Wagner model are in good coincidence with the experimentally obtained stress-strain rate hysteresis loops both in linear and nonlinear viscoelastic regions and are independent of the number of relaxation spectrum parameters used in the calculation of memory function. (2) The effect of damping function on the predictive ability of the Wagner model is more sensitive than that of memory function. When the damping function is smaller than that of the experimental data, the stress amplitude predicted by the Wagner model also becomes smaller. (3) The Wagner model predictions are closely coincident with the experimental results in the linear viscoelastic region. As the strain amplitude is increased, the predicted nonlinear viscoelastic functions are somewhat larger than that of the experimental data. Nevertheless, all trends of the nonlinear viscoelastic behavior are in good agreement with the experimental results in a qualitative sense. (4) The Wagner model predicts the first harmonic loss modulus more exactly than the first harmonic storage modulus. As the strain amplitude is increased, the first harmonic storage modulus is somewhat overpredicted. The third and fifth harmonic storage and loss moduli exhibit an overshoot or an undershoot at large strain amplitudes. This constitutive equation has an ability to qualitatively describe well such dramatic behavioral changes.

절단 방지용 방검소재의 가속수명시험

장갑식(Gap-Shik Chang),정예리(Ye-Lee Jung),전병대(Byong-Dae Jeon) 한국신뢰성학회 2015 신뢰성응용연구 Vol.15 No.4

Purpose : UHMWPE (Ultra-high-molecular-weight-polyethylene) is one of the most widely used material in knife protection clothes because of high strength, elasticity, and light weight. The purpose of this study is to develop the accelerated life test method and predict the lifetime for the knife protection fabric composed by UHMWPE. Methods : In this study, degradation characteristics of UHMWPE fibers and knife protection fabric for cut resistance were evaluated under the hydrolysis and photo-degradation conditions. It was found out that the degradation rate of retained tensile strength was more significant in the photo-degradation than hydrolysis. Therefore, the failure time was determined as the time that the retained tensile strength in photo-degradation is less than 50%. Considering an acceleration factor for irradiance and exposure time, the lifetime was predicted from the calculated failure time. Results : As a result of the accelerated life test, the B10 lifetime of knife protection fabric composed by UHMWPE fibers is estimated as 2.8 years for a 90% statistical confidence level. Conclusion: Since the lifetime is predicted by the view-point of radiant exposure in this study, there is a possibility that the estimated lifetime may differ from the actual lifetime. However, it is considered as an useful methodology to estimate the long-term lifetime of knife protection fabrics.

A Simple Analysis Method to Predict the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

장갑식,안혜진,송기원,Chang, Gap-Shik,Ahn, Hye-Jin,Song, Ki-Won The Korean Fiber Society 2015 한국섬유공학회지 Vol.52 No.3

Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly(ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated in large amplitude oscillatory shear (LAOS) flow fields over a wide range of strain amplitudes. In order to predict the nonlinear viscoelastic behavior of polymer liquids in strain-sweep experiments, a new analysis method including a simple empirical model was proposed and then its validity was thoroughly evaluated in this study. The results have shown that the suggested model is significant in 95% confidence level and predicts exactly the nonlinear viscoelastic behavior of polymer liquids over a whole range of strain amplitudes tested. The strain limits of linear viscoelastic response and nonlinear behavior indices were determined using this model to estimate the LAOS flow behavior in strain-sweep experiments. The master curves of strain limits and nonlinear behavior indices can be obtained by representing these data against the product of angular frequency by characteristic time. The LAOS flow behavior of polymer systems with various molecular weights and different concentrations can well be predicted from these master curves.

Wall slip of vaseline in steady shear rheometry

Song, Ki-Won,Chang, Gap-Shik,Koo, Ja-Seung The Korean Society of Rheology 2003 Korea-Australia rheology journal Vol.15 No.2

The steady shear flow properties of vaseline generally used as a base of the pharmaceutical dosage forms were studied in the consideration of wall slip phenomenon. The purpose of this study was to show that how slip may affect the experimental steady-state flow curves of semisolid ointment bases and to discuss the ways to eliminate (or minimize) wall slip effect in a rotational rheometer. Using both a strain-controlled ARES rheometer and a stress-controlled AR1000 rheometer, the steady shear flow behavior was investigated with various experimental conditions ; the surface roughness, sample preparation, plate diameter, gap size, shearing time, and loading methods were varied. A stress-controlled rheometer was suitable for investigating the flow behavior of semisolid ointment bases which show severe wall slip effects. In the conditions of parallel plates attached with sand paper, treated sample, smaller diameter fixture, larger gap size, shorter shearing time, and normal force control loading method, the wall slip effects could be minimized. A critical shear stress for the onset of slip was extended to above 10,000 dyne/$\textrm{cm}^2$. The wall slip effects could not be perfectly eliminated by any experimental conditions. However, the slip was delayed to higher value of shear stress by selecting proper fixture properties and experimental conditions.

Effects of Recycling Processes on Physical, Mechanical and Degradation Properties of PET Yarns

Koo, Hyun Jin,Chang, Gap Shik,Kim, Seong Hun,Hahm, Wan Gyu,Park, Seong Yoon 한국섬유공학회 2013 FIBERS AND POLYMERS Vol.14 No.12

Mechanical properties and the long-term degradation properties of the recycled PET yarns are typically lower than the virgin PET yarns due to the contaminants coming from non-PET bottles, labels and caps etc. For environmental reasons, recycling of post-consumer polyester bottles into textile fibers has become commercially attractive. We studied mechanical and chemical recycling processes and examined their effects on yarn properties such as tensile properties, thermal characteristics, hydrolysis and photo-degradation. It was found that the virgin and the chemical recycled yarns with sufficient purification show similar processability, physical and mechanical properties, and long-term degradation behavior. The results provide useful information on recycled PET yarns for processability and serviceability for the high-end use.

Discrete Fourier Transform Analysis to Characterize the Large Amplitude Oscillatory Shear (LAOS) Flow Behavior of Viscoelastic Polymer Liquids

장갑식,안혜진,송기원,Chang, Gap-Shik,Ahn, Hye-Jin,Song, Ki-Won The Korean Fiber Society 2016 한국섬유공학회지 Vol.53 No.5

The objective of the present study is to systematically characterize the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields by means of discrete Fourier transform (DFT) analysis. Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly(ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated with several fixed strain amplitudes and constant angular frequencies. The nonlinear viscoelastic functions and the degree of nonlinearity were derived from the Fourier spectra of stress responses, and then the nonlinear behavior was interpreted by the use of 3D and contour plots, respectively. The effects of strain amplitude and angular frequency on the nonlinear viscoelastic behavior were nextly discussed in depth. In addition, the strain limits of linear viscoelastic response were determined from the ratio of harmonic contributions, and then the validity of Pipkin diagram with regard to characteristic time was evaluated for all PEO solutions. The main findings obtained from this study are summarized as follows: (1) At small strain amplitudes, the influence of the first harmonic contribution is dominant. As the strain amplitude becomes larger, however, the effect of higher odd harmonic contributions is increased, resulting in an occurrence of a nonlinear viscoelastic behavior. (2) The degree of nonlinearity is increased with an increase in strain amplitude. This is also increased with increasing angular frequency until reaching the maximum value at a certain angular frequency and then decreased with a further increase in angular frequency. (3) The Pipkin diagram with regard to characteristic time is a very effective method to explore the nonlinear regime of viscoelastic polymer liquids in LAOS deformations.

플라스틱 연직배수재의 배수성능시험법 국제표준화

구현진(Hyun-Jin Koo),장갑식(Gap-Shik Chang) 한국지반신소재학회 2012 한국지반신소재학회 학술발표회 Vol.2012 No.11

Prefabricated vertical drains(PVDs) are used to accelerate the settlement of clays and silts under a given surcharge loading. Therefore, the discharge capacity is the most important property for PVDs. According to EN 15237, the soil compression, taking place during the consolidation process, may cause buckling or kinking of the PVDs, which may seriously reduce their discharge capacity. However, the previously developed test methods are not enough to measure the discharge capacity of straight and buckled PVDs considering the installation and consolidation processes with acceptable repeatability and reproducibility. Therefore, it is necessary to develop the ISO standard test method considering the following factors which affect the discharge capacity: hydrualic gradient, static or stepwise cell pressure, test duration, creep effect and buckling geometry etc.

생분해성 섬유소재의 복합 분해성 평가

구현진(Koo, Hyun-Jin),장갑식(Chang, Gap-Shik) 한국지반신소재학회 2015 한국지반신소재학회 학술발표회 Vol.2015 No.10

배수용 지오신세틱스의 압축 크리프 거동

구현진(Hyun-Jin Koo),장갑식(Gap-Shik Chang) 한국토목섬유학회 2008 한국토목섬유학회 학술발표회 Vol.2008 No.11

Long-term compressive creep behavior of geocomposites was measured with various inclined conditions [horizontal, I-to-6(9.5˚), l-to-4(l4.0˚)] and applied stresses[200 kPa, 400 kPa, 50% of compressive strength] using stepped isothermal method. The reduction in hydraulic transmissivity(i.e creep reduction factor) was calculated based on the relationship between hydraulic transmissivity and thickness reduction. As the inclined angle and the applied load increase, it is found that the creep reduction factor increases and predicted lifetime decreases. This method can estimate the hydraulic transmissivity at longer than 100 years of service life with short test time and provide the useful information on designing drainage materials for long-term applications, particularly in inclined conditions.