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.

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.

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.

The Doi-Edwards Constitutive Equation to Predict 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 predict the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields by means of the Doi-Edwards constitutive equation. 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 also obtained to determine the relaxation spectrum parameters. The experimentally obtained Lissajous patterns (stress-strain rate hysteresis loops) were compared with the Doi-Edwards model predictions over a wide range of strain amplitudes and angular frequencies for all polymer solutions prepared in this work. 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 Doi-Edwards model. The main findings obtained from this study are summarized as follows : (1) The Lissajous patterns predicted by the Doi-Edwards model represent a good agreement with the experimentally obtained stress-strain rate hysteresis loops both in linear and nonlinear viscoelastic regions. (2) The predictions of the Doi-Edwards model 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 qualitatively in good agreement with the experimental results. (3) The Doi-Edwards model gives a very good prediction for the first harmonic storage modulus and loss modulus up to the nonlinear viscoelastic region. The third and fifth harmonic storage and loss moduli exhibit an overshoot or an undershoot at large strain amplitudes. This constitutive equation can describe well such excessive behavioral changes in a qualitative sense. (4) The Doi-Edwards model has a slightly better ability than the Wagner model to predict the LAOS flow behavior of concentrated polymer systems.

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.

플라스틱 연직배수재 배수성능 평가 개선방안 연구

구현진(Koo, Hyun-Jin),장갑식(Chang, Gap-Shik),김기준(Kim, KiJoon) 한국지반신소재학회 2016 한국토목섬유학회 학술발표회 Vol.2016 No.4

플라스틱 연직배수재의 굴곡조건하에서의 배수성능시험법 개발

구현진(Hyun-Jin Koo),장갑식(Gap-Shik Chang) 한국지반신소재학회 2013 한국토목섬유학회 학술발표회 Vol.2013 No.11

플라스틱 연직배수재의 굴곡조건하에서의 배수성능을 객관적으로 평가하기 위하여 굴곡 시험장비를 개발하였으며 굴곡형태, 굴곡부여 방식 및 pin 직경 등 굴곡조건에 대한 영향을 분석하였다. 이러한 연구결과를 바탕으로 현재 플라스틱 연직배수재의 굴곡조건하에서의 배수성능 시험방법의 국제표준화가 진행 중에 있다. The most important property of prefabricated vertical drains (PVDs) is the discharge capacity. After the installation of PVDs, water is discharging from compressible soil layers which causes a vertical deformation of the PVDs, resulting in buckling. However, there are many different practices are present all over the world for the testing of the discharge capacity of PVDs, especially in buckled condition. In this study, the effects of buckling shape, pin diameter and buckling procedure on discharge capacity were investigated to develop the standardized test method and apparatus for discharge capacity of PVDs in buckled condition.