This study presents an overview of viscoelastic characteristics of biocomposites derived of natural-fibre-reinforced thermoplastic polymers and predictive models have been presented in order to understand their rheolo...This study presents an overview of viscoelastic characteristics of biocomposites derived of natural-fibre-reinforced thermoplastic polymers and predictive models have been presented in order to understand their rheological behavior. Various constitutive equations are reviewed for a better understanding of their applicability to polymer melt in determining the viscosity. The models to be investigated are the Giesekus-Leonov model, the Upper Convected Maxwell (UCM) model, the White-Metzner model, K-BKZ model, the Oldroyd-B model, and the Phan-Thien-Tanner models. The aforementioned models are the most powerful for predicting the rheological behavior of hybrid and green viscoelastic materials in the presence of high shear rate and in all dimensions. The Phan-Thien Tanner model, the Oldroyd-B model, and the Giesekus model can be used in various modes to fit the relaxation modulus accurately and to predict the shear thinning as well as shear thickening characteristics. The Phan-Thien Tanner, K-BKZ, Upper convected Maxwell, Oldroyd-B, and Giesekus models predicted the steady shear viscosity and the transient first normal stress coefficient better than the White-Metzner model for green-fibre-reinforced thermoplastic composites.展开更多
The process of liver fibrosis changes the rheological properties of liver tissue.This study characterizes and compares liver fibrosis stages from F0 to F4 in rats in terms of shear viscoelastic moduli.Here two viscoel...The process of liver fibrosis changes the rheological properties of liver tissue.This study characterizes and compares liver fibrosis stages from F0 to F4 in rats in terms of shear viscoelastic moduli.Here two viscoelastic models,the Zener model and Voigt model,were applied to experimental data of rheometer tests and then values of elasticity and viscosity were estimated for each fibrosis stage.The results demonstrate that moderate fibrosis（≤F2） has a good correlation with liver viscoelasticity.The mean Zener elasticity E1 increases from（0.452±0.094） kPa（F0） to（1.311±0.717） kPa（F2）,while the mean Voigt elasticity E increases from（0.618±0.089） kPa（F0） to（1.701±0.844） kPa（F2）.The mean Zener viscosity increases from（3.499±0.186） Pa·s（F0） to（4.947±1.811） Pa·s（F2） and the mean Voigt viscosity increases from（3.379±0.316） Pa·s（F0） to（4.625±1.296） Pa·s（F2）.Compared with viscosity,the elasticity shows smaller variations at stages F1 and F2 no matter what viscoelastic model is used.Therefore,the estimated elasticity is more effective than viscosity for differentiating the fibrosis stages from F0 to F2.展开更多
The focus of this paper is on determination of the dynamic parameters of structural systems with viscoelastic (VE) dampers described by Maxwell rheological models. Such parameters could be obtained after solving the a...The focus of this paper is on determination of the dynamic parameters of structural systems with viscoelastic (VE) dampers described by Maxwell rheological models. Such parameters could be obtained after solving the appropriately defined nonlinear eigenvalue problem for frames with VE dampers. The solution to the nonlinear eigenvalue problem is obtained by equating to zero the determinant of the considered system of equations. Apart from complex conjugate eigenvalues, the real ones occurred when dampers that are described by the classic Maxwell model, are also determined.展开更多
文摘This study presents an overview of viscoelastic characteristics of biocomposites derived of natural-fibre-reinforced thermoplastic polymers and predictive models have been presented in order to understand their rheological behavior. Various constitutive equations are reviewed for a better understanding of their applicability to polymer melt in determining the viscosity. The models to be investigated are the Giesekus-Leonov model, the Upper Convected Maxwell (UCM) model, the White-Metzner model, K-BKZ model, the Oldroyd-B model, and the Phan-Thien-Tanner models. The aforementioned models are the most powerful for predicting the rheological behavior of hybrid and green viscoelastic materials in the presence of high shear rate and in all dimensions. The Phan-Thien Tanner model, the Oldroyd-B model, and the Giesekus model can be used in various modes to fit the relaxation modulus accurately and to predict the shear thinning as well as shear thickening characteristics. The Phan-Thien Tanner, K-BKZ, Upper convected Maxwell, Oldroyd-B, and Giesekus models predicted the steady shear viscosity and the transient first normal stress coefficient better than the White-Metzner model for green-fibre-reinforced thermoplastic composites.
基金supported by the National Natural Science Foundation of China(Nos.61031003,81271651,and 61101025)the Shenzhen Basic Research Project(No.JC201005280501A),China
文摘The process of liver fibrosis changes the rheological properties of liver tissue.This study characterizes and compares liver fibrosis stages from F0 to F4 in rats in terms of shear viscoelastic moduli.Here two viscoelastic models,the Zener model and Voigt model,were applied to experimental data of rheometer tests and then values of elasticity and viscosity were estimated for each fibrosis stage.The results demonstrate that moderate fibrosis（≤F2） has a good correlation with liver viscoelasticity.The mean Zener elasticity E1 increases from（0.452±0.094） kPa（F0） to（1.311±0.717） kPa（F2）,while the mean Voigt elasticity E increases from（0.618±0.089） kPa（F0） to（1.701±0.844） kPa（F2）.The mean Zener viscosity increases from（3.499±0.186） Pa·s（F0） to（4.947±1.811） Pa·s（F2） and the mean Voigt viscosity increases from（3.379±0.316） Pa·s（F0） to（4.625±1.296） Pa·s（F2）.Compared with viscosity,the elasticity shows smaller variations at stages F1 and F2 no matter what viscoelastic model is used.Therefore,the estimated elasticity is more effective than viscosity for differentiating the fibrosis stages from F0 to F2.
基金the financial support received from the Poznan University of Technology(Grant No.DS 11-088/12)in connection with this work.
文摘The focus of this paper is on determination of the dynamic parameters of structural systems with viscoelastic (VE) dampers described by Maxwell rheological models. Such parameters could be obtained after solving the appropriately defined nonlinear eigenvalue problem for frames with VE dampers. The solution to the nonlinear eigenvalue problem is obtained by equating to zero the determinant of the considered system of equations. Apart from complex conjugate eigenvalues, the real ones occurred when dampers that are described by the classic Maxwell model, are also determined.
