Wall slip behavior of three commercial polymer melts polypropylene(iPP),low-density polyethylene(LDPE)(branched chains) and high-density polyethylene(HDPE)(linear chains) were studied by using a capillary rheometer wi...Wall slip behavior of three commercial polymer melts polypropylene(iPP),low-density polyethylene(LDPE)(branched chains) and high-density polyethylene(HDPE)(linear chains) were studied by using a capillary rheometer with twin bores at different temperatures.The results show that a sudden first-stick-then-slip transition was observed for HDPE and a first-slip-then-stick transition was observed for LDPE and iPP as the shear rate sweep was done in an increased order,which shows that the chain structure has an obvious effect on the wall slip behavior of polymers.The critical shear stress for the onset of stick-slip transition increases linearly with temperature for HDPE,which accords with the disentanglement mechanism proposed by Brochard and de Gennes.While the extrapolation length used to quantify the magnitude of the transition remains about 0.05-0.09 mm for HDPE at 150-230 ℃.Also the relationship between the critical shear stress for the onset of wall slip and the molecular mass for polymer samples agrees with the disentanglement model of Brochard and de Gennes.The onset of slip-stick transition for LDPE and iPP at a critical shear stress may be interpreted as the shear thinning of the polymer chains at high shear rates,preventing further development of wall slip behavior.展开更多
The operating principle of measuring rheological properties of magnetorheological(MR) fluid was expounded by means of a new rheometer with double driving discs rotating at the same speed in the opposite directions.The...The operating principle of measuring rheological properties of magnetorheological(MR) fluid was expounded by means of a new rheometer with double driving discs rotating at the same speed in the opposite directions.The constitutive equation of MR fluid was established with theoretical analysis from experimental data.The conventional power spectrum approach was unable to detect the existence of quadratic phase coupling for dynamic rheological measurement.Bispectrum analysis is emerging as a new powerful technique in signal processing,which can describe nonlinear coupling,restrain Gaussian noise and reserve phase component.An autoregressive(AR) model of the third order cumulant,the bispectra and bispectral contours were utilized for analyzing the dynamic characteristics of the MR rheometer by merely using the sampled output torque signals when a zero mean non-Gaussian white noise interferes with the rotary disc system.The measurement and analysis process based on virtual instruments were automatically controlled by computer in this paper.The experimental and theoretical results show that rheological properties and dynamic characteristics of MR fluid can be measured with this double disc rheometer.展开更多
A new testing procedure to estimate the low-temperature stiffness of the reclaimed asphalt pavement （RAP） binder was developed. In the testing procedure, the SuperpaveTM Bending Beam Rheometer （BBR） with special m...A new testing procedure to estimate the low-temperature stiffness of the reclaimed asphalt pavement （RAP） binder was developed. In the testing procedure, the SuperpaveTM Bending Beam Rheometer （BBR） with special modifications and binder blending charts by Asphalt Institute were utilized. Modifications involved the development of a new kind of sample mold and different testing parameters were made to BBR testing procedure to capture the theological properties of bitumen mortars produced by mixing fresh binder with fine RAP materials or RAP aggregate. The stiffness relationship between binder and bitumen mortar was established based on the BBR test results. The blended binder stiffness in bitumen RAP mortar was estimated from the RAP mortar stiffness based on the binder-mortar relationship. And finally, the RAP binder stiffness was estimated from the blended binder and fresh binder stiffness based on the blending charts by Asphalt Institute. The results indicate that the new procedure can capture the rheological properties of bitumen mortar and can be used to estimate the low temperature stiffness of RAP binder without binder extraction and/or any chemical treatments.展开更多
The work principle of flat-plate structure under shearing mode is expounded based on a vertical type rheometer for MRF which combined data acquisition with treatment and result display.The formula to calculate shearin...The work principle of flat-plate structure under shearing mode is expounded based on a vertical type rheometer for MRF which combined data acquisition with treatment and result display.The formula to calculate shearing stress is deduced.Based on different recipe for MRF,experiments under different working gap length were done by altering the intensity of magnetic field.The rheological model for MRF was established and the relationships between shearing stress,viscosity and magnetic field intensity were deduced.Experiments indicate that MRF has the flowing characters:with an increase of the magnetic induction and the nominal shear rate,the shear stress of MRF increases.However,as the working gap decreases,the shear stress increases.MRF has shear thinning property under magnetic field.展开更多
基金Projects(ZMF07020038) supported by the Young Teacher's Scientific Research Fund of Jiangsu Polytechnic University,China
文摘Wall slip behavior of three commercial polymer melts polypropylene(iPP),low-density polyethylene(LDPE)(branched chains) and high-density polyethylene(HDPE)(linear chains) were studied by using a capillary rheometer with twin bores at different temperatures.The results show that a sudden first-stick-then-slip transition was observed for HDPE and a first-slip-then-stick transition was observed for LDPE and iPP as the shear rate sweep was done in an increased order,which shows that the chain structure has an obvious effect on the wall slip behavior of polymers.The critical shear stress for the onset of stick-slip transition increases linearly with temperature for HDPE,which accords with the disentanglement mechanism proposed by Brochard and de Gennes.While the extrapolation length used to quantify the magnitude of the transition remains about 0.05-0.09 mm for HDPE at 150-230 ℃.Also the relationship between the critical shear stress for the onset of wall slip and the molecular mass for polymer samples agrees with the disentanglement model of Brochard and de Gennes.The onset of slip-stick transition for LDPE and iPP at a critical shear stress may be interpreted as the shear thinning of the polymer chains at high shear rates,preventing further development of wall slip behavior.
基金Project(2005H035) supported by the Programs of Science and Technology of Fujian Province of China
文摘The operating principle of measuring rheological properties of magnetorheological(MR) fluid was expounded by means of a new rheometer with double driving discs rotating at the same speed in the opposite directions.The constitutive equation of MR fluid was established with theoretical analysis from experimental data.The conventional power spectrum approach was unable to detect the existence of quadratic phase coupling for dynamic rheological measurement.Bispectrum analysis is emerging as a new powerful technique in signal processing,which can describe nonlinear coupling,restrain Gaussian noise and reserve phase component.An autoregressive(AR) model of the third order cumulant,the bispectra and bispectral contours were utilized for analyzing the dynamic characteristics of the MR rheometer by merely using the sampled output torque signals when a zero mean non-Gaussian white noise interferes with the rotary disc system.The measurement and analysis process based on virtual instruments were automatically controlled by computer in this paper.The experimental and theoretical results show that rheological properties and dynamic characteristics of MR fluid can be measured with this double disc rheometer.
基金Project(200831800044) supported by the Ministry of Communication of ChinaProject(50878054) supported by the National Natural Science Foundation of ChinaProject(06Y31) supported by the Department of Communication of Zhejiang Province,China
文摘A new testing procedure to estimate the low-temperature stiffness of the reclaimed asphalt pavement （RAP） binder was developed. In the testing procedure, the SuperpaveTM Bending Beam Rheometer （BBR） with special modifications and binder blending charts by Asphalt Institute were utilized. Modifications involved the development of a new kind of sample mold and different testing parameters were made to BBR testing procedure to capture the theological properties of bitumen mortars produced by mixing fresh binder with fine RAP materials or RAP aggregate. The stiffness relationship between binder and bitumen mortar was established based on the BBR test results. The blended binder stiffness in bitumen RAP mortar was estimated from the RAP mortar stiffness based on the binder-mortar relationship. And finally, the RAP binder stiffness was estimated from the blended binder and fresh binder stiffness based on the blending charts by Asphalt Institute. The results indicate that the new procedure can capture the rheological properties of bitumen mortar and can be used to estimate the low temperature stiffness of RAP binder without binder extraction and/or any chemical treatments.
基金Projects(10472134,50490274) supported by the National Natural Science Foundation of China
文摘The work principle of flat-plate structure under shearing mode is expounded based on a vertical type rheometer for MRF which combined data acquisition with treatment and result display.The formula to calculate shearing stress is deduced.Based on different recipe for MRF,experiments under different working gap length were done by altering the intensity of magnetic field.The rheological model for MRF was established and the relationships between shearing stress,viscosity and magnetic field intensity were deduced.Experiments indicate that MRF has the flowing characters:with an increase of the magnetic induction and the nominal shear rate,the shear stress of MRF increases.However,as the working gap decreases,the shear stress increases.MRF has shear thinning property under magnetic field.
