The dynamic nonlinear viscoelasticity of an MR fluid in oscillatory pressure flow under magnetic flux normal to the flow direction has been investigated by using a newly developed oscillatory pressure flow type rheometer. The MR fluid consisting of micron-sized magnetically polarizable particles (carbonyl iron) dispersed into a carrier medium (hydrocarbon oil) was evaluated. The dependence of viscoelasticity of the MR fluid on magnetic field strengths, fluid strain amplitudes and fluid oscillation frequencies have been already investigated. Generalized viscoelastic mechanical models of the MR fluid in oscillatory slit flow are very important for analyzing various MR dampers using MR valves. In this work, a nonlinear dynamic viscoelastic mechanical model of the MR fluid in oscillatory slit flow is proposed, based on the data which have been already measured. The proposed viscoelastic mechanical model of an MR fluid is discussed and compared with the experimental results.
Rheological behavior of agar microgel dispersion was studied. Agar microgel dispersion was prepared from agar bulk-gel containing 1.3-1.7% agar which was determined by a high-speed-mixer (5,000 rpm). To confirm the mechanical property of the microgel, we measured the dynamic modulus of the microgel dispersion. The microgel dispersion showed a gel-like nature in a small deformation range (γ < 1%), while the dispersion showed a fluid-like nature in a large deformation range (γ > 1%). The flow characteristic parameters including yield stress and apparent viscosity of the dispersion were calculated by using Herschel-Bulkley equation of the scaling law model. The microgel showed pseudoplastic-flow with a yield stress (about 13 Pa). The apparent viscosity of the dispersion depended on the hardness of the individual microgel particles. To investigate the effect of the microgel volume fraction on its flow characteristic parameters, we examined the parameters of several microgel dispersions with various volume fractions ranging from Φgel = 1.0 to 0.3. The yield stress of the microgel dispersion decreased suddenly at around Φgel = 0.7 and disappeared at around Φgel = 0.4. The apparent viscosity of the microgel dispersion also decreased with the decrease of Φgel. The result indicates that packed condition of the microgel particles mainly reflects the rheological properties of the microgel dispersion.
Viscosity and viscoelasticity were measured for potassium neutralized telechelic poly(ethylene-butylene) ionomer, CTPEB-K, as well as the original polymer, CTPEB, in a non-polar solvent of decalin in a concentration range from dilute to semidilute regime. CTPEB-K was found to associate with each other even in the dilution limit. With increasing the polymer concentration, CTPEB-K solution showed a rapid increase in viscosity due to the formation of a huge cluster and further increase in the concentration lead to formation of a viscoelatic network with finite but quite high viscosity. The time-temperature superposition could be applied for the viscoelasticity of the network and the Arrhenius type of temperature dependence was observed. The viscoelastic network exhibited two or three relaxation modes. The fast mode may be assigned to the network rearrangement and the slow mode possibly to the cluster migration in the viscous fluid.
The transverse Young's modulus of unidirectional carbon fiber reinforced plastics(CFRP) was measured by three points bending tests and compared with values calculated using finite element method(FEM). To calculate the transverse Young's modulus, we developed a 3-dimensional finite element method program by modifying the hexagonal array model in consideration of the anisotropy of carbon fiber and the effect of interface between carbon fiber and matrix. The values calculated without consideration of the effect of interface were smaller than the experimental data. The FEM analysis indicated that the transverse Young's modulus of CFRP was changed largely with the change of the Young's modulus of the interface layer when the modulus of the interface was less than that of the matrix.
An aqueous cationic surfactant solution, CTAB/NaSal, forms wormlike micelles and shows viscoelastic properties. It also shows shear-induced structure change at shear rates higher than 4 s-1. Full components of the refractive index tensor under step shear flow were measured by using double-beam rheo-optical analyzer in addition of shear stress and first normal stress difference measurement. Each component of the refractive index tensor is proportional to the corresponding component of the stress tensor when shear rate is lower than 6 s-1. However, a stress-optical coefficient, C, suddenly decreases above 4 s-1. At shear rates between 4 to 6 s-1, the stress-optic rule holds, but micellar structure might change.