Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Strong Extensional and Shearing Flows of a Branched Polyethylene

Abstract: Simultaneous fits of the Kaye‐BKZ and Wagner equations to shear and uniaxial extensional flow data are not the most critical tests of these equations, because their memory functions depend on two strain invariants, and this dependence can be varied independently for shear and for uniaxial extension to obtain a fit for each. In planar deformations, however, the memory function depends on only one invariant; this dependence can be measured in single‐step shear experiments, as is reported here for a branched polyethylene, IUPAC X, using a sliding plate rheometer. Predictions are then made for three different planar deformation histories: start‐up of steady simple shear and steady planar extension, and exponentially growing shear, all tests in which the memory function depends on only one invariant. The predictions in steady shear and exponential shear are in rough agreement with the data. The theory for planar extension, however, greatly underpredicts the experimental strain hardening of IUPAC X, which has been reported to be similar to the strain hardening usually seen in uniaxial extension for LDPE. Thus, the Kaye‐BKZ and Wagner single‐integral equations cannot simultaneously describe both strain softening in shear and extreme strain hardening in planar extension using a damping function obtained from one of these flows.

Effect of Particle Size on Shear Stress of Magnetorheological Fluids

Abstract: Magnetorheological fluids (MRF), known for their variable shear stress contain magnetisable micrometer-sized particles (few micrometer to 200 micrometers) in a nonmagnetic carrier liquid To avoid settling of particles, smaller sized (3-10 micrometers) particles are preferred, while larger sized particles can be used in MR brakes, MR clutches, etc as mechanical stirring action in those mechanisms does not allow particles to settle down Ideally larger sized particles provide higher shear stress compared to smaller sized particles However there is need to explore the effect of particle sizes on the shear stress In the current paper, a comparison of different particle sizes on MR effect has been presented Particle size distributions of iron particles were measured using HORIBA Laser Scattering Particle Size Distribution Analyser The particle size distribution, mean sizes and standard deviations have been presented The nature of particle shapes has been observed using scanning electron microscopy To explore the effect of particle sizes, nine MR fluids containing small, large and mixed sized carbonyl iron particles have been synthesized Three concentrations (9%, 18% and 36% by volume) for each size of particles have been used The shear stresses of those MRF samples have been measured using ANTON PAAR MCR-102 Rheometer With increase in volume fraction of iron particles, the MR fluids synthesized using “mixed sized particles” show better shear stress compared to the MR fluids containing “smaller sized spherical shaped particles” and “larger sized flaked shaped particles” at higher shear rate

A novel method for visualising and quantifying through-plane skin layer deformations

Abstract: Skin is a multilayer composite and exhibits highly non-linear, viscoelastic, anisotropic material properties In many consumer product and medical applications (eg during shaving, needle insertion, patient re-positioning), large tissue displacements and deformations are involved; consequently large local strains in the skin tissue can occur Here, we present a novel imaging-based method to study skin deformations and the mechanics of interacting skin layers of full-thickness skin Shear experiments and real-time video recording were combined with digital image correlation and strain field analysis to visualise and quantify skin layer deformations during dynamic mechanical testing A global shear strain of 10% was applied to airbrush-patterned porcine skin (thickness: 12-16mm) using a rotational rheometer The recordings were analysed with ARAMIS image correlation software, and local skin displacement, strain and stiffness profiles through the skin layers determined The results of this pilot study revealed inhomogeneous skin deformation, characterised by a gradual transition from a low (20-50%; epidermis) to high (10-22%; dermis) shear strain regime Shear moduli ranged from 20 to 130kPa The herein presented method will be used for more extended studies on viable human skin, and is considered a valuable foundation for further development of constitutive models which can be used in advanced finite element analyses of skin

Unsteady rheometry: can we characterize weak gels with a controlled stress rheometer?

Abstract: This paper is concerned with the influence of apparatus inertia effects in controlled stress rheometry. As evidenced on creep experiments, the coexistence of apparatus inertia and viscoelasticity leads to a coupling frequency. For weak gels, this coupling frequency is typically between 1 and 100 Hz. Therefore, frequency sweeps around and above this coupling frequency also corresponds to an effective shear stress sweep evolution due to a non-trivial resonant effect. In other words, frequency sweep experiments are not made at constant shear stress. The detailed modelling and analysis of this inertia effect on a typical weak gel shows a clear and fundamental limitation for its characterization using a controlled stress rheometer. Also, alternative approaches to standard rheometer software analysis are proposed to take this coupling effect into account.