In the approach presented, attrition of bulk solids in pneumatic conveying is regarded as a result of a process function (stress conditions) and a material function (influence of material ...properties). The paper focuses on dilute phase conveying (homogeneous flow) and in the first part describes the determination of the process function by employing computational fluid dynamics (CFD). In the second part, experimental results for the determination of the material function by means of simulating the previously identified stress modes of impact and friction under well-defined stress conditions are presented. Contrary to what was expected initially, the numerical simulations as well as experimental results indicate that sliding friction is apparently of importance in dilute phase conveying. This conclusion can be drawn from the low calculated impact angles in a pipe bend (r B /D=5; D=80 mm), which lie between 10 and 35°. Consequently, the tangential impact velocity components ranging from 32 to 40 m/s are considerably higher than the normal ones (5 to 22 m/s). These results are confirmed by observations made in experiments to determine the material function. The relative attrition behavior of four different polypropylenes under pure sliding friction conditions closely resembles that observed in attrition experiments carried out in a pipe bend of the above geometry, while differences are observed for normal impact conditions.
Rheological material functions are used to form our conceptual understanding of a material response. For a nonlinear rheological response, the possible deformation protocols and material measures ...span a high-dimensional space. Here, we use asymptotic expansions to outline low-dimensional measures for describing leading-order nonlinear responses in large amplitude oscillatory shear (LAOS). This amplitude-intrinsic regime is sometimes called medium amplitude oscillatory shear (MAOS). These intrinsic nonlinear material functions are only a function of oscillatory frequency, and not amplitude. Such measures have been suggested in the past, but here, we clarify what measures exist and give physically meaningful interpretations. Both shear strain control (LAOStrain) and shear stress control (LAOStress) protocols are considered, and nomenclature is introduced to encode the physical interpretations. We report the first experimental measurement of all four intrinsic shear nonlinearities of LAOStrain. For the polymeric hydrogel (polyvinyl alcohol - Borax) we observe typical integer power function asymptotics. The magnitudes and signs of the intrinsic nonlinear fingerprints are used to conceptually model the mechanical response and to infer molecular and microscale features of the material.
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•Simple method for predicting particle collision related to attrition was developed.•The method does not require the use of complicated simulations such as DEM–CFD.•Machine functions ...are defined based on empirical correlations and bend geometry.•The calculated results are in good agreement with the experimental ones.•The calculation time is a few seconds.
This paper presents a simple method for predicting particle attrition during pneumatic conveying. The model calculates the changes in the particle size during pneumatic conveying (as a result of the collisions between the particles and bend walls) by using empirical correlations for both the machine and material functions. The method does not require the use of complicated simulations such as DEM–CFD. Furthermore, the computational model was written in MATLAB, and the results agree well with the experimental results for salt particles. The computation time was very short: a few seconds for the first collision (particles passed through one bend), and below one minute for six collisions. The experimental results and parametric study show that higher bend radius ratios caused less damage to the conveyed material. Moreover, higher air velocities and larger pipe diameters caused more damage to the conveyed material.
Asphalt rubbers mixed with untreated and plasticized crumb rubbers and a compounding coupling agent were investigated in this study. The low-temperature rheological properties of asphalt rubbers at ...different aging levels were tested using a dynamic shear rheometer (DSR). An interconversion between linear viscoelastic material functions was used to obtain converted evaluation indexes for the asphalt rubbers at low temperatures. Lastly, the physicochemical characteristics and the microscopic morphology of the asphalt rubbers were evaluated using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. In conclusion, the storage moduli of the asphalt rubbers containing heterogeneous crumb rubbers increased with the plasticized crumb rubber content and the aging level. The converted relaxation moduli were consistent with the change trend of the storage moduli, and the relaxation rate decreased as the plasticized crumb rubber content and the aging level increased. The process of mixing the base asphalt with crumb and plasticized crumb rubbers was physical blending, and the effect of aging on the absorption peak change of asphalt rubber with plasticized crumb rubbers was less than that of asphalt rubber with ordinary crumb rubbers. Aging deteriorated the blending between the crumb rubber and the base asphalt, and a distinct interface appeared between the crumb rubber and the base asphalt. The particle cores of the plasticized crumb rubber in the asphalt rubber were difficult to maintain. Furthermore, as the plasticized crumb rubber content increased, more fine particles stripped off the plasticized crumb rubber after aging.
Model-based material functions for SAOS and LAOS analyses Thompson, Roney L.; Alicke, Alexandra A.; de Souza Mendes, Paulo R.
Journal of non-Newtonian fluid mechanics,
January 2015, 2015-01-00, 20150101, Letnik:
215
Journal Article
Recenzirano
•In general, material functions originate from a constitutive model.•SAOS and LAOS analyses are based on either the Kelvin–Voigt or the Maxwell model.•The Jeffreys model is the simplest one that is ...able to predict the complete spectrum of mechanical behavior.•The analysis based on the Jeffreys framework is applicable to both SAOS and QL-LAOS data.
In this paper we argue that material functions usually originate from some constitutive model, and demonstrate the importance of determining the model involved in the material function of interest and of evaluating its appropriateness vis-à-vis the material under rheological characterization. In particular, we demonstrate that the usual material functions that arise in the analyses of SAOStrain and LAOStrain experiments are directly related to the Kelvin–Voigt model, while the ones that appear in the analyses of SAOStress and LAOStress experiments are directly related to the Maxwell model. Then we argue that it would be more appropriate to use a framework for data analyses of generic materials that is capable of predicting qualitatively the whole range of mechanical behavior. Finally we demonstrate that the Jeffreys model is the simplest appropriate framework for SAOS and LAOS data analyses. Since this model has three parameters and hence generates three material functions, these are determined with the aid of steady-flow data. The arguments presented in this paper are useful not only for determining the mechanical behavior of general non-Newtonian materials, but can also aid in the prediction of the behavior of these materials in complex flows.
This paper aims at providing a simplified analytical solution for functionally graded beam stress analysis and optimized material gradation on the beam deflection. The power-law (P-FGM) and ...exponential (E-FGM) material functions were considered for an exact solution of the normal and shear stress distributions across the beam thickness. Optimization of material function on the FGM beam deflection, which is new of its kind, was also investigated considering both simply supported and cantilever beams. It was observed that the non-dimensional normal stress and shear stress are independent of the elastic moduli values of the constituent materials but rather depends on both the ratio of the elastic moduli and the location across the beam thickness in the E-FGM material function model. This observation was first validated from available kinds of literature and through numerical simulation using ABAQUS and extended to the P-FGM stress analysis. The maximum deflection on the FGM beam occurred for a homogenous steel beam while the minimum deflection was observed on the beam with a P-FGM material function. The results of this work demonstrate that if properly designed and optimized, FGMs can provide an alternative material solution in structural applications.
Giesekus viscoelastic fluid is solved analytically for purely tangential flow in a concentric annulus at laminar and steady state conditions. Flow is created by a relative rotational motion between ...the cylinders. The analytical expressions for yield dimensionless velocity profile, pressure distribution, (f and Re are Fanning friction factor and Reynolds number) and material functions (viscosity, first and second normal stress difference coefficients) are obtained in cylindrical coordinates. Results show that difference between the values of lower as well as upper critical limits of the velocity ratio (where the minimum velocity happens) with their corresponding Newtonian values increase when mobility factor and Deborah number increase. The results also show that viscometric functions decrease by increasing elasticity because the viscoelastic fluid shows the shear thinning behavior which is strengthened by increasing elasticity. It is found that, for all values, profiles are symmetrical around ( and k are velocity ratio and radius ratio) because no relative motion exists.
For isotropic elastic continuous media, we consider a class of tensor nonlinear constitutive relations connecting stresses with small strains and including three material functions from any triple of ...independent invariants. General conditions are derived for these material functions, under which the deviatory and spherical properties of the tensor function defining the operator of the constitutive relations are not related to each other. These conditions are narrowed if the medium has a scalar potential, as well as if tensor linearity is additionally required. In the latter case, possible parametrizations of the stress and strain deviators and their representations in five-dimensional vector spaces are given.
Polymeric composites are rheonomic materials and their deformation can be described using the hereditary elasticity relations which allow for describing the mechanical behavior under time-variable ...loading with consideration of the influence of temperature and other operational factors. A system of hereditary-type constitutive relations is proposed for off-axis specimens of a unidirectional carbon fiber-reinforced plastic subjected to loading at different strain rates. Using the algebra of resolvent operators and inverted transformation, the constitutive equations allowing of description of anisotropy of rheological properties and, in particular, sensitivity to strain rates are derived.
Dynamic oscillatory shear flow has been widely used to investigate viscoelastic material functions. In particular, small amplitude oscillatory shear (SAOS) tests have become the canonical method for ...characterizing the linear viscoelastic properties of complex fluids based on strong theoretical background and plenty of experimental results. Recently, there has been increasing interest in the use of large amplitude oscillatory shear (LAOS) tests for the characterization of complex fluids. However, it is difficult to define material functions in LAOS regime due to an infinite number of higher harmonic contributions. For this reason, many recent studies have focused on intrinsic nonlinearities obtained in medium amplitude oscillatory shear (MAOS) regime, which is a subdivision of the full LAOS regime. In this study, we reviewed recent experimental and theoretical results of nonlinear material functions in the MAOS regime, which contain four MAOS moduli (two first-harmonic moduli and two third-harmonic moduli) from Fourier and power series of shear stress, and a nonlinear material function
Q
0
and its elastic and viscous parts from Fourier-transform rheology (FT rheology). Furthermore, to identify linear-to-nonlinear transitions in stress response of model polystyrene (PS) solutions, we presented Pipkin diagrams in frequency ranges from the rubbery plateau region to the terminal region.
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