Abstract
The novel magnetorheological shear thickening polishing fluids (MRSTPFs) were developed by mixing micro cubic boron nitride (CBN) abrasive particles into traditional magnetorheological shear ...thickening fluids. MRSTPFs were constructed by uniformly fumed silica and polyethylene glycol as shear thickening fluids, carbonyl iron particles (CIPs) as ferromagnetic phase and CBN particles as abrasive phase. In this work, various MRSTPFs were prepared to explore their rheological characteristics. Sweeps of steady shear rate and dynamic shear frequency were conducted under different magnetic flux densities, respectively. A mathematical model was presented to explain shear rate variation with shear stress. The magnetorheological shear thickening mechanism was well described. The rheological experiment results have revealed that shear thickening effect was still existing in magnetic flux density. However, the increased magnetic flux density played a negative role on the shear thickening effect. Particle size optimization of CIPs was thus essential to maximize the shear thickening effect. On the other hand, with increased shear frequency, the viscoelastic feature of MRSTPFs was converted from linear to non-linear. It was found that the shear yield stress of the MRSTPFs was magnified with the stronger magnetic flux density and larger CIPs size. The investigation of rheological characteristics demonstrated that MRSTPFs could enhance polishing performance, which contributed to developing a high-efficiency and ultra-precision polishing process.
Magnetorheological (MR) fluid is a typical intelligent material which is widely adopted in the mitigation of civil engineering structures, and it is normally composed of nano-sized or micro-sized ...iron particles, carrier fluids and additives. Because of the complexity of its composition, it is one of the research hotspot to propose a micromechanical model which can effectively describe the micromorphological transformation as well as characteristics of MR fluids. In this study, a single-double chains micromechanical model of MR fluids is proposed by taking into consideration of the influence of volume fraction and magnetic induction on the microstructure evolution of MR fluids based on the coupled field as well as magnetic dipole theory. Additionally, the shear yield stress test of the self-prepared MR fluids with multi-wall carbon nanotubes(MWCNTs) and graphene oxide (GO) composites coated ferromagnetic particles is carried out by MCR302 rotational rheometer and the results have been compared with the theoretical values of the single-double chains micromechanical model to verify the effectiveness and accuracy of the proposed model.
•Mechanical properties of MRF were studied using the theory of electromagnetic-thermal effects.•Testing of the coupling effect of multiple physical fields.•Temperature affects magnetic field strength ...and magnetization rate of magnetic particles.•Magnetic field strength and temperature influences the shear yield stress of MR fluid.
The mechanical properties of magnetorheological fluid are influenced by multiple factors in multi-physical field environments. To precisely characterize the mechanical properties and variations under the influence of multi-physical field coupling, this study analyzes the mechanism of electromagnetic-thermal multi-physical field coupling based on the principles of electromagnetic thermal effects. Furthermore, it derives formulas to describe the changes in resistance of the excitation coil, electric current, and magnetic field strength resulting from the influence of temperature. A physical model of the excitation coil is constructed for conducting numerical simulations, and a test bench is assembled to validate the magnetic field strength generated by the excitation coil. By considering the impact of temperature on both the magnetic field strength and the magnetization rate of the particles in the magnetorheological fluids, an analytical calculation is performed to determine the shear yield stress of the fluid under multi-physical field conditions. The results showed that the magnetic field strength generated by the excitation coil as temperature decreased with increasing, and with an increase in temperature from 30 °C to 80 °C, the magnetic induction strength decreased by 17.1 % from 22.88 mT to 18.96 mT, while the shear yield stress decreases by 29.2 % from 35.9 kPa to 25.4 kPa. These findings have a significant effect on the performance of magnetorheological fluids materials, underscoring the necessity of considering multi-physical field effects when researching their performance and verifying the performance degradation and failure of magnetorheological devices under high-temperature conditions.
Abstract
The flow and consolidation of strongly flocculated particulate suspensions in water are common to a range of processing scenarios in the minerals, food, water and wastewater industries. ...Understanding the compressive strength or resistance to consolidation of these suspensions is relevant to processes such as filtration, centrifugation and gravity settling, where the compressive strength defines an upper boundary for processing. New data for the compressive strength of consolidating flocculated particulate suspensions in water, including alumina and calcium carbonate, are compared with earlier data from the literature and from our own laboratories for several systems, including two earlier sets of data for alumina. The three sets of data for the compressive strength of alumina agree well. Differences are noted for data measured in shear between our own laboratories and others. New data for the shear strength of AKP-30 alumina are also presented, and although the agreement is not as good, the difference is implied to be due to wall slip associated with a difference in measurement techniques. A simple nonlinear poro-elastic model of the compressive strength was applied to the eight sets of compressive strength data and was found to account for most features of the observed behaviour. The agreement strongly supports the mechanistic failure mode in compression for these systems to be one of simple strain hardening. The one feature that it does not account for without invoking a ‘ratchet’ is the irreversibility of consolidation. It is, however, suspected that wall adhesion might provide such a ratchet in reality, since wall adhesion has been neglected in the analysis of raw compressive strength until recently, notwithstanding the pioneering work of Michaels and Bolger (30). Overall, the data analysis and fitting presented herein indicate a new future for the characterisation of aggregated particulate suspensions in shear and compression whereby a limited data set in both compression and shear, albeit targeted across a wide concentration range, can now be used to predict comprehensive curves for the shear yield stress and compressive yield stress of samples using a simple poro-elastic model. The veracity of the approach is indicated through a knowledge that the behaviour of both parameters is scalar across a wide range of materials and across a wide range of states of aggregation.
•A micromechanical model of three-diameter magnetorheological fluids is established by analyzing the particle size of magnetic particles, based on the theory of magnetic dipoles, using mechanical and ...mathematical statistics method.•The particle size analysis of carbonyl iron powder was firstly analyzed by laser particle size meter.•The average improvement in accuracy of three-diameter model over single diameter model is 13.46%.
In this article, a micromechanical model of three-diameter magnetorheological fluids is established by analyzing the particle size of magnetic particles, based on the theory of magnetic dipoles, using mechanical and mathematical statistics method. To simplify the analysis of the problem, this study makes assumptions including: (1) Assume that the magnetic particle size in each cell is large: medium: small is 1:8:1, and the large particles and small particles are located at both ends of the cell; (2) During the shearing process, the slope angle of each chain obeys normal distribution. The oil-based magneto-rheological fluids with different volume fractions were also prepared to test the mechanical properties of the magneto-rheological fluids. By comparing the model with the experimental data, it is found that the micromechanical models of magnetorheological fluids with three different particle sizes were more accurate compared with the mechanical models of magnetorheological fluids with single-particle size at the same magnetic particle volume fraction, shear rate, and magnetic field strength, with an average optimization accuracy of 13.46%. The model can be used to improve the performance and accuracy of magnetorheological devices.
3D printing has become one of the most innovative technologies for cement-based systems (CBS). However, recent studies have shown some issues related to printability and buildability (water drainage, ...plugs on extruder die, spreading of first layer, etc). To achieve a proper rheology control of CBS, it is essential to adapt the material fresh state properties (initial shear yield stress and structural build-up). In this study, a reference cement-based mortar with fly ash (25%), a 1:1.5 binder to sand ratio and a 0.38 water to binder ratio was used. A polycarboxilate ether-based superplasticizer was added until a consistency of around 1 kPa, measured with the cone-penetration test, was reached. Then, small amounts of several types of nanoclays (NC) in powder and slurry form (sepiolite, attapulgite and bentonite) and natural fibers were added to modify mortar rheological properties. The aim of the study was to characterize the rheological properties of 3D printing mortar samples with NC and basalt fibers (BF) to understand printability and buildability of this material. Cone-penetration test, flow table test and slump test were used to characterize 3D printing capacities. The cone-penetration test was performed in stirred and left at rest samples to assess shear yield stress before and after material deposition. Nanoclays showed a remarkable capacity to retain water and avoid drainage during extrusion but also to increase fresh state strength of material over time. Besides, they increased shear yield stress over time when left at rest. On the contrary, samples stirred over time did not show any increase of shear yield stress, especially samples with slurry nanoclays. Natural fibers also reduced drainage and enhance printability control regarding to reference mortar. BF also enhanced a performance on stirred sample but showed slightly changes on structural build-up at rest, mainly governed by NC effect.
The modern wood converting processes consists of several stages and material drying belongs to the most influencing future performances of products. The procedure of drying wood is usually realized ...between subsequent sawing operations, affecting significantly cutting conditions and general properties of material. An alternative methodology for determination of mechanical properties (fracture toughness and shear yield stress) based on cutting process analysis is presented here. Two wood species (pine and beech) representing soft and hard woods were investigated with respect to four diverse drying methods used in industry. Fracture toughness and shear yield stress were determined directly from the cutting power signal that was recorded while frame sawing. An original procedure for compensation of the wood density variation is proposed to generalize mechanical properties of wood and allow direct comparison between species and drying methods. Noticeable differences of fracture toughness and shear yield stress values were found among all drying techniques and for both species, but only for beech wood the differences were statistically significant. These observations provide a new highlight on the understanding of the effect of thermo-hydro modification of wood on mechanical performance of structures. It can be also highly useful to optimize woodworking machines by properly adjusting cutting power requirements.
A nanosectioning (cutting) method was used to test the local shear yield stress and fracture toughness (specific work of surface formation) of multiwall carbon nanotube (MWCNT) poly(methyl ...methacrylate) (PMMA) composites, and the effects of MWCNT content on the yield stress and toughness were investigated. The composites were prepared by a solution casting method, with MWCNT content varying from 0.05 to 1.0 wt%. Above 0.1 wt% MWCNT content, the yield stress reduced by the addition of MWCNTs. The fracture toughness of the composite was effectively enhanced by the addition of MWCNTs, ranging from 17 J/m2 for the neat PMMA to 25 J/m2 for the 1.0 wt% composite. The shear yield stresses obtained by nanosectioning were correlated to nanoindentation measurement, and possible contributions from the MWCNTs to the fracture toughness of the composite were analysed.
The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the ...structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress
and shear yield stress
of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of
were also examined and the variation of
became largely dependent on the fiber morphology and mass concentration.
Wood drying is an important stage in the woodworking process. After drying, wood is subject to a re-sawing process, for which a high quality surface, low material loss, and high efficiency are often ...required. In this paper, forecasted values were presented of cutting power for the re-sawing process of pine and beech wood that were dried with four different methods. Forecasting of cutting power for an industrial band saw machine that works daily in a Polish sawmill was determined. Values of cutting power were forecasted for a full range of feed speeds of the analyzed band saw machine. The achieved results allowed the observation of noticeable changes in the forecasted cutting power for a given sawing process as a function of the wood drying method applied. Significant changes were observed for pine wood, especially between air-dried pine wood and wood dried with warm air-steam mixture, and between pine wood dried in a conventional kiln and with warm air-steam mixture.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
PDF
