High shear granulation of dolomite – I: Effect of shear regime on process kinetics

Wet granulation of previously unreported formulation system is presented. Dolomite powder is granulated under different shear regimes by using three-component binder formulation, water-molasses-polyvinylpyrrolidone. 1-D discretized population balance equation (PBE) and Equi-Partition of Kinetic Energy (EKE) coalescence kernel are applied to modelling granulation in a high shear mixer. Process modelling is focused to simulation of changes of the property of a group of entities, granule size distribution (GSD). The GSD predictions indicate the presence of coalescence growth as a dominant mechanism in the dolomite granulation process. Minor deviations between simulated and real GSDs signify the probability of other granulation mechanism(s) existence. A posteriori approach by integral method was used for coalescence rate constant estimation. This research highlights discrepancy in the coalescence rate of dolomite granulation process, between its early and later stages. Moreover, kinetic analysis of the high shear granulation process provides quantification of the macroscopic variable (impeller speed) influence on regarded property of a group of granules in terms of values of growth rate parameter.     

Evaluation of the shear characteristics of steel–asphalt interface by a direct shear test method

Shear characteristics of steel–asphalt interface under the influences of temperature, normal stress level and tack coat material were investigated. The direct shear tests were conducted on composite specimens with epoxy asphalt (EA) and polymer modified asphalt (PMA) tack coat materials at temperatures of 25 and 60 °C and normal stress levels of 0, 0.2, 0.4, and 0.7 MPa for each temperature. Results show that the failure modes include adhesive failure at the primer-tack coat interface and material failure of asphalt concrete. Steel–asphalt interface shows strain softening behavior until it reaches the sliding state. The shear strength and the shear reaction modulus increase with decreasing temperature and increasing normal stress levels. The specimens with EA tack coat provides much higher interface shear strengths than those with PMA tack coat at 25 and 60 °C. In addition, the failure envelopes of the shear strength and residual shear strength were obtained for combinations of tack coat materials and temperature conditions based on the Coulomb failure law.     

Why is fresh self-compacting concrete shear thickening?

The rheological properties of fresh concrete are mostly described by means of the Bingham model. For self-compacting concrete, the Bingham model is applicable in a lot of cases, but some authors report that the rheological behaviour is non-linear. The apparent viscosity increases with increasing shear rate and the SCC shows shear thickening behaviour. Shear thickening becomes important in operations occurring at high shear rates, like mixing and pumping. In these cases, shear thickening should not be forgotten in order to avoid breaking of the mixer, pump or pipes.This paper will describe two possible theories for shear thickening behaviour of SCC, based on results published in the rheology literature. The first theory consists of the formation of so-called (hydro-)clusters, which are temporary assemblies of small particles. These clusters start being formed from a certain shear stress on: the critical shear stress. They cause the viscosity to increase with increasing shear rate. A second theory is based on grain inertia, where a part of the shearing force is transmitted through direct momentum transfer between solid particles. Results on cement pastes prove that the grain inertia theory is not the main cause of shear thickening in self-compacting concrete. The influence of several parameters on the shear thickening behaviour of SCC can be well explained by means of the cluster theory.     

Modelling the nonlinear shear stress–strain behavior of a carbon fabric reinforced polyphenylene sulphide from rail shear and [(45°,−45°)]4s tensile test

In this article, the nonlinear shear stress–strain relationship of a carbon fabric-reinforced polyphenylene sulphide is investigated by performing and comparing both the [+45°/−45°]_ns tensile test and the three-rail shear test. First, quasi-static and hysteresis tests are performed to obtain the data necessary for the material model. Then, the material constants are optimized by comparing finite element simulations with the data derived from the experiments. The conducted experiments are simulated and the results are compared with the experiments, with excellent correspondence. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Mechanical,acoustic, and thermal performances of shear thickening fluid–filled rigid polyurethane foam composites: Effects of content of shear thickening fluid and particle size of silica

Shear thickening fluid (STF) features a rheological property, and rigid polyurethane (PU) foams feature low thermal conductivity and excellent acoustic insulation. In this study, an STF/PU rigid foam composite sandwich structure was designed using different contents (0, 0.5, 1, or 1.5 wt %) of STF that contained 14 nm, 40 nm, or 75 nm silicon dioxide (SiO₂). The effects of STF content and silica size on the cell structure, mechanical performance, acoustic absorption, and thermal performance of the STF/PU foam were explored. The test results show that STF/PU foam exhibited three characteristic acoustic absorption peaks, and the maximum acoustic absorption coefficient reached 0.841. STF addition increased compression, bending strength, and maximum acoustic coefficient, as well as initial mass loss temperature. STF-filled PU foam composites containing 14 nm and 40 nm SiO₂ had a mild rise in thermal insulation. The rigid STF/PU foam composites with a cell structure had the maximum thermal conductivity of 0.22 W m⁻¹ K⁻¹ and sound absorption coefficient of 0.841, which confirm that they are a good candidate for sound-absorbing energy conservation materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47359.     

Formation of β-cylindrites under supercooled extrusion of isotactic polypropylene at low shear stress

Formation of β-cylindrites of isotactic polypropylene under various wall shear stress (σ_w), supercooled temperature of melt (T_e) and crystallization temperature (T_c) has been investigated by polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD), and differential scanning calorimeter (DSC). To have better control over the thermomechanical history, instead of a reciprocating screw, the samples were prepared by extruding supercooled melt through capillary die. β-cylindrites can be observed by PLM in the extruded specimen even at a lower σ_w (0.020 MPa), and the number of β-cylindrites nuclei increases rapidly with the lowering of T_e. The nucleation density of β-cylindrites increases with the raising of wall shear stress under a given T_e of 160 °C. Furthermore, at lower supercooled temperature of melt (145 °C), the radius of β-cylindrites decreases with the increasing of σ_w, and the number of β-cylindrites nuclei almost remain invariant. At relatively higher σ_w (0.090 MPa), a saturation of β-cylindrites nuclei is observed with decreasing T_c. A modified model based on above results has been proposed to explain the effect of the original structure of quiescent supercooled melt on the formation of β-cylindrites under low shear stress.     

Compaction and shear failure of refractory mortars – effects of porosity and binder hardening

With the aim to correlate the global properties of refractory mortars with the micro-mechanical processes, a series of uni-axial compression and shear tests was conducted. The test program was developed with the view that the shear grain slip and cracks are frequent failure mechanism under compressive loads. The micro-structural changes during compression were monitored by X-ray micro focus computed tomography. Discrete element modelling was used to highlight the effects of individual factors of influence. Mortars with a water glass binder of different maturity were tested. In compression the mortars demonstrated cracking and pore closure. Shear tests showed that the failure process consists of multiple local failure events. The combined effects of the porosity and immature binder promote increased tendency for crack branching and arrest. This results in low shear strength and high compressibility. Cohesion and interlocking between the grains prevents crack branching and increases the stiffness and the strength.     

Comment on “Synthesis and electrorheological characteristics of titanate nanotube suspensions under oscillatory shear”

We comment on the recently published dielectric properties of titanate nanotubes (TNTs)- and titania nanoparticles (P25)-based electrorheological (ER) fluids in this note aiming to make a better understanding of their ER performance. Based on our Cole–Cole model plot, it is found that we can fit the dielectric spectra (dielectric constant/dielectric loss vs. frequency) of two ER fluids well with a better explanation of their polarizability by differentiating their ER performance.     

Fluid–particle correlated motion and turbulent energy transfer in a two-dimensional particle-laden shear flow

Discrete vortex simulations of a dilute two-dimensional particle-laden shear layer with one-way coupling were performed to study fluid–particle correlated motion and the transfer of turbulent kinetic energy between the phases. The resulting modification of carrier phase turbulence, estimated according to current computational models, was evaluated. Particle Stokes numbers were between 1.0 and 4.5, so that the particles showed considerable temporal concentration fluctuations due to centrifuging by the fluid flow structures, and the mass loading was 12% corresponding to a volume fraction of 6.0×10^?5.Fluid velocities and particle concentration and velocities and their covariances, which appear in a commonly used model equation for carrier phase turbulence modification, were evaluated. Additionally, the probability density functions of fluid velocity fluctuations viewed by the particles are presented and compared with their Eulerian counterparts. It was found that particles view reduced velocity fluctuations due to preferential clustering. The model for carrier-phase turbulence modification predicted turbulence reduction, depending on the particle Stokes number. The mechanism responsible for turbulence reduction was the correlated velocity fluctuations of fluid and particles and this reduction could reach values up to one third of the fluid flow dissipation. Preferential particle concentration together with a relative velocity between the phases could generate turbulent kinetic energy of the gas phase, however this production was nearly an order of magnitude smaller compared to reduction of turbulence due to the correlated motion. The findings were compared with experiments available in the literature and help to clarify the view when turbulence reduction or augmentation occurs.     

Do hemostatic agents affect shear bond strength and clinical bond failure rate of orthodontic brackets?

To evaluate the effects of different hemostatic agents on the shear bond strength (SBS) in vitro and clinical bond failure rate of orthodontic metal brackets in vivo. A total of 100 human premolar teeth were randomly divided into five groups: control, blood, Viscostat, hydrogen peroxide (H₂O₂), and epinephrine. Teeth were bonded with same light-cured adhesive and composite. After storage in distilled water for 24 h, thermal cycling was used as an aging procedure on all samples. The brackets were subjected to an SBS test at a speed of 0.5 mm/min until bracket debonding. SBS values and the adhesive remnant index were evaluated. Ninety-nine patients (52 female, 47 males) undergoing routine orthodontic treatment were recruited for this controlled clinical study at bonding stages. All patients with bleeding on the buccal surface of any premolar tooth or teeth at bonding were included in this study. Over 6 months, the bond failure rate was calculated. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s post-hoc test (p < .05). The McNemar test was used to compare bracket-bond failure. ANOVA showed a significant difference (p < .001) between the groups. No significant differences were found between the hemostatic agent groups (p > 0.05) in the in vitro part. The lowest failure rate was obtained in the control group rather than the hemostatic agent groups during clinical follow-up (p < 0.05). Each of the hemostatic agents (Viscostat, H₂O₂, and epinephrine) can be used for bleeding management during the orthodontic bonding process. Epinephrine application showed a high bond-failure rate at clinical follow-up.     

Interfacial shear strength of wood–plastic composites: a new pullout method using wooden dowels

This preliminary study examined the relationship of interfacial shear strength (IFSS) to modulus of rupture (MOR) for several different wood–plastic composites (WPCs). Plastics utilized were high-density polyethylene (HDPE) and polypropylene (PP). Pine and oak were used as the wood species. Compatibilizers used included maleic-anhydride-grafted polyethylene (MAPE) and maleic-anhydride-grafted polypropylene (MAPP). A strong correlation between IFSS and MOR was observed in a limited composition region. PP/oak WPCs showed poor correlation between MOR and IFSS, probably due to the roughness of the oak surface. Compatibilizer systems incorporating liquid components did not give good results and appeared to be inappropriate for this test method.     

Tensile shear strength of wood bonded with urea–formaldehyde with different amounts of microfibrillated cellulose

Urea–formaldehyde (UF) adhesive mixtures with a 5% suspension of microfibrillated cellulose (MFC) at 0.5, 1, 3, and 5 wt% loading levels based on the solid weight (62.4%) of the UF adhesive were prepared. Beech lamellas with dimensions of 5 mm×20 mm×150 mm were prepared from beech lumbers using a planer saw. The UF adhesive (E0 class) was mixed with the MFC using a magnetic stirrer to achieve a proper distribution of the MFC in the UF adhesive. The tensile shear strength of single lap-joint specimens bonded with UF adhesive containing MFC was determined in accordance with EN 205 (2003). The specimens bonded with UF adhesive containing the MFC showed better tensile shear strengths as compared to the control. As compared to the control specimens, the tensile shear strength of the specimens increased by 5.7% as 3 wt% of the MFC was incorporated into the UF adhesive. However, a further increment in the MFC content up to 5 wt% decreased the tensile shear strength of the specimens (−14.3% of control specimen). The MFCs were well dispersed in the UF resin and were cross-linked to form a network to reinforce the bond line, improving bonding performance.     

High shear granulation of dolomite – II: Effect of amount of binder liquid on process kinetics

This paper, the second of a series, analyzes the effect of binder amount on the kinetics of wet granulation process. Granulation experiments were conducted in batch, lab-scale high shear mixer with formulation system that was initially studied in first part of a series. First, we identify the effect of binder content on the net granulation behaviour during early stage of the process. Single entity property (its size) was accounted only within this research. The results indicate that binder content strongly promotes growth of dolomite entities. Secondly, 1-D discretized population balance equation (PBE) and Equi-Partition of Kinetic Energy (EKE) theory were used to simulate the net granulation process. Tested “coalescence-only” models provide good prediction of real dolomite granule size distributions (GSDs) during early stage of the process for each binder content value. By using modelling procedure granule growth rates were quantified. Ultimate goal of relating the coalescence rates of dolomite entities with binder amount variable is provided. This will result in a better perspective of the meso-scale of the dolomite granulation process.     

Experimental electrohydrodynamics of poly(γ-Benzyl-L-Glutamate) in M-Cresol solution subjected to shear flow and electric fields

Electrohydrodynamics of a dilute solution of rigid macromolecules was experimentally studied in a continuation of previous theoretical work. We used poly(γ-benzyl-L-glutamate), having 4 different molecular weights ranging from 15,000 to 236,000, dissolved in m-cresol. Poly(γ-benzyl-L-glutamate) solutions were subjected to combinations of simple shear flow field and uniform electric field perpendicular to the shear direction. Transient birefringence and extinction angle were simultaneously measured using the phase-modulated birefringence method. Steady state results were compared with the theoretical prediction from previous works and rotational difiusivity and permanent dipole strength of PBLG were obtained from multiple parameter fitting. Consequently, the optical state of PBLG solution could be explained to a certain extent by the dimensionless field parameters established in the previous theory.     

Nucleation and growth behavior of β-nucleated iPP during shear induced crystallization investigated by in-situ synchrotron WAXS and SAXS

Polymer crystallization under flow was investigated because final properties of polymers strongly depend on the crystalline structure and morphology formed during processing. In-situ synchrotron WAXS and SAXS were used to investigate the structure formation and morphological developments during quiescent and shear-induced crystallization of iPP with 3 different concentrations (0.01, 0.03 and 0.1 wt%) of β-nucleating agent. Under quiescent conditions, a high β-content was obtained at all those concentrations indicating the high β-nucleating efficiency of the nucleating agent. After application of shear, the β-nucleating ability at small concentration was retained, while at larger concentrations it was strongly retarded. Furthermore, the addition of β-nucleating agent was beneficial for the molecular alignment during processing, the anisotropic particles of β-nucleating agent were much more effective to align the molecular chains in the flow direction compared to isotropic ones. A crystallization scheme for the iPP β-nucleating agent under shear was proposed.     

High shear strength and ductile ZrC–SiC/austenitic stainless steel joints bonded with Ti/Ni foam interlayer

A transient-liquid-phase (TLP) diffusion bonding method was employed to join ZrC–SiC ceramic and austenitic stainless steel by using Ti foil and various density Ni foam as interlayer. The Ti–Ni TLP contributed to a firm bonding between ceramic and foam interlayer while avoiding liquid infiltration in foam structure. The influence of holding time on the microstructure of the TLP reaction layer was investigated. The shear tests showed the joints with foam interlayer exhibited ductile failure mode and improved fracture work in comparison with the one with dense Ni interlayer. A maximum shear strength of 117.2 MPa was reached when the relative density of Ni foam was 0.57. The fracture behaviors of the joints during shear test were in-situ observed.     

High-frequency welding of glass–fibre-reinforced polypropylene with a thermoplastic adhesive layer: Effects of ceramic type and long-term exposure on lap shear strength

In this study, high-frequency (HF) welding of glass–fibre-reinforced polypropylene (GF/PP) with thermoplastic adhesive layers consisting of zinc oxide (ZnO), anatase-type titanium oxide or silicon carbide was investigated. Effects of the ceramic type and content on the dielectric and temperature characteristics of these adhesive layers were evaluated experimentally, and the ratio of the dielectric loss tangent to the relative dielectric permittivity (tanδ/ε′), which was the index of the HF heating efficiency, exhibited different tendencies by these parameters. This value increased rapidly with increasing temperature even at 10 vol% ZnO, suggesting that the heating of the adhesive layer may be accelerated by combining temperature rise with a small amount of ZnO. During the HF welding process, the ZnO-containing adhesive layer bound to GF/PP in the shortest time (18 s) with high bond strength (~14 MPa). The effects of temperature (50 °C) and moisture (80% relative humidity) on the mechanical strength of the HF-welded specimens after a long-term exposure were also examined.     

Fiber/matrix interfacial shear strength of C/C composites with PyC–TaC–PyC and PyC–SiC–TaC–PyC multi-interlayers

The fiber/matrix (F/M) interfacial shear strength (IFSS) of carbon/carbon (C/C) composites with PyC–TaC–PyC and PyC–SiC–TaC–PyC multi-interlayers was investigated. To obtain C/C composites with PyC–TaC–PyC and PyC–SiC–TaC–PyC multi-interlayers, a thin layer of PyC was deposited on carbon fibers. After this, TaC and SiC–TaC layer(s) were uniformly deposited on the PyC coated carbon fibers. As an outer-layer, a PyC layer was deposited on these TaC and/or SiC–TaC coated carbon fibers by isothermal chemical vapour infiltration (CVI) and then densified with resin carbon by impregnation and carbonization. Finally, C/C composites with PyC–TaC–PyC and PyC–SiC–TaC–PyC multi-interlayers were obtained. The effects of PyC–TaC–PyC and PyC–SiC–TaC–PyC multi-interlayers on interfacial shear strength (IFSS) of C/C composites were investigated. Single fiber push-out tests were conducted on the fibers aligned perpendicularly on the thin slices specimen surface using nano-indentation. Results showed that the IFSS of C/C composites decreased with the introduction of PyC–TaC–PyC and PyC–SiC–TaC–PyC multi-interlayers. After heat treatment (at temperatures ranging from 1400 to 2500 °C) of C/C composites with PyC–TaC–PyC multi-interlayers, it was found that the IFSS decreased with the increase in temperature. This decrease in IFSS is explained by taking into account the microstructural variations on heat treatment.