Yield Stress Values Research Articles

Evaluation of the aminosilane and colloidal silica treated red iron oxide pigment effects in styrene acrylic and polyurethane dispersion

PurposeThis study aims to perform the surface treatment of synthetic α-Fe2O3 red iron oxide pigment with hydrolysate 3-aminopropyl silane (A) and colloidal silica (CS) and investigate the effects of surface-treated pigment on the styrene acrylic (SA) emulsion and polyurethane (PU) dispersion.Design/methodology/approachFor this purpose, firstly red iron oxide particles were modified with A and CS separately in an aqueous medium. After isolation of the modified iron oxide were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). Moreover, the degree of the dispersion stability of the modified pigment in coatings with SA emulsion and PU dispersion was investigated by using an oscillation rheometer. Loss (G''), storage (G') modulus, loss factor [tan(δ)] and yield stress (τ0) values were determined by performing amplitude and frequency sweep tests.FindingsThe τ0 in SA coatings decreases with the amount of used A and increases with the amount of used CS. The τ0 decreases as the amount of used A and CS in PU coatings increases. The use of CS on red iron oxide pigments causes storage modulus to increase in SA coatings at low angular frequencies, while it causes a decrease in PU coatings.Originality/valueTo the best of the authors’ knowledge, for the first time, the suspended state of the iron oxide hybrid pigment formed with CS in the coating was investigated rheologically in this study.

Microstructure and deformation behavior of MoReW in the temperature range from 25°C to 1500°C

Refractory alloys which retain high strength above 1000 °C and, at the same time, have excellent malleability, are in high demand for high temperature structural applications. Here we report the microstructure and mechanical properties of an equiatomic MoReW alloy, which has demanding combination of strength and ductility in the temperature range of 25 °C to 1500 °C. The alloy was prepared by arc melting followed by hot isostatic pressing at 1400 °C, 207 MPa for 5 h and it has a single-phase BCC structure with the average grain size of ∼170 μm. The alloy yield stress is relatively low (555 MPa) at 25 °C, but it has weak temperature dependence resulting in remarkably good yield stress values at high temperatures, e.g. 402 MPa at 1000 °C and 247 MPa at 1400 °C. The alloy shows strong strain hardening at 25–1000 °C, with the true flow stress tripled at 25 °C and doubled at 1000 °C after true strain of 0.4. The microstructural analysis of the deformed specimens reveals extensive deformation twinning activity at the beginning of deformation and activation of other deformation modes at later deformation stages in this temperature range. This is unusual behavior as generally activation of twinning occurs at high stresses, after extensive dislocation activity, and deformation twinning in refractory alloys has never been reported above 400 °C. To understand and explain the observed behaviors of the alloy, a detailed analysis of strengthening mechanisms associated with screw and edge dislocation glide, as well as with twin nucleation and propagation, has been conducted and reasonable qualitative models of yielding, strain hardening and ductility of the studied MoReW alloy have been proposed.

Stress-Invariants-Based Anisotropic Yield Functions and Its Application to Sheet Metal Plasticity

The yield criterion, or so-called yield function, plays an important role in the study of the plastic working of a sheet because it governs the plastic deformation properties of the sheet during the plastic-forming process. In this paper, we propose a novel anisotropic yield function useful for describing the plastic behavior of various anisotropic sheets. The proposed yield function includes the anisotropic version of the second stress invariant J2 and the third stress invariant J3. The proposed yield function can explain the anisotropic plastic behavior of various sheets by introducing the parameters α and β and also exhibits both symmetrical and asymmetrical yield surfaces. The parameters included in the proposed model were determined with an optimization algorithm from uniaxial and biaxial experimental data under a proportional loading path. In this study, the validity of the proposed anisotropic yield function was verified by comparing the yield surface shape, normalized uniaxial yield stress value, and Lankford anisotropic coefficient R-value derived from the experimental results. Applications of the proposed anisotropic yield functions to an aluminum sheet showed symmetrical yielding behavior and, to pure titanium sheets, showed asymmetric yielding behavior; thus, it was shown that the yield curve and yield behavior of various types of sheet materials can be predicted reasonably by using the proposed new yield anisotropic function.

Instant yield stress measurement from falling drop size: The “syringe test”

We analyze different flow regimes of a filament formed by extrusion of a material through a cylindrical die. We deduce that the elongational yield stress of a simple yield stress fluid (i.e., with negligible thixotropy effects) can be determined from the mass of the droplet after filament breakage and an estimation of the critical radius at pinch-off at the solid-liquid regime transition. We demonstrate that such a simple characterization is relevant in a relatively wide range of extrusion velocities, i.e., this velocity slightly affects the drop mass in this range. For the simple yield stress fluids used, Carbopol gel, clay-water paste at different concentrations, and emulsion, covering a large range of yield stress values (50–1000 Pa), the elongational yield stress appears to be equal to the simple shear yield stress times a factor equal to about 1.53. As a consequence, this simple test may be used to obtain, almost instantaneously and without sophisticated apparatus (a syringe and a balance are sufficient), a good estimate of the shear yield stress of simple yield stress fluids. In that case, the main source of uncertainty (up to about 20%) is the value of the critical radius at the solid-liquid transition. Finally, we review the operating conditions (material properties and extrusion characteristics) for which we can expect this approach to be valid.

Atomistic mechanisms underlying plastic flow at ultralow yield stress in ductile carbon aerogels.

We investigated carbon aerogel samples with super low densities of 0.013 g cm-3 (graphite is 2.5) and conducted compression experiments showing a very low yield stress of 5-8 kPa. To understand the atomistic mechanisms operating in these super low density aerogels, we present a computational study of the mechanical response of very low-density amorphous carbonaceous materials. We start from our previously derived atomistic models (based on the DynReaxMas method) with a density of 0.16 g cm-3 representing the core regions of carbon aerogels. We considered three different phases exhibiting either a fiber-like clump morphology interconnected with string-like units or a more reticulated framework. We subjected these phases to compression and shear deformations and analyzed the resulting plastic response via an inherent-structure protocol. Strikingly, we find that these materials possess shear plastic relaxation modes with extremely low values of yield stress, negligible with respect to the finite values predicted outside this "zero-stress" region. This is followed by a succession of two additional regimes with increasing yield stress values. Our analysis of the atomistic relaxation mechanisms finds that these modes have a collective and cooperative character, taking the form of nanoscopic shear bands within the clumps. These findings rationalize our experimental observations of very low-stress plastic deformation modes in carbon aerogels, providing the first steps for developing a predictive multi-scale modeling of the mechanical properties of aerogel materials.

Mechanical properties research of carbon fibre composites incorporating nanoclay and graphene

Study purpose is to determine the interactions between the widely-used graphene and nanoclay on carbon fiber composite materials. They are produced using the vacuum infusion method by reinforcing the nanoclay and graphene, which have a montmorillonite structure organized at various ratios via homogenizer, into the resin that is to be applied to carbon fiber layers. Eczac?ba?? EsanNANO 1-140 was used as nanoclay, and GRAFEN NG5 of the Nanografi Co. Ltd. was used as graphene. The graphene ratio was kept constant by taking reference from antecedent studies. Tensile test was applied to the produced samples. Graphene in the resin is expected to increase the saturation in the layers and improve mechanical properties. After nanoclay ratio exceeds a certain limit, it acts negatively rather than positively in the tensile test, their cracked roads are then rendered easier to traverse by them combining. This is why there is a certain bell-shaped curve in the strain values measured in samples. The result that gives the optimum values is sought after. Additionally, there are studies previously conducted with polymer matrix composite, from which samples that could reach to certain strains or to higher yield stress values in certain intervals are obtained. By increasing the strength and toughness of the graphene and nanoclay resin, they gain more rigidity, which raises an expectation of increment to be observed in the yield and tensile strengths.

TEMPERATURE DEPENDENCE OF THE DEFORMATION BEHAVIOR OF HIGH-ENTROPY ALLOYS CO20CR20FE20MN20NI20, CO19CR20FE20MN20NI20С1 AND CO17CR20FE20MN20NI20С3. MECHANICAL PROPERTIES AND TEMPERATURE DEPENDENCE OF YIELD STRENGTH

This paper discusses the temperature dependence of the mechanical properties of multicomponent alloys Co20Cr20Fe20Mn20Ni20 (Cantor alloy), Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 under uniaxial static tension in the temperature range from 77 to 473 K. It is shown that after thermomechanical treatment all the alloys have an fcc crystal structure, but unlike single-phase Co20Cr20Fe20Mn20Ni20 and Co19Cr20Fe20Mn20Ni20С1 alloys, the alloy with 3 at % carbon exhibits large incoherent chromium carbides. Alloying with carbon causes solid solution strengthening of the austenitic phase and dispersion hardening, and promotes grain refinement in the Cantor alloy. Solid solution strengthening contributes to an increase in the athermal and thermal stress components of σ0.2, leading to higher yield stress values and stronger temperature dependences σ0.2( T ) in Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 alloys than in the Cantor alloy. The results of X-ray diffraction and microscopic analysis indicate that despite the differences in the total concentration of interstitial atoms in Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 alloys, the concentrations of carbon dissolved in the crystal lattice of the austenite phase are close. However, the higher strength properties of Co17Cr20Fe20Mn20Ni20С3 compared to Co19Cr20Fe20Mn20Ni20С1 are determined primarily by grain boundary strengthening and, to a lesser extent, by dispersion hardening. Both factors such as lowering the deformation temperature and alloying with carbon contribute to an increase in the deforming stresses of the Cantor alloy. It is shown that alloying with carbon affects the staged plastic flow of the Cantor alloy: the tensile curves of Co19Cr20Fe20Mn20Ni20С1 carbon alloy exhibit a well-defined stage of microplastic deformation, and the flow curves of Co17Cr20Fe20Mn20Ni20С3 alloy at the initial stages of plastic flow have a parabolic shape, typical of the deformation of alloys with large incoherent particles. The elongation to failure of Co20Cr20Fe20Mn20Ni20 and Co19Cr20Fe20Mn20Ni20С1 alloys increases linearly with decreasing deformation temperature, i.e., the mechanical properties of single-phase alloys are improved in the region of low test temperatures. For Co17Cr20Fe20Mn20Ni20С3 alloy, an increase in strength properties during low-temperature deformation is accompanied by a decrease in ductile characteristics, and the alloy becomes brittle from the viewpoint of macromechanical behavior.

Effect of metakaolin utilization ratio and loop method-pre-shearing process variation on rheological properties of cementitious systems having different C3A content

Thixotropic behavior, which directly affects the fresh state properties of cementitious systems such as pumpability, compressibility and hydrostatic mold pressure, is determined by applying the loop method, step change and constant shear rate. This behavior is seriously affected by parameters such as the type, amount and fineness of the binder and the process applied in rheological measurements. In this study, the effect of cement C3A content, metakaolin utilization ratio, resting time of the mixture, pre-shear rate and applying pre-shear rate on the thixotropic behavior of the mixtures at the beginning and 20th-minutes were investigated. For this purpose, 4 types of cement having different C3A contents (2.13%, 3.60%, 6.82% and 9.05%) were used. By testing each of the 4 cements (2.13%, 3.60%, 6.82% and 9.05%) for 5 conditions (no metakaolin, 3%, 6%, 9% and 12% metakaolin), a total of 20 mixtures were prepared. For each cement type, 0, 3, 6, 9 and 12% of the total binder volume was replaced with metakaolin. The loop method was used to determine the rheological parameters. According to the results, irrespective of all parameters examined, the structural build-up area values were higher than the structural breakdown ones in the mixtures and the structure formation that occurred after 20 min was mostly reversible. It was determined that rheological parameters, structural build-up area value and rate of reversible structure formation increased with the increase in cement C3A content and metakaolin utilization rate. The increase in the initial dynamic yield stress values of the mixtures with the increase of the cement C3A ratio was more pronounced in the case where the measurement is made without waiting immediately after the pre-shear application. The effect of C3A content on dynamic yield stress and viscosity values was more pronounced with an increasing pre-shear rate. The opposite was observed for the structural build-up area values.

Effect of Different C<sub>3</sub>A Content on Rheological Parameters in Paste Mixtures

C3A content of cement is of great importance in connection with the fresh and early age mechanical properties of cementitious systems. In this study, the effects of different C3A content on the static and dynamic yield stress and viscosity values of paste mixtures were examined. Consequently, the use of polycarboxylate ether-based water reducing admixture (PCE) up to a certain dosage affected adversely the rheological characteristics of the mixtures. The dispersion effect, which increased with the increment of the PCE dosage, increased the hydration rate of C3A by increment its contact with water by dispersing it. Therefore, dynamic yield stress and viscosity were adversely affected by the increment in PCE dosage in high C3A-containing mixtures, while rheological parameters improved after a certain dosage in low C3A ones.

Geopolymeric Composite Materials Made of Sol-Gel Silica and Agroindustrial Wastes of Rice, Barley, and Coffee Husks with Wood-Like Finishing

Geopolymers have been mainly utilized as structural materials; their chemical structure and morphologies have been explored for their potential as a high-performance material in emerging applications. Geopolymer composites reinforced with materials based on agro-waste are attracting interest in engineering applications due to their easy processing, low cost, low density, and high strength-to-weight ratio. This investigation pursues an experimental methodology that consists of a scheme to make composites with a geopolymer matrix and agro-waste (rice husk, barley, and coffee) as aggregate material, that can be applied in various fields of construction. The study was intended to determine the influence of adding various agro-wastes on the mechanical properties of the geopolymer. According to the respective ASTM standards, the materials obtained were prepared and analyzed to determine their compressive strength, flexural strength, hardness and scanning electron microscopy (SEM)-determined characteristics. The results revealed that, for the compression tests, the composites formed by a sol-gel matrix and barley husk showed a better yield, obtaining the highest value of 3.5 N/mm2. Concerning hardness testing, the composites with a geopolymer matrix and coffee husks obtained higher values compared to the other composites. For the flexural tests, the compounds with the sol-gel/fly ash matrix obtained the highest yield stress value, which was 5.25 MPa with an elastic modulus of 7.59 GPa. The results of the microstructural analysis showed good husk-matrix interaction, together with failure mechanisms. The conformation of such waste-based compounds may enable them to replace natural wood in some applications, such as in the finishing of interiors of homes, during the final stages in the construction of buildings, or in the decoration of inhabited houses, as well as in finishing in the manufacture of furniture.

Impact of uncertainties associated with the choice of the yield stress on the prediction of subsurface reservoir compaction: A field study

The compaction of subsurface chalk during hydrocarbon production leads to technical and societal issues related to well trajectory design, wellbore collapse, seafloor subsidence, and seismic events. Predicting reservoir deformation over time requires well-calibrated constitutive equations to capture the viscoplastic response of chalk according to several parameters including porosity, age, water saturation, and rate of applied stress or strain. The experimental data used to extrapolate trends between e.g., porosity and yield stress, show a non-negligible data scattering, thereby raising questions about the reliability of the predicted compaction. The present study aims at assessing how the uncertainty associated with the determination of the yield stress manifests itself at the field scale. To this purpose, one-dimensional simulations are performed on four producing hydrocarbon reservoirs from the Danish North Sea and quality-checked against seafloor subsidence measurements. Two simulations are run per case study by considering in the constitutive equations the initial (conservative approach) and final (optimistic approach) yield stress values, which delimit the transition between the elastic and plastic regime of chalk. The results indicate that the accumulated strain and the seafloor subsidence vary by a factor of up to 73% and 50%, respectively between the conservative and optimistic approaches. These differences in the compaction behaviour are influenced by three parameters, the initial porosity, the virgin stress condition, and the stress history of the reservoir. This study demonstrates that the uncertainty analysis of compaction simulation studies is essential for estimation of compaction drive of hydrocarbon fields and to identify the locations potentially subject to failure in the context of hydrocarbon production and field abandonment as well as CO2 and thermal storage projects.

Measures of the yield stress fluids oriented for dysphagia management using steady-state shear, transient shear, and large-amplitude oscillatory shear (LAOS)

Dysphagia has become a highly prevalent and ever-growing disease among the elderly in today's society. Polysaccharide-thickened food with yielding features oriented toward dysphagia management has been recognized as a suitable diet capable of alleviating the swallowing risk by allowing the swallow-related muscles to coordinate this activity with appropriate timing. However, the divergence of different measures and the resultant discrepancy between yield stress values remains that experimentally and theoretically impedes the understanding of yielding features of food on the efficiency of dysphagia management. Herein, we compared the typical rheological approaches to yielding measurement, including steady-state shear, transient shear rate ramp, and large-amplitude oscillatory shear (LAOS), based on three polysaccharide-thickened solutions and nutrition emulsions. As a hallmark of thixotropy properties, the hysteresis loop was quantitatively illustrated for the three polysaccharide emulsions to distinguish them as simple or complex yield stress fluids. The Herschel–Bulkley model was employed to obtain the dynamic yield stress in steady-state shear mode. Yield stress estimated by transient shear and small oscillatory shear methods is comparable. Importantly, different from the common approaches that acquire only one critical yield stress value, the stress bifurcation method from LAOS employed in this work enabled us to estimate the yielding onset and end in the solid–liquid transition process of the fluids, which may bring new insight and motivate innovative idea in the diet design in dysphagia management.

Strength-hardness relationship for AlSi10Mg alloy produced by laser powder bed fusion: An experimental study

In this work, significant strength and ductility variations are reported for AlSi10Mg parts fabricated at different orientations using laser powder bed fusion (LPBF). Hardness and surface roughness of the specimens at different orientations were measured. Tensile testing together with digital image correlation technique were conducted on the specimens. XY specimens showed the highest yield stress and ultimate tensile strength while XZ specimens showed the highest ductility. Hardness measurements for different specimens were in accordance with the tensile test results, following the same order as the UTS values, XY specimens being the highest and XY-45° (out-of-plane) specimens being the lowest. Fractography of the broken surfaces of the specimens under tensile testing revealed the microstructural features and various defects in the tensile fracture. The anisotropy in mechanical properties is attributed to the microstructural anisotropy as well as presence of various types of defects induced by the AM process, which affects the deformation and failure mechanism of the parts. Linear relationships between experimental Vickers hardness versus yield stress and UTS measurements were developed. In case of material selection for different applications, these relationships can be used as a simple tool for converting hardness and yield stress (or UTS) values to each other. An equivalent strain-hardness relationship was also proposed which can be used for health monitoring of parts subject to tensile loading.

Effect of Layer Thickness and Heat Treatment on Microstructure and Mechanical Properties of Alloy 625 Manufactured by Electron Beam Powder Bed Fusion.

This research program investigated the effects of layer thickness (50 µm and 100 µm) on the microstructure and mechanical properties of electron beam powder bed fusion (EBPBF) additive manufacturing of Inconel 625 alloy. The as-built 50 µm and 100 µm layer thickness components were also heat treated at temperatures above 1100 °C which produced a recrystallized grain structure containing annealing twins in the 50 µm layer thickness components, and a duplex grain structure consisting of islands of very small equiaxed grains dispersed in a recrystallized, large-grain structure containing annealing twins. The heat-treated components of the microstructures and mechanical properties were compared with the as-built components in both the build direction (vertical) and perpendicular (horizontal) to the build direction. Vickers microindentation hardness (HV) values for the vertical and horizontal geometries averaged 227 and 220 for the as-built 50 µm and 100 µm layer components, respectively, and 185 and 282 for the corresponding heat-treated components. The yield stress values were 387 MPa and 365 MPa for the as-built horizontal and vertical 50 µm layer geometries, and 330 MPa and 340 MPa for the as-built 100 µm layer components. For the heat-treated 50 µm components, the yield stress values were 340 and 321 MPa for the horizontal and vertical geometries, and 581 and 489 MPa for the 100 µm layer components, respectively. The elongation for the 100 µm layer as-built horizontal components was 28% in contrast with 65% for the corresponding 100 µm heat-treated layer components, an increase of 132% for the duplex grain structure.

Effect of Uncertainties in Design Variables on the Hysteresis Response of 2D Steel Moment-Resisting Frames

Reliability theory considers the effect of uncertainty in the modeling and design of structures. Uncertainty in variables such as the material properties, geometric dimensions, and external loads during the analysis of steel moment-resisting frames can have significant effects on structural safety. This study evaluated the safety probability of two two-dimentional steel moment-resisting frames and examined the effect of uncertainly on each design parameter on the maximum frame drift using sensitivity analysis. It also evaluated the robustness index of energy dissipated in the stories of the frames. The uncertainties were modeled with normal probabilistic distribution of random variables. The Monte Carlo simulation method and the maximum story drift constraint were used to calculate the probability of safety and define the limit state function, respectively. Nonlinear time-history analysis was performed on the frames under seven ground motion records having an exceedance probability of 10% in 50 years. The modified Ibarra-Krawinkler behavioral model has been used to define the potential plastic hinges of the frame. The results indicated that the values of the probability of safety may be appropriate for evaluation of the 3-story frame, but be undesirable for a design based on reliability assessment. Sensitivity analysis showed that the steel modulus of elasticity and yield stress values having the greatest effects, whereas the web thickness of the sections and gravity loads applied to the stories had the least effects on the maximum drift of the structure. Using the probability of safety and robustness index, this study has produced useful information for the seismic rehabilitation of structures relating to design variable uncertainty on the hysteresis response for steel moment-resisting frames.

Effect of Potato Starch Hydrogel:Glycerol Monostearate Oleogel Ratio on the Physico-Rheological Properties of Bigels.

Bigel (BG) has been shown to be promising for the food industry due to the possibility to manipulate the properties of the system by adjusting the ratio of each individual phase, namely the hydrogel (H) and oleogel (O) phases. This work aimed to evaluate the influence of the O:H ratio on the physical-rheological properties of BG produced with potato starch (PS) and glycerol monostearate (GM). The hydrogel hardness (i.e., 1423.47 g) directly influenced the viscosity of the BG samples, as BG with a higher H-phase presented the highest viscosity and firmness. All BG samples presented shear-thinning behavior and structural breakdown at ~50 °C. BG with a higher O-phase had superior results for thermal stability, softer texture, and yield stress values, representative of good plasticity and spreadability, as compared to BG with less O-phase. The BG with 80% H-phase was less stable during the 21 days of storage in relation to the other BG samples. This study showed the role that the O:H ratio plays in the development of PS-GM-based BGs with tailor-made physical-rheological properties. In addition, the BG is an easily reproduced system with great potential to be used as a trans and saturated fat substitute in food applications.

Rheological behavior, mechanical properties, fire resistance, and gamma ray attenuation capability for eco-friendly cementitious mixes incorporating thermally treated lead sludge

The main objective of this study is to develop eco-friendly innovative binding materials based on lead sludge (sludge generated during glass polishing) for various advanced applications. The challenge with using lead sludge (LS) in cementitious blends is the presence of a considerable quantity of organic matter, which has a detrimental impact on the workability and mechanical characteristics of such blends. As a result, this study focused on comparing the influence of untreated and thermally-treated LS (ULS and TLS, respectively) on rheological behavior, mechanical characteristics, fire resistance, and harmful gamma-radiation shielding for various cementitious mixes. When compared to ULS, the results demonstrate that TLS has a greater pozzalnicity (as evaluated by modified Chapelle and Abo-El-Enein et al. methods), a bigger particle size (as established by particle size distribution and SEM analysis), and no organic matter content (as determined by FTIR technique). TLS incorporation in cement composite enhanced rheological parameters (lowest yield stress and plastic viscosity values) through eliminating organic matter that may adsorb a large amount of water. The specimen containing up to 20 % TLS achieved significant compressive strength value because it improved by 45.3 % when compared to ULS. This may be attributed to improved workability followed by a decrease in the water/solid ratio (as determined by the water consistency test), decomposition of organic matter that impedes the hydration process, and high pozzolanicity, which resulted in the creation of additional hydration products as confirmed by TGA/DTG and SEM/EDX analyses, as well as pore structure redistribution from macro to meso-pores validated by textural characteristics study(N2 adsorption/desorption isotherm) and total porosity measurement. The composite containing 10 wt% TLS had the best fire-resistant behavior up to 900 °C; it has a compressive strength that is 15.8 and 57.1 wt% greater than OPC and a specimen containing 10 % ULS, respectively. Although TLS-containing composites displayed excellent mechanical characteristics, ULS-containing composites exhibited exceptional radiation shielding properties because the organic matter, when exposed to gamma-rays, may be transformed into a cross-linked structure that reduces radiation intensity. The immobilization test was developed to guarantee the safety of produced composites. It was discovered that both ULS and TLS specimens had a Pb-concentration in leachate solution that was lesser than the toxicity limit (5 ppm). The immobilization process in TLS-containing specimens is more effective than in ULS; rather than narrow pores identified in TLS-containing specimens, the PbO2 was transformed to stable Pb3SiO5, as shown by XRD.

Electronic, nanomechanical and smart reversible phase transition behaviours of sputtered titanium oxide-vanadium oxide composite thin films

Crystalline vanadium oxide-titanium oxide (VO-TO) composite thin films of 197 nm are developed on quartz and silicon substrates by RF magnetron sputtering technique. A thorough structural investigation of deposited thin films is carried out by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. Differential scanning calorimetry (DSC) and temperature-based sheet resistance measurement techniques reveals the Smart (i.e., reversible) phase transition behaviour of VO-TO films at about 45 °C. Further selective depth analysis by XPS on the VO-TO films shows the variation of the Ti doping amount along the thickness. The top region of VO-TO thin film possess lower Ti species, while beyond 50 nm thickness from the surface possess comparatively rich Ti species. This graded Ti species along the depth also results in the variation of nanomechanical properties along the depth as confirmed by nanoindentation. The simulation through the finite element approach is also carried out to depict the experimental results of nanoindentation. The nanohardness and modulus of the presently developed VO-TO composite film were measured as 6.7 GPa and 158.7 GPa, respectively at 50 nm depth. Beyond 50 nm, nanohardness and modulus were 5.6 GPa and 116.6 GPa, respectively. Further, finite element simulation predicted yield stress value of 3.52 GPa at 50 nm depth whereas higher yield stress of 4.68 GPa was predicted beyond 50 nm.

Investigation of Flexure Strength of Aluminum Composites Reinforced with Iron Fibers

Flexure strength of Aluminum composite reinforced with iron fiber has been investigated.Atomization procsses method were used to prepare sheet of aluminum reinforced with iron fiber with direction (0-90°) and (0-45°) to cognition fiber direction effect on flecture strength values.The results shows that the values of maximum bending stress, yield stress and young modulus of aluminum reiforced with iron fibers direction (0-90) higher than for the aluminum reinforced with fibers direction (0-45). The optical microscopy and photographic pictures shown the fracture surface of the tested specimens and fibers segmented and supported the rising in the flecture strength values of the aluminum composites(0-90).

Analysing of nano-silica usage with fly ash for grouts with artificial neural network models

When grout is used to penetrate voids and cracks in soils and rock layers, easy and effective pumping of the grouts is vital, especially for grouting works during geotechnical improvements. For this reason, improving the rheological parameters of cement-based grouts and increasing their fluidity are important for effective grouting injection. In this study, an experimental investigation and analysis using artificial neural network (ANN) models were used to discover how nano silica (n-SiO2) together with fly ash affects the rheological behaviour of cement-based grouts. The effects of nano silica (n-SiO2) additions at different contents by mass (0.0%, 0.3%, 0.6%, 0.9%, 1.2% and 1.5%) on the plastic viscosity and yield stress values of cement-based grouts incorporating fly ash as a mineral additive at different amounts (0% – as a control, 5%, 10%, 15%, 20%, 25% and 30%) were investigated. Using the experimental data obtained, a feed-forward (FF) back-propagation (BP) multi-layer perceptron (MLP) artificial neural network (ANN) was developed to predict the plastic viscosity and yield stress of cement-based grouts with nano silica nanoparticle additives. The ANN model developed can predict the plastic viscosity and yield stress values of cement-based grouts containing nano silica nanoparticle-doped fly ash with high accuracy.