Papers by Keyword: Yield Stress

Abstract: The bulk density of the injection grout is an important factor, as its additional weight could cause damage to hardened decorative plasters. This can be particularly noticeable on larger surfaces. This study used five types of lightweight filler as a density-reducing component in hydrated lime-based grouts. The commonly used limestone filler was completely replaced by an expanded or granulated filler with a loose bulk density of up to 900 kg m⁻³; the rheological properties of the prepared grouts were then studied using a hybrid rheometer. The lime grouts were non-Newtonian, shear-thickening fluids exhibiting rheopectic behaviour (i.e. they stiffened over time). The type of filler dramatically affected the flowability of the grouts. The yield stress and plastic viscosity of the grouts decreased when lightweight fillers were used. As the filler density decreased, the grouts became expectantly less stiff. However, they showed a higher proportion of elastic behaviour than viscous behaviour, indicating that they have a strong microstructure that is resistant to external influences. There was no increase in loss factor values at higher frequencies, indicating that there was no separation of the liquid from the grout structure. From a rheological point of view, expanded glass appeared to be the most effective of the lightweight fillers used.

Abstract: The effect of the inhomogeneity of the material properties on the quenching residual stress in the aluminum alloy was studied by using the finite element method simulation and the evolution of the quenching residual stress during the pre-stretching process was discussed in this paper. The results show that both the x-component and y-component of the quenching residual stresses in the non-uniform model are nearly overlapped with that in the uniform model. The effect of the inhomogeneity of the material properties on the quenching residual stress is negligible. After pre-stretching, the surface stress of the non-uniform model decreases from the middle line to the edge while the center stress increases. Contrastingly, both the surface and center stress of the uniform model are nearly stable along the same path, and the stress magnitudes are lower than that in the non-uniform model. The inhomogeneity of material properties mainly affects the pre-stretching residual stress distribution, while it has little effect on the quenching residual stress distribution.

Abstract: This paper aims to discuss the influence of mix composition of cement mortar on fresh and rheological properties of cement mortar. Two different natural fibres, basalt (BA) and sisal (SL) are selected based on fresh and rheological behaviour for its usability in a cementitious mixture. The workability and rheological behaviour are evaluated by flow table test, cone penetrometer and slump test of the mixture. A full factorial design method was used to investigate the effects of four mix components: dosage of cement content (B), percentage of fly-ash (FA) by mass of cement, dosage of basalt fibre (BA) and dosage of superplasticizer (SP) along with a water/binder ratio of 0.41. A mathematical model which predicts the main effect and interactions of these components for each of the measured properties are derived using the factorial design. The proposed mixtures consist of two levels of binder content as 550 kg/m3 and 650 kg/m3, FA as 5% and 20% by mass of cement, BA as 1 kg/m3 to 3 kg/m3 and SP as 2 kg/m3 to 4 kg/m3. By reducing the number of test batches needed, the mathematical models produced with this method can expedite optimizing the mixture proportions of cement mortar to achieve desired fresh and rheological properties.

Abstract: High temperature ternary Ti₅₀Ni₂₅Pd₂₅ and quaternary Ti₅₀Ni₂₀Pd₂₅Cu₅ shape memory alloys were developed in vacuum arc melting furnace using high purity constituent elements. Half numbers of samples were solution treated at 900 °C for 2 hrs and remaining were aged at 600 °C for 3 hrs. Both alloys were characterized for microstructure analysis and mechanical properties. After aging the alloys, no significant change in microstructure was observed in ternary alloy however, fine precipitates of bright color were found along the grain boundaries in quaternary alloy. The mechanical properties of ternary and quaternary alloys were found to be improved significantly. Microhardness of ternary alloy was increased by 18 Hv whereas for quaternary alloy the same property was improved by 24 Hv. Yield stress of ternary and quaternary was observed to be enhanced by 10 MPa and 9 MPa respectively. Similarly the fracture stress was observed to be increased by 9 MPa and 13.4 MPa. Conversely, the fracture strain of ternary and quaternary alloys was reduced by 0.5% and 0.35% respectively. From these results it can be established that aging at 600 °C is beneficial to improve the mechanical properties of both alloys however, quaternary alloy responded more actively as compared to ternary alloy.

Abstract: Tensile tests of Mg-Y single crystals with different yttrium concentrations: 0.07 and 0.3 at.% were carried out to investigate effects of yttrium on pyramidal <c+a> slip system. In Mg-0.07at%Y alloy single crystals, {11 2}< 23> second order pyramidal <c+a> slip was activated and yield stress increased, compared to pure Mg single crystals. On other hand, in Mg-0.3at%Y alloy single crystals, {10 1}< 23> first order pyramidal <c+a> slip was activated and yield stress increased, compared to Mg-0.07at%Y alloy single crystals. The change in slip system by yttrium addition would be caused by increasing critical resolved shear stress (CRSS) for second order pyramidal slip.

Abstract: Soft soil is normally associated with high moisture content and fine content which result in high compressibility and low strength. However, a proper treatment such as solidification by means of hydraulic binders is required in order to be usable for beneficial purposes (e.i backfilling). This paper experiments the effects of cement treatment on the one-dimensional (1D) consolidation behavior of a high moisture content (MC) soil (twice liquid limit), based incremental loading test. The effects of Portland cement addition are evaluated for dosages ranging from 0 % to 15% by dry mass of soil. After curing, it was found that 10 % cement was required to make meaningful reduction in MC for kaolin while no major difference was noted between after mixing and after curing for DMS. In kaolin the moisture content decreased by 6.5 % for each 5 % increment of cement. Similarly, the MC of DMS reduced by 10 % for each 5 % increment. Thus, the reduction, immediately after mixing, in DMS was higher by 3.5 % compared to kaolin. The most evident effect of the treatment feasibility is the development of a cementation-induced yield stress after 7 days of curing: the bigger the cement dosage, the greater the yield stress and the greater the vertical effective stress that can be sustained at any void ratio. The maximum yield stress at 15 % cement content was found 30 kPa and 70 kPa for DMS and kaolin respectively. The highest void ratio values were found in the control specimens (3.77) in kaolin and DMS (5.66) whereas the lowest void ratio was corresponded to 15 % cement 3.35 and 4.65 for kaolin and DMS respectively. The control specimens decreased dramatically from 38.93 m² / KN - 0.13 m² / KN and 36.03 m² / KN - 0.19 m² / KN for kaolin and DMS specimens respectively. The results correspondingly provide a consistent depiction of the effects of cement treatment on MC, void ratio and coefficient of volume compressibility. The effectiveness of the treatment is obvious compared to the untreated soil.

Abstract: The main causes of early failure of reaction furnaces coils are diffusion processes in the material as a result of which structural changes occur, new phases are formed and void structure is formed in the surface layers of the metal, which has a negative effect on the mechanical characteristics. In this regard as a structurally sensitive method, which allows evaluating the changes occurring in the metal, the response parameters of the electrical signal are used which are sensitive to pore formation and allow predicting the zone of formation of the breaking crack. Fragments of the coils of the reaction furnaces from the radiant section, which were in operation for 750, 1300, 8000, and 10000 hours and the pipe element in the delivery condition were chosen as the objects of the study. As a result of the research a correlation between the amplitude of the first harmonic of the electrical signal output voltage with the results of static tests for tensile and impact bending was established. This happens due to the fact that during operation there is an increase in the relative impact viscosity and relative tensile strength, and the relative magnitude of the voltage amplitude of the first harmonic of the output electrical signal also increases. These results can be used as a method of mechanical properties assessment by non-destructive testing, and also they can be used to develop a criterion for the rejection of reaction furnace coils.

Abstract: This study aims to investigate the effect of processing routes (A and Bc) and temperature on microstructure, texture and mechanical properties of pure magnesium was studied in this research. An extruded pure magnesium (~99,9 %) was subjected to severe plastic deformation (SPD) by ECAP. Deformation was conducted at 523K and 473K and two different processing routes (A and Bc) were used to control the texture. The microstructure and texture characterization of the pressed materials were carried out. It was found that the microstructure displayed a bimodal grain structure after two passes and then became homogeneous after four passes following both routes A and Bc. The misorientation distribution was examined and the results revealed that the fraction of high angle grain boundaries (HAGB) was higher at temperature 473K. The texture was randomized following route Bc whereas it became strengthened in route A after four passes. According to the Hall-Petch (HP) relationship, the yield stress of polycrystalline metals increases with a decrease in grain size. In this study, a positive slope k was achieved in the strengthened texture while a negative one was obtained in the softened texture. The ductility of ECAP processed material was considerably improved (from 23% to 38%) without sacrificing the yield stress by route Bc at 423K.

Abstract: The cemented coal gangue-fly ash backfill (CGFB) slurry has commonly been used to control subsidence damage caused by underground coal mining. This paper discusses the CGFB slurry rheological characteristic associated with the various percentage of the fly ash within the configuration of the mixture. A general description about CGFB slurry fluidity in the pipe transportation is provided. The physical, chemical and rheological characteristic of the CGFB have been determined in the test. The fly ash was mixed with 18%, 20% and 22% of solid concentration with respects to 12%, 10% and 8% for cement on various concentrated CGFB slurry ranges 76.05%, 78.05% and 80.05%. The tests verify the CGFB slurry exhibits non-Newtonian behavior in nature as Bingham plastic fluid. The experimental data show CGFB slurry rheological characteristic is noticeable influenced by the slurry solid concentration and the proportion of the fly ash, which affects the value of yield stress and viscosity. The lower value of the rheological parameters was observed on 22 % fly ash other than the 18 % case based on the same solid concentration of CGFB slurry.

Abstract: A study of the mechanical properties of the finished metal products was carried out. All types of metal products are subjected to continuous quality control, both on the production output at the manufacturer of billets, and on the production entrance at the consumer of metal. Control subject are: strength characteristics (tensile strength σ_в and yield stress σ₀₂ and the characteristics of plasticity (relative elongation δ and relative necking ψ). The pipe steels have another important controlled characteristic: the impact toughness КСU-60. All the test methods are the destroying ones and are characterized by high complexity. The task of reducing the types of tests, the introduction of a comprehensive indicator of product quality is an urgent technical task. The purpose of this work is to study the regularities of changes in the indicators that determine the quality of the sheet metal from the pipe steel.