Variation Of Yield Stress Research Articles

The effects of SKO on Assam crude oil

The energy demand for crude oil (CO) has increased globally which encourages the growth in the petroleum industry worldwide. When CO is transported through a pipeline over long distances, due to the change in environmental circumstances, the flow behavior of CO also changes. To improve the flowability of CO through the pipeline, a better understanding of the rheological behavior of CO is very important. In this paper, several experiments were conducted to improve the flowability of CO through pipeline transportation. Dilution of CO with its products like Superior Kerosene Oil (SKO) was selected as it improves the CO flowability through the pipeline and is economically affordable. In this study, the effect of SKO on oAPI gravity, Pour Point, Gel Point, Viscosity Gravity Constant, and rheological parameters were studied for the CO of Upper Assam Basin, Assam. SKO was mixed with CO in different ratios to examine the effect of SKO on it. The results obtained showed that with the addition of SKO, oAPI increases, the minimum limit of attaining paraffinic nature of CO samples can be determined, heavier CO may not always have high Pour Point and Gel Point. The variation in yield stress of CO with SKO was also observed. Hershel-Buckley Model (HBM) was used and from the three parameters of HBM, the shear-thinning or shear thickening behavior of CO was determined. Therefore, this paper attempts to study the flow behavior of CO and also to identify the % of SKO required for improving their flowability through the pipeline.

Effect of aging time on microstructural and mechanical properties of 6061 aluminum alloy

Aluminum alloy 6061 have moderate strength, good formability, and excellent corrosion resistance, it has a wide use in several engineering sectors. Age hardening is the main feature of this alloy. In this study, some mechanical characteristics of Aluminum 6061 samples aged to different times has been studied. The specimen’s mechanical properties were improved in general; best mechanical properties were achieved after 2 hours of heat treatment at 200oC. Ultimate tensile stress, yield stress, ductility and microhardness variation with aging time are discussed regarding to the microstructural alteration caused by heat treatment. We found that the Mg2Si initiation and growth was a function for aging time, which was the main cause for improvement of the alloy mechanical features.

High temperature hardness testing of [formula omitted]-zirconium hydride: Yield stress estimation by analytical and numerical models

The mechanical properties of δ-zirconium hydrides were studied using a combination of nanoindentation techniques and numerical and analytical models. Two different alloys, containing different forms of δ-zirconium hydride (blister and rim), were analyzed at room temperature and at elevated temperatures up to 300 ∘C. A reduction of hardness from RT to 300 ∘C showed an approximately linear relationship with the change in temperature. For the δ-zirconium hydride rim, the hardness reduced from 3.73GPa at RT to 1.49GPa at 300 ∘C, a reduction of 61%. For the δ-zirconium hydride blister, hardness decreased from 3.5GPa at RT to 1.91GPa at 300 ∘C, a reduction of 45%. The yield stresses were calculated using two approaches: a numerical model proposed by Johnson to calculate values at RT, and another proposed by Dao for values up to 300 ∘C. At RT, the yield stress for the δ-zirconium hydride rim obtained was 883±21MPa, 224MPa at 300 ∘C. The δ-zirconium hydride blister showed a reduction from 879.5±10.5MPa at RT to 324MPa at 300 ∘C, a reduction in 61% and 45% for the hydride rim and blister, respectively. Through this combination of experimental and modeling techniques, this study showed the variation of hardness and yield stress in complex systems, and in different environments, using nanoindentation as the main characterization technique.

Analysis of material properties and strain hardening behaviour of brass at different temperature and quasi-static strain rate conditions

ABSTRACT The α-Brass alloy is gaining special attention for electrical and thermal conductivity applications because of being easily formed/workability and retaining high strength after forming. This makes crucial to understand the plastic deformation behaviour and work hardening behaviour of a material for reliable finite element simulations. In present study, the hot uniaxial tensile flow stress analysis of α-Brass alloy thin sheet has been carried out under a quasi-static strain rates of 0.1–0.001/s at the temperature range of 300 K–773 K. Flow stress behaviour has significantly affected with test temperatures, strain rates and sheet orientations. Anisotropy in terms of yield stress variation and % elongation by in-plane anisotropy and Anisotropy index have been evaluated. Further, stress–strain relation has been analysed by popular empirical strain hardening equation namely, Hollomon and Swift. The work hardening behaviour of alloy has been well-defined by Swift relationship compare to Hollomon empirical relation.

A multi-scale approach for assessing the robustness of cement-based materials from a yield stress perspective

In practice, the variation of component content can result in unsatisfactory workability in flowable cement-based materials containing multi-components. Hence, the accurate prediction of the rheological property is essential in dealing with such a robustness issue. In the current work, we aim at proposing a generic approach to predict the yield stress of flowable concretes. We first measure the variation of yield stress by tailoring the component content of cement-based materials containing binary blends of powders. The result shows that the yield stress is more sensitive to variations of polymer dosage and water content than variations of powder and aggregate for the given variation range of components. We then combine a geometric relation based on the particle size distribution (PSD) of powders with a recently proposed multi-scale model for the robustness assessment. Our results indicate that by knowing the packing property and size distribution of particles and the chemical property of polymers, the proposed approach can be successfully applied to predict the variation of the yield stress of cement-based materials containing multiple types of powders.

A numerical solution to thermo‐mechanical behavior of temperature dependent rotating functionally graded annulus disks

PurposeThe purpose of this study is to investigate Thermo-mechanical limit elastic speed analysis of functionally graded (FG) rotating disks with the temperature-dependent material properties. Three different material models i.e. power law, sigmoid law and exponential law, along with varying disk profiles, namely, uniform thickness, tapered and exponential disk was considered.Design/methodology/approachThe methodology adopted was variational principle wherein the solution was obtained by Galerkin’s error minimization principle. The Young’s modulus, coefficient of thermal expansion and yield stress variation were considered temperature-dependent.FindingsThe study shows a substantial increase in limit speed as disk profiles change from uniform thickness to exponentially varying thickness. At any radius in a disk, the difference in von Mises stress and yield strength shows the remaining stress-bearing capacity of material at that location.Practical implicationsRotating disks are irreplaceable components in machinery and are used widely from power transmission assemblies (for example, gas turbine disks in an aircraft) to energy storage devices. During operations, these structures are mainly subjected to a combination of mechanical and thermal loadings.Originality/valueThe findings of the present study illustrate the best material models and their grading index, desired for the fabrication of uniform, as well as varying FG disks. Finite element analysis has been performed to validate the present study and good agreement between both the methods is seen.

Microstructure Evolution and Mechanical Properties of a Wire-Arc Additive Manufactured Austenitic Stainless Steel: Effect of Processing Parameter.

Two single track multi-layer walls with linear energy inputs (LEIs) of 219 and 590 J/mm were deposited by cold metal transfer-based wire arc additive manufacturing system. Combined with the X-ray diffraction technique, scanning electron microscope and uniaxial tensile tests, the influences of LEI and cooling rate (CR) on the microstructure evolution, mechanical properties and fracture mechanisms of the studied steel are analyzed. It is observed that the microstructures of the studied steel are mainly composed of δ-ferrite and austenite dendrites. σ phase is formed on the δferrite–austenite interface under low CR. Meanwhile, the primary dendrites’ spacing decreases with the decrease in LEI or the increase in CR, and the maximal primary dendrites’ spacing is 32 μm. The values of elongation to fracture roughly decline with the decrease in LEI or the increase in CR, but the variations of ultimate tensile strength and yield stress show an opposite trend. In addition, the mesoscopic damages in the studied steel under low LEI are mainly caused by the coalescence of pores. While under high LEI, the cracks are induced by the dislocations piling up around δ-ferrite.

Prediction of critical cutting condition for onset of serrated chip in ductile metallic material using dynamic yield stress

Abstract Anticipation of the critical cutting condition for the transition of continuous chip to serrated chip is a fundamental task in machining of ductile metallic material. In this study, the variation of the dynamic yield stress with the increase of cutting speed was utilized as the criterion to predict the critical cutting condition for onset of the serrated chip. In order to accurately and conveniently determine the value of dynamic yielding strength of the workpiece material during the cutting process, an improved Williams’ model in conjunction with a 2D orthogonal slot milling test is proposed. Two typical ductile metals of silicon brass and Ti6Al4V were used as the workpiece material in this framework. Also, the chip morphology obtained in cylindrical turning test was used to validate the predicted results. For the two workpiece materials tested, it is observed that the error between the predicted result and the experimental result is always lower than 12%. The proposed methodology in this work exhibits its superiority in terms of calculation and predicting efficiency, which is still a challenge for traditional analytical method and finite element method.

Modeling plastic anisotropy evolution of AISI 304 steel sheets by a polynomial yield function

In this study, a numerical model for the evolution of plastic anisotropy is investigated for the purpose of stamping method design by Finite Element (FE) analysis and proved experimentally via process simulations of a cold-rolled austenitic stainless steel (AISI 304) sheet. The plastic anisotropy of the sheets is described with a fourth-order homogenous polynomial yield function and this modelling approach is enhanced by plastic strain dependent material coefficients. Tensile tests of coupon specimens taken along the different directions from rolling direction, and flow strength and deformation anisotropies are described with the planar variations of yield stress and plastic strain ratio computed at four plastic strain levels (0.002, 0.02, 0.05 and 0.18). A new numerical approach is, then, applied to identify polynomial coefficients ensuring an orthotropic positive-definite, convex yield surface with a well-defined stress gradient at every loading point on plane stress subspace. The developed computational model is implemented into general purpose explicit FE analysis software Ls-Dyna by a user-defined material model subroutine (UMAT) and applied in the stamping simulation of AISI 304 steel rectangular cups for the house-hold applications. The computed thickness distributions and the flange geometries were compared with measurements and it was observed that the best predictions were done with material parameters at %5 plastic strain level.

Shear response of magnetorheological fluid with Zn0.2Fe2.8O4 sub-micron hollow spheres

Magnetorheological (MR) fluids with Fe3O4 particles are widely studied nowadays due to their soft magnetic nature, controllable morphology, and better chemical stability as compared to their metallic counterpart. However, they can be even more advantageous under Zn doping with elevated magnetization and hollow configuration with low density, making them more active, stable, and dispersible in the carrier fluid. Here, we report the preparation of MR fluids with Zn0.2Fe2.8O4 sub-micrometer hollow spheres and their steady-state MR response under the application of a magnetic field. The MR fluid follows the Bingham plastic nature with a yielding behavior. The variation of yield stress with the applied magnetic field is explained in the context of a newly developed dipolar interaction model.

Rod-plate interactions in sepiolite-LAPONITE® gels: microstructure, surface chemistry and rheology.

Pure and composite clay gels of sepiolite and LAPONITE® at 4 wt% solids were characterised microstructurally and rheologically. They all displayed time-dependent behaviour, i.e. yield stress increased with aged time. The microstructures captured by cryo-SEM on the samples prepared by high pressure and rapid freezing showed the presence of bonding between LAPONITE® sheets and sepiolite fibres. These bonds are likely to be formed between the positive sheet edge and the negative fibre silica face as suggested by the upright orientation adopted by most LAPONITE® sheets. The sheets formed isolated open networks at a low content and a continuous open network at a high content. The fibres of the pure sepiolite gel formed a relatively strong network. However, the composite networks formed at a low LAPONITE® content between 5 and 25% must be discontinuous as the yield stress is zero. At a higher LAPONITE® content, the composite structure displayed increasing strength. The time-dependent ageing behaviour is due to the electric double layer (EDL, face-face) repulsive force governing the development of the 3D network structure. The Leong model described this behaviour well. All the clay gels displayed a maximum yield stress at a pH of 9 to 10. Pyrophosphate additive reduced the maximum yield stress and shifted the yield stress-pH curve to a lower pH. The Herschel-Bulkley model described the flow behaviour of all the gels well. The variation of the model yield stress with gel composition is similar to that obtained by the vane yield stress technique.

Sensitivity Analysis in the Modelling of a High Speed Steel Thin-Wall Produced by Directed Energy Deposition

This paper reports the sensitivity of the thermal and the displacement histories predicted by a finite element analysis to material properties and boundary conditions of a directed-energy deposition of a M4 high speed steel thin-wall part additively manufactured on a 42CrMo4 steel substrate. The model accuracy was assessed by comparing the simulation results with the experimental measurements such as evolving local temperatures and distortion of the substrate. The numerical results of thermal history were successfully correlated with the solidified microstructures measured by scanning electron microscope technique, explaining the non-uniform, cellular-type grains depending on the deposit layers. Laser power, thermal conductivity, and thermal capacity of deposit and substrate were considered in the sensitivity analysis in order to quantify the effect of their variations on the local thermal history, while Young’s modulus and yield stress variation effects were evaluated on the distortion response of the sample. The laser power showed the highest impact on the thermal history, then came the thermal capacity, then the conductivity. Considering distortion, variations of the Young’s modulus had a higher impact than the yield stress.

Full-field stress computation from measured deformation fields: A hyperbolic formulation

Recent developments in imaging techniques and correlation algorithms enable measurement of strain fields on a deforming material at high spatial and temporal resolution. In such cases, the computation of the stress field from the known deformation field becomes an interesting possibility. This is known as an inverse problem. Current approaches to this problem, such as the finite element update method, are generally over-determined and must rely on statistical approaches to minimize error. This provides approximate solutions in some cases, however, implementation difficulties, computational requirements, and accuracy are still significant challenges. Here, we show how the inverse problem can be formulated deterministically and solved exactly in two or three dimensions for large classes of materials including isotropic elastic solids, Newtonian fluids, non-Newtonian fluids, granular materials, plastic solids subject to co-directionality, and some other plastic solids subject to associative or non-associative flow rules. This solution is based on a single assumption of the alignment of the principal directions of stress and strain or strain rate. No further assumptions regarding incompressibility, pressure independence, yield surface shape or the hardening law are necessary. This assumption leads to a closed, first order, linear system of hyperbolic partial differential equations with variable coefficients. The solution of this class of problems is well established and hence the equations can be solved to give the solution for any geometry and loading condition, enabling broad applicability to a variety of problems. We provide a numerical proof-of-principle study of the plastic deformation of a two-dimensional bar with spatially varying yield stress and strain hardening coefficient. The results are validated against the solution of the corresponding forward problem – solved with a commercial finite element solver – indicating the solution is exact up to numerical error (the normalized root mean square error of the stress is 1.63×10−4). No model calibration or material parameters are required. The sensitivity of the solution to error in the input data is also analyzed. Interestingly, this solution procedure lends itself to a simple physical interpretation of stress propagation through the material. Finally, we provide some examples showing how this approach may be analytically applied to both solid and fluid mechanics problems.

Study of Khan-Huang-Liang (KHL) Anisotropic Deformation Model for Deep Drawing Behaviour of Inconel 718 Alloy

Study of anisotropic deformation behavior of a material plays a crucial role in optimizing hot working process parameters and trustworthy Finite Element (FE) analysis in sheet metal forming processes. In this work, Khan–Huang–Liang (KHL) phenomenological based constitutive model and anisotropic yield criteria has been formulated for Inconel 718 alloy. Firstly, uniaxial tensile tests have been conducted at different temperatures (room temperature -700°C) and slow strain rates (0.0001-0.1s-1) conditions. KHL constitutive model has been formulated and validated with experimental flow stress data. The prediction capability of the model is evaluated based on correlation coefficient (R), average absolute error, AAE (Δ) and its standard deviation (s). Subsequently, anisotropic yielding behavior of Inconel 718 alloy is predicted based on KHL yield criterion. Anisotropic coefficient (Lankford parameters) and tension compression asymmetry parameters have been calculated experimentally. The prediction capability of KHL yield criterion is analyzed based on yield locus, yield stress variation and anisotropic coefficient variation. The quality index of performance, namely global accuracy index (β) is evaluated. Further, Finite Element (FE) analysis has been carried out for deep drawing of Inconel 718 alloy using commercially available ABAQUS software. The developed KHL constitutive model and anisotropic yield criterion has been incorporated in FE simulation using UMAT/VUMAT code. The FE results are validated with experimental deep drawn cups at different process conditions.

Rheological and pumping behaviour of 3D printable cementitious materials with varying aggregate content

3D printing with cementitious materials is an emerging technology and provides an active area of research. Despite this, there are only limited studies that examine the pumping behaviour of high yield stress fluids such as printable concrete. We present a study on the rheological behaviour of 3D printable cementitious materials with different aggregate-to-binder ratios (a/b) and analyse the pumping and printing characteristics with the measured rheological parameters. We observed that an increase in a/b resulted in a significant increase of plastic viscosity, and a nominal increase in yield stress and storage modulus. The variation in plastic viscosity and yield stress with increasing aggregate content was analysed with the Krieger-Dougherty and Chateau-Ovarlez-Trung model, respectively. Also, the rheological properties of the paste rich lubrication layer during pumping were determined with the help of a tribometer. The yield stress and viscous constant of the lubrication layer increase with the increase in a/b. The pumping pressure predictions were carried out by a suitable theoretical model by considering appropriate flow conditions for different mixtures. The variation in critical height of printed elements with an increase in a/b was correlated with the observed rheological parameters.

High pressure densification behavior of alumina particles

Pressure is an important thermodynamic parameter in addition to temperature and chemical composition during material sintering process. However, few experimental images intuitively describing the densification process of grains during compression, especially for the high melting point ceramics. Here we observed deformation evolution and mechanical response of spherical alumina particles after high pressure treatment. By analyzing the plastic deformation and grain boundary characters of spherical alumina particles, and the boundary stress and yield stress variation of grains under various pressures and temperatures, a clear picture of the high-pressure powder densification and sintering process is depicted.

High Pressure Densification Behavior of Alumina Particles

Pressure is an important thermodynamic parameter in addition to temperature and chemical composition during material sintering process. However, few experimental images intuitively describing the densification process of grains during compression, especially for the high melting point ceramics. Here we observed deformation evolution and mechanical response of spherical alumina particles after high pressure treatment. By analyzing the plastic deformation and grain boundary characters of spherical alumina particles, and the boundary stress and yield stress variation of grains under various pressure temperature, a clear picture of the high-pressure powder densification and sintering process is depicted.

Testing and Evaluation of Linear Shear Mode Magnetorheological (MR) Damper Based on Rheological Properties of MR Fluid

Abstract Magnetorheological (MR) fluid exhibits variable yield stress and viscosity with the magnetic field, which is why it is classified under smart materials. Because of its controllable properties, MR fluid has many applications. The most common application of MR fluid is MR fluid damper. According to the flow of MR fluid, three types of dampers are possible; flow mode, squeeze mode, and shear mode. In this article, rheological properties of MR fluid, which has a high Bingham number (ratio of MR force on-state to off-state), are synthesized and the MR properties are studied. Based on these properties, a linear shear mode MR damper is designed and evaluated for its performance. A unique model is adopted to evaluate the performance of MR damper. In this model, the dimensionless Mason number is applied to establish the relation between test data of damper and rheological properties of MR fluid. This is verified for two different volume fractions of magnetic particles in MR fluid.

Plastic hinges mechano-reliability analysis in the beams of RC frames structures

Purpose The purpose of this study is to establish a relationship between causes and effects, the respect of materials characteristics values [concrete compressive strength (fc) and steel yield stress (fy)] and the norms of the construction dispositions value (covers). This study is motivated by the post-seismic damages related to the plastification of the reinforced concrete (RC)/beams sections, named plastic hinges. The results are given by fragility curves representing the failure probability (Pf) of the plastic hinges versus covers value. Design/methodology/approach A mechanical-reliability coupling methodology is proposed and performed on three frames (three, six and nine storey). For each frame, seven covers the value of reinforcement steel bars has been taken into account in the beams. After definition of the limit state function G(x), a process of idea to twin-track; deterministic and probabilistic, is considered. Thus, numerical simulations are carried out under ETABS© software, to extract a soliciting moments Ms(x). Then, ultimate moments Mu(x), the result of reliability approach are calculated using Monte Carlo Simulations. In this step, two random variables; concrete compressive strength in 28 days of age (fc) and steel yield stress (fy), have been studied. Findings In the mechanical study, the results show that, the first plastic hinge appears at the beams for all frames. In the reliability study, the (fy) variation shows that all plastic hinges are in failure domain, nevertheless, the (fc) variation leads to have all sections in the safety domain, except A7 and B7 models. The failure probability (Pf) calculation according to (fc) and (fy) shows that an absolute error of 0.5 cm in the steel bars covers can switch the frame from the safety domain to the failure domain. Originality/value The plastic hinges reliability of the RC/ frame structures is independent on the high of the structure. The (fc) random variable according to the used distribution law does not affect the reliability (safety or failure). However, the impact of the steel yield stress variation (fy) is not negligible. The errors in covers affect considerably the strength of the elements.

Limit speeds and stresses in power law functionally graded rotating disks

Limit elastic speed analysis of Al/SiC-based functionally graded annular disk of uniform thickness has been carried out for two cases, namely: metal-rich and ceramic rich. In the present study, the unknown field variable for radial displacement is solved using variational method wherein the solution was obtained by Galerkin\'s error minimization principle. One of the objectives was to identify the variation of induced stress in a functionally graded disk of uniform thickness at limit elastic speed using modified rule of mixture by comparing the induced von-Mises stress with the yield stress along the disk radius, thereby locating the yield initiation. Furthermore, limit elastic speed has been reported for a combination of varying grading index (n) and aspect ratios (a/b). Results indicate, limit elastic speed increases with an increase in grading indices. In case of an increase in aspect ratio, limit elastic speed increases up to a critical value beyond which it recedes. Also, the objective was to look at the variation of yield stress corresponding to volume fraction variation within the disk which later helps in material tailoring. The study reveals the qualitative variation of yield stress for FG disk with volume fraction, resulting in the possibility of material tailoring from the processing standpoint, in practice.