Yield Stress Of Material Research Articles

Rheology of paste-like food inks for 3D printing: Effects of nutrient and water content

This research delves into understanding the effects of composition on the rheological response of multi-component food inks for 3D food printing. Accordingly, the motivation is to decouple the nutrient and water content effects on the rheology. We formulated inks by combining pea fractions with water and employing a water-holding-capacity based hydration method. Rheology is characterized by steady shear rate and oscillatory strain amplitude sweeps. Strain sweep curves infer that the deformation response of all inks follows a similar trend, and samples sharing the same macronutrient formulation are mapped to a master curve after scaling with the elastic plateau modulus. Samples sharing the same macronutrient formulation mapped to a master curve after scaling with the elastic modulus. Shear rate testing showed that the inks were shear thinning yield stress materials. Shear rate sweeps also collapsed on a master curve scaled by the yield stress and critical shear rate on the y and x axes. The yield stress and the plateau modulus appeared to be controlled by the water content, while the shear and strain thinning exponents were independent of the formulations, inferring that the rheology is scaled by the water content while preserving the shear thinning response. Observing the independence of the rheological properties from the nutrient composition and scalability of the rheology by the water content provided a step forward in developing formulations with various nutrient content at desired ow properties, which promises personalized nutrition. Furthermore, the study shows the applicability of various rheological techniques, which are expected to contribute to the literature on the rheology of granular pastes.

Estimating the yield stress of soft materials via laser-induced breakdown spectroscopy

Taking three typical soft samples prepared respectively by loose packings of 77-, 95-, and 109-μm copper grains as examples, we perform an experiment to investigate the energy-dependent laser-induced breakdown spectroscopy (LIBS) of soft materials. We discovered a reversal phenomenon in the trend of energy dependence of plasma emission intensity: increasing initially and then decreasing separated by a well-defined critical energy. The trend reversal is attributed to the laser-induced recoil pressure at the critical energy just matching the sample’s yield strength. As a result, a one-to-one correspondence can be well established between the samples’ yield stress and the critical energy that is easily obtainable from LIBS measurements. This allows us to propose an innovative method for estimating the yield stress of soft materials via LIBS with attractive advantages including in-situ remote detection, real-time data collection, and minimal destructive to sample.

Safety evaluation of tubing and sucker rod vertically handling equipment under stochastic wind load

Workover operations are crucial for maintain the normal production of oil, gas and water wells and require significant manpower and material resources. In recent years, automation equipment has become more widely used in the operations of oilfield workover operations. The present paper established the finite element model of the newly developed tubing and sucker rod vertically handling equipment, and the deformation, equivalent stress and wind-resistant ability of the structure model under dead weight load and wind load are investigated. The wind load is equivalent to the wind pressure acting on the structural unit, and the transient wind field is composed through linear superposition of harmonic function with random amplitude and frequency. Results show that the maximum equivalent stress is much lower than the yield stress of the structural material under typical working conditions, the maximum displacement of the manipulator position meets the design requirements of positioning accuracy.

A generalized, computationally versatile plasticity model framework - Part I: Theory and verification focusing on tension‒compression asymmetry

Microstructural characteristics and complex loading conditions in the deformation of metallic materials lead to complexity in mechanical responses. In this study, we propose a generalized constitutive framework that reproduces the plastic anisotropy and asymmetry under various loading conditions. Particularly, the developed model can accurately capture distinctive flow stress, plastic flow and strain hardening between tensile and compressive dominant loadings under a wide range of stress states. The model is based on the stress triaxiality dependence of state variable (or weighting factor) newly incorporated in the existing plasticity theory to keep the computational efficiency and versatility. For example, the new generalized framework can be applied to widely employed Hill48, Yld2k-2d, and Poly6 as a class of associated flow rule-based yield functions, as well as Stoughton-Yoon2009 and Min2016 yield functions for the non-associated flow rule. Also, the model is adaptable when selecting the yield function under tension or compression, which efficiently controls the degree of accuracy in anisotropic modeling under tension and compression. The generalized plasticity framework is validated comprehensively by demonstrating the predictive capability for anisotropy in yield stress and plastic flow of metallic materials with different crystal structures. Moreover, the model can efficiently capture the continuous evolution of asymmetric yield surfaces as functions of strain, temperature, and strain rate. Finally, the identification procedure of the model is discussed by demonstrating the analytical determination of model parameters utilizing the experimental or generic material data obtained from various loading conditions such as tension, compression, plane strain loading, and pure shear.

Quasistatic deformation of yield stress materials: Homogeneous or localized?

We analyze a mesoscopic model of a shear stress material with a three-dimensional slab geometry, under an external quasistatic deformation of a simple shear type. Relaxation is introduced in the model as a mechanism by which an unperturbed system achieves progressively mechanically more stable configurations. Although in all cases deformation occurs via localized plastic events (avalanches), we find qualitatively different behavior depending on the degree of relaxation in the model. For no or low relaxation, yielding is homogeneous in the sample, and even the largest avalanches become negligible in size compared with the system size (measured as the thickness of the slab L_{z}) when this is increased. On the contrary, for high relaxation, the deformation localizes in an almost two-dimensional region where all avalanches occur. Scaling analysis of the numerical results indicates that in this case, the linear size of the largest avalanches is comparable with L_{z}, even when this becomes very large. We correlate the two scenarios with a qualitative difference in the flow curve of the system in the two cases, which is monotonous in the first case and velocity weakening in the second case.

ESTIMATION OF DYNAMIC YIELD STRESS BY TAYLOR TEST WITH REDUCED CYLINDRICAL HEAD PART OF SAMPLES

A simple method is proposed to estimate the dynamic yield stress of materials using modified Taylor tests for high-velocity impact of profiled cylinders with a reduced diameter of the head part. Assuming the uniformity of deformations and stresses in the head part, formulas are derived for estimating the yield stress and strain rate from the change in the length of the reduced head part, as well as the mass of the sample and the impact velocity. This estimation is verified by comparison with the results of numerical calculations by the SPH method based on the dislocation plasticity model parameterized for cold-rolled oxygen-free copper. It is shown that the stopping time of the sample and the strain rate are reproduced with good accuracy, and the shear strength estimate gives an error that increases with the impact velocity. At velocities that do not lead to deformation of a wide part of the sample (up to 90 m/s in the case under consideration), the error increases linearly up to 30%, which can be taken into account by a correction factor. The proposed estimate, taking into account the correction factor, was applied to analyze the results of previous experiments; the obtained values correspond to the literature data on the rate dependence of the shear strength.

Investigation of ultrasonic mechanism and development of tool wear model in ultrasonic elliptic vibration assisted cutting of stainless steel

By analyzing the kinematics and dynamics of ultrasonic vibration under various conditions, the tool wear mechanism in Ultrasonic Elliptic Vibration-Assisted Cutting (UEVAC) were investigated. Two distinct mechanisms for mitigating tool wear emerge: In non-separated UEVAC, the pivotal factor is the reduction of material yield stress through the acoustic softening effect. Conversely, in separated UEVAC, tool wear reduction is attributed to the decrease in average contact stress via stress superposition and the hammer effect. These findings highlight the effectiveness of aligning ultrasonic energy field action times and intensity to reduce stainless steel tool wear rates in non-separated UEVAC. Furthermore, the proposed tool wear model demonstrates robust reliability for separated UEVAC processes.

DESIGN OF UNDIRECT GUY WIRE TENSION METER BASED ON STRAIN GAUGE

The safety of the tower is depend the tension of guy wire, where it must have the same tensile stress at all positions. To meet this requirement, the load cell guy wire is designed based on strain gauge. Load cell guy wire is designed portable and it can detect stress of the guy wire indirectly. The main component of load cell is a beam, two hooks and a cylinder to form a bending moment force in the beam, the value of the bending moment on the beam will be directly proportional to the increase or decrease in force drag on guy wire. Design process of load cell doone using mathematical analysis, and then the load cell is calibrated by standard load cell, based on the data result of calibration is known that the stress at the guy wire load cell is close and under the yield stress of the load cell material, it is proved that load guy wire cell’s design result is safe to use.

Study on the evolution of material microstructure and constitutive relation during rail corrugation development

The difference between the evolution of wear mechanism, microstructure and constitutive relation of the near-surface material at the corrugation peaks and those at the troughs were studied using a twin-disc roller type set-up. The results show that the depths of corrugation increase gradually and tend to slow down at high running cycle numbers. Significant plastic deformation can be observed near the rail surface and subsurface. When the corrugation changes from uniform stage to steady stage, the thickness of the plastic deformation layer increases gradually and slows down and the wear mechanisms changes from adhesion to fatigue. The elastic modulus and hardness of material near rail surface were obtained at different wear stages during the development of corrugation and the material constitutive relations were established with the aid of finite element method. It is found that the yield stress at the peak is higher than the trough surface at the initiation and developing stages of corrugation, however, it is higher at the trough on the steady stage. The yield stresses of surface material was found to have a good correlation with the thickness of plastic deformation.

Drop rise and interfacial coalescence initiation in Bingham materials

Drop coalescence in viscoplastic materials is present in various industrial applications and the environment. The plasticity of the surrounding material affects drop rise, collision, and film drainage dynamics, and knowledge about these is essential for designing and operating industrial mixer and separator units. Despite its importance, the coalescence of drops in yield stress materials is not entirely understood. In this work, we investigate the effects of the surrounding material plasticity on the rise and interfacial coalescence initiation of Newtonian drops using direct numerical simulations. Plastic effects contribute to the formation of smaller and spherical films, which facilitate the film drainage process on the one hand, but also to an increase in the resistance of the film to flow, which makes the drainage process more difficult on the other hand. The fluids’ interfaces are less deformable for high surface tension regimes, and the flow resistance effects become more significant than the film shape change effects. As a result, the drainage time tends to increase with the level of plasticity. For low surface tension regimes, the fluid interface is more deformable, and film drainage time tends to decrease with an increase in the level of plasticity.

Heat transfer in the Jeffery-Hamel flow of a yield-stress fluid

Heat transfer in the Jeffery-Hamel flow of a yield-stress fluid that obeys the Bingham-Papanastasiou model is investigated in the present study. Among various rheological models proposed to formulate the flow of yield-stress fluids, the Bingham model is usually used to address the effect of yield-stress. A fluid that obeys the Bingham model does not show any shear-thinning or shear-thickening behaviors; this makes the interpretation of the results much easier. Addressing the unyielded regions (regions at which the yield-stress material behaves like a solid) in a yield-stress fluid flow is not a trivial task, and it could be impossible, especially in complex geometries. Unfortunately, the Bingham model itself cannot be used to formulate complex fluid flow problems due to the mathematical difficulties (i.e., addressing the unyielded regions); hence it is usually regularized to avoid these mathematical challenges. One of these regularized models is the Bingham-Papanastasiou model. Using an exponential term enables the Bingham-Papanastasiou model to address the unyielded regions. However, this exponential term results in highly non-linear equations, which are difficult to be handled mathematically. In the present study, the effect of the yield-stress (Bingham number) on the hydrodynamics and heat transfer in the Jeffery-Hamel flow is investigated by using the Bingham-Papanastasiou model. The momentum transfer in the Jeffery-Hamel flow of a Bingham-Papanastasiou fluid is governed by a highly non-linear ordinary differential equation (ODE) which is a boundary value problem. Assuming that the fluid's properties are independent of the temperature and pressure, this highly non-linear ODE is solved numerically. The heat transfer in the flow, with a constant wall temperature boundary condition, is investigated, assuming the flow to be an equilibrium viscous dissipation flow (the fluid's mixed mean temperature variation is negligible along the channel). The resultant linear energy equation is also solved numerically to obtain the temperature distribution across the channel. The results obtained in this work show that the yield-stress increases the wall shear stress, Nusselt number, and Stanton number. In fact, the effect of the yield-stress on the Nusselt number is comparable to the effects of Prandtl and Eckert numbers. It is also found that the yield-stress can prevent the flow separation in a divergent channel. Considering the advantages of using the yield-stress fluids as the working fluids in the Jeffery-Hamel flow, they can be considered as an alternative to nanoparticles which are usually used to enhance the fluid's thermal conductivity and also the Nusselt number.

The effect of the backfill on the integrity of a buried pipeline upon heavy-duty vehicle crossings

The aim of this work was to determine stresses in the wall of a buried empty gas pipeline caused by the weight of backfill as well as by heavy-duty vehicles crossing the pipeline, and, on their basis to assess the applicability of protective sleeves. A buried pipeline with zero internal pressure of transported medium (empty pipeline) differs from an unburied pipeline by the vertical load due to the weight of the backfill which causes an ovalness of the circular cross section of the pipeline. This leads to the rise of through-wall bending stresses with the tensile stress at the outside surface at the 3 and 9 o´clock positions and compressive stress at the inside surface. At the 6 and 12 o´clock positions the stresses are tensile at the inside surface and compressive at the outside surface. The current depth of soil cover above gas pipelines is 0.5 m. For pipes DN500, t ~ 6.5 mm the through-wall bending stress is found to be σb ≈ ±10 MPa. In comparison with the yield stress of pipeline material, this stress is negligible. The situation is changed when heavy-duty vehicles cross the pipeline. For example, when a MAN truck with the mass load 3270 kg acting on a single wheel of the front axle crosses this pipeline, the pressure transmitted to the pipe will cause the through-wall bending stress σb ≈ ±76 MPa. This stress is superimposed to that of the backfill to give the total value ±86 MPa. When dead loads, imposed by backfill cover, together with live loads, caused by truck-wheel loads, are excessive a crushing of side walls of the pipeline and/or ring buckling of the pipe cross section can happen.

ANALISA DESAIN KEKUATAN STUKTUR PART KONEKTOR DAN TUBE FRAME UAV VTOL MENGGUNAKAN FINITE ELEMENT ANALYSIS

UAV The purpose of this study was to determine the effect of the use of carbon fiber and aluminum materials on the structural strength of the tube and connector parts by considering the safety factor obtained from the analysis results. This study uses the finite element method with the help of solidworks software. The research was conducted in stable flight conditions, namely the UAV's gravity was the same as the UAV's lift. From the results of the frame design, the weight mass is 25.6 kg. From the simulation results, the tube with carbon fiber material and aluminum 6061 alloy both have good strength because the maximum stress values ​​that occur are 15.71 MPa and 15.64 MPa, and these values ​​are still below the yield stress of carbon fiber material which is 551 MPa and aluminum 6061 alloy material, namely 55.1 MPa, with a safety factor obtained of 35 for carbon fiber and 3.5 for aluminum 6061 alloy, and a maximum displacement of 0.056 mm for carbon fiber and 0.812 mm for aluminum 6061 alloy. Whereas the connectors with carbon fiber and aluminum 6061 alloy materials also have good strength because the maximum stress values ​​that occur are 4,266 MPa and 4,139 MPa, and these values ​​are still below the yield stress of carbon fiber material and aluminum 6061 alloy material. with a safety factor obtained of 130 on carbon fiber and 3.5 on aluminum 6061 alloy, and the maximum displacement is 3,734 x 10-5 mm on carbon fiber and 5,416 x 10-4 mm on aluminum 6061 alloy. The use of carbon fiber material in tubes and connectors has better strength than aluminum 6061 alloy, due to the safety factor the value obtained is greater.

Prediction of transverse welding residual stress considering transverse and bending constraints in butt welding

Welding residual stress is generated by the thermal stress caused by rapid local heating and cooling during welding using a welding heat source. The distribution and size of the residual welding stress are affected by the joint type, welding conditions, constraints, etc., which also affect the fatigue, fracture, and buckling strengths. Therefore, because the magnitude and distribution of residual stress are very important for the safety evaluation of structures, guidelines for structural integrity evaluation suggest a method for deriving the welding residual stress. However, the welding residual stress presented in the guidelines is in a state without constraint; if a constraint exists, it is suggested to use the yield stress of the base material. This can lead to a very conservative design using the yield stress as the welding residual stress in the recent trend of the increasing use of high-strength steels with increased yield stress. Therefore, it is very important to investigate the relationship between constraint and residual stress during welding and to predict the residual stress according to the degree of constraint. In this study, the effects of member thickness, yield stress, lateral constraint, and bending constraint on the welding residual stress in butt welding were investigated, and predictive factors for welding residual stress were established. To this end, a thermal elastic–plastic analysis was performed by changing the thickness, yield strength, lateral constraint, and bending constraint size of the member. Subsequently, the analysis results were used to train a deep neural network (DNN) to predict the residual stress at the center of the weld and toe. In addition, the influence of input factors that affect the prediction accuracy during DNN learning was considered.

Analytical flow equation for irradiated low-alloy steels established by multiscale modeling

In this paper, we show how results of multiscale modeling can be condensed to establish a simple analytical flow equation for irradiated low-alloy steels. The flow equation accounts for temperature, strain rate, the initial and irradiation microstructure. Starting from a complete set of constitutive equations describing crystal plasticity of irradiated ferritique steels, simple assumptions and approximations are used to integrate the equations over the homogenized polycrystal. The final flow equation incorporates the lattice friction resistance, the Hall-Petch effect, the forest strengthening and irradiation hardening. Every component is established by multiscale modeling at lower scales. Irradiation hardening is attributed to solute clusters. Their size and density are determined in experiment, their shear resistance computed by atomistic simulations and their contribution to the flow stress assessed using dislocation dynamics simulations. The formation of solute clusters is found to increase the flow stress and the strain hardening modulus. Irradiation hardening decreases with temperature and with the yield stress of the unirradiated material. Predictions of the tensile curves and irradiation hardening are compared with many experimental results. A special section is dedicated to the interpretation of irradiation hardening measured in a surveillance program.

Effect of nano clay and PCE on the buildability of ultra-fine dredged sand-based 3D printing materials

The use of ultra-fine dredged sand instead of natural sand in construction 3D printing materials can significantly reduce the cost. However, ultra-fine dredged sand has fine particles and high angular morphology, which can hinder the buildability and continuous printability of construction 3D printing materials. The addition of polycarboxylate superplasticizer (PCE) can effectively solve this problem. Considering that the change of PCE (content of 0, 0.1%, 0.2%, 0.3%) content has a great influence on the printing performance of mortar, in order to make up for this deficiency, nano clay (content of 0,1%) is added to the mortar. The experimental results showed that the addition of nano clay can significantly reduce the negative effects of PCE on the yield stress and apparent viscosity of 3D printing materials (3DPM). When the content of PCE is 0.2%, the addition of 1% NAC could increase the static yield stress and viscosity growth rate of 3DPM by 111.8% and 115.3% respectively. In addition, unconfined compressive strength test, isothermal calorimetry, Mercury invasion porosity method and thermogravimetric analysis were used to characterize the hardening properties of 3DPM. The results of heat of hydration showed that the addition of nano clay reduced the hydration exothermic peak of 3DPM, but increased the total heat release. The results of pore structure analysis showed that the addition of nano clay reduced the macropore (>1000 nm) of 3DPM from 19.31% to 18.82%. Thermogravimetric analysis showed that the addition of nano clay increased the hydration products. Therefore, the compressive strength of 3DPM was kept within an acceptable range. Finally, the laboratory’s printing results indicated that the 3DPM can print up to 20 layers continuously.

Temperature effects and a prediction method of field-dependent yield stress in graphite magnetorheological grease

Graphite additives have become increasingly prevalent in magnetorheological (MR) materials, as they can substantially improve the shear yield stress of such materials. However, the effect of graphite additive proportion and temperature on graphite magnetorheological grease (GMRG) has not yet been fully reported, which limits the engineering application of GMRG. This work prepared magnetorheological greases with five different graphite ratios and investigated how their steady-state shear properties responded to temperature. The shear yield stress and relative MR effect of GMRG at different magnetic field strengths were measured and calculated. The results verified that the yield stress of GMRG increased with the increase of graphite additive ratio, but the relative MR effect decreased significantly. Besides, the steady-state shear mode was employed to evaluate the rheological properties of GMRG under varying magnetic field strengths and temperatures. The yield stress was analyzed through fitting experiments conducted under different magnetic field strengths and temperatures. The results showed that the addition of graphite powder increased the shear yield stress of the GMRG. But the enhancement effect was weakened by increasing temperature. In addition, a support vector machine (SVM)-based prediction method was proposed to predict the performance of GMRG with different ratios under complex operating conditions. The SVM-based estimation results showed good agreement with actual experimental values. This method provides a new approach for proportioning, characterization, and performance prediction of other materials.

Assessment of buckling strength curves in Direct Strength Method for estimating axial strengths of Cold-formed Steel members considering average yield stresses of cross-sections

The Direct Strength Method (DSM) is incorporated in current design specifications for designing Cold-formed Steel (CFS) members under compression. The North American design specification AISI S100 allows taking advantage of the increased material yield stress due to cold-forming in the application of the DSM only for members subjected to (i) local buckling and having slenderness ratios (λl) ≤ 0.776 or (ii) global buckling and having strengths not reduced by local buckling. This study aims to explore whether this limit could be released. First, Karren’s model for predicting the yield stresses of corners in CFS members was modified to improve the performance and extend the application limit. Second, Karren’s expression for estimating the average full-section yield stresses of CFS members was refined. Third, an extensive experimental database established previously by the authors was employed to assess the buckling strength curves in the DSM. Nominal axial strengths of the CFS members in the database were calculated using the average cross-section yield stresses as design parameters, which were then compared with the tested axial strengths. The modified Karren’s model and expression were used to estimate the average cross-section yield stresses of these members. Finally the LRFD resistance factors (ϕc) for the DSM buckling strength curves were calculated for a target reliability index of 2.5, and the results were compared with their counterparts obtained previously, considering the yield stress of virgin material as the design parameter. The results show that the design parameter of average cross-section yield stress was safe to be used with the DSM for estimating the axial strengths of solid CFS members subjected to local or global buckling.

Yield-stress transition in suspensions of deformable droplets.

Yield-stress materials, which require a sufficiently large forcing to flow, are currently ill-understood theoretically. To gain insight into their yielding transition, we study numerically the rheology of a suspension of deformable droplets in 2D. We show that the suspension displays yield-stress behavior, with droplets remaining motionless below a critical body-force. In this phase, droplets jam to form an amorphous structure, whereas they order in the flowing phase. Yielding is linked to a percolation transition in the contacts of droplet-droplet overlaps and requires strict conservation of the droplet area to exist. Close to the transition, we find strong oscillations in the droplet motion that resemble those found experimentally in confined colloidal glasses. We show that even when droplets are static, the underlying solvent moves by permeation so that the viscosity of the composite system is never truly infinite, and its value ceases to be a bulk material property of the system.

Jammed microgel growth medium prepared by flash-solidification of agarose for 3D cell culture and 3D bioprinting

Although cells cultured in three-dimensional (3D) platforms are proven to be beneficial for studying cellular behavior in settings similar to their physiological state, due to the ease, convenience, and accessibility, traditional 2D culturing approaches are widely adopted. Jammed microgels are a promising class of biomaterials extensively suited for 3D cell culture, tissue bioengineering, and 3D bioprinting. However, existing protocols for fabricating such microgels either involve complex synthesis steps, long preparation times, or polyelectrolyte hydrogel formulations that sequester ionic elements from the cell growth media. Hence, there is an unmet need for a broadly biocompatible, high-throughput, and easily accessible manufacturing process. We address these demands by introducing a rapid, high-throughput, and remarkably straightforward method to synthesize jammed microgels composed of flash-solidified agarose granules directly prepared in a culture medium of choice. Our jammed growth media are optically transparent, porous, yield stress materials with tunable stiffness and self-healing properties, which makes them ideal for 3D cell culture as well as 3D bioprinting. The charge-neutral and inert nature of agarose make them suitable for culturing various cell types and species, the specific growth media for which do not alter the chemistry of the manufacturing process. Unlike several existing 3D platforms, these microgels are readily compatible with standard techniques such as absorbance-based growth assays, antibiotic selection, RNA extraction, and live cell encapsulation. In effect, we present a versatile, highly accessible, inexpensive, and easily adoptable biomaterial for 3D cell culture and 3D bioprinting. We envision their widespread application not just in routine laboratory settings but also in designing multicellular tissue mimics and dynamic co-culture models of physiological niches.