Determination Of Yield Stress Research Articles

Stress wave effects and their mechanisms on stress-strain curves in the elastic phase of SHPB tests

In Split Hopkinson Pressure Bar (SHPB) tests, the stress wave effects during the elastic phase of the stress-strain curve and their influence mechanisms are crucial. Due to the extremely short duration of the elastic deformation phase, the stress wave effects on the specimen during this stage cannot be ignored. This leads to significant errors in the obtained elastic stress-strain curves. However, the dynamic compressive elastic stress-strain relationship forms the basis for studying the viscoelastic behavior of materials. Accurate determination of elastic yield stress and yield strain is also essential for deriving accurate plastic stress-strain relationships. Quantitative research on the stress wave effects during the elastic compression phase of SHPB tests is fundamental for decoupling and obtaining accurate material elastic curves. This paper conducts a quantitative theoretical analysis of the structural effects caused by stress wave evolution during the elastic compression phase, based on the assumption of plane waves. It studies the deviation characteristics and main factors of the phenomenological engineering stress-strain curves of the specimen compared to the actual material stress-strain curves under different conditions, revealing the influence rules and mechanisms of this deviation. The maximum stress deviation value and its corresponding dimensionless time, as well as the variation trend of the maximum stress deviation value within different fluctuation intervals, are calculated. Additionally, the study investigates the cases where the incident wave is arc-shaped or a combination of arc and linear waves. The findings provide theoretical references for the precise design and accurate data processing of SHPB tests.

Application of lubrication theory to determine yield stress in slump tests

The slump test can determine the yield stress of slurries by measuring the slump height. The convex shape in the slumped slurry profile cannot be characterised by the Tresca criterion. Lubrication theory has been widely applied to analyse the slow flow of yield stress fluids. Thus, the present study incorporates lubrication theory and the Tresca criterion to establish a generalized model for reconstructing the slurry profile based on the yield stress. The convex profile in the lower zone can be well represented by the novel method. The predicted yield stresses by the slump tests are larger than those determined using the vane method. Slump height and spread are equally accurate for predicting yield stress via the proposed method. Overall, the combination of lubrication theory and Tresca criterion yields a good prediction of yield stress based on slump height.

Spherical Indentation and Implementation of S3/P for yield stress determination of brittle materials

A mathematically transparent and robust experimental method has been developed to estimate the yield stress of brittle materials through the analysis of depth-sensing spherical indentation. Employing Hertzian contact mechanics, an elastically invariant ratio based on the simple equation S3/P=6REr2, (where S and P are contact stiffness and indentation load, respectively) has been derived that enables more accurate and confident determination of the transition from elastic to inelastic deformation; a transition that the yield stress dictates and represents. Using two diamond spheres with radii of 3.2 and 8.6 μm, the indentation test method and analyses are applied to two vitreous silicates: Corning's HPFS 7980® fused silica and Vitro's Starphire® soda-lime silicate. The estimated yield strengths are 8.15 GPa ± 2.5 % for the fused silica and 6.1 GPa ± 3.3 % for the soda-lime silicate, and both were independent of indenter radius. Verification of this new experimental method is demonstrated with an as-drawn titanium by showing equivalence of measured yield stress by its spherical indentation and that from uniaxial compression testing. This method will enable easier and more confident estimation of yield stress in brittle materials - a property that historically has been elusive to measure for these materials using common laboratory mechanical test methods.

Assessing the effect of test parameters on the determination of the rheological behavior of calcium sulfoaluminate cement pastes

Calcium sulfoaluminate cement (CSA) is renowned for its application in technologies that require rapid setting and high initial strengths, such as 3D concrete printing and repairs. However, their rheological behavior needs to be more adequately explored. This study assesses the impact of rotational rheometer test conditions on CSA pastes with different water-to-cement ratios. For the determination of static yield stress (τ0s), stress growth test with shear rates between 0.01 and 0.05 s−1 were employed. The results revealed that higher shear rates anticipated the occurrence of the material's peak destructuring and resulted in lower values of τ0s. In addition, the effects of geometry and testing routine on the flow curve were analyzed. The results showed that the use of vane geometry provides more consistent results of the measured dynamic yield stress, viscosity, and hysteresis area of CSA pastes than parallel plate geometry.

A modified small punch testing scheme to investigate the circumferential mechanical behavior of nuclear fuel cladding tubes

The manufacturing process of nuclear fuel cladding tubes endows them with anisotropic material properties. In this study, a small punch testing (SPT) method was established to investigate the circumferential tensile behavior of nuclear fuel cladding tubes. The specimen of the proposed SPT method was bended and stretched in a single stress state under a punching force. The proposed SPT method was then used to analyze the circumferential tensile behavior of a FeCrAl fuel cladding tube. Finite element simulation results indicated that the SPT method established herein determined ultimate tensile stress with higher accuracy than standard SPT because the plastic strain in the proposed method under maximum force is considerably smaller than that in standard SPT. Moreover, the proposed method can more accurately determine yield stress compared with standard SPT, as reflected by the elastic stage in the load–displacement curve that was a straight line. The test results indicated that the proposed SPT can be used to accurately determine the circumferential yield stress and ultimate tensile stress of nuclear fuel cladding tubes.

Effect of operational factors on reproducibility of yield stress measurement based on the vane method for cemented paste backfill

• Precise measure of yield stress is critical for CPB and vane method is widely used. • The reproducibility is subject to instrumental, analytical and operational influence. • Various vane positions, standing times and rotation speeds were tested. • A satisfactory reproducibility requires consistent preparation and operation. • A lower rotation speed facilitates a closer result to the true value. • Equilibrium time of 1 min and rotation speed of 0.1 rpm are suggested for CPB. Precise determination of yield stress with the desired reproducibility is critical for cemented paste backfill (CPB). An overview of the instrumental, analytical and operational factors was carried out to evaluate the key factors in CPB measurement using the vane method. Therewith the effects of vane inserted depth (10 to 40 mm), standing time (0 to 6 min), and rotational speed (0.05 to 5 rpm) were tested. The results show that an increased rotation speed or prolonged standing time leads to higher measured values and poorer reproducibility. The ESEM images indicate that larger yield stress values correspond to denser microstructures and the deterioration in structural homogeneity leads to pronounced deviation in results. Increasing the rotation speed enhances the role of viscous resistance and leads to an overestimation of yield stress. It is recommended that a consistent operation should be followed with the vane centered in the sample, resting for less than 1 min, and rotating below 0.1 rpm.

Determination of Static and Dynamic Yield Stress of Chengdu Clay Slurry

The yield stress of mud is one key to analyze the initiation and deposition of debris flow. Taking Chengdu clay as the experimental material, slurries with different solid volume concentrations were prepared. Using the blade rotor system of mcr301 rheometer and the continuous shear experimental method, the dynamic change process of shear stress of slurries with different solid volume concentrations was obtained with the shear rate increasing and decreasing continuously. According to the experimental results, the static and dynamic yield stress of Chengdu clay slurry is determined, and the influence of solid volume concentration on the yield stress is analyzed. The following conclusions are obtained: Chengdu clay slurry is a non-Newtonian fluid with yield stress. In the process of accelerated shear, for Chengdu clay slurry with solid volume concentration exceeding 35%, the shear rate is in the range of 0.01–1 s−1, and the shear stress increases rapidly to the maximum. When the shear rate exceeds 1 s−1, the shear stress decreases rapidly and finally tends to be stable. The shear rate appears stress overshoot near 1s−1. However, in the process of increasing shear rate, for Chengdu clay slurry with solid volume concentration of no more than 35%, the shear stress increases rapidly in the range of shear rate of 0.01–0.1 s−1, and the shear rate exceeds 0.1 s−1. The shear rate has little effect on the shear stress, and the stress overshoot disappears. In the process of deceleration shear, for all solid volume concentrations in the semi logarithmic coordinate system, the mud shear stress decreases steadily with the decrease of shear rate. The static and dynamic yield stress of slurry increases exponentially with particle concentration.

Generalized models of slump and spread in combination for higher precision in yield stress determination

The cone slump test is a simple alternative for on-site measure of yield stress, and on this principle, cylinder mold is employed owing to its easy accessibility. As an extension of the previous investigation which has validated the cone's cylinder-like behavior in the slump geometry, this work adopted an equivalent cylinder to facilitate comparison in the spread geometry, together with cylinders of various dimensions to explore dimensionless spread to yield stress relation. Good consistency was observed in both slump profiles and spread contours between the mini cone and its equivalent cylinder. The spread diameters after normalization displayed a definite common correlation with dimensionless yield stress. After integrating the corrective coefficient β, the models of slump and spread were generalized to both cylinder and cone molds with desired accuracy, alleviating the overall deviation of 14.88 % by individual slump height to 10.25 % combining with spread and enhancing the robustness of predicted values.

Irradiation hardening of advanced tungsten grades: An experimental and inverse finite element method study

The effect of neutron irradiation on mechanical properties of various advanced W grades (pure, doped by K, alloyed by Re) was assessed by means of mechanical testing using miniaturized tensile and sub-miniaturized three-point bending (3PB) specimens. Different irradiation conditions in terms of temperature (400, 600, 800 and 1100 °C) and irradiation dose (0.2–0.25 dpa, 1.0–1.1 dpa) were considered. In order to extract the yield stress from the flexural load-displacement data, the empirical correlation between the flexural stress at a specific reference point on the flexural stress-strain curve and uniaxial tensile yield stress was established. The empirical ratio identified can be applied for the 3PB testing in a wide range of temperatures and plastic properties of un-irradiated and irradiated W alloys. The accuracy of the yield stress determination deduced using the empirical correlation from the 3PB tests was compared with the inverse FEM modelling procedure applied to the 3PB tests carried along with reference data extracted from the dedicated tensile tests. The information on the tensile yield stress and work hardening rate of all studied materials at different irradiation conditions was summarized and discussed in the view of the irradiation hardening.

Rheological Characterization of Fine-Grained Sediments under Steady and Dynamic Conditions

The objective of this study is to investigate the steady and dynamic rheological behavior and characteristics of fine-grained sediments. A series of laboratory tests were conducted using an Anton Paar MCR 102 rheometer to investigate the rheological properties of the fine-grained sediments at various water to solid (W/S) ratios. In the steady-state measurement condition, the results indicate that fine-grained sediments are a non-Newtonian viscous fluid, and the presence of yield stress of fine-grained sediments is evident and is influenced by the W/S ratios. For the determination of yield stress, two types of methods were used: by defining the minimum value of shear stress from flow curves experimental data in semilog scale and by modeling the flow curves following different rheological models. From the results obtained, it appears that the Casson model was the best one to characterize the rheological behavior of fine-grained sediments, because of its high coefficient of determination R2 and the lowest mean absolute percentage error, also close to the measured yield stress value. In the dynamic state measurement condition, the loss modulus (G″) is markedly smaller than the elastic modulus (G′), indicating that fine-grained sediments are predominantly elastic (in the range of amplitude and frequencies explored). The complex viscosity (η*) sharply decreases with the frequency increase, but the frequency dependence of the G′ and G″ is rather weak. The G′, G″, η*, and loss factor (tan δ) significantly reduced with the increase of the W/S ratio. In the end, the dynamic rheological properties of fine-grained sediments can be expressed as appropriate functions of the W/S ratios. This study not only provided a guideline for having a better understanding of the rheology of fine-grained sediments but will also provide scientific support for understanding and solving all kinds of natural and manmade activities involving fine-grained sediments, such as dredged sediments handling and transport by pipelines, landslides caused by rainfall or earthquake; generation and movement of mudflows, laying and maintenance of submarine cables and pipelines, and deep-sea mining engineering.

Composition dependence of positive temperature dependence of yield stress for Co3(Al, W)–Co3Ti pseudo-binary alloy with the L12 structure

Variations in the positive temperature dependence of yield stress for L12 intermetallic compounds in pseudo-binary alloys with the composition of Co3(Al, W)–Co3Ti have been investigated. Polycrystalline L12 compounds in the pseudo-binary system with a Co3(Al, W) to Co3Ti composition ratio of approximately 1:3 and 1:9 were prepared. The temperature dependence of the yield stress ranging from 293 to 1273 K was determined. The onset temperature for the positive temperature dependence of yield stress for each compound is located between that of Co3(Al, W) and Co3Ti. The activation energies for the positive temperature dependence of these compounds are evaluated to be 47.0 and 43.6 kJmol-1, respectively. The activation energies are also intermediate values between those of Co3(Al, W) and Co3Ti.The composition dependence of the positive temperature dependence of yield stress is estimated from the physical properties of Co3(Al, W) and Co3Ti. Although the activation energies estimated for the present compounds are slightly different from the experimentally determined values, the temperature dependences of the experimentally determined yield stress are almost represented from the estimated parameters. The composition dependence of the positive temperature dependence of the yield stress can be predicted from the physical properties of the base compounds.

Penetration test as a fast method to determine yield stress and structural build-up for 3D printing of cementitious materials

3D printing technology is becoming increasingly important in the construction sector, leading to changes in material requirements compared to traditional manufacturing methods. To characterize the rheological properties (yield stress, viscosity, and structural build-up) of printable mortars, suitable methods are necessary. However, with a rheometer, this is problematic because a time-resolved determination of the properties is complicated, time-consuming, and the torque limitation is often too low. For this reason, a penetration test, and a formula for calculating the yield stress are introduced. To validate the formula, it is determined that the results are comparable with the calculated yield stress based on a rheological test. Furthermore, it is shown that it is possible to extrapolate the data and to determine structural build-up. This paper is intended to give an up-to-date overview of the penetration method and to illustrate the advantages and possibilities of the method in the field of 3D printing. Moreover, it is discussed in which areas improvement and further investigations are needed.

Development of hydroxyapatite reinforced alginate–chitosan based printable biomaterial-ink

This study reports synthesis of sodium alginate/ chitosan/ hydroxyapatite (HAp) based biomaterial-ink. An ionic interaction between polyanionic alginate and polycationic chitosan has been observed that forms a physical gel. The dispersion of HAp has been achieved through ultra-sonication, and stability of HAp in the hydrogel system has been achieved through hydrogen bonding with chitosan. Post printing crosslinking has been carried out with a 10 w/v % aqueous calcium chloride (CaCl2) solution. The combinations of biomaterial-ink have been characterized through Attenuated Total Reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Scanning Electron Microscope (SEM), contact angle measurements. Further, the inks were characterized to estimate the printability and rheological responses. ATR-FTIR study confirms the ionic interaction between alginate and chitosan and identifies the presence of HAp in the biomaterial-ink. SEM morphology depicted the post-printing shape retention ability of the bioprinted constructs and revealed the structure’s rough morphology. All the biomaterial-ink combinations depicted hydrophilic nature as confirmed by the contact angle measurements. Rheological studies of the printable ink with hydroxyapatite revealed shear thinning properties and acceptable viscosity, essential for extrusion during bioprinting. The biomaterial-ink comprised only sodium alginate, and chitosan also displayed shear thinning abilities and showed lower working viscosity resulting in poor printability. The addition of hydroxyapatite to the hydrogel revealed acceptable post-printing structural stability. However, beyond 0.2% by weight of HAp imparts brittleness in the final structure. The linear viscoelastic regime, elastic modulus, and viscous modulus of the inks have been determined through the oscillatory strain sweep test. Creep recovery study, essential for predicting material behaviour immediately after ejection from the nozzle, indicated the material’s viscoelastic behaviour. The power law model has been used to estimate the flow index that predicted shear thinning abilities of the biomaterial-ink, and a correlation between the experimental and theoretical model was established. Herschel–Bulkley empirical model was used to determine yield stress (minimum stress required for extrusion from the nozzle) of the biomaterial-ink. Rheological studies and printability studies indicated Ink 5% 2% 0.1% as a promising combination for tissue engineering applications.

Valorization of hazelnut cake in compound chocolate: The effect of formulation on rheological and physical properties

The aim of this study was to valorize hazelnut (Corylus avellana L) cake (HC), which is a by-product of hazelnut oil industry, in compound chocolate (HCC) as a partial replacer of sugar and milk originated powders (MOP: skimmed milk and whey powder in equal amounts). D-optimal mixture design was used to optimize HCC formulation. The optimum sugar, MOP, and HC amount were selected as 25.0–40.0, 6.0–21.0, and 0.0–15.0 g/100 g, respectively. The Casson model with high R2 values (0.9882–0.9948) was used to determine yield stress and plastic viscosity values of samples which were varied between 1.47 and 2.35 Pa, and 1.17–1.42 Pa s, respectively. Furthermore, particle sizes and water activity were determined between 25.67 and 78.20 μm and 0.31–0.38, respectively. Total phenolic content in HCC samples, their digestibility, and bioaccessibility ranged from 1389 to 3367; 2601–3955 mg GAE/kg, and 112–187% respectively. Also, hardness and brittleness were ranged between 7.85 and 11.55 N and 0.52–1.02 mm, respectively. The sensorial characteristics of the samples along with flow behavior and physico-chemical properties indicated that HC may be used as a healthy and low-cost ingredient in HCC formulation to partially substitute sugar and MOP.

Determination of Material and Failure Characteristics for High-Speed Forming via High-Speed Testing and Inverse Numerical Simulation

In conventional forming processes, quasi-static conditions are a good approximation and numerical process optimization is the state of the art in industrial practice. Nevertheless, there is still a substantial need for research in the field of identification of material parameters. In production technologies with high forming velocities, it is no longer acceptable to neglect the dependency of the hardening on the forming speed. Therefore, a method for determining material characteristics in processes with high forming speeds was developed by designing and implementing a test setup and an inverse parameter identification. Two acceleration concepts were realized: a pneumatically driven one and an electromagnetically driven one. The method was verified for a mild steel and an aluminum alloy proving that the identified material parameters allow numerical modeling of high-speed processes with good accuracy. The determined material parameters for steel show significant differences for different stress states. For specimen geometries with predominantly uniaxial tensile strain at forming speeds in the order of 104–105/s the determined yield stress was nearly twice as high compared to shear samples; an effect which does not occur under quasi-static loading. This trend suggests a triaxiality-dependent rate dependence, which might be attributed to shear band induced strain localization and adiabatic heating.

Numerical homogenization of elastic properties and plastic yield stress of rock-like materials with voids and inclusions at same scale

Mechanical properties of rock-like materials are affected by voids and mineral inclusions. Different kinds of analytical solutions have been established for the determination of effective elastic properties and plastic yield stress or failure strength of those materials. However, voids and inclusions are generally considered at different scales. By adopting the Fast Fourier Transform technique, we propose in this paper a numerical homogenization method for modeling the effective elastic properties and plastic yield stress of rock-like materials having voids and mineral inclusions at the same scale. Both are embedded in an elastic-perfectly plastic matrix. The overall elastic-plastic properties are estimated by taking into account the morphology and spatial distribution of pores and inclusions. It is found that the macroscopic elastic modulus is sensitive to both void and inclusion geometry and orientation. The overall yield stress is mainly controlled by the porosity, the inclusion volumetric fraction, the void shape, distribution and orientation. Due to the presence of voids, the influences of inclusion geometry and orientation on the overall yield stress are significantly reduced. This is an important difference with inclusion-reinforced materials without voids.

Rheological properties for fresh cement paste from colloidal suspension to the three-element Kelvin–Voigt model

In the present work, rheological behaviors of fresh cement paste are studied based on multi-disciplinary approaches, i.e., colloidal suspension using attractive van der Waals force, rheology using the Bingham model and Bingham–Papanastasiou model, which are able to describe the behavior of cement pastes before and after yield stress, and finally the continuum mechanics based on Maxwell and Kelvin–Voigt models. To achieve this, the fresh cement paste with different water-to-cement ratios of 0.3 up to 0.6 is prepared. The attractive van der Waals forces are estimated based on the distances between solid cement particles, which vary at every single water-to-cement ratio. The rheology experiments of all water-to-cement ratios are performed using a rheometer. According to our experimental outcomes, the Bingham and Bingham–Papanastasiou models are applied in the modeling of the experimental curves and determination of yield stress and viscosity. Maxwell and the Kelvin–Voigt models are utilized in describing solid-like behavior before yield stress and fluid-like behavior beyond yield stress. It is observed that the increase of water generates a decrease in the viscosity, yield stress, and packing concentration of solids. It also increases the distances between two cement particles in the cement pastes. According to the modeling results, the Bingham–Papanastasiou model is well adapted for the cement paste flow due to its additional modeling parameter, which is known as m. The role of m is understood and described by linking the van der Waals interaction, rheology, and three-element Kelvin–Voigt model as a whole in function of water-to-cement ratio. m is understood as a key parameter in which the distance between particles affects the rheological behavior of fresh cement pastes. Lastly, the two-phase flow simulations have been successfully achieved and compared with the experiments. The conclusion and outlooks are summarized and discussed at the end of the paper.

Characterization on the yield stress and interfacial coefficient of friction of glasses from scratch tests

Based on dimensional analysis and finite element simulation, a new method is proposed to characterize the yield stress and interfacial coefficient of friction of materials by scratching with a Vickers indenter. Two simple equations are obtained: one is for determining the interfacial coefficient of friction between the scratched material and scratch tip via the ratio of tangential to normal force, and the other is for calculating the yield stress of scratched material with the groove width and normal force. In a case study, the method is applied to soda-lime and borosilicate glasses. It is shown that the measured results of yield stress and interfacial coefficient of friction between glasses and a diamond tip are consistent with that obtained by other methods, with a high accuracy. The quick and accurate determination of yield stress and interfacial friction coefficient provides important information for the design and processing of glass products.

Shear Rate-Dependent Rheological Properties of Mine Tailings: Determination of Dynamic and Static Yield Stresses

In this paper, shear rate-dependent rheological properties of mine tailings taken from abandoned mine deposits prone to mass movements are examined using a commercial ball-measuring rheological system. The yield stresses (i.e., dynamic and static yield stresses) and viscosity of sand-rich materials are examined by the shear rate-controlled flow curve and time-dependent stress growth methods. Before yielding, the shear stress reaches a peak value (i.e., yield stress) observed for all flow curves. In the steady-state condition, the materials have a minimum shear stress (i.e., dynamic yield stress). The static yield stress can be determined under a constant applied shear rate with different initial values ranging from 10−4 to 10−1 s−1. As a result, the Bingham yield stress and viscosity can be used as a first approximation for estimating the debris flow mobility of post-failure materials. However, the Bingham yield stress is competitive with the static yield stress measured from stress growth methods. Upon comparison of the dynamic and static yield stresses, the static yield stress is approximately 35–45 times greater than the dynamic yield stress, and may be strongly related to microstructural changes (i.e., thixotropy). In this context, special attention must be paid to the determination of yield stresses in debris flow mitigation programs.

Comparative study of the yield stress determination of cement pastes by different methods

Different methods have been proposed in the literature to determine the yield stress of cement grouts. These methods may present wide differences especially for thixotropic materials such as cement pastes. In this paper, different mixtures of water–cement–superplasticizer were studied for various w/c ratios and superplasticizer dosages. From shear tests of the mixtures in a rheometer, yield stress was determined in different ways: by identification on the experimental flow curve or by modelling flow curve through different rheological models. The conventional rheological models as Bingham model and Herschel–Bulkley model are not in agreement in the majority of the cases studied especially at low shear rates where thixotropy can be observed. In order to enhance the modelling in this area and allows to accurately determine the yield stress, we compared the results obtained through the conventional rheological models to that obtained by a thixotropy model. From the obtained results, it turns out that the latter allows to better predict the behaviour of thixotropic cement grouts and their yield stress.