Experimental Flow Curves Research Articles

On the utilization of Sachs model in modeling deformation of surface grains for micro/meso scale deformation processes

Finite element method simulations have become a crucial tool in conventional metal forming process design. Microforming, which is a technology for the production of miniature parts by metal forming, is a potential process for mass production of microcomponents. However, to use finite element analysis in the design of microforming processes, material models that take into account size effects are needed. In this research, the surface layer model and the Hall-Petch relationship are combined to model materials deformation at the meso/micro-scale. Sachs model is used to model the deformation of surface grains. To validate this newly developed materials model, scaled-down compression tests were conducted, and a good agreement between predicted and experimental flow curves was obtained. In addition, the model was used to predict the experimental results of previous research for three other materials, as well. Again, a good agreement between the predicted and experimental results was obtained. Thus, the model showed a satisfactory capability to predict flow curves for different specimen size and grain size combinations for different materials. To further verify the materials model, micro-extrusion experiments were also performed. Simulations of the micro-extrusion experiments were carried out by implementing the newly developed materials model. A reasonable agreement between the experimental and predicted micro-extrusion results was found, which validates the utilization of the newly developed material model in microforming process simulations.

Constitutive modelling of Usibor® 1500 sheets after intercritical quenching

In this study, 0.9 and 1.8 mm thick Usibor® 1500 sheets were subjected to intercritical quenching by heating to 760-930°C and quenching at a controlled rate. The tensile behavior of as-quenched Usibor® 1500 was experimentally obtained using uniaxial tension tests at strain rates ranging from 0.001 to 0.25 s−1. The constants in the hardening models, including Johnson-Cook, were optimized using a Genetic algorithm and linear regression for each condition at each strain rate. Then, these models were numerically modified to account for heat treatment dependency. Uniaxial tensile tests were simulated using the fitted models and compared to experimental flow curves and strain distribution maps to determine the accuracy of the prediction of each model. Optical microscopy was used to determine the volume fraction of each phase using image processing tools and these characteristics were used to explain the behavior of Usibor® 1500 after intercritical quenching. It was found that intercritical quenching process parameters determine the distribution and morphology of each phase and consequently the range of mechanical properties. This model can be used to simulate the deformation of hot-stamped components with tailored properties produced under controlled austenitization.

Approximation of the filtration flow curve through the layers of sorbents and ionites in petrochemical and environmental mass transfer equipment

A modified equation is presented for approximating experimental filtration flow curves through layers of sorbents and ionites in petrochemical and environmental mass transfer equipment, which makes it possible to decipher the contribution of the increasing inertial component of the filtration flow structure and to estimate the intensity of the upgrowth of filtration flow turbulence. The prospects of using the modified equation for solving spatial filtration problems are shown, since it ensures the continuity of the velocity fields and pressure gradients with successive changes in the filtration flow mode.

Influence of different fumed silica as thixotropic additive on carbonyl particles magnetorheological fluids for sedimentation effects

The present work reports the influence of different types of surface area, hydrophobic, and hydrophilic fumed silica mixed in silicone oil as a thixotropic additive on carbonyl particles based magnetorheological fluids (MRFs) were prepared. Scanning electron microscopy analysis confirms the fumed silica particles attached to the surfaces of CIPs. The vibrating sample magnetometer result shows the MRF4 and 5 have a better magnetic saturation value of 30.12 emu/gm and 40.12 emu/gm, respectively. The experimental rheological flow curve behaviours are investigated using the magnetorheometer. The Herschel–Bulkley rheological model is found to be in good agreement with the experimental curves and suggested shear thinning property is observed. The results showed that the hydrophilic silica with larger surface area type presented (i.e.MRF 4 and 5) better magnetorheological fluid characteristics in terms of shear stress, with a high value of dynamic yield stress, and have much-improved sedimentation ratio up to seven days.

A “new” empirical equation to describe the strain hardening behavior of steels and other metallic materials

The strain hardening behavior of five different steels of varying carbon content, ranging between 0.007 and 0.71%, such as an Interstitial free (IF), a microalloyed, and a low, medium and high carbon steels, have been critically examined using tensile loading. The test results for the IF and the microalloyed steels having only ferritic structure, exhibit a two-stage strain hardening behavior. On the other hand, the low, medium, and high carbon steels having a two-phase microstructure (ferrite-pearlite/cementite) exhibit three-stage strain hardening. A number of existing and frequently used empirical equations, such as the Hollomon, Ludwik, Ludwigson and Voce were used to explain the strain-hardening characteristics of these steels; however, none of the above could fully and satisfactorily explain the flow behavior especially at high strain region. In order to remedy this deficiency, a modification to Ludwigson equation has been suggested by the authors by introducing an extra exponential term to the existing Ludwigson equation. The modelled flow curves, on the basis of this proposed new equation, could explain the strain hardening behavior of these steels very satisfactorily over the entire strain range. In addition, the excellent matching of the flow curves, based on the proposed equation with the experimental flow curves of a number of metallic materials, as diverse as multiphase steel, TRIP-assisted steel, dual-phase steel, stainless steel (316L), Mg-alloy, Ti-alloy and a high entropy (Cantor) alloy, indicates its wider applicability.

Rheological Behavior of a VT23 Alloy during Deformation in a Wide Temperature Range

Upsetting tests of a two-phase VT23 titanium alloy are carried out in the temperature range 700–1200°C. The phase composition of the alloy after deformation on a plastometer is studied by X-ray diffraction. Experimental plastic flow curves are plotted.

On the rule of mixtures for bimetal composites without bonding

Abstract In the present study, three types of bimetal composites, Al 6082 sleeve/Al 6082 core, Mg AZ31 sleeve/Mg AZ31 core and Al 6082 sleeve/Mg AZ31 core, were fabricated by drilling and assembling. The rule of mixtures (ROM) for the flow curves and yield strengths during compressive test were addressed. Our results show that the ROM can predict well the experimental flow curves and yield strengths of bimetal composites without bonding, irrespectively of the different strain hardening behavior between the two components.

Validation of homogeneous anisotropic hardening model using non-linear strain path experiments

We conducted non-linear strain path experiments on a dual-phase steel-sheet sample. The first strain path in each of these experiments, called pre-strain, was always uniaxial tension in the direction transverse to the sheet (90° from the rolling direction). For this purpose, we clamped large tensile specimens in a suitable gripping system and deformed them to produce a sufficiently large area with a uniform strain distribution. We machined new specimens from this area, and we subjected them to different modes of deformation, namely uniaxial tension in different directions from the transverse direction, simple shear, and biaxial tension with different load ratios. In addition, we performed uniaxial tension-compression tests consisting of either one or three full cycles. We obtained the coefficients of a distortional plasticity model—the homogeneous anisotropic hardening (HAH) model—using an inverse analytical identification tool. First, we calibrated two sets of reverse loading coefficients using the tension-compression stress–strain curves obtained with either one or three full cycles. Then we used the 90° tension–45° tension and the 90° tension–0° simple-shear sequences to determine two sets of cross-loading coefficients. We compared the other independent experimental flow curves with simulations using the HAH model with combinations of the different sets of coefficients. These comparisons showed the influence of the selected input data on the calculations of the coefficients calibrated and demonstrated the advantages and limitations of the present HAH model.

New magneto-rheological fluids with high stability: Experimental study and constitutive modelling

Magneto-rheological fluids (MRF) are known as a category of smart materials because they exhibit sudden viscosity changes upon application of magnetic field. In contrast to normal fluids, MRFs can sustain shear up to a yield stress. Stability and resistance against movement are important factors which determine the extent of application of a MRF. In this work, new MRFs are developed using engine oil as carrier liquid, carbonyl iron powder as magnetic particle, stearic acid and CHRYSO® Optima100 as additives. Stability of the samples is measured over time. The samples are exposed to magneto-rheological tests with combined liquid and Peltier temperature control. Samples A, B and C are prepared with low, medium and high particle fractions respectively and tested at different temperatures (−10 °C, 5 °C, 60 °C) but for samples D, E, F and G the rheology tests are conducted in room temperature (25 °C) but at variable magnetic field and shear rate. Inherent assumption of the existing constitutive models is that the flow curve of MRF is shifted by a field-dependent yield stress. In this paper the effect of magnetic field is formulated and based on the physical properties of MRFs, a new method is introduced for identification of material parameters. This method predicts the yield stress by comparing the storage and shear moduli. Obtained results are compared with those obtained from fitting the experimental flow curves and also with those obtained from Bingham model. It is shown that, results of the proposed model are in good agreement with the experimental data. Moreover, the calculated sedimentation ratio shows that simultaneous use of stearic acid and Optima100 significantly improves stability of MRFs.

Design, rheology and microstructure of food-grade emulsion-based systems for delivery of vitamin D

The fortification of food with vitamin D has several limitations because this group of fat-soluble compounds may degrade or undergo undesirable changes during technologic processing and storage of food. The purpose of this study was to investigate emulsions for vitamin D3 delivery in commercial foods. Oil-in-water (o/w) emulsions stabilized by mixture of various proteins (whey protein isolate (WPI), skimmed milk powder (SMP) and vegan protein isolate (VPI)) as emulsifiers and carboxymethylcellulose as thickening agent were used. The shear stress and effective dynamic viscosity of the emulsions in the wide range of shear rates were experimentally determined. By approximating experimental flow curves using the power-law model, the values of the consistency coefficient and flow behavior index were obtained, which made it possible to classify the emulsions as systems with pseudoplastic flow. Within the framework of the structural approach, the rheological data were analyzed on the basis of the generalized rheological model of Casson. The contributions to the process of viscous flow calculated from the experimental data from the integral characteristics of associates of droplets and individual particles during their hydrodynamic interaction made it possible to explain the effect of changing the viscosity of emulsions from the nature of the emulsifier used. The zeta potential values determined by the dynamic light scattering method indicate the existence of a strong repulsive force as a factor for the stability of emulsions. The sign of the potential and its magnitude indicate the process of adsorption on the surface of fat droplets molecule of protein. The presence of a peak of flocculated particles in the histograms of the particle size distribution is explained by the presence of non-adsorbing polysaccharides, which are capable of the generation of aggregated emulsion structures through depletion flocculation. Regardless of the choice of the type and nature of the protein emulsifier - animal or plant origin, all studied systems were stable and can be considered for use as emulsion-based delivery systems of vitamin D. From an economic point of view, it is advisable to use dry milk as an emulsifier. The resulting emulsions can be used as a basis for the production of vitamin D3-fortified foods, in particular for dairy products.

A Phenomenological Mechanical Material Model for Precipitation Hardening Aluminium Alloys

Age hardening aluminium alloys obtain their strength by forming precipitates. This precipitation-hardened state is often the initial condition for short-term heat treatments, like welding processes or local laser heat treatment to produce tailored heat-treated profiles (THTP). During these heat treatments, the strength-increasing precipitates are dissolved depending on the maximum temperature and the material is softened in these areas. Depending on the temperature path, the mechanical properties differ between heating and cooling at the same temperature. To model this behavior, a phenomenological material model was developed based on the dissolution characteristics and experimental flow curves were developed depending on the current temperature and the maximum temperature. The dissolution characteristics were analyzed by calorimetry. The mechanical properties at different temperatures and peak temperatures were recorded by thermomechanical analysis. The usual phase transformation equations in the Finite Element Method (FEM) code, which were developed for phase transformation in steels, were used to develop a phenomenological model for the mechanical properties as a function of the relevant heat treatment parameters. This material model was implemented for aluminium alloy 6060 T4 in the finite element software LS-DYNA (Livermore Software Technology Corporation).

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.

The Role of Microstructure on the Tensile Plastic Behaviour of Ductile Iron GJS 400 Produced through Different Cooling Rates—Part II: Tensile Modelling

Tensile testing on ductile iron GJS 400 with different microstructures produced through four different cooling rates was performed in order to investigate the relevance of the microstructure’s parameters on its plastic behaviour. Tensile flow curve modelling was carried out with the Follansbee and Estrin-Kocks-Mecking approach that allowed for an explicit correlation between plastic behaviour and some microstructure parameters. In the model, the ferritic grain size and volume fraction of pearlite and ferrite gathered in the first part of this investigation were used as inputs, while other parameters, like nodule count and interlamellar spacing in pearlite, were neglected. The model matched very well with the experimental flow curves at high strains, while some mismatch was found only at small strains, which was ascribed to the decohesion between the graphite nodules and the ferritic matrix that occurred just after yielding. It can be concluded that the plastic behaviour of GJS 400 depends mainly on the ferritic grain size and pearlitic volume fraction, and other microstructure parameters can be neglected, primarily because of their high nodularity and few defects.

Modeling the Dynamic Recrystallization and Flow Curves Using the Kinetics of Static Recrystallization.

The results of modeling the dynamic recrystallization of steels during hot deformation on the basis of information on their static recrystallization kinetics are presented. The results of predicting the amount of deformation accumulated in the metal under the conditions of dynamic recrystallization development were used for calculating the metal flow curves. The model was validated by comparing the calculated flow curves with the experimental flow curves determined on the 1045 steel by means of hot torsion tests carried out from 1000 °C to 1100 °C and at strain rates from 0.1 to 10 s‒1. The difference between the experimental and predicted flow stress values did not exceed 6%. The influence of the chemical element content in low-alloyed steels on the magnitude of the critical strain for the initiation of dynamic recrystallization is assessed. The method of predicting the kinetics of dynamic recrystallization by recalculating the kinetics of static recrystallization to the conditions of continuous growth of the strain degree during metal deformation implemented in the model can be used in designing and optimizing technologies associated with metal hot forming processes.

Validation of a New Quality Assessment Procedure for Ductile Irons Production Based on Strain Hardening Analysis

A mathematical procedure based on the analysis of tensile flow curves has been proposed to assess the microstructure quality of several ductile irons (DIs). The procedure consists of a first diagram for the assessment of the ideal microstructure of DIs, that is, the matrix where mobile dislocations move, and a second diagram for the assessment of the casting integrity because of potential metallurgical discontinuities and defects in DIs. Both diagrams are based on the dislocation-density-related constitutive Voce equation that is used for modeling the tensile plastic behavior of DIs. The procedure stands on the fundamental assumption that the strain hardening behavior of DIs is not affected by the nature and the density of the potential metallurgical discontinuities and defects, which are expected to affect only the elongations to fracture. However, this fundamental assumption is not obvious, and so its validity was evaluated through tensile testing Isothermed Ductile Irons (IDIs) 800, showing a wide scatter of elongations to rupture. The analysis of the strain hardening behaviors supported by strain energy density calculations of IDIs tensile tests proved that the fundamental assumption was valid and the quality assessment procedure could be applied to IDIs. A modified Voce equation was also introduced to improve the fitting of the experimental tensile flow curves and the strain energy density calculations.

Hot Flow Curve Description of CuFe2 Alloy via Different Artificial Neural Network Approaches

In this research, a mathematical description of hot flow curves of CuFe2 copper alloy has been assembled. Experimental flow curves of the investigated alloy were created on the basis of hot compression dataset. This dataset was acquired in the temperature range of 923-1223 K and the strain rate range of 0.1-10 s−1, with the maximum true strain value of 1.0. The experimental flow curves were described by two artificial neural network approaches. In the first case, a neural network has been created to approximate the experimental flow curves with respect to the true strain, strain rate and temperature. In the second case, a hybrid approach based on the combination of predictive models with neural networks has been utilized. In this case, five neural networks were used to describe parameters of these models in relation to the temperature and strain rate. Results have shown that the hybrid approach allows an accurate description of the experimental data and also provides more reliable prediction.

COMPOSITIONS BASED ON AQUEOUS SOLUTIONS OF CHITOSAN AND GLUTAR ALDEHYDE FOR EMBOLIZATION OF BLOOD VESSELS

The article investigates the aqueous solutions of food chitosan and glutaraldehyde to determine the feasibility of their use as components of an embolizing composition. It was shown on the basis of experimental flow curves, viscosity and velocity curves that test solutions have low viscosity and exhibit Newtonian flow behavior. The activation energy of viscous flow of the fluids was estimated in the temperature range of 25-37 °C within the Arrhenius - Frenkel - Eyring equation. It varies within a narrow range: 17-24 kJ/mol. When mixing the aqueous solutions of food chitosan and glutaraldehyde, chemical interaction of the solutes occurs. It is accompanied by an increase in viscosity and formation of a covalently crosslinked gel. Using a simple exponential equation the effective rate constant of the chemical process was calculated. It varies in a wide range: 1.9-82.7∙103 1/s. These values can be used when selecting an optimal region of food chitosan-glutaraldehyde ratios and concentrations of their aqueous solutions to generate embolizing agents. The conditions at which gel formation takes place over forty seconds were determined. Differential scanning calorimetry indicated a negligible thermal effect of food chitosan reaction with glutaraldehyde in the aqueous medium, which ensures no thermal burn during the formation of an embolus in the blood vessel in situ. As a result of the work elastic solid gels suitable for use as embolizing agents were obtained.

Thermo-Mechanical Constitutive Equation of 22MnB5 Steel Sheet for Hot Press Forming Process

The 22MnB5 steel sheet is applied to the hot press forming process to enhance the strength of the final product with guaranteeing sufficient formability. Since it undergoes the austenitizing process up to 850 °C and is quenched down to room temperature, it does not only occur large plastic deformation, but also induce the phase transformation. It is substantially difficult to take into consideration of the flow stress variations with respect to the temperature and strain rate associated with the phases such as the austenite, ferrite/pearlite, bainite, and martensite in the numerical simulation for the HPF process. This paper mainly proposes a generalized form of thermo-mechanical constitutive equation which is able to capture the experimental flow curves, precisely, in terms of the strain and strain rate hardening including the temperature softening, simultaneously.

A comparative study on the hot deformation behavior of Ti[sbnd]5Al[sbnd]5Mo[sbnd]5V[sbnd]3Cr and newly developed Ti[sbnd]4Al[sbnd]7Mo[sbnd]3V[sbnd]3Cr alloys

Hot deformation behavior of Ti-5553 and newly-developed Ti-4733 β-Ti alloys were compared by hot compression tests at 930–1080 °C and strain rates of 0.001–1 s−1. The flow curves and microstructures showed that dynamic recovery and partial continuous dynamic recrystallization are the dominant microstructural mechanisms at hot working condition. It was observed that the flow stress of Ti-4733 lies over that of Ti-5553. Using the M¯d¯-B¯O¯diagram, Mo equivalent number and the valence electron count, it was shown that β-phase in Ti-4733 is more stable than that in Ti-5553. The higher strength of Ti-4733 was attributed to the more stability of β and its higher Mo equivalent number. While the β quenched microstructure in Ti-5553 contained parallel layers of α′ martensite, it was absence in Ti-4733 due to the more stability of β. Using the hyperbolic-sine constitutive equation the values of apparent activation energy for Ti-5553 and Ti-4733 were determined as 380 and 315 kJ/mol, respectively. The Kocks-Mecking dislocation evolution model was used to model the flow curves. The recovery and hardening parameters for Ti-4733 in the developed model were found lower than those for Ti-5553. The model could satisfactorily predict the experimental flow curves at various conditions.

Microstructure Evolution of Ti-5Al-5V-5Mo-3Cr after Hot Deformation at Large and Moderate Strains

This work deals with the analysis and modelling of the microstructural evolution of the metastable titanium alloy Ti-5Al-5V-5Mo-3Cr during hot deformation up to moderate and large strains. Experimental flow curves and deformed samples are obtained by hot compression and hot torsion tests using a Gleeble ® 3800 device. The samples are deformed above and below the beta transus temperature and in a wide range of strain rates. Microstructures are characterized after deformation and in-situ water quenching using light optical and scanning electron microscopy and electron back scattered diffraction (EBSD). Dynamic recovery of the beta phase is found to be the main deformation mechanism up to moderated strains. By increasing the strain, continuous dynamic recrystallization (cDRX) is confirmed by the progressive conversion of low angle boundaries into high-angle boundaries. Alpha phase plays a secondary role in the deformation of the material by pinning the movement of beta high angle grain boundaries (HAGB). The evolution of the microstructure is modelled using dislocation density as internal variable in the single β field.