Flow Curves Research Articles

An Alternative Method of Investigating the Thermal Stability of Shoe-Braked Railway Wheel Steels Based on Strain Hardening Analysis

During service, shoe-braked railway wheel steels are often subjected to a severe thermal cycle. Therefore, understanding the evolution of the microstructure and the resulting changes in mechanical properties during service is fundamental in the choice of steel. In previous research, the effects of the thermal loading on the microstructure and mechanical properties of five different steels for railway wheels (ER7, HYPERLOS®, Class B, SANDLOS® and Class C) were investigated by hardness, tensile and toughness tests, in the as-supplied condition and after different heat treatments designed to replicate the modification of the microstructure due to braking. In this paper, the tensile work hardening behavior was studied by interpolating the tensile flow curves with the constitutive equation related to the dislocation density proposed by Voce, which correlates the Voce equation parameters with the microstructural features of metallic materials. The work hardening analysis revealed that there is a good correlation between the Voce parameters and the microstructure of the five steels in as-supplied condition and after heat treatments. An interesting correlation was found between Voce parameters and apparent fracture toughness. After heat treatments at 700 °C and 750 °C the properties of the steels decreased, which was consistent with the evolution of the microstructure. However, after exposure at 970 °C with subsequent cooling in air, Class C steel appears to have a microstructure similar to the original microstructure, with tensile and toughness properties very similar to the as-supplied condition, demonstrating better microstructural stability compared to steels ER7, HYPERLOS®, Class B and SANDLOS®.

Valorization of brewer's spent grains (BSG) through alkaline hydrogen peroxide processing: Effect on composition, structure and rheological properties

This study investigated the impact of alkaline processing with hydrogen peroxide (AHP) on the chemical composition, structure, and rheological properties of brewer's spent grains (BSG). Suspensions with different concentrations of BSG (2–8 %) and AHP (1–8 %) were subjected to different processing times (0–12 h). The BSG chemical composition, morphology, crystallinity, modifications of functional groups, and rheological behavior were evaluated over processing. Increasing the concentration of AHP in the suspension and the processing time improved the removal of proteins, lignin, and extractives from BSG into the suspension and, consequently, increased the cellulose and hemicellulose content in the processed BSG. On the other hand, higher concentrations of BSG in the suspension slightly reduced the removal efficiency of these components. AHP processing also induced thinning of the cell wall and changes in particle shape. These changes together with the increase in crystallinity of the processed BSG indicated the material destructuring. FTIR spectra showed reduced intensity of lignin and protein post-processing, indicating their removal, while peaks related to cellulose and hemicellulose increased in processed BSG. The flow curves of the suspensions were adjusted to the Herschel-Bulkley model, exhibiting non-Newtonian behavior with flow yield stress (1.529 Pa < τ0 < 4.646 Pa) and pseudoplasticity (0.830 < n < 0.969) in all conditions. Flow resistance increased with increasing concentration of AHP, BSG, and processing time. Notably, the increase in processing time resulted in greater removal of BSG components, especially proteins, lignin, and extractives, which significantly contributed to the increase in both the flow yield stress and the consistency index of the suspensions. All this information is useful and will support the design of equipment and processes, especially those involving the extraction of proteins and the conversion of the BSG lignocellulose fraction into biofuels.

Singularities of the network flow with symmetric initial data

We study the formation of singularities for the curvature flow of networks when the initial data is symmetric with respect to a pair of perpendicular axes and has two triple junctions. We show that, in this case, the set of singular times is finite.

Effects of Adding Pectin to Milk in Varying Amounts on the Rheological Properties of Milk

Pectin, which is used as an additive in the food, cosmetics, pharmaceutical, and health sectors due to its safety, non-toxicity, low production cost, and high availability, is used as a thickener, gelling agent, brightener, stabilizer, emulsifier, and fat and sugar replacer in low-calorie foods. It is also used in milk and dairy products as a stabilizer to prevent proteins from clumping. In this study, the rheological properties of pectin and milk mixtures with pectin/milk powder (w/w) ratios of 0.1, 0.25, 0.5, 0.75, 1 and 1.5 were examined. First, a flow curve test was applied in the range of 0,01-1000 s-1 to obtain the viscosity curves and yield stress values of the samples. Then, an amplitude sweep test was performed at a fixed frequency of 10 rad/s and in the strain range of 0.01-100% to determine the linear viscoelastic range (LVR) of the samples and the solid and liquid structure of the samples. To determine the time-dependent behavior of the samples in non-destructive deformation, frequency sweep tests were performed at constant strain (0.01%) in the LVR range obtained from the amplitude sweep test and in the range of 0.1-100 rad/s. Finally, three interval thixotropy tests (3ITT) were performed to observe the structural recovery of the samples. As a result of rheological tests, it was determined that pectin-free milk showed Newtonian properties, other samples showed shear thinning properties, and viscosity values increased as the pectin rate increased. While all samples are solid at low strains, the liquid feature becomes dominant at high strains. It has been observed that as the pectin ratio in milk increases, the strain values at the yield point, where the liquid feature becomes dominant, also increase. Except for the sample with the highest pectin content, it was observed that the dominance of the storage modulus over the loss modulus was greater at low frequencies than at high frequencies. As a result of 3ITT, it was determined that the percentage of recovery at the 600th second increased as the pectin rate increased.

Synthesis and Polymerization of the Bio‐Benzoxazine Derived from Resveratrol and Thiophenemethylamine and Properties of its Polymer

AbstractResveratrol and 2‐thiophenemethylamine have been employed in the synthesis of a novel tri‐functional benzoxazine (RES‐th) to develop the bio‐benzoxazine monomer. The chemical structure of the synthesized monomer is confirmed by various characterization technics. The polymerization behavior is monitored by in situ Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The in situ FTIR results reveal distinct reaction mechanisms for the three oxazine rings presented in RES‐th, with both ether and phenolic Mannich bridge structures observed in the products. The activation energy values of RES‐th are calculated to be 119.05, 120.97, and 119.44 kJ mol−1 by Kissinger, Ozawa, and Starink methods, respectively, which are all based on the heat flow curves at various heating temperatures. The thermal stability and flame retardancy of the resulting polybenzoxazine (poly(RES‐th)) are investigated by thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC). The values of Td5 and Td10 of polybenzoxazine are found to be 356 °C and 399 °C, respectively, with a char yield of 66.3% at 800 °C. The prepared polybenzoxazine also demonstrates nonflammability characteristics with the values of heat release capacity (HRC) and total heat release rate (THR) of 18.65 J (g K)−1 and 2.69 kJ g−1, respectively. These findings suggest that the thermoset, poly(RES‐th), is a promising candidate for fire‐resistant applications.

Greedy Kernel Methods for Approximating Breakthrough Curves for Reactive Flow from 3D Porous Geometry Data

Greedy Kernel Methods for Approximating Breakthrough Curves for Reactive Flow from 3D Porous Geometry Data

Extension of a phase-field KKS model to predict the microstructure evolution in LPBF AlSi10Mg alloy submitted to non isothermal processes

The out-of-equilibrium heterogeneous microstructure typical of AlSi10Mg processed by Laser Powder Bed Fusion (LPBF) is often modified by further heat treatment to improve its ductility. According to literature, extensive experimental investigations are generally required in order to optimize these heat treatments. In the present work, a phase-field approach is developed based on an extended Kim–Kim–Suzuki (KKS) model to guide and accelerate the post-treatment optimization. Combined with CALculation of PHAse Diagrams (CALPHAD) data, this extended KKS model predicts microstructural changes under anisothermal conditions. To ensure a more physical approach, it takes into account the enhanced diffusion by quenched-in excess vacancies as well as the elastic energy due to matrix/precipitate lattice mismatch. As the developed model includes the computation of the evolution of the thermo-physical properties, its results are validated through comparison with experimental DSC curves measured during the non-isothermal loading of as-built LPBF AlSi10Mg. The computed microstructure evolution reproduces the microstructural observation and successfully explains the peaks in the DSC heat flow curve. It thus elucidates the detailed microstructural evolution inside the eutectic silicon phase by considering the growth and coalescence of silicon precipitates and the matrix desaturation.

Changes of crystalline structure and physicochemical properties of Pueraria lobata var. thomsonii starch under water deficit.

Crystal type is an important physicochemical property of starch. However, it is currently unclear whether changes in crystal type affect other properties of starch. This study discovered that water deficit resulted in an increase in small starch granules and transparency in Pueraria lobata var. thomsonii, while causing a decrease in amylose content and swelling power. Additionally, the crystal type of P. Thomsonii starch changed from CB-type to CA-type under water deficit, without significantly altering the short-range ordered structure and chain length distribution of starch. This transformation in crystal type led to peak splitting in the DSC heat flow curve of starch, alterations in gelatinization behavior, and an increase in resistant starch content. These changes in crystalline structure and physicochemical properties of starch granules are considered as adaptive strategies employed by P. Thomsonii to cope with water deficit.

Inverse mean curvature flow and Ricci-pinched three-manifolds

Abstract Let ( M , g ) (M,g) be a noncompact, connected, complete Riemannian three-manifold with nonnegative Ricci curvature satisfying Ric ≥ ε ⁢ tr ⁡ ( Ric ) ⁢ g \mathrm{Ric}\geq\varepsilon\operatorname{tr}(\mathrm{Ric})g for some ε &gt; 0 \varepsilon&gt;0 . In this note, we give a new proof based on inverse mean curvature flow that ( M , g ) (M,g) is either flat or has non-Euclidean volume growth. In conjunction with the work of J. Lott [On 3-manifolds with pointwise pinched nonnegative Ricci curvature, Math. Ann. 388 (2024), 3, 2787–2806] and of M.-C. Lee and P. Topping [Three-manifolds with non-negatively pinched Ricci curvature, preprint (2022), https://arxiv.org/abs/2204.00504], this gives an alternative proof of a conjecture of R. Hamilton recently proven by A. Deruelle, F. Schulze, and M. Simon [Initial stability estimates for Ricci flow and three dimensional Ricci-pinched manifolds, preprint (2022), https://arxiv.org/abs/2203.15313] using Ricci flow.

Effect of dynamic strain ageing on flow stress and critical strain for jerky flow in Al-Mg alloys

A comprehensive approach addressing the flow behavior and the critical strain for the initiation of serrations in Al-Mg alloys is developed in the present work. The basic premise of the approach is that the solute atmosphere influences the friction as well as the strain hardening component of the flow stress. The friction effect of the solute cloud is modeled by considering the interplay between the characteristic solute migration time and the dislocation waiting time according to the cross-core diffusion mechanism. The impact on strain hardening is modeled by considering the apparent strengthening of the forest dislocations because of formation of solute aggregates near the vicinity of dislocation junctions. The apparent forest strengthening effect scales as the square root of the ratio of solute concentration in vicinity of the dislocation junctions and the bulk solute concentration. The modified constitutive model is validated against experimental flow curves obtained for strain rates varying over several orders of magnitude. It was observed that the modified constitutive model outperforms the standard constitutive model (considers only the friction effect of solute atmosphere) in predicting the flow curves in the dynamic strain aging domain. Furthermore, the modified constitutive model also accurately predicts the critical strain for the initiation of the jerky flow in both the normal and inverse regimes of the critical strain versus strain rate curve. Additional validation of the modified constitutive model is provided by dislocation character and density measurements via X-ray diffractograms, dislocation structure investigation via transmission electron microscopy along with fracture surface analysis.

Unveiling the Impact of Gelation Temperature on the Rheological and Microstructural Properties of Type A Gelatin Hydrogels.

Gelatin-based hydrogels have garnered significant attention in the fields of drug delivery systems and tissue engineering owing to their biodegradability, biocompatibility, elasticity, flexibility and nontoxic nature. However, there is a lack of information regarding type-A-gelatin-based hydrogels. In this sense, the main aim of this work was the evaluation of the properties of type-A-gelatin-based hydrogel achieved using two different gelation temperatures (4 °C and 20 °C). Thus, the main novelty of this study lies in the analysis of the impact of gelation time on the rheological and microstructural properties of type-A-gelatin-based hydrogels. Moreover, the addition of a drug was also analyzed in order to evaluate the hydrogels' behavior as a drug delivery system. For this purpose, rheological (strain, frequency sweep tests and flow curves) and microstructural (SEM) characterizations were carried out. The results demonstrated that lowering the gelation temperature improved the rheological properties of the systems, obtaining hydrogels with an elastic modulus of 20 kPa when processing at 4 °C. On the other hand, the increase in the gelation temperature improved the critical strain of the systems at low temperatures. In conclusion, this work showed the feasibility of producing hydrogels with potential application in drug delivery with different properties, varying the testing temperature and incorporating tetracycline into their formulation.

An inverse Gauss curvature flow to the Lp-Gauss Minkowski problem

In this paper, we confirm the existence of asymmetric smooth solutions to the Lp-Gauss Minkowski problem for p>0 by a class of inverse Gauss curvature flows. Furthermore, asymmetric weak solution for p>0 is obtained by a parabolic approximation method.

Hot deformation behavior and microstructural characterization of a novel high entropy steel

In this study, a novel high entropy steel (HES) was meticulously engineered to have an austenitic structure with a medium stacking fault energy. To investigate the hot deformation behavior of the developed HES, hot compression tests were carried out at 950 °C–1100 °C, coupled with strain rates ranging from 0.001 to 1 s−1, to reach a true strain level of 0.5. The comprehensive microstructural analyses on the hot compressed samples revealed the occurrence of partial dynamic recrystallization (DRX) at the majority of the deformation conditions. The appearance of flow curves as well as the characterized microstructures suggest the notably sluggish recrystallization kinetics when compared to more common austenitic steels. The underlying cause behind the sluggish DRX was attributed to the sluggish diffusion and pronounced lattice distortion in the HES. Further investigations by the electron back-scattered diffraction (EBSD) established that the discontinuous DRX (DDRX) is the dominant mechanism, while the continuous DRX (CDRX) serves as a secondary, auxiliary mechanism governing the microstructural evolutions.

Influence of Temperature on the Rheological Properties of Selected Mango Products with ‘Saba’ Banana (Musa acuminata x Musa balbisiana BBB Group) Peel Pectin

Saba banana peel pectin (BPP) was applied to mango jelly and mango juice. The rheological characteristics (flow curve, viscosity curve) of mango products at different temperatures (15°C, 25°C, 35°C, 45°C and 55°C) were then evaluated. The rheological data were fitted using the Hershel-Buckley model and the yield stress, consistency index, and flow behavior were identified. Values obtained from BPP mango products were compared to those with commercial low methoxyl pectin (LMP) and high methoxyl pectin (HMP). Results showed that all types of pectin resulted in non-Newtonian mango jelly and mango juice at all temperatures. For both mango jelly and mango juice, the yield stress contributed by BPP was similar to that of HMP. For the consistency, BPP and LMP had same effects on mango jelly while BPP and HMP had the same effects on mango juice at lower temperatures. For the flow behavior, BPP and HMP showed shear thinning effects for most of the temperatures tested.

A Note on Alexandrov Immersed Mean Curvature Flow

We demonstrate that the property of being Alexandrov immersed is preserved along mean curvature flow. Furthermore, we demonstrate that mean curvature flow techniques for mean convex embedded flows such as noncollapsing and gradient estimates also hold in this setting. We also indicate the necessary modifications to the work of Brendle–Huisken to allow for mean curvature flow with surgery in the Alexandrov immersed, 2-dimensional setting.

Rheological aspects of solid-to-liquid phase transitions in paraffin wax/bitumen blends for thermal energy storage applications

This paper correlates the evolution of the rheological and thermal properties with microstructure during the phase change of a blend of bitumen with a selected paraffin wax, having a melting point centred around 60 °C, for the development of bituminous based membranes for thermal energy storage applications. For this purpose, temperature sweep tests within the linear viscoelastic range, stationary state flow curves, Differential Scanning Calorimetry (DSC), polarised optical microscopy observations and solar irradiation tests were performed. The reported rheological results clearly point out a gel-like behaviour for both paraffin and paraffin/bitumen blend that is preserved almost up to the end of the phase change interval. This is consequence of the development of a network of interconnected crystals of paraffin wax which progressively disappear as temperature increases. Interestingly, a weak gel structure is kept even at low crystallinity levels since only a few junctions among structures are necessary to build a spanning network. Finally, the large degree of crystallinity of paraffin wax retained in the bitumen/paraffin wax is behind its thermoregulation ability, as was corroborated by solar irradiation tests. Therefore, results indicated the great potential of these formulations for thermal energy storage and related applications.

Lode-dependent anisotropic-asymmetric yield function for isotropic and anisotropic hardening of pressure-insensitive materials. Part II: Stress invariant-based coupled quadratic and non-quadratic function

This research couples a Lode-dependent anisotropic-asymmetric (LAA) frame (Lou and Yoon, 2023. International Journal of Plasticity, 166, 103,647) with a stress-invariant-based coupled quadratic-non-quadratic (CQN) anisotropic hardening function to analytically characterize the anisotropic-asymmetric hardening of sheet metals under uniaxial tension and uniaxial compression. Experiments are conducted for AA2A12-O under uniaxial tension, uniaxial compression, equibiaxial tension, plane strain tension and shear. Anisotropy is investigated by conducting the experiments along different loading directions from the rolling. The flow curves are obtained from these experimental data at distinct stress states and loading directions. The plastic hardening is represented by the CQN-coupled LAA function to verify its accuracy. The CQN-coupled LAA model is also utilized to represent the plastic flow of DP980 under uniaxial tension, uniaxial compression, shear and plane strain tension along different loading directions as well as equibiaxial tension. The application to AA2A12-O and DP980 demonstrates that the CQN-coupled LAA function is capable of modeling plastic hardening behaviors under uniaxial tension, uniaxial compression, equibiaxial tension and equibiaxial compression and dramatically improving the prediction accuracy of flow curves under plane strain tension.

The Assessment of Physicochemical and Antimicrobial Properties of Hydrophilic Gels Containing Tetracycline Hydrochloride and Various Concentrations of Ethanol.

The high prevalence of acne, which affects nearly 85% of adolescents and young adults, underscores the importance of exploring new therapeutic solutions. The aim of the present study was to design a stable hydrogel formulation containing tetracycline hydrochloride (TC) in the presence of ethanol at various concentration levels. The antibiotic stability was assessed over a period of 84 days using the HPLC method. The rheological properties of the formulations and their microbiological activity were also evaluated. Hydrogels without ethanol and those containing 5% and 25% alcohol showed similar rheological properties and high stability of the antibiotic throughout the observation period. The formulation with the highest ethanol content of 50% differed significantly from the others in terms of rheological properties. Although the flow and viscosity curves were like those of the other formulations, the viscosity values were significantly lower. The stability of tetracycline in this formulation was also significantly lower, and by the 84th day of observation, the concentration of the drug had decreased to almost 45% of its initial content. The formulations containing the highest concentration of ethanol displayed the highest activity against the biofilm of the acne-causing agent, Cutibacterium acnes. The study demonstrated the possibility of developing stable and antimicrobial effective hydrogel formulations with tetracycline and ethanol as a substance enhancing drug penetration into the hair follicles.

Poincaré Inequality and Topological Rigidity of Translators and Self-Expanders for the Mean Curvature Flow

We prove an abstract structure theorem for weighted manifolds supporting a weighted f-Poincaré inequality and whose ends satisfy a suitable non-integrability condition. We then study how our arguments can be used to obtain full topological control on two important classes of hypersurfaces of the Euclidean space, namely translators and self-expanders for the mean curvature flow, under either stability or curvature asumptions. As an important intermediate step in order to get our results we get the validity of a Poincaré inequality with respect to the natural weighted measure on any translator and we prove that any end of a translator must have infinite weighted volume. Similar tools can be obtained for properly immersed self-expanders permitting to get topological rigidity under curvature assumptions.

User friendly FE Formulation for anisotropic distortional hardening model based on non-associated flow plasticity and its application to springback prediction

Based on non-associated flow plasticity, a newly developed anisotropic distortional hardening model developed by Hu and Yoon [15] is implemented in finite element analysis in a user-friendly manner. The derivatives of complex hardening models are calculated using the Finite Difference Method (FDM), which is much more convenient than using the analytical derivatives. To further improve the accuracy of the proposed method, the step size analysis in FDM is performed by analyzing the derivative formation. To evaluate the accuracy and computational efficiency of a proposed step size for FDM, single element simulations are performed under different loading paths. It has been found that the maximum absolute error of the flow curves between the simulation and the theoretical result is less than 0.3%. The U-bending tests for DP600 and TRIP1180 are used to verify the ability of the distortional hardening model for springback prediction. The simulation result of the strain hardening model is in good agreement with the experiment. The computational efficiency is also increased by 24% due to the improved convergence rate.