Uniaxial Flow Research Articles

Mechanical properties and flow stress constitutive relationship of Ti–6Al–4V alloy with equiaxed microstructure at cryogenic temperatures

This paper investigates the uniaxial tensile mechanical properties and flow behavior of Ti-6Al-4V alloys with equiaxed microstructure at cryogenic temperatures ranging from 77 K to 298 K and strain rates from 10−4/s to 10−2/s. Scanning electron microscopy is utilized to analyze the fracture morphology, aiming to reveal the fracture behavior at various temperatures. The applicability of the Zener-Hollomon parameter and the Johnson-Cook model in describing the flow stress of Ti-6Al-4V at cryogenic temperatures is analyzed. Moreover, a constitutive relationship modeling method based on the variational recurrent networks is proposed. Mechanical test results show a significant increase in the strength of equiaxed Ti-6Al-4V alloy under cryogenic conditions while the plastic deformation process is shortened. However, the fracture analysis indicates that even at 77 K, the fracture process is still dominated by ductile fracture, and brittle fracture does not occur within the range of 77 K to 298 K. The fitting results validate the performance of the Zener-Hollomon parameter and the Johnson-Cook model in describing the deformation flow stress of Ti-6Al-4V alloy at cryogenic temperatures. The results also indicate that the proposed constitutive relationship modeling method based on the variational recurrent network performs better, making it a potential method for widespread applications.

In Situ Study on the Structural Evolution of Flexible Ionic Gel Sensors

With the development of society, the demand for smart coatings is increasing. The development of flexible strain sensors using block copolymer self-assembled ionic gel materials provides a promising method for promoting the development of smart coatings. The ionic liquid in the ionic part of the material is crucial for the performance of the sensor. In this study, the structural changes within FDA/dEAN (self-assembly of acrylated Pluronic F127 (F127-DA) in partially deuterated ethylammonium nitrate (dEAN)) triblock copolymer ionic gel during uniaxial tensile flow were characterized using an in situ SAXS technique. The results revealed that the characteristics of the responses of the ionic gel to strain resistance were intricately linked to the evolution of its microstructure during the tensile process. At low levels of strain, the face-centered cubic lattice arrangement of the micelles tended to remain unchanged. However, when subjected to higher strains, the molecular chains aligned along the stretching direction, resulting in a more ordered structure with reduced entropy. This alignment led to significant disruption in bridging structures within the material. Furthermore, this research explored the impact of the stretching rate on the relaxation process. It was observed that higher stretching rates led to decreases in the average relaxation time, indicating rate dependence in the microstructure’s behavior. These findings provide valuable insights into the behavior and performance of flexible strain sensors based on ionic gel materials in smart coatings.

Impact of surface rheology on droplet coalescence in uniaxial compressional flow

Impact of surface rheology on droplet coalescence in uniaxial compressional flow

Atomistic Simulation of Flow-Induced Microphase Separation and Crystallization of an Entangled Polyethylene Melt Undergoing Uniaxial Elongational Flow and the Role of Kuhn Segment Extension.

Atomistic simulations of the linear, entangled polyethylene C1000H2002 melt undergoing steady-state and startup conditions of uniaxial elongational flow (UEF) over a wide range of flow strength were performed using a united-atom model for the atomic interactions between the methylene groups constituting the polymer macromolecules. Rheological, topological, and microstructural properties of these nonequilibrium viscoelastic materials were computed as functions of strain rate, focusing on regions of flow strength where flow-induced phase separation and flow-induced crystallization were evident. Results of the UEF simulations were compared with those of prior simulations of planar elongational flow, which revealed that uniaxial and planar flows exhibited essentially a universal behavior, although over strain rate ranges that were not completely equivalent. At intermediate flow strength, a purely configurational microphase separation was evident that manifested as a bicontinuous phase composed of regions of highly stretched molecules that enmeshed spheroidal domains of relatively coiled chains. At high flow strength, a flow-induced crystallization (FIC) occurred, producing a semicrystalline material possessing a high degree of crystallinity and primarily a monoclinic lattice structure. This FIC phase formed at a temperature (450 K) high above the quiescent melting point (≈400 K) and remained stable after cessation of flow for temperature at or below 435 K. Careful examination of the Kuhn segments constituting the polymer chains revealed that the FIC phase only formed once the Kuhn segments had become essentially fully extended under the UEF flow field. Thermodynamic properties such as the heat of fusion and heat capacity were estimated from the simulations and found to compare favorably with experimental values.

Nanoval Technology—An Intermediate Process between Meltblown and Spunbond

The idea of "Nanoval technology" origins in the metal injection molding for gas atomization of metal powders and the knowledge of spunbond technologies for the creation of thermoplastic nonwovens using the benefits of both techniques. In this study, we evaluated processing limits experimentally for the spinning of different types of polypropylene, further standard polymers, and polyphenylene sulfide, marked by defect-free fiber creation. A numerical simulation study of the turbulent air flow as well as filament motion in the process visualized that the turnover from uniaxial flow (initial stretching caused by the high air velocity directed at the spinning die) to turbulent viscoelastic behavior occurs significantly earlier than in the melt-blown process. Modeling of the whole process showed that additional guide plates below the spinneret reduce the turbulent air flow significantly by regulating the inflow of secondary process air. The corresponding melt flow index of processible polymer grades varied between 35 g·10min-1 up to 1200 g·10min-1 and thus covering the range of extrusion-type, spunbond-type, yarn-type, and meltblown-type polymers. Hence, mean fiber diameters were adjustable for PP between 0.8 and 39.3 μm without changing components of the process setup. This implies that the Nanoval process enables the flexibility to produce fiber diameters in the typical range achievable by the standard meltblown process (~1-7 μm) as well as in the coarseness of spunbond nonwovens (15-30 μm) and, moreover, operates in the gap between them.

Extensional Rheology of Poly(vinylidene fluoride)/N,N-dimethylformamide Solutions

Typical extension flow occurs in electrospinning process of Poly(vinylidene fluoride) (PVDF) solutions such that researchers focus on extensional rheological behaviors of PVDF solutions. The extensional viscosity of PVDF solutions is measured to know the fluidic deformation in extension flows. The solutions are prepared by dissolving PVDF powder into N,N-dimethylformamide (DMF) solvent. A homemade extensional viscometric device is used to produce uniaxial extension flows and the feasibility of the viscometric device is verified by applying the glycerol as a test fluid. Experimental results show that PVDF/DMF solutions are extension shinning as well as shear shinning. The Trouton ratio of thinning PVDF/DMF solution is close to three at very low strain rate and then reaches a peak value until it drops to a small value at high strain rate. Furthermore, an exponential model may be used to fit the measured values of uniaxial extensional viscosity at various extension rates, while traditional power-law model is applicable to steady shear viscosity. For 10~14% PVDF/DMF solution, the zero-extension viscosity by fitting reaches 31.88~157.53 Pa·s and the peak Trouton ratio is 4.17~5.16 at applied extension rate of less than 34 s-1. Characteristic relaxation time is λ~100 ms and corresponding critical extension rate is ε˙c~5 s-1. The extensional viscosity of very dilute PVDF/DMF solution at very high extension rate is beyond the limit of our homemade extensional viscometric device. This case needs a higher sensitive tensile gauge and a higher-accelerated motion mechanism for test.

Shear-mediated ALK5 expression regulates endothelial activation

Calcific aortic valve disease affects the aortic side of the valve, exposed to low magnitude multidirectional (“disturbed) blood flow, more than it affects the ventricular side, exposed to high magnitude uniaxial flow. Overt disease is preceded by endothelial dysfunction and inflammation. Here we investigate the potential role of the transforming growth factor-β (TGF-β) receptor ALK5 in this process. Although ECs are always subject to shear stress due to blood flow, and their responses to shear stress are important in healthy valve development and homeostasis, low magnitude multidirectional flow can induce pathophysiological changes. Previous work has shown ALK5 to be an important mechanosensor. ALK5 transduces mechanically sensed signals via the activation of the SMAD2/3 transcriptional modulators. However, it is currently unclear precisely how ALK5-mediated shear stress responses translate into pathological changes under conditions of chronically disturbed flow. Here, we demonstrate that ALK5 mechanosensory signalling influences flow-induced endothelial leukocyte adhesion and paracellular permeability. Low magnitude multidirectional flow resulted in downregulation of the receptor, accompanied by increased SMAD2 phosphorylation, in human umbilical vein endothelial cell (HUVEC) monolayers. These changes correlated with elevated monocyte adhesion and significantly increased transendothelial transport of an albumin-sized tracer. These effects were abolished by inhibition of ALK5 kinase activity. Analysis of ALK5 expression patterns in porcine aortic valve tissue corroborated the findings from cell-based experiments. Together, these results suggest that ALK5 has a role in shear stress-associated cardiovascular disease pathology, emphasising the importance of further mechanistic investigations and supporting it as a potential therapeutic target.

Low Temperature Thermal Properties of Nanodiamond Ceramics

The temperature dependence of thermal conductivity and specific heat for detonated nanodiamond ceramics is investigated on specially designed experimental setups, implementing the uniaxial stationary heat flow method and the thermal relaxation method, respectively. Additionally, complementary studies with a commercial setup (Physical Property Measurement System from Quantum Design operating either in Thermal Transport or Heat Capacity Option) were performed. Two types of samples are under consideration. Both ceramics were sintered at high pressures (6–7 GPa) for 11–25 s but at different sintering temperatures, namely 1000 °C and 1600 °C. The effect of changing the sintering conditions on thermal transport is examined. In thermal conductivity κ(T), it provides an improvement up to a factor of 3 of heat flow at room temperature. The temperature dependence of κ(T) exhibits a typical polycrystalline character due to hindered thermal transport stemming from the microstructure of ceramic material but with values around 1–2 W/mK. At the lowest temperatures, the thermal conductivity is very low and increases only slightly faster than linear with temperature, proving the significant contribution of the scattering due to multiple grain boundaries. The specific heat data did not show a substantial difference between detonated nanodiamond ceramics obtained at different temperatures unlike for κ(T) results. For both samples, an unexpected upturn at the lowest temperatures is observed—most likely reminiscent of a low-T Schottky anomaly. A linear contribution to the specific heat is also present, with a value one order of magnitude higher than in canonical glasses. The determined Debye temperature is 482 (±6) K. The results are supported by phonon mean free path calculations.

Simple periodic boundary conditions for molecular simulation of uniaxial flow

We present rotating periodic boundary conditions (PBCs) for the simulation of nonequilibrium molecular dynamics (NEMD) under uniaxial stretching flow (USF) or biaxial stretching flow (BSF). Such nonequilibrium flows need specialized PBCs since the simulation box deforms with the background flow. The technique builds on previous models using one or two lattice remappings, and is simpler than the PBCs developed for the general three dimensional flow. For general three dimensional flows, Dobson [1] and Hunt [2] proposed schemes which are not time-periodic since they use more than one automorphism remapping. This paper presents a single automorphism remapping PBCs for USF and BSF which is time periodic up to a rotation matrix and has better minimum lattice spacing properties.

Role of anisotropy on strain localization at high-strain rates in Ti6Al4V

A systematic experimental investigation of the plastic anisotropy at high strain-rates of Ti6Al4V was carried out using a Split Hopkinson bar system. Dynamic tensile tests were conducted on flat specimens cut at seven orientations with respect to the rolling direction of the sheet. To quantify the effect of anisotropy on both the global response prior to necking as well as on the inclination of the strain localization bands that developed in the neck, both surface strains and local displacements were measured using high speed imaging in conjunction with digital image correlation. It was found that the material has a weak anisotropy in uniaxial yield stresses while it displays a strong anisotropy in Lankford coefficients; the inclinations of the bands in the neck depend on the loading orientation. Moreover, only for the rolling direction specimen, the neck contains two localization bands equally inclined to the loading axis. These observations confirm the correlations established in the theoretical study of Cazacu and Rodríguez-Martínez (2019) between the necking band angles and the variation in the uniaxial flow stresses with the loading direction. A constitutive model with yielding described with the orthotropic criterion of Cazacu and Barlat (2001) and a hardening law accounting for the strain rate effects was used to model the observed behavior. Comparison between finite element simulations, analytical calculations, and test data show that the experimental trends are captured.

Prediction and Validation of Stress Triaxiality Assisted by Elasto-Visco-Plastic Polycrystal Model

The ΔEVPSC numerical code based on the elasto-visco-plastic HEM (Homogeneous Effective Medium) provides a multiscale constitutive modeling framework that is suitable for describing a wide range of mechanical behaviors of polycrystalline metals. In this study, an AA6061-T6 aluminum sample was chosen to validate the predictive capability of the ΔEVPSC stand-alone (ΔEVPSC-SA) code on stress triaxiality and its evolution until fracture. The model parameters were calibrated by fitting the uniaxial flow stress-strain curve, and the initial crystallographic orientation distribution (COD) was obtained using X-ray diffraction and electron backscattered diffraction (EBSD) methods. The statistical representativeness of the COD was further examined by comparing the experimental R-values with model predictions based on a set of CODs obtained via the two mentioned diffraction methods. The results suggest that the X-ray scan does not represent the texture very well, and instead, an entire cross-sectional EBSD scan is required, even though the texture gradient along the through-thickness direction is not very significant. The model-calculated triaxiality based on the ΔEVPSC-SA code was verified by comparison with the experimental results from the uniaxial tension, the notched tension, and the plane strain tests. The results were in good agreement with the ΔEVPSC finite element (FE) simulation results and other similar experimental results reported in the literature.

Forming a composite model for non-Brownian suspensions

We propose a two-part composite model to describe the rheology of non-Brownian suspensions. The stress response is composed of the sum of a matrix part (Tm) described by a multi-mode Oldroyd-B model and a second component (To) which is assumed to be a Thompson–Souza Mendes model. We show how to determine the parameters to satisfy agreement with experiments in steady viscometric flows, uniaxial elongation flows, small to medium size sinusoidal strains, and reversing shear strain rates. Where possible, comparison is made with computations. Agreement with experiments and computations is reasonable, but more accurate computations and experiments would be welcome.

Flow stress and work hardening behaviour of Mg-3Al-1Zn alloy

In the present study, the uniaxial tensile flow stress behaviour and work hardening behaviour of AZ31B alloy has been investigated across a wide range of temperature (25 °C–250 °C) at quasi-static strain rates (10−1·s−1–10−3·s−1). The flow stress behaviour of the AZ31B sheet has been analysed at different temperatures, quasi-static strain rates and sheet orientations. It has been found that flow stress behaviour is highly influenced by the variation of temperatures, strain rates, and sheet orientations. The various important mechanical properties such as yield strength, ultimate tensile strength, percentage elongation, strain hardening exponent, and strain rate sensitivity have been determined. There has been a significant improvement in ductility (201.71%) of AZ31B alloy at 250 °C compared to 25 °C. The decrement in yield strength and ultimate strength has been found to be 47.52% and 53.66%, respectively. It has been observed that the AZ31B alloy is found to be more strain rate sensitive at elevated temperature (m = 0.11, at 250 °C) as compare to 25 °C. The various empirical hardening equations such as Hollomon, Ludwik, Ludwigson, Swift, and modified Voce have been formulated for a wide range of temperatures, strain rates, and sheet orientations. The K-M plots show three-stage of work-hardening behaviour for AZ31B alloy. Based on the performance comparison of different models, the Swift and Modified Voce efficiently predict the flow curve with correlation (more than 99%) at different temperature ranges. The fracture surface is analysed by FESEM. The quasi cleavage and river-like pattern are observed for the room temperature fractured specimen. The increase in temperature converts the mode of fracture from cleavage to ductile fracture.

ALTERNATIVE USE OF THE SENTMANAT EXTENSIONAL RHEOMETER TO INVESTIGATE THE RHEOLOGICAL BEHAVIOR OF INDUSTRIAL RUBBERS AT VERY LARGE DEFORMATIONS

ABSTRACT Extensional deformations represent an effective stimulus to explore the rich rheological response of branched polymers and elastomers, enabling the design of polymers with specific molecular structure. However, probing the polymer behavior at large deformations is often limited by the experimental devices. We here present an alternative use of the Sentmanat Extensional Rheometer (SER) that allows Hencky strain units much larger than the maximum value achievable, ∼3.6. The proposed procedure consists of an oblique positioning of the sample in the measuring area. If a small inclination of the sample is used, the departure from the ideal uniaxial flow is negligible at Hencky strains <1, and nearly zero for larger values. Experimental results in the linear viscoelastic regime are compared with the double reptation model in order to discern polydispersity and branching effects, whereas the extensional rheology data are contrasted with the molecular stress function theory (MSF), revealing important information about the polymer structure, especially on the long-chain branching (LCB). Finally, the analysis of sample failure upon elongation allowed us to correlate the polymer structure to the rheological behavior during mixing processes.

Composite entanglement topology and extensional rheology of symmetric ring-linear polymer blends

Extensive molecular simulations are applied to characterize the equilibrium dynamics, entanglement topology, and nonlinear extensional rheology of symmetric ring-linear polymer blends with systematically varied ring fraction ϕR. Chains with degree of entanglement Z≈14 are mixed to produce 10 well-entangled systems with ϕR varying from neat linear to neat ring melts. Z is large enough that except for very large ϕR, the rings are threaded by multiple linear chains in equilibrium. Primitive path analysis is used to visualize and quantify the structure of the composite ring-linear entanglement network. We measure the quantity of ring-linear threading and linear-linear entanglement as a function of ϕR and identify with simple arguments a ring fraction ϕR≈0.4 where the topological constraints of the composite entanglement network are maximized. These topological analyses are used to rationalize the ϕR-dependence of ring and linear chain dynamics, conformations, and rheology. Simulations of startup uniaxial elongation flows demonstrate the extensional stress overshoot observed in recent filament stretching experiments and characterize how it depends on the blend composition and entanglement topology. The overshoot is driven by an overstretching and recoil of ring polymers due to the convective unthreading of rings from linear chains.

New Inverse Method for Determining Uniaxial Flow Properties by Spherical Indentation Test

The spherical indentation test has been successfully applied to inversely derive the tensile properties of small regions in a non-destructive way. Current inverse methods mainly rely on extensive iterative calculations, which yield a considerable computational costs. In this paper, a database method is proposed to determine tensile flow properties from a single indentation force-depth curves to avoid iterative simulations. Firstly, a database that contain numerous indentation force-depth curves is established by inputting varied Ludwic material parameters into the indentation finite elements model. Secondly, for a given experimental indentation curve, a mean square error (MSE) is designated to evaluate the deviation between the experimental curve and each curve in the database. Finally, the true stresses at a series of plastic strain can be acquired by analyzing these deviations. To validate this new method, three different steels, i.e. A508, 2.25Cr1Mo and 316L are selected. Both simulated indentation curves and experimental indentation curves are used as inputs of the database to inversely acquire the flow properties. The result indicates that the proposed approach provides impressive accuracy when simulated indentation curves are used, but is less accurate when experimental curves are used. This new method can derive tensile properties in a much higher efficiency compared with traditional inverse method and are therefore more adaptive to engineering application.

Interferons Are Pro-Inflammatory Cytokines in Sheared-Stressed Human Aortic Valve Endothelial Cells.

Calcific aortic valve disease (CAVD) is an athero-inflammatory process. Growing evidence supports the inflammation-driven calcification model, mediated by cytokines such as interferons (IFNs) and tumor necrosis factor (TNF)-α. Our goal was investigating IFNs’ effects in human aortic valve endothelial cells (VEC) and the potential differences between aortic (aVEC) and ventricular (vVEC) side cells. The endothelial phenotype was analyzed by Western blot, qPCR, ELISA, monocyte adhesion, and migration assays. In mixed VEC populations, IFNs promoted the activation of signal transducers and activators of transcription-1 and nuclear factor-κB, and the subsequent up-regulation of pro-inflammatory molecules. Side-specific VEC were activated with IFN-γ and TNF-α in an orbital shaker flow system. TNF-α, but not IFN-γ, induced hypoxia-inducible factor (HIF)-1α stabilization or endothelial nitric oxide synthase downregulation. Additionally, IFN-γ inhibited TNF-α–induced migration of aVEC. Also, IFN-γ triggered cytokine secretion and adhesion molecule expression in aVEC and vVEC. Finally, aVEC were more prone to cytokine-mediated monocyte adhesion under multiaxial flow conditions as compared with uniaxial flow. In conclusion, IFNs promote inflammation and reduce TNF-α–mediated migration in human VEC. Moreover, monocyte adhesion was higher in inflamed aVEC sheared under multiaxial flow, which may be relevant to understanding the initial stages of CAVD.

Numerical assessment on liquid mixing in a T‐mixer containing tri‐fin

AbstractLiquid mixing in channel with laminar uniaxial flow is inefficient, and the mixing channel length required for diffusive mixing is immensely large. In the attempt to enhance liquid mixing, this study presents computational evaluation of mixing performance of tri‐fin configuration in a T‐mixer. Two parameters, that is, transverse spacing (ST) and width (Lw) of the upstream fin, are studied to evaluate the geometrical scaling effect of the tri‐fin configuration. It is shown that tri‐fin unit withST/H = 0.2 andLw/H = 0.2 yields superior overall mixing performance, amongst the geometrical parameters investigated. For flow at low Reynolds number (Re ≤ 1), 20 periodic units of tri‐fin are sufficient to achieve maximum enhancement with 29% reduction of mixing efficiency lengthLM = 99%. It is also shown that there exists a progressive mixing enhancement with increasing number of tri‐fin periodic units employed. Taking into consideration of the pumping power limitation, it would be ideal to employ tri‐fin feature to improve liquid mixing for fluids with high Schmidt number, flowing at low Reynolds number.

Analysis of Tensile Deformation Behaviour of Dual Phase -590 Steel at Different Temperatures and Strain Rates

ABSTRACT An accurate uniaxial constitutive model is necessary to analyse the plastic deformation behaviour of metal and for reliable finite element simulations in sheet metal forming operations. In the present study, the hot uniaxial tensile flow stress analysis of dual phase (DP590) steel thin sheet has been carried out under a quasi-static strain rates of 0.1–0.001/s at the temperature range of 723–1073 K. The flow stress behaviour is significantly affected by test temperatures, strain rates and sheet orientations. Further, the Fields–Backofen constitutive flow relationship has been used to investigate the flow stress behaviour. This predicted flow stress curves shows a good fit to the experimentally measured stress at the work-hardening stage. Furthermore, a modified Fields–Backofen constitutive equation with a softening term has been considered to predict the flow behaviour. The capability of models has been evaluated based on the correlation coefficient (R), average absolute error AAE (Δavg) and root mean square error (RMSE). A better prediction of flow stress behaviour is observed by modified modified Fields–Backofen model with R = 0.9552, Δ = 0.034 and s = 0.0564.

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

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