Shear Strain Rate Research Articles

Thermal-Mechanical Fatigue Behavior and Life Assessment of Single Crystal Nickel-Based Superalloy

Thermal-mechanical fatigue (TMF) tests and isothermal fatigue (IF) tests were conducted using thin-walled tubular specimens under strain-controlled conditions. The results of TMF tests showed a strong correlation between mechanical behavior and temperature cycling. Under different phases of temperature and mechanical loading, the hysteresis loop and mean stress of the single crystal superalloy showed noticeable variations between the stress-controlled and strain-controlled conditions. In the strain-controlled TMF test, temperature cycling led to stress asymmetry and additional damage, resulting in a significantly lower TMF life compared to IF life at the maximum temperature. Moreover, the OP TMF life is generally lower than that of the IP TMF at the same strain amplitude. The Walker viscoplastic constitutive model based on slip systems was used to analyze the TMF mechanical behavior of the single crystal superalloy, and the change trends of the maximum Schmid stress, the maximum slip shear strain rate, and the slip shear strain range were analyzed, and their relationship with the TMF life was investigated. Finally, a TMF life prediction model independent of the loading mode and phase was constructed based on meso-mechanical damage parameters. The predicted TMF lives for different load control modes and phases fell within the twofold dispersion band.

Rheological Properties of Small-Molecular Liquids at High Shear Strain Rates.

Molecular-scale understanding of rheological properties of small-molecular liquids and polymers is critical to optimizing their performance in practical applications such as lubrication and hydraulic fracking. We combine nonequilibrium molecular dynamics simulations with two unsupervised machine learning methods: principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE), to extract the correlation between the rheological properties and molecular structure of squalane sheared at high strain rates (106-1010s-1) for which substantial shear thinning is observed under pressures P∈0.1-955 MPa at 293 K. Intramolecular atom pair orientation tensors of 435×6 dimensions and the intermolecular atom pair orientation tensors of 61×6 dimensions are reduced and visualized using PCA and t-SNE to assess the changes in the orientation order during the shear thinning of squalane. Dimension reduction of intramolecular orientation tensors at low pressures P=0.1,100 MPa reveals a strong correlation between changes in strain rate and the orientation of the side-backbone atom pairs, end-backbone atom pairs, short backbone-backbone atom pairs, and long backbone-backbone atom pairs associated with a squalane molecule. At high pressures P≥400 MPa, the orientation tensors are better classified by these different pair types rather than strain rate, signaling an overall limited evolution of intramolecular orientation with changes in strain rate. Dimension reduction also finds no clear evidence of the link between shear thinning at high pressures and changes in the intermolecular orientation. The alignment of squalane molecules is found to be saturated over the entire range of rates during which squalane exhibits substantial shear thinning at high pressures.

A Time-Scale Varying Finite Difference Method for Analyzing the Influence of Rainfall and Water Level on the Stability of a Bank Slope

A time-scale varying finite difference method (TSFDM) was proposed to analyze the influence of rainfall infiltration and water level fluctuation on the stability of a bank slope in the Yunnan Pulang tailings pond. The stability of the slope obtained by the TSFDM and the limit equilibrium method (LEM) were compared. The result indicates that the TSFDM can obtain reliable spatiotemporal variation features of geotechnical parameters of the bank slope under different conditions. The water level fluctuation has a greater impact on the stability than rainfall infiltration. In addition, the safety factor decreases as the shear strain rate increases on the weathering interface. The safety factors under all conditions are smaller than one, so corresponding measures should be taken. The research provides references for preventing disasters caused by bank slope failure.

Shear Transformation Zone and Its Correlation with Fracture Characteristics for Fe-Based Amorphous Ribbons in Different Structural States

Fe-based amorphous alloys often exhibit severe brittleness induced by annealing treatment, which increases the difficulties in handling and application in the industry. In this work, the shear transformation zone and its correlation with fracture characteristics for FeSiB amorphous alloy ribbons in different structural states were investigated. The results show that the bending strain decreases sharply with the annealing temperature increase, accompanied by decreased shear band density and the induced plastic deformation zone. Furthermore, the microscopic fracture surface features transform from a micron-scale dimple pattern to nano-scale dimples and periodic corrugations. According to nano-indentation results, the strain rate sensitivity and shear transformation zone volume change significantly upon annealing treatment, which is responsible for the deterioration of bending ductility and the transition of microscopic fracture surface features.

Acoustic Emissions of Nearly Steady and Uniform Granular Flows: A Proxy for Flow Dynamics and Velocity Fluctuations

AbstractThe seismic waves emitted during granular flows are generated by different sources: high frequencies by interparticle collisions and low frequencies by global motion and large scale deformation. To unravel these different mechanisms, an experimental study has been performed on the seismic waves emitted by dry, dense, quasi‐steady granular flows. The emitted seismic waves were recorded using shock accelerometers and the flow dynamics were captured with a fast camera. The mechanical characteristics of the particle collisions were analyzed, along with the intervals between collisions and the correlations in particles' motion. The high‐frequency seismic waves (1–50 kHz) were found to originate from particle collisions and waves trapped in the flowing layer. The low‐frequency waves (20–60 Hz) were generated by particles' oscillations along their trajectories, that is, from cycles of dilation/compression during coherent shear. The profiles of granular temperature (i.e., the mean squared value of particle velocity fluctuations) and average velocity were measured and related to each other, then used in a simple steady granular flow model, in which the seismic signal consists of the variously attenuated contributions of shear‐induced Hertzian collisions throughout the flow, to predict the rate at which seismic energy was emitted. Agreement with the measured seismic power was reasonable, and scaling laws relating the seismic power, the shear strain rate and the inertial number were derived. In particular, the emitted seismic power was observed to be approximately proportional to the root mean square velocity fluctuation to the power 3.1 ± 0.9, with the latter related to the mean flow velocity.

CFD simulation of hydrodynamics and mixing performance in dual shaft eccentric mixers

This work aims to systematically study hydrodynamics and mixing characteristics of non-Newtonian fluid (carboxyl methyl cellulose, CMC) in dual shaft eccentric mixer. Fluid rheology was described by the power law rheological model. Computational fluid dynamics was employed to simulate the velocity field and shear rate inside the stirred tank. The influence mechanism of the rotational modes, height difference between impellers, impeller eccentricities, and impeller types on the flow field have been well investigated. We studied the performance of different dual-shaft eccentric mixers at the constant power input with its fluid velocity profiles, average shear strain rate, mixing time and mixing energy. The counter-rotation mode shows better mixing performance than co-rotation mode, and greater eccentricity can shorten mixing time on the basis of same stirred condition. To intensify the hydrodynamic interaction between impellers and enhance the overall mixing performance of the dual shaft eccentric mixers, it is critical to have a reasonable combination of impellers and an appropriate spatial position of impellers.

Mechanism on Material Strengthening of Metastable Precipitate and Edge Dislocation in Al–Mg–Si Alloy

The metastable precipitate β″ plays a key role in material strengthening in Al–Mg–Si alloys. To investigate the mechanism on material strengthening of metastable precipitates, the interaction between β″ metastable precipitates and edge dislocations is studied using molecular dynamics. It is indicated in the results that the precipitate can be overcome by shearing without the formation of Orowan loops in case of smaller precipitate sizes. By increasing the temperature and reducing the shear strain rate, the critical resolved shear stress (CRSS) can be decreased. Larger precipitate sizes can lead to higher CRSS due to larger interaction area. Shear deformation can be clearly found on the precipitate when dislocations interact with the precipitate. When newly generated dislocations further interact with the sheared precipitate, the strengthening can be reduced due to the smaller cut width. This is the reason that strain hardening decreases with the increase of plastic deformation in macro scale.

Shear strain rate sensitivity and crystallisation kinetics investigation in melt spun Cu64Zr36 binary metallic glass

Abstract Shear strain rate effect on crystallisation behaviour and characteristic temperatures of the three well-known glass formers in Cu–Zr binary amorphous system, namely Cu50Zr50, Cu56Zr44 and Cu64Zr36, were investigated. The crystallisation behaviour of Cu64Zr36 was uniquely found to be heavily dependent on shear strain rate. Crystallisation kinetics were studied through Isochronal transformation and isothermal transformation. The activation energy of crystallisation of each case was compared and contrasted. Johnson-Mehl-Avrami (JMA) analyses were also employed to study its kinetics behaviour. Finally, high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) combined with laser-assisted local electrode atom probe (LEAP) investigation revealed no detectable clustering or phase separation.

Superplasticity in a coarse-grained as-cast magnesium alloy

Superplasticity of a coarse-grained cast Mg–2.5Gd–0.5Zr alloy was investigated by assessing the strain rate sensitivity index (m-value) through the shear punch testing (SPT) method in the temperature range of 623–748 K and shear strain rate range of 2.8 × 10−3–2.2 × 10−2 s−1. The initial as-cast grain size of about 150 μm was reduced to about 3.5 μm at the end of the test. This severe grain refinement caused by dynamic recrystallization (DRX) facilitated superplasticity in the studied cast alloy. According to the respective m-values of 0.51 and 0.53 obtained at 698 and 723 K, and the activation energy of 80 kJ mol−1, the prevailing mechanism of deformation was suggested as grain boundary sliding (GBS) controlled by grain boundary diffusion.

Steady rheological behavior and unified strength model for reconstituted deep-sea sediments

Investigation of the rheological characteristics of deep-sea sediments is very important for understanding submarine disasters. Three reconstituted deep-sea soils with different plasticity and activity values from the South Sea China are considered in this study. A series of steady rheological tests are conducted on samples of three soils with different water contents and temperatures by a rate-controlled rotational rheometer operated in a steady-state regime. Rheological results show that shear stress and apparent viscosity can be decreased by a maximum of 65% when the temperature varies from 1 °C to 25 °C, and the three deep-sea soils are typical shear thinning non-Newtonian fluids with yield stress. The state of the samples can be divided into three phases during the shearing process, which implies that with an increase in the shear strain rate, all samples first behave as a solid, then transition from solid to liquid, and last behave as a liquid. The three phases are distinguished by the static yield stress (SYS) and fluidic yield stress (FYS), and a simple method for dividing the three phases is proposed. The SYS and FYS decreased with increasing temperature and water content. The relationships between yield stresses (SYS and FYS) and soil properties (water content and activity) and temperature are established. In addition, a unified strength model for deep-sea sediments is suggested, and the validity of the model is verified by comparing the prediction results of the model and test results. The results of this study could be useful for deep-sea submarine mudflow and landslide modelling.

A response to the discussion paper on “Numerical flow simulation of fresh concrete with viscous granular material model and smoothed particle hydrodynamics”

The parameter L0 with a unit length (=1.0 m) was omitted in our paper, and the unit of loading speed s1 and the expression of parameter c7 were not shown, which result in that the dimensions of shear strain and shear strain rate shown in Eq.(16) were misinterpreted. In this response paper, we added the L0 in the expressions of parameters c6 and q, and explained the unit of s1, as well as gave the expression for the c7. The addition of L0 do not change the simulation results and conclusions of our paper.

Hot deformation constitutive analysis and processing maps of the as-cast and wrought Mg–2.5Gd–0.5Zr alloy

Hot deformation behavior and constitutive analysis of the as-cast and extruded Mg–2.5Gd–0.5Zr alloy were compared, using the shear punch testing (SPT) method in the temperature range of 623–723 K and shear strain rate range of 2.8 × 10–3–2.2 × 10–2 s–1. The respective hyperbolic-sine exponents of 2.67 and 2.59 as well as activation energies of 183 and 275 kJ mol–1 obtained for the as-cast and extruded alloy suggested grain boundary sliding as the prevailing deformation mechanism. Surprisingly, regardless of the instability domains, the efficiency of power dissipation exceeded 30% in most areas in the processing maps of both cast and wrought conditions. The safe and instability domains were rather similar in both processing maps. The relatively high potential of the as-cast alloy for hot deformation, despite its initial coarse grain size of about 150 µm, can be ascribed to the severe dynamic recrystallization (DRX) during hot deformation caused by Zr. This could be economically advantageous, as there would be no need for homogenization of the as-cast material before deformation processing. The most noticeable optimum window occurred in the temperature range of 673–723 K for both as-cast and extruded conditions with a vaster strain-rate range for the extruded one (5.6 × 10–3–1.4 × 10–2 s–1), owing to its initial finer grain size. The instability domains, however, took place for both conditions in the temperature range of 648–673 K and strain rates of about 5.6 × 10–3 s–1, manifested by cracking in the deformed zone, and also at temperatures higher than 673 K and medium to high strain rates.

Numerical investigation of clocking effect on irreversible energy loss in volute for centrifugal pump with vaned diffuser based on entropy generation method

In order to study temporal and spatial variation of energy loss and reveal influence rule of clocking effect on energy loss and flow field in centrifugal pump with vaned diffuser, numerical simulations were carried out. Numerical simulations were validated by experiments. Local equilibrium of turbulence generation and dissipation was verified to state feasibility of energy loss methods. Hydraulic loss in each component was assessed, which shows that variation of hydraulic loss in volute is more significant due to clocking effect than that in other components. Vortical structure in volute varies greater under different guide vane positions than it in other components. The results show that positive and negative flow angle appears interlaced in tongue region with high velocity gradient, especially when diffuser is mounted at θd1. Since a clearance presents between tongue and vane trailing edge at θd1, a small vortex forms. Which promotes the blocking effect of the large-scale vortex at volute outlet pipe. Therefore, high velocity gradient appears at small vortex region and volute outlet pipe region. The shear strain rate at the tongue and volute outlet pipe is more significant than that at other diffuser mounted positions. Energy loss at these regions increases. This situation can be improved by a more suitable diffuser mounted position θd4, where the clearance and small vortex vanishes, the shear strain rate, velocity gradient, and energy loss decrease.

In-vivo high-speed biomechanical imaging of the cornea using Corvis ST and digital image correlation

In-vivo corneal biomechanical characterization has gained significant clinical relevance in ophthalmology, especially in the early diagnosis of eye disorders and diseases (e.g. keratoconus). In clinical medicine, the air-puff-based tonometers such as Ocular Response Analyzer (ORA) and Corvis ST have been used in the in-vivo biomechanical testing. In the test, the high-speed dynamic deformation of the cornea under air-puff excitation is analyzed to identify the abnormities in the morphological and biomechanical properties of the cornea. While most existing measurements reflect the overall corneal biomechanical properties, in-vivo high-speed strain and strain rate fields at the tissue level have not been assessed. In this study, 20 subjects were classified into two different groups: the normal (NORM, N = 10) group and the keratoconus (KC, N = 10) group. Image sequences of the horizontal cross-section of the human cornea under air puff were captured by the Corvis ST tonometer. The macroscale mechanical response of the cornea was determined through image analysis. The high-speed evolution of full-field corneal displacement, strain, velocity, and strain rate was reconstructed using the incremental digital image correlation (DIC) approach. Differences in the parameters between the NORM and KC groups were statistically analyzed and compared. Statistical results indicated that compared with the NORM group, the KC corneas absorbed more energy (KC: 8.98 ± 2.76 mN mm; NORM: 4.79 ± 0.62 mN mm; p-value <0.001) with smaller tangent stiffness (KC: 22.49 ± 2.62 mN/mm; NORM: 24.52 ± 3.20 mN/mm; p-value = 0.15) and larger maximum deflection (KC: 0.99 ± 0.07 mN/mm; NORM: 0.92 ± 0.06 mN/mm; p-value <0.05) on the macro scale. Further, we also observed that The maximum displacement (KC: 1.17 ± 0.06 mm; NORM: 1.06 ± 0.07 mm; p-value <0.005), velocity (KC: 236 ± 29 mm/s; NORM: 203 ± 17 mm/s; p-value <0.01), shear strain (KC: 24.43 ± 2.59%; NORM: 20.26 ± 1.54%; p-value <0.001), and shear strain rate (KC: 69.74 ± 11.99 s−1; NORM: 54.84 ± 3.03 s−1; p-value <0.005) in the KC group significantly increased at the tissue level. This is the first time that the incremental DIC method was applied to the in-vivo high-speed corneal deformation measurement in combination with the Corvis ST tonometer. Through the image registration using incremental DIC analysis, spatiotemporal dynamic strain/strain rate maps of the cornea can be estimated at the tissue level. This is constructive for the clinical recognition and diagnosis of keratoconus at a more underlying level.

Исследование псевдопластических свойств жидкостей, применяемых для гидроразрыва пласта, в широком диапазоне скоростей сдвига и давлений

Experimental data on quasi-static and dynamic loading of fluids with viscoelastic surfactants are used for the prediction of hydraulic fracturing. The paper proposes the dependence of viscosity on shear rate and pressure in a wide range of loading conditions. Experimental studies of liquids were carried out with the use of a falling ball rheometer (the Stokes method), industrial rheometers with a measuring system ‘cone-plane’ or ‘coaxial cylinders’; studies at high shear strain rates were car-ried out by the method of electrical explosion of the conductor. The proposed power-law depend-ence of viscosity on the shear strain rate with taking into account pressure, makes it possible to adequately describe experimental data from laboratory tests in the range of the shear strain rate and fluid pressure characteristic of hydraulic fracturing.

Development and performance evaluation of galactomannan polymer based abrasive medium to finish atomic diffusion additively manufactured pure copper using abrasive flow finishing

Abrasive flow finishing (AFF) is an advanced finishing process where the surface roughness of the component is gradually reduced by reciprocating an abrasive medium. A typical abrasive medium consists of base polymers, rheological additives, and abrasive particles. In most cases, the base polymer chains are based on siloxane, natural or synthetic elastomers, thermoplastic polymers, etc. The abrasive media developed with these polymer chains are expensive, and most of them are not biodegradable. In the recent past, hydrogel-based abrasive media gained significant attention as it results in a cost-effective, eco-friendly, and biodegradable abrasive medium. Since water is the main constituent in these media, this may cause corrosion of the component surfaces. Due to the high shear strain rates involved in the AFF process, the hydrogel-based media quickly lose moisture and becomes dry; thus, the life of the media reduces. In the present work, a long-lasting and noncorroding abrasive medium was indigenously developed for the AFF process. This medium constitutes galactomannan polymer, glycerol solution, cross-linker, and abrasive particles. The developed medium was absolutely free from expensive rheological modifiers. In addition to the rheological characterization, the developed medium was characterized using scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis. The finishing performance of the developed media was assessed by finishing atomic diffusion additively manufactured (ADAM) pure copper curved samples. The effect of the number of finishing cycles, extrusion pressure, and abrasive mesh size was investigated on the amount of material removed and the percentage change in average surface roughness (Ra). A reduction of Ra up to 90% in the longitudinal direction and 75% in the transverse direction was obtained using the developed abrasive medium. Based on the obtained finishing results, the material removal mechanism from the ADAM surface was proposed.

Three-dimensional deformation velocity field and kinematic characteristic of the middle and east parts of Haiyuan fault zone from InSAR and GPS observations

Three-dimensional deformation velocity field can reveal fine characteristics of surface deformation, and provide data support for the research on crustal motion mechanism and seismic hazard. In this study, the ascending and descending InSAR deformation velocity fields in the middle and east parts of Haiyuan fault zone are firstly obtained with Sentinel-1A data and SBAS InSAR technology. Then, by combining with GPS observations, the three-dimensional deformation velocity field is extracted and analyzed. Finally, the locking depths and deep slip rates at different locations are inverted by using the classical two-dimensional screw dislocation model, and the maximum shear-strain rate is investigated. The results indicate that there are significant differences in the InSAR deformation velocity field between both sides of the middle and east parts of Haiyuan fault zone. The east–west deformation velocity field clearly reveals the left-lateral strike-slip characteristic of the fault zone. The northward movement gradually changes to southward movement from northwest to southeast. The vertical deformation velocity field displays significant differences on both sides of the section between MMSF and the middle of LHSF, and the middle and eastern of HYE fault. For LHSF, the locking depth and deep slip rate are 9.7 km and 4.9 mm/a; for HYW fault, they gradually decrease from west to east, with the locking depths of 6.4 km, 3.6 km and 3.2 km, respectively, and the deep slip rates of 5.5 mm/a, 4.2 mm/a and 3.8 mm/a, respectively; for HYM fault, they are 7 km and 4.7 mm/a; for HYE fault, they are 5.8 km and 3.6 mm/a. There are two obvious extreme regions of maximum shear-strain rate along the fault strike. This study can provide a reference for investigating the mechanism of regional uplift and extension and seismic hazard.

Experimental analysis of shear strength and strain rate on H2/CH4 pinch-off flames

An experiment was conducted under acoustic excitation conditions for the physical understanding of the pinch-off phenomenon in non-premixed flames. For fuel conditions, H2/CH4 has a volume ratio of 75/25 %, and for acoustic excitation conditions, experiments were performed at a forcing frequency of 80 Hz and velocity perturbation intensity of 50 %. In addition, experiments were performed in the range of 1.0–4.5 m/s of air and fuel velocity. OH* chemiluminescence analysis using a high-speed camera was performed for flame structure analysis, while particle image velocimetry was performed for flow-field analysis. Simultaneous measurement of OH* chemiluminescence and particle image velocimetry allowed observing the flame separation. Strain rate and shear strength were introduced for pinch-off and non-pinch-off analysis, and the correlation between the two factors was analyzed. Pinch-off mapping analysis at various velocities confirms the presence of a physical boundary. The direction of vortex roll-up reverses depending on the fuel and air velocities, indicating the formation of different flame structures. When acoustic excitation dominates, the strain rate increases and flame pinch-off occurs. In contrast, when the shear effect dominates, a non-pinch-off flame is obtained and the shear strength decreases. Accordingly, the strain rate and shear strength are correlated, and the approximate pinch-off threshold can be determined at various experimental points. These findings suggest that the shear strength and the strain rate can be used as parameters to distinguish pinch-off.

Influence of Slip and Orientation on Entropy Generation Due to Natural Convection in a Square Cavity

Abstract Numerical simulations are performed to deduce the effects of slip wall and orientation on entropy generation due to natural convection (NC) in a square cavity for Rayleigh number (Ra) = 105. The laterally insulated square cavity, heated at the bottom wall and cooled at the top wall, is subjected to various orientation angles (ϕ) and slip velocities characterized by the Knudsen number (Kn). The two components of entropy generation, i.e., entropy generation due to heat transfer (SΘ) and entropy generation due to fluid friction (SΨ), are separately investigated by varying the orientation from 0 deg to 120 deg in steps of 15 deg and Knudsen number from 0 (no-slip) to 1.5 in steps of 0.5. Evidence indicates that, for most cases considered, entropy generation due to fluid friction (SΨ) dominates the one due to heat transfer (SΘ). It is observed that the slip velocity on the isothermal walls (us,iso) has a strong influence on SΘ whereas the variations in SΨ are closely connected to the change in the rate of shear strain. Interestingly, the presence of corner vortices and the secondary circulations near the core of the cavity are also found to affect the variation in entropy generation. The existence of active zones of SΘ in the vicinity of isothermal walls and their elongation and migration while changing the orientation is another unique characteristic noticed in this study. A new parameter called maximum velocity ratio (MVR) is also proposed to highlight the variation in velocity components within the enclosure.

Influence of shearing strain rate on the mechanical behaviour of three structured clays

This paper presents the stress–strain behaviour of three structured clays subjected to a number of stepwise changes in strain rate during shearing in a triaxial apparatus. Undrained compression tests were performed on clay specimens in both undisturbed and reconstituted states. As a result, it has been possible to identify the influence of structure on the rate-dependent response of the clays. Step changes in applied shearing strain rates for all tests resulted in predominately isotache-type behaviour within the range of strains from very small strains to large strains at failure. At very small strains, evidence of a limiting elastic modulus was established for both the stiff sedimentary and artificially cemented soil, which is consistent with published literature on other structured geomaterials. The stress–strain behaviour of all three materials was affected by both the degradation of structure with increasing strain and applied strain rate. The influence of structure on the time-dependent behaviour of the clays is discussed by comparing the response of undisturbed and reconstituted specimens and following normalisation by the equivalent pressure. Results indicate that the rate sensitivity evolves with increasing strains and reaches a maximum at strain levels associated with peak shearing resistance.