Asymmetric Shear Research Articles

Tailoring microstructure and texture of Mg–3Al–1Zn alloy sheets through curve extrusion process for achieving low planar anisotropy

• Symmetric curve extrusion (SCE) and asymmetric curve extrusion (ACE) processes were firstly proposed to fabricate AZ31 Mg alloy sheets. • The SCE and ACE sheets exhibited unique textures which were ascribed to the introduction of additional flow velocity difference along transverse direction during extrusion. • The ACE sheet exhibited the lowest basal pole intensity because of the introduction of extra asymmetric shear deformation during ACE process. Curve extrusion processes, including symmetric curve extrusion (SCE) and asymmetric curve extrusion (ACE) processes, were proposed to fabricate Mg–3Al–1Zn (AZ31) alloy sheets with the aim of improving planar anisotropy. For comparison, traditional extrusion (TE) was conducted on producing AZ31 sheets. The dynamic recrystallization and flow behavior of AZ31 Mg alloy during extrusion were examined and analyzed, and the final microstructures and mechanical properties of AZ31 sheets were investigated. In comparison with the TE sheet, finer grain size, more uniform microstructure and weaker tilted basal texture were achieved in the SCE and ACE sheets. Both the SCE and ACE sheets exhibited unique textures which basal poles tilted to extrusion direction (ED) and new transverse direction (TD)-tilted texture component was developed. The reasons were mainly ascribed to the introduction of additional flow velocity difference along TD during extrusion. Furthermore, the ACE sheet exhibited the lowest basal pole intensity, which was attributed to the introduction of extra asymmetric shear deformation during extrusion process. As a result, the ACE sheet showed the lowest yield strength and r -value, but highest elongation and n -value. Improving the planar anisotropy of AZ31 sheet was achieved by the ACE process.

Numerical study on the flow-induced vibrations of two elastically mounted side-by-side cylinders at subcritical Reynolds numbers

Two-degree-of-freedom (2DOF) flow-induced vibrations (FIV) of an elastically mounted circular cylinder pair arranged in parallel are numerically investigated in a subcritical Reynolds number range of 1470–10320. The two cylinders are identical with mass ratios of m⁎ = 2.6 and mass-damping parameters of (m⁎ + Ca)ζ = 0.013. The transverse centre-to-centre spacing ratio (Sy/D) between them is varied from 4.0 to 10.0 with an increment of 2.0. The effect of Sy/D on the FIV responses, hydrodynamic features and wake patterns is evaluated. It is found that the response amplitudes of the two cylinders show similar variation trends and both drop to smaller values earlier than an isolated cylinder when Sy/D = 4.0, 6.0 and 10.0. Whereas, their response characteristics are different at Sy/D = 8.0. Cylinder #1 reaches its peak in-line (IL) and cross-flow (CF) amplitudes equivalent to those of the single cylinder, while the vibration amplitudes of Cylinder #2 experience decreases at Vr = 8.0. Moreover, the results suggest that the interference between the two cylinders is nonnegligible for all the Sy/D values considered in the present study. Six wake patterns are identified including the asymmetric long period flip-flopping (ALFF), asymmetric shear layer (ASL), biased in-phase synchronised (BIS), asymmetric shedding (A-Shed), in-phase synchronised (IS) and anti-phase synchronised (AS) patterns. The asymmetric wake patterns give rise to the distinct vibration modes of the two cylinders.

Drag reduction of a square-back bluff body under constant cross-wind conditions using asymmetric shear layer forcing

Highly resolved computations using Delayed Detached Eddy Simulations (DDES) of a canonical Windsor body are carried out. The flow around the car model, which is investigated imposing different yaw angles (up to 10°), is perturbed via a small square cylinder. This control element, whose length covers the whole height of the car model, is positioned at different streamwise locations on the windward face of the model. Depending on the location of the cylinder and the initial yaw angle of the model, drag increase or decrease up to 8% are observed. This sensitivity of the drag to the streamwise location of the cylinder is connected with the relative position of the flow reattachment on the side of the model after separation, which is caused by the cylinder. In the drag-optimal case where the flow reattachment occurs just at the streamwise location of the base, the asymmetry of the wake is reduced and the pressure in the wake is globally recovered. The flow mechanisms by which the drag reduction occur are twofold: (i) the flow is deviated inwards by the in-wash induced by the flow reattachment at the trailing-edge, thus acting as an inward-oriented flap, and (ii) the windward shear layer is forced by the turbulent field developing along the separated region of the perturbing cylinder.

Rayleigh Wave-Shear Wave Coupling Mechanism for Large Lateral Deformation in Level Liquefiable Ground

Large lateral deformation in almost level liquefiable ground has been observed during past strong earthquakes, which cannot be explained by the same driving force as that in sloping ground. This study proposes a Rayleigh wave-shear wave coupling mechanism for this phenomenon, which is evaluated on the element and site levels. A simple element level elasto-plastic force–displacement model reveals that the combination of the symmetrical shear force with the asymmetrical shear resistance under Rayleigh wave-shear wave coupling can be a major contributor for the accumulation of lateral soil deformation. Finite element method numerical results for a site level ground model shows that Rayleigh wave-shear wave coupling can induce significantly greater lateral displacement compared to pure shear wave input, and further highlight the importance of soil liquefaction for this phenomenon. The amplitudes and frequencies of the shear wave and the Rayleigh wave and their phase difference are shown to affect the accumulation of lateral deformation. The findings of Rayleigh wave-shear wave coupling induced lateral deformation are consistent with observations in past earthquakes, and should be considered in geotechnical earthquake engineering.

Effect of slip to roll ratio on cyclic plastic deformation response at subsurface during rolling contact fatigue

The objective of this investigation is to evaluate the cyclic plastic deformation response at the subsurface during rolling contact fatigue (RCF) under the conditions of pure rolling and rolling-sliding. The finite element simulation results indicate that the slip-to-roll ratio (SRR)has an immense effect on the cyclic plastic deformation evolution at the subsurface during RCF. At SRR of 0% (pure rolling), symmetric shear stress cycling is evident at the subsurface, and as a result plastic shakedown takes place. On the other hand, at SRR of 5% (rolling-sliding), asymmetric shear stress cycling is noticed at the subsurface, and consequently ratcheting i.e. progressive accumulation of shear strain is evident. Rolling-sliding results in the shear flow of the subsurface material along the sliding direction.

Interfacial Behavior of Particle-Laden Bubbles under Asymmetric Shear Flow.

The behavior of moving bubbles has mostly been studied in an axisymmetric flow field. To extend the knowledge to practical conditions, we investigate the interfacial and hydrodynamic properties of bubbles under asymmetric shear forces. Experiments are performed with a buoyant bubble at the tip of a capillary placed in a defined shear flow in the presence of surfactants, nanoparticles, and glass beads. The response of the interface to the surrounding asymmetric flow is measured under successive reduction of the surface area. Profile analysis tensiometry is utilized to investigate the dynamic surface tension and the surface rheology of the surfactant- and nanoparticle-laden interfaces. Microscopic particle image and tracking velocimetry are used to study the bulk flow and the interfacial mobility of the buoyant bubble. According to our results, the rotational component of the shear flow provokes an interfacial flow, which redistributes the adsorbed surfactants and particles at the interface. In the presence of NPSCs, a contiguous network of particles forms at the interface through densification of surface structures. We show that this interconnected nanoparticle network eventually stops the interfacial flow and decreases the mobility of the glass beads at the interface. The immobilization of the interface is characterized by a dimensionless number, defined as the ratio of the interfacial elasticity to bulk shear forces. This number provides an estimate of the interfacial forces required to impose interfacial immobility at a defined flow field. Our findings can serve as a basis to formulate boundary conditions for refined modeling and to predict the hydrodynamics of bubbles and droplets.

Numerical Simulation Study on Compression Characteristics of Gravelly Soil Mixture Based on Soft Servo Method

Because of complex mechanical properties and deformation mechanism, gravel soil mixture is an important medium of concern in the field of geotechnical engineering. Based on the continuous-discontinuous coupling algorithm formed by the structure shell elements and the particle discrete element method (PFC3D), the soft servo loading of the sample is realized, and the typical triaxial compression test data are used to calibrate mesoscale parameters. Furthermore, the numerical tests under different rock contents and confining pressure are carried out. The change rule of shear strength of mixed medium is discussed. It shows that the continuous-discontinuous coupling algorithm achieves a good effect in reflecting the deformation process. Under the mechanism of the flexible servo, the failure mode of the sample takes on drum-failure mode, and the internal of the damaged sample forms an obvious asymmetric X-shaped shear band. With the increase of stone content, the internal friction angle and cohesive force distribution of the sample have certain discreteness, but on the whole, the internal friction angle and cohesive force increase with the increase of stone content. The results can provide a reference for the parameter determination of mixed mediums such as gravel soil.

Interfacial flow of a surfactant-laden interface under asymmetric shear flow

HypothesisThe shear stress of the axisymmetric flow field triggers a nonuniform distribution of the surfactants at the surface of a rising bubble, known as stagnant cap. The formation of the stagnant cap gives rise to Marangoni stresses that reduce the mobility of the interface, which in return reduces the rising velocity. However, the conditions in technological processes usually deviate from the linear rise of a single bubble in a quiescent unbounded liquid. Asymmetric shear can act on the bubble surface e.g. due to the vorticity in the surrounding flow, bubble–bubble interactions, or influence of the reactor wall. A different surfactant distribution at the interface is expected under asymmetric shear, which can change the hydrodynamic behavior of the interface drastically. ExperimentsHere we conduct model experiments with a bubble or a drop at the tip of a capillary placed in a defined flow field. Thereby we investigate the influence of asymmetric shear forces on the interface in the presence of surfactants. Microscopic particle tracking velocimetry is employed to measure the velocity of the surfactant-laden interface for different degrees of asymmetry in the surrounding liquid flow. FindingsWe show a direct experimental observation of the circulating flow at the interface under asymmetric shear, which prevents the formation of the typical stagnant cap. Additionally, we reveal that the interface remains mobile regardless of the surfactant concentration. Our results confirm that increasing the degree of asymmetry increases the shear forces and thus the interfacial velocity.

Experimental failure analysis of adhesively bonded steel/CFRP joints under quasi-static and cyclic tensile-shear and peel loading

Epoxy resin adhesives are widely used in lightweight and structural applications and are suitable for mixed structures with steel and CFRP. The design of composite structures, especially under cyclic loading, is often carried out without consideration of interphase-specific effects. In this study, shear and peel test specimens made of steel and CFRP are tested under static load. The influences of material combinations and fiber orientation on strength and failure are evaluated. Cyclic tests are carried out on shear and peel test specimens to describe the evolution of damage and to determine crack initiation. For this purpose, a method is presented with which crack initiation can be determined based on the dynamic compliance. The main experimental results are as follows. The shear strength in mixed structures is reduced due to asymmetric shear stress distribution, which is intensified by the reduction of CFRP stiffness due to varying fiber angles. For specimens under peel load, the fillet size is an essential factor, since it can lead to high stress peaks and thus to delamination. Mixed structures show a reduced fatigue strength under cyclic loading due to earlier crack initiation. Peel loads lead to an accelerated crack growth and reduce the fatigue strength significantly.

Numerical Investigation of Reinforced Concrete Beam Due to Shear Failure

This paper investigates the possibility of using a multi-surface plasticity model to predict shear failure in reinforced concrete beams. The analysis is carried out using the in-house software called 3D-NLFEA. The constitutive model for the concrete material is based on the plasticity-fracture model, which had previously developed to simulate the behavior of concrete cover spalling in reinforced concrete columns. To obtain the asymmetric shear failure pattern, random material properties imperfection for each meshed element is used. Two beams available in the literature are investigated and compared with the analysis results using 3D-NLFEA. From the comparisons, excellent agreement between the analysis and the test result was obtained. 3D-NLFEA can predict the peak load accurately. The peak load prediction only varies 2.19% for beam OA1 and 3.28 % for beam OA2, and it was lower than the test results. The failure crack patterns also show a typical diagonal crack extension from the support to the loading steel plate.

Static and dynamic analysis of homogeneous Micropolar-Cosserat panels

This paper communicates an analytical study on computing the natural frequencies and in-plane deflections caused by static forces in the panel walls using Euler-Bernoulli, Timoshenko, Timoshenko and Goodier, Couple-stress, and Micropolar-Cosserat theory. The study highlights the formulation of the transfer matrix via the state-space method in the spatial domain; from coupled governing equations of motion that arises from the Micropolar-Cosserat theory. This theory captures the novel curvature of edges and moments of the panels at energy density level due to its unique feature of asymmetric shear stresses; that emphasizes the loss of ellipticity of governing equations. The analytical solution of the Micropolar-Cosserat theory yield appropriate results compared to plane-stress simulation of the panels using finite element analysis.

Complete Strain Record of a Highly Asymmetric Shear Zone: From Fault Core Gouges to Surface Rupture of Historical Earthquakes in the Alhama de Murcia Fault (SE Iberian Peninsula)

Complete Strain Record of a Highly Asymmetric Shear Zone: From Fault Core Gouges to Surface Rupture of Historical Earthquakes in the Alhama de Murcia Fault (SE Iberian Peninsula)

Examination of selected failure criteria with asymmetric shear stresses in the collapse analysis of laminated shells

The paper is concerned with failure analysis of composite shells performed with the usage of the nonlinear 6-parameter shell theory with drilling rotation degree of freedom. This special theory embodies naturally unlimited translations and rotations and is suitable for analysis of irregular shells for instance with various, particularly orthogonal, intersections. The presence of the drilling rotation is inherently accompanied with asymmetry of in-plane shear stresses and strains which must be taken into account in the composite failure criteria. In the paper in general two failure measures are applied: Hashin criterion and Tsai-Wu criterion which are appropriately modified to accommodate the stress asymmetry. It is shown, that depending on the used failure criterion, it is possible to obtain slightly different damage zones and values of the first ply failure and ultimate load. These values are compared with those obtained experimentally.

Flow physics of normal and abnormal bioprosthetic aortic valves

Flow physics of transvalvular flows in the aorta with bioprosthetic valves are investigated using computational modelling. For the efficient simulations of flow-structure-interaction in transvalvular flows, a simplified, reduced degree of freedom valve model is employed with a sharp interface immersed boundary based incompressible flow solver. Simulations are performed for normal as well as abnormal valves with reduced leaflet motion that models the effect of early leaflet thrombosis. The structure of the aortic jet and the hemodynamic stresses on the aortic wall are analysed to understand the hemodynamic impacts and possible long-term clinical implications of sub-clinical, reduced leaflet motion. The simulation results have shown that the reduced leaflet motion tilts the direction of aortic jet and generates stronger flow separation and re-attachment on the aortic wall downstream from the reduced motion leaflets. The modified flow pattern increases the wall pressure fluctuation and average wall shear stress on the downstream aortic wall, and results in the asymmetric oscillatory shear index distributions, which may have long-term clinical implications such as aortic wall damage and remodelling.

Development of the Physics–Based Morphology Model as the Platform for the Optimal Design of Beach Nourishment Project: A Numerical Study

In this study, a physics-based morphology model is developed and to test the feasibility of the morphology model proposed in this study as the platform for the optimal design of the beach nourishment project, the beach restoration process by the infra-gravity waves underlying the swells in a mild sea is numerically simulated. As a hydrodynamic module, the IHFOAM wave toolbox having its roots in the OpenFoam is used. Speaking of the morphology model, a transport equation for suspended load and the Exner type equation constitute the morphology model. In doing so, the probability theory first introduced by Einstein and the physical model test by Bagnold are used as the constituent sub-model of the morphology model. Numerical results show that among many flow features that are indispensable in forming sand bars over the flat bottom and swash zone, the partially skewed and asymmetric bottom shearing stresses, a shoreward Stokes drift near the free surface, boundary layer streaming near the seabed, and undertow toward the offshore were successfully simulated using the morphology model proposed in this study. It was also shown that plunging type breaker occurring at the final stage of the shoaling process, and its accompanying second breaker, sediment entrainment at the seabed, and the redistribution of suspended load by the down rush of preceding waves were successfully reproduced in the numerical simulation, and agreements with our experience in the field were very encouraging. In particular, the sand bar formation process over the flat bottom and backshore were successfully reproduced in the numerical simulation, which has been regarded as a challenging task.

Geneses of Two Contrasting Antigorite Crystal Preferred Orientations and Their Implications for Seismic Anisotropy in the Forearc Mantle

AbstractCrystal preferred orientation (CPO) of antigorite is an important parameter for the interpretation of seismic anisotropies and related geodynamic processes in subduction zones. However, mechanisms for the development of various antigorite CPOs and their effects on seismic anisotropies in the forearc mantle still remain to be constrained. In this study, we investigated olivine and antigorite CPOs and calculated seismic anisotropies of the serpentinized peridotites from Val Malenco, Central Alps. The results show that antigorite in the olivine‐rich (weakly serpentinized) layer displays an L‐type CPO (i.e., (h0l) plane//foliation and [010] axis//lineation), whereas antigorite in the antigorite‐rich (highly serpentinized) layer develops an LS‐b‐type CPO (i.e., (001) plane//foliation and [010] axis//lineation). The antigorite L‐type CPO is most likely formed by diffusion and dislocation creep accommodated phase boundary sliding and substantial grain rotation at a higher temperature and smaller strain regime. In contrast, the development of an antigorite LS‐b‐type CPO requires diffusion and dislocation creep accommodated grain boundary sliding, smaller contribution of grain rotation, and significant role of dissolution‐precipitation creep at a lower temperature and larger strain regime. In this context, we propose an antigorite CPO distribution model in the forearc mantle. Based on this model and under vertically incident teleseismic waves, if significant serpentinization and asymmetric shearing do indeed occur within serpentinized layers, then strong and weak trench‐parallel seismic anisotropies can be expected for cold and warm moderate‐angle subduction zones, respectively. This model may provide an alternative interpretation on the seismic anisotropy observations in some modern subduction systems.

Hysteretic Behavior of Moment-Resisting Frames Considering Slab Restraint and Framing Action

This paper examines the influence of framing action and slab continuity on the hysteretic behavior of composite steel moment-resisting frames (MRFs) by means of high-fidelity continuum finite-element (CFE) analyses of two-bay subsystems and typical cruciform subassemblies. The CFE model, which is made publicly available, was thoroughly validated with available full-scale experiments and considers variations in the beam depth and the imposed loading history. The simulation results suggest that beams in subsystems may experience up to 25% less flexural strength degradation than those in typical subassemblies. This is because of local buckling straightening from the slab continuity and framing action evident in subsystems. For the same reason, beam axial shortening attributable to local buckling progression is up to five times lower in subsystems than in subassemblies, which is consistent with field observations. While the hysteretic behavior of interior panel zone joints is symmetric, exterior joint panel zones in subsystems experience large asymmetric shear distortions regardless of the employed lateral loading history. From a design standpoint, it is found that the probable maximum moment in deep and slender beams (db≥700 mm) may be up to 25% higher than that predicted by current design provisions with direct implications to capacity design of steel MRFs. The 25% reduction in the shear stud capacity as proposed by current seismic provisions is not imperative for MRFs comprising intermediate to shallow beams and/or featuring a high degree of composite action (η>80%) as long as ductile shear connectors are employed.

Asymmetric in-plane shear behavior of isolated cadaveric lumbar facet capsular ligaments: Implications for subject specific biomechanical models

The facet capsular ligaments (FCLs) flank the spinous process on the posterior aspect of the spine. The lumbar FCL is collagenous, with collagen fibers aligned primarily bone-to-bone (medial-lateral) and experiences significant shear, especially during spinal flexion and extension. We characterized the mechanical response of the lumbar FCL to in-plane shear, and we evaluated that response in the context of the fiber architecture. In-plane shear tests with both positive and negative shear (i.e., corresponding to flexion and to extension) were performed on eight cadaveric human L4-L5 FCLs. Our most striking observation was subject-dependent asymmetry in the response. All samples showed a toe region of low stiffness, transitioning to greater stiffness at higher strains, for both shear directions. Different samples showed profoundly different transition strains, with some samples stiffening more rapidly in positive shear and some in negative shear. This unpredictable asymmetry, which did not correlate with age, side, or degeneration state, suggesting that collagen fibers in the FCL are sometimes aligned at a slight positive angle from the bone-to-bone axis and sometimes at a negative angle. Fitting the experimental data to a fiber-composite-based finite element model supported this idea, yielding optimal fits with positive or negative off-axis fiber directions (−40° to +40°). Subsequent examination of selected FCLs by small-angle x-ray scattering (SAXS) showed a similar variability in fiber direction. We conclude that small individual differences in lumbar FCL architecture may have a significant effect on lumbar FCL mechanics, especially at moderate strains.

A pilot study of aortic hemodynamics before and after thoracic endovascular repair with a double-branched endograft

Branched endografts have been developed to treat complex pathology in the aortic arch and ascending aorta. This study aims to evaluate the haemodynamic performance of a double-branched thoracic endograft by detailed comparison of flow patterns and wall shear stress in the aorta and supra-aortic branches before and after stent-graft implantation. Pre- and post-intervention CT images were acquired from two patients who underwent thoracic endovascular aortic repair (TEVAR) with a double-branched endograft for thoracic aortic aneurysms. These images were used to reconstruct patient-specific models, which were analysed using computational fluid dynamics employing physiologically realistic boundary conditions. Our results showed that there was sufficient blood perfusion through the arch branches. The presence of inner tunnels caused flow derangement and asymmetric wall shear stress in the ascending aorta, where shear range index was up to 6 times higher than in the pre-intervention model. Wall shear stress in the aortic arch increased considerably after intervention as a result of accelerated flow. The maximum flow-induced displacement forces on the branched endografts were around 22 ​N for both patients, which was below the threshold for device migration. Results from this pilot study demonstrated that aortic flow patterns were significantly altered by the branched endograft which caused increased spatial variation of wall shear stress in the ascending aorta and the arch. Although no obvious adverse hemodynamic features were found immediately after intervention for the cases we analysed, follow-up studies will be needed to assess durability of the device.

Lower Crustal Heterogeneity Beneath the Northern Tibetan Plateau Constrained by GPS Measurements Following the 2001 Mw7.8 Kokoxili Earthquake

AbstractWe use GPS measurements across the Xidatan segment of the Kunlun fault in the Tibetan Plateau to investigate the surface deformation following the 2001 Mw 7.8 Kokoxili earthquake. We find significant postseismic deformation during the period 2007–2015, characterized by an asymmetric shear across the 2001 rupture, with average velocities reaching ~10 mm/year about 30–45 km south of the coseismic rupture. We also find that the postseismic transients diffused away from the coseismic rupture through time, with a shift of the maximum transient rates from ~20–30 km south of the rupture in 2001–2002 to ~30–45 km in 2007–2015. Viscoelastic relaxation is the dominant physical process during the period 2007–2015. The estimated effective viscosity of the lower crust beneath the Songpan‐Ganzi terrane is 2 × 1018–3 × 1018 Pa s from the 2001–2002 data, and it has increased to ~2 × 1019 Pa s for the period 6 to 14 years after the event. The large asymmetry in the postseismic deformation field indicates a laterally heterogeneous lower crust beneath the northern Tibetan Plateau. Viscoelastic relaxation models show that the viscosity of the lower crust beneath the Qaidam basin is ~2 and ~4 times larger than the viscosity of the lower crust beneath the Songpan‐Ganzi terrane in 2001–2002 and 2007–2015, respectively. Based on these data and results from previous studies, we postulate that the Kunlun fault itself is not the unique rheological boundary and that additional domains with viscosity increasing from the Qiangtang terrane to the Qaidam basin appear to be required.