Non-uniform Shear Research Articles

Transmission and reflection of three-dimensional Boussinesq internal gravity wave packets in nonuniform retrograde shear flow

Simulated fully localized internal gravity wave packets with moderately large initial amplitude exhibit finite transmission across a reflection level, due to the combined effects of the wave-induced shear locally cancelling the retrograde background shear, modulational instability, and the nonlinear generation and evolution of secondary wave packets.

High-fidelity simulation of ship and linear shear current interaction

In this paper, the hydrodynamic performance of KCS (KRISO Container Ship) in the presence of a non-uniform shear current is investigated for the first time using high-fidelity CFD (Computational Fluid Dynamics) simulations. Various shear current strength conditions Frs with different directions were considered and results were compared to the ones with no shear current. The studies were conducted for the ship advancing at Fr = 0.26, 0.367. The focus is laid on the shear current effects on the ship resistance as well as the free surface elevation, pressure distribution, vortex structures, boundary layer, and nominal wake. Results showed that the presence of the shear current affects the hydrodynamic performance of the ship profoundly such that it increases/decreases the ship resistance in heading/following shear current with the largest change for the cases with the strongest shear current. The viscous resistance is dominant at Fr = 0.26 for all shear current conditions while the wave resistance is dominant for most cases at Fr = 0.367. The wave resistance reduces as the shear current direction varies from head to following shear current, similar to the theoretical model predictions. The viscous component follows a similar trend. The lateral resistance generated by the cross flow in beam shear current increases with the increase of Frs and the reduce of Fr and it is strongly dominated by the lateral pressure resistance. The Kelvin angle reduces in the head shear current and increases in the following shear current while the beam shear current reduces the Kelvin angle on the windward side of the ship and increases on the leeward side. The shear current also altered the transverse wavelength such that it increased in head shear current and reduced in following shear current. The predicted Kelvin angles and transverse wavelengths confirmed the finding of simplified theories on ship-shear current interaction. The presence of shear current also significantly affects the boundary layer, vortical structures, and the wake field.

Moiré Tuning of the Dynamic Behavior of a Twisted Bilayer van der Waals Material Resonator

Abstract Fully atomistic simulations and a sandwich plate model are used to study the dynamic behavior of twisted 3R-MoS2 bilayers. The simulations demonstrate that for a very small twist angle, the Moiré pattern leads to the symmetry breaking of the interlayer van der Waals energy on the scale of tens of nanometers and causes the dynamic behavior of twisted 3R-MoS2 bilayers to show strong position dependence. In particular, obvious mode pair splitting is observed in twisted 3R-MoS2 bilayer resonators where the interlayer van der Waals energy distribution is nonaxisymmetric. An analysis of the results of these molecular dynamic calculations shows that this behavior can be well explained using the sandwich plate model considering the nonuniform interlayer shear effect. Moreover, the twisted 3R-MoS2 bilayer relaxation mechanism involves the transition from AA stacking order with higher interlayer van der Waals potential energy to AB or BA stacking order, resulting in local buckling in the bilayers. The natural frequencies of resonators dominated by AA domains are much lower than those of resonators dominated by AB domains and even less than those of single-layer 3R-MoS2. Furthermore, as the radius increases, the frequency shows an abnormal trend, and a frequency gap is observed in the resonators dominated by AA domains.

Axial tensile test and design method of special-shaped rigid flange

Unlike the conventional flange with 90°-connecting angle, the new type of special-shaped rigid flange adopting non-90°-connecting angle can effectively reduce the joint region dimensions of steel tube connection in some conditions. Three special-shaped rigid flanges that adopt 45°, 60° and 75°-connecting angles were designed and tested under axial tensile load to investigate the mechanical characteristics and design method. The slip and open deformations occurred between two flange plates under axial tensile load, and the connecting bolts bore non-uniform tensile and shear forces along the bolt elliptical circle, which increase from the short axis to the long axis of elliptical flange plate. In addition, the nonlinear finite element model, whose accuracy was validated by the test results, were built to further inspect the bearing capacity and force-transfer mechanism. The results reveal that the bolt tensile forces are larger than the design values, and the corresponding modified factor was proposed. The stress developments of different fan-shaped sectors were analyzed, and the sectors located on the short axis are suggested to be selected for strength design of flange plate. The stiffener of these sectors has larger load allocation factor, and should be chosen for the strength design of stiffener weld lines. Lastly, the design method of special-shaped rigid flange under axial tensile load was provided, in which the combined tensile and shear forces should be considered for the connecting bolts and weld lines.

A 2D warping theory for shear deformable elastic beams of axisymmetric cross section in flexure

Shear deformable elastic beam models in flexure are considered in the hypothesis of cross section symmetric with respect to the flexure axis, whereby the external transverse forces act as distributed body forces. A 2D warping theory is presented where the shear-warping process is driven by a shear-warping parameter, say τ, 0≤τ≤1, in such a way that equilibrium between zero external (t(n)i=0) and internal (σ(n)i=0) tractions upon the lateral surface of the beam is complied with no matters the value of τ∈(0,1). On letting τ vary within (0,1), a continuous beam family, say B≔{Bτ:0≤τ≤1}, is generated, which spans from the Euler–Bernoulli (EB) beam model B0 at τ=0 (no shear strain, nor warping effects), to a series of shear deformable beam models Bτ up to τ=1. For intermediate values of τ, 0<τ<1, every beam model is featured by transversally nonuniform shear stresses accompanied by suitable 2D warping effects, while the boundary equilibrium condition with zero applied tractions is satisfied. The warping theory herein presented is an original generalization of a previous 1D type warping theory devised for rectangular cross sections. Applications are reported in which a circular cross section is considered and a beam problem in static conditions is worked out.

Symplectic analysis of thin-walled curved box girders with torsion, distortion and shear lag warping effects

Shear lag effect and torsional and distortional warping can significantly affect the performance of thin-walled curved box girders used in modern bridge engineering. The structural behaviour of these bridges exhibits complexity due to coupled bending and torsion together with warping effects of non-uniform torsion, distortion and shear lag. A practical method of analysis, based on the symplectic approach, with the same perspective as the Higher Order Beam Theories, is presented for overcoming the difficulties of numerical approaches via the Finite Element Method. In this paper, the Hamiltonian Structural Analysis method implements the analysis of the shear lag effect together with non-uniform torsion and distortion, for curved box girder bridges. The examples given can allow engineers to evaluate the effects of the negative shear lag phenomenon and the distribution of axial stresses in box slabs and webs, due to different warping effects, which strongly influence thin-walled box sections subjected to point loads and restrained areas.

Stress concentration effect on deflection and stress fields of a master leaf spring through domain decomposition and geometry updation technique

Abstract Theoretical and experimental large deflection and stress analysis of a master leaf spring considering stress concentration effect of clamping is reported. The non-uniformly curved master leaf spring under three point bending subjected to moving boundaries is modeled. Geometrically nonlinear strain-displacement relations, as necessary for the theoretical analysis, are derived through visualization of physics behind the large deformation problem. An embedded curvilinear coordinate system is considered, to study the combined effects of non-uniform curvature, bending, stretching and shear deformation including cross-sectional warping. Governing equation of the non-uniformly curved beam system is derived in variational form using energy method, based on linear material constitutive relations and the derived nonlinear kinematic relations. An iterative solution scheme through successive geometry updation is developed and executed in MATLAB® software to solve the governing equation involving strong geometric nonlinearity together with complicating moving boundary effect. Experimental deflection profiles under static loading are obtained through manual image processing technique using AutoCAD® software. Whereas, strain measurements are performed using strain gauges with data acquisition system (HBM-MX840B). Comparison between the theoretical and experimental results lead towards observation on stress concentration effect due to presence of geometric discontinuity in form of a small hole in the physical system. A modified formulation is proposed using domain decomposition method incorporating effect of geometric discontinuity through an equivalent curved beam geometry of variable cross-section. The modified theoretical model is validated successfully with the experimental results, and observations on stress characteristics and effect of hole diameter to beam width ratio are made.

Self-diffusion of spherocylindrical particles flowing under non-uniform shear rate.

This work is devoted to study numerically the self-diffusion of spherocylindrical particles flowing down an inclined plane, using the discrete element method (DEM). This system is challenging due to particles being non-spherical and because they are subjected to a non-uniform shear rate. We performed simulations for several aspect ratios and inclination angles, tracking individual particle trajectories. Using the simulation data, we computed the diffusion coefficients D, and a coarse-graining methodology allowed accessing the shear rate spatial profiles (z). This data enabled us to identify the spatial regions where the diffusivity strongly correlates with the local shear rate. Introducing an effective particle size d⊥, we proposed a well-rationalized scaling law between D and . Our findings also identified specific locations where the diffusivity does not correlate with the shear rate. This observation corresponds to zones where  has non-linear spatial variation, and the velocity probability density distributions exhibit asymmetric shapes.

Modelling of stress transfer in root-reinforced soils informed by four-dimensional X-ray computed tomography and digital volume correlation data.

Vegetation enhances soil shearing resistance through water uptake and root reinforcement. Analytical models for soils reinforced with roots rely on input parameters that are difficult to measure, leading to widely varying predictions of behaviour. The opaque heterogeneous nature of rooted soils results in complex soil–root interaction mechanisms that cannot easily be quantified. The authors measured, for the first time, the shear resistance and deformations of fallow, willow-rooted and gorse-rooted soils during direct shear using X-ray computed tomography and digital volume correlation. Both species caused an increase in shear zone thickness, both initially and as shear progressed. Shear zone thickness peaked at up to 35 mm, often close to the thickest roots and towards the centre of the column. Root extension during shear was 10–30% less than the tri-linear root profile assumed in a Waldron-type model, owing to root curvature. Root analogues used to explore the root–soil interface behaviour suggested that root lateral branches play an important role in anchoring the roots. The Waldron-type model was modified to incorporate non-uniform shear zone thickness and growth, and accurately predicted the observed, up to sevenfold, increase in shear resistance of root-reinforced soil.

Mechanics of self-rotating double-disc grinding process

Unlike most double-disc grinding processes, which use forced workpiece rotation, some double-disc processes rely on workpiece self-rotation driven by non-uniform shear forces resulting from partial wheel-workpiece coverage. This self-rotation is poorly understood, with workpiece angular frequency remaining unknown despite its importance. This paper investigates the kinematics of self-rotation via analytical modelling of the moment-equilibrium conditions, derived from experimentally determined specific-energy values. The model showed that workpiece coverage ratio is the dominant factor governing workpiece angular frequency, allowing for the choice of optimal workpiece coverage ratios that avoid (i) workpiece-stoppage and (ii) excessive frictional heat generation. The predicted velocity was validated with acoustic-emission measurements.

Specific Dissipated Energy as a Failure Predictor for Uniform Sands under Constant Volume Cyclic Simple Shear Loading

An experimental study was performed to investigate the dissipated energy to failure of sand samples subjected to uniform and non-uniform cyclic simple shear loading. The hypothesis evaluated was that for a given initial sample state the specific dissipated energy required to reach failure should be reasonably constant independent of the type of stress-time history used in the testing. Test samples consisted of dry Ottawa sand prepared at nine different initial states that were subjected to different stress controlled cyclic horizontal shear loading waveforms that included 15 uniform sinusoidal waves and up to 33 non-uniform loading wave forms. The experimental program presented showed that the measured cumulative dissipated specific energy to failure, defined when the double amplitude shear strain reaches 7.5%, for the different sample initial states was reasonably constant but with coefficients of variation ranging between 13 to 44%. As expected, the cumulative dissipated energy increased with increasing initial stress level and relative density. The findings support the notion that specific dissipated energy can be used as a reasonable failure predictor for uniform dry sands based on their initial state and are independent of the type of cyclic simple shear loading waveform using in the testing.

Exact Solutions to the Navier–Stokes Equations with Couple Stresses

This article discusses the possibility of using the Lin–Sidorov–Aristov class of exact solutions and its modifications to describe the flows of a fluid with microstructure (with couple stresses). The presence of couple shear stresses is a consequence of taking into account the rotational degrees of freedom for an elementary volume of a micropolar liquid. Thus, the Cauchy stress tensor is not symmetric. The article presents exact solutions for describing unidirectional (layered), shear and three-dimensional flows of a micropolar viscous incompressible fluid. New statements of boundary value problems are formulated to describe generalized classical Couette, Stokes and Poiseuille flows. These flows are created by non-uniform shear stresses and velocities. A study of isobaric shear flows of a micropolar viscous incompressible fluid is presented. Isobaric shear flows are described by an overdetermined system of nonlinear partial differential equations (system of Navier–Stokes equations and incompressibility equation). A condition for the solvability of the overdetermined system of equations is provided. A class of nontrivial solutions of an overdetermined system of partial differential equations for describing isobaric fluid flows is constructed. The exact solutions announced in this article are described by polynomials with respect to two coordinates. The coefficients of the polynomials depend on the third coordinate and time.

Free vibration of functionally graded graphene platelet reinforced plates: A quasi 3D shear and normal deformable plate model

Present article deals with the free vibration response of composite plates which are reinforced with graphene platelets (GPLs). Each layer of the composite media may have different amount of graphene platelets which leads to a functionally graded (FG) pattern. Elastic modulus of the reinforced composite (RC) is evaluated based on the Halpin-Tsai model which captures the dimensions of the reinforcement. Following a quasi-3D plate model which captures the thickness stretching effects and non-uniform shear strains through the thickness, the complete set of governing equations dealing with free vibration response of the plate are obtained. These equations are six in number since the adopted plate theory has six unknowns. With the aid of the Navier solution suitable for plates with all edges simply supported, Fourier expansions are implemented for the essential variables of the displacement field. Closed form expressions are given to obtain the natural frequencies of FG-GPLRC plates. Present results may be valid for arbitrary thick plates. Results of the present study are compared with the available data in the open literature. After that novel results are given to obtain the frequencies of FG-GPLRC plates with arbitrary thickness. It is shown thatthe adopted theory accurately estimates the frequencies of FG-GPLRC plates.

Effects of low-temperature neutron irradiation on the microstructure and tensile properties of duplex 2304 stainless steel and its electron-beam welds

A lean duplex stainless steel material (2304-grade) in its base metal and electron beam (e-beam) welded conditions were studied microstructurally and mechanically as a function of irradiation conditions to evaluate its use as a structural material at low temperatures (60–100 °C). Neutron irradiation up to a fluence of 1.40 × 1019 n/cm2 (E > 0.1 MeV) or ~0.011 dpa decreased the total elongation of both base metal and e-beam welded samples. Overall, radiation hardening was observed in all the samples. The transversely cut irradiated samples showed some nonuniform quasi-cleavage and shearing in their fracture surfaces, indicating the variance of ductile nature of the two-phased (deformable austenite and harder ferrite) duplex structure. The e-beam welded samples also showed quasi-cleavage fracture, which is a characteristic of radiation-induced embrittlement. These observations of the e-beam welded samples were attributed to the formation of coarse ferrites, grain boundary and intragranular phases such as γ2 and γ3, and minor impurity phases such as CrN and Cr2N in the weld pool and/or heat-affected zone of the samples. Radiation-induced elemental segregation was also identified in the post-irradiated base metal.

KLF2 Mediates the Suppressive Effect of Laminar Flow on Vascular Calcification by Inhibiting Endothelial BMP/SMAD1/5 Signaling.

[Figure: see text].

Numerical investigation into I-shape brace connections of conventional concentrically braced frames

In many low and moderate seismic regions, a low-ductility concentrically braced frame (CBF) is used as the seismic force resisting system for steel structures. The design of such CBFs is straightforward: all members and connections are designed based on the seismic force demand obtained through linear elastic structural analysis; capacity-based design and additional seismic detailing are not required. There is no designated energy-dissipating fuse in the lateral load-carrying path. Such CBFs are referred to as Conventional CBFs (CCBFs) in this study. In CCBFs, the brace-to-gusset connections are inherently weaker in tension than the adjoining gusset plates and braces. This occurs because both the gusset plates and the braces are selected on the basis of their respective compressive buckling resistances, and hence, typically have a much greater resistance in tension. Described herein is a numerical study of the popular flange plate bolted I-shape brace connection configuration. A high-fidelity finite element (FE) simulation procedure was developed and validated against laboratory test results. The resulting numerical models were created with the objective of improving our understanding of the inelastic response of these brace connections. The force transfer mechanism within the two branches of the connection was characterized. Significant nonuniform shear distribution was found to exist within the bolt group in the flange branch, which may be detrimental to the safe functioning of these bolts in the seismic design context. The loading eccentricity on the weld group was quantified. Recommendations on how to avoid brittle bolt shear rupture and premature weld fracture are proposed.

Cyclic behavior of sand under non-uniform shear stress waves

During an earthquake, soil deposits are often subjected to complex stress/strain time histories that are quite different from the simplified ones used in laboratory tests for evaluation of the stress-strain-strength of these soils. To mimic the stress/strain time histories experienced at different depths of a mildly sloping soil deposit, a series of direct simple shear tests were conducted on Ottawa F65 sand specimens. The trends observed in these experiments were then used to estimate the lateral spreading of mildly sloping saturated deposits of the same sand subjected to various base motion time histories measured in the centrifuge tests conducted as part of an international research project (Liquefaction Experiment and Analysis Project, LEAP-2015 and LEAP-2017).In each CDSS test, after imposing the initial stress state, the specimen was subjected to non-uniform stress waves that resembled the shear stress time histories likely to develop in the LEAP-2015 and LEAP-2017 centrifuge specimens. A total of 17 CDSS tests were performed on specimens with relative densities of approximately 66%. Initial vertical and shear stresses were imposed on each soil specimen to correspond to the state of stress in a mildly sloping soil layer at two depths of about 4 m and 3 m. A ramped sinusoidal shear stress wave similar to the ramped sinusoidal base motion used in the LEAP centrifuge experiments was employed. The test results displayed a consistent trend between the peak cyclic stress ratio and the permanent shear strain that developed in the soil. The effects of overburden stress on the magnitude of permanent deformations were observed. Smaller initial vertical stress resulted in a more dilative response and smaller permanent shear strain. The observed permanent shear strain vs. peak cyclic stress ratio curves were then used to predict the lateral spreading of mildly sloping deposits tested in the LEAP-2015 and LEAP-2017 centrifuge experiments. Reasonably close correlation between the predicted and measured displacements were obtained. The developed dataset, made publicly available on DesignSafe-CI, can be used for calibration, evaluation, and further development of constitutive models for liquefiable soils.

Shear-driven density segregation: an experimental study

Granular materials can segregate spontaneously due to differences in particle properties when subjected to vibrations, shear strain or because of the equipment geometries. Although the difference in particle size is the most critical factor that drives segregation, the effects of large density difference may also be detrimental for a lot of industries. In this work, we experimentally investigate density-driven segregation in bi-disperse mixtures of particles having the same size but different density when subjected to non-uniform shear rates. We found that the features of the segregation process are related to the density ratio as well as to the dimensionless loaded mass. The experimental outcomes are then compared with the solution of a simple density-driven segregation model. The model can successfully capture the main features of segregation driven by density for a range of density ratios.

Numerical Simulation of the Shear Behaviour of Cement Grout

Cement grout is widely used in civil engineering and mining engineering. The shear behaviour of the cement grout plays an important role in determining the stability of the systems. To better understand the shear behaviour of the cement grout, numerical direct shear tests were conducted. Cylindrical cement grout samples with two different strengths were created and simulated. The numerical results were compared and validated with experimental results. It was found that, in the direct shear process, although the applied normal stress was constant, the normal stress on the contacted shear failure plane was variable. Before the shear strength point, the normal stress increased slightly. Then, it decreased gradually. Moreover, there was a nonuniform distribution of the normal stress on the contacted shear failure plane. This nonuniform distribution was more apparent when the shear displacement reached the shear strength point. Additionally, there was a shear stress distribution on the contacted shear failure plane. However, at the beginning of the direct shear test, the relative difference of the shear stresses was quite small. In this stage, the shear stress distribution can be assumed uniform on the contacted shear failure plane. However, once the shear displacement increased to around the shear strength point, the relative difference of the shear stresses was obvious. In this stage, there was an apparent nonuniform shear stress distribution on the contacted shear failure plane.

Concrete Floor with GFRP-Embedded I-Beams and Stay-in-Place Structural Forms

This paper introduces a new concrete floor concept comprising embedded glass fiber-reinforced polymer (GFRP) I-beams and GFRP stay-in-place (SIP) structural forms spanning between the lower flanges of the I-beams. The forms are flat plates with T-up ribs. The flexural behavior in the direction transverse to the I-beams, which is more critical because of the bonded connection between SIP forms and I-beam, is investigated using 2,575 × 610 × 225 mm slab segments. Both connection tests and member tests were conducted. Different SIP forms, concrete thicknesses, and surface treatments were explored. Both adhesive bonding and mechanical fasteners were explored for the connection. Also, behavior in the negative moment regions of the floor was simulated by testing the specimen inverted. The connection with adhesive and mechanical fasteners failed at a 48% higher bending than that with adhesive only. Increasing GFRP form size (reinforcement ratio) increased stiffness but not strength, neither for the connection nor for the member, due to debonding failure modes. A case study of a floor design was presented and showed that adhesively bonded connections met the strength requirement. A design-oriented analytical model was developed to predict connection strength based on bond failure. It accounts for the nonuniform shear and peeling stresses and includes corrections for the imbalance between the SIP form and the I-beam flange, as well as the additional peeling due to bending in the SIP form.