Shear Axis Research Articles

A high sensitivity, low cost and fully decoupled multi-axis capacitive tactile force sensor for robotic surgical systems.

This paper presents the design of a multi-axis capacitive tactile force sensor with a fully decoupled output response for input normal and shear forces. A patterned elastomer is used as a dielectric layer between capacitive electrodes of the sensor that allows to achieve relatively higher sensitivity. The sensor is fabricated utilizing a low-cost rapid prototyping technique and is characterized for normal and shear forces in the range of 0 ~ 10 N and 0 ~ 3.1 N respectively. The achieved force sensitivity for the normal axis is 2.03%/N and for shear axes is 1.67%/N. The difference between the estimated force from the sensor and actual force applied is negligible, which demonstrates the accuracy of the sensor. The reliability of the sensor is analysed by performing hysteresis and repeatability tests. The hysteresis error is found to be 4.94% and 4.69% for normal and shear forces respectively. The repeatability error of the sensor is less than 5%, which shows the stability of the sensor. The high sensitivity, linear output response, high force measurement range, reliability and low cost make the proposed tactile sensor suitable for the force feedback in the robotic surgical systems.

Inertial and elastic properties of general composite beams

Slender composite structures can be modeled using engineering beam models with properties computed using a cross-sectional analysis program, such as VABS. These properties are given in terms of the mass matrix, stiffness matrix, and compliance matrix in a general coordinate system. The invariance of strain energy and kinetic energy is employed to rigorously transform sectional properties into different coordinate systems with parallel shifts and rotations. Additionally, the computation of commonly used inertial properties (mass center, principal inertial axes, and mass moments of inertia) from the mass matrix, and commonly used elastic properties (extension stiffness, bending stiffness, torsion stiffness, tension center, shear center, principal bending axes, principal shear axes, etc.) from the compliance matrix, is elucidated. The elastic properties are given for both the Timoshenko model and the Euler–Bernoulli model. The definitions for shear center and twist center are clarified and consistently generalized for composite beams. Isotropic homogeneous beams are used to illustrate how to relate commonly used engineering beam properties with the compliance matrix and the stiffness matrix for composite beams. Finally, engineering beam properties necessary for general-purpose aeromechanical analysis programs such as CAMRAD II are derived from the properties computed by VABS.

Viscous tweezers: Controlling particles with viscosity

Control of particle motion is generally achieved by applying an external field that acts directly on each particle. Here, we propose a global way to manipulate the motion of a particle by dynamically changing the properties of the fluid in which it is immersed. We exemplify this principle by considering a small particle sinking in an anisotropic fluid whose viscosity depends on the shear axis. In the Stokes regime, the motion of an immersed object is fully determined by the viscosity of the fluid through the mobility matrix, which we explicitly compute for a pushpin-shaped particle. Rather than falling upright under the force of gravity, as in an isotropic fluid, the pushpin tilts to the side, sedimenting at an angle determined by the viscosity anisotropy axis. By changing this axis, we demonstrate control over the pushpin orientation as it sinks, even in the presence of noise, using a closed feedback loop. This strategy to control particle motion, that we dub viscous tweezers, could be experimentally realized in systems ranging from polyatomic fluids under external fields to chiral active fluids of spinning particles by suitably changing their direction of global alignment or anisotropy. Published by the American Physical Society 2024

Numerical investigation study on tensile-shear failure behavior of rock bolts in inclined strata mining tunnels

In response to the problem of severe deformation and failure of the surrounding rock of the mining tunnels in inclined strata, a tensile-shear failure numerical model of rock bolts was adopted to analyze the rock bolts failure behavior and the surrounding rock mechanical response, and explore the influence of different factors on rock bolts failure. The results indicate that: (1) As angle between the rock bolt and the interface decreases, the shear force of increases, and the rock bolt is easier to fracture. The maximum displacement is 250.2 mm of fractured position. A new evaluation index of shear axis ratio was proposed. The larger the shear axis ratio, the rock bolt is easier to fracture. The shear axis ratio at the interface has increased by 95 % compared to the non interface. (2) The plastic zone and the surrounding rock deformation exhibit the same inclination trend as the strata. In final state, the maximum deformation is 297.7 mm at the bottom and top position perpendicular to the rock bolts at the interface. At the moment of rock bolts fracture, the interface displacement of surrounding rock immediately increased by about 10 mm. And the stress in the surrounding rock decreased about 1 MPa. The weakening effect of surrounding rock stress shifts with the change of rock bolt fracture position. The stress at the arch waist decreases by 44 %, the stress at the arch crown decreases by 25 %. When the fracture of the rock bolts at the arch crown and arch waist ends, the stress at the side wall begin to decrease by 40 %. (3) As the inclination angle increases, the deformation of the surrounding rock and the number of rock bolt failures increase. The range of the plastic zone in the surrounding rock gradually increases, and the degree of rock bolts asymmetric fracture more aggravated. As the diameter of the rock bolt increases, the fractured number of the rock bolts and range of plastic zone decreases.

Touch, press and stroke: a soft capacitive sensor skin

Soft sensors that can discriminate shear and normal force could help provide machines the fine control desirable for safe and effective physical interactions with people. A capacitive sensor is made for this purpose, composed of patterned elastomer and containing both fixed and sliding pillars that allow the sensor to deform and buckle, much like skin itself. The sensor differentiates between simultaneously applied normal force and shear using summation and differences of signals from four deformable capacitors. Cross talk from shear to normal force is less than 2.5%, and between shear axes is less than 10%. Normal and shear stress sensitivity is 0.49 kPa and 0.31 kPa respectively, with a minimum displacement resolution of 40 μm. In addition, finger proximity is detectable at a range of up to 15 mm. The operation is demonstrated on a simple gripper holding a cup. The combination of features and the straightforward fabrication method make this sensor a candidate for implementation as a sensing skin for humanoid robotics applications.

Anomalous tumbling of colloidal ellipsoids in Poiseuille flows.

Shear flows cause aspherical colloidal particles to tumble so that their orientations trace out complex trajectories known as Jeffery orbits. The Jeffery orbit of a prolate ellipsoid is predicted to align the particle's principal axis preferentially in the plane transverse to the axis of shear. Holographic microscopy measurements reveal instead that colloidal ellipsoids' trajectories in Poiseuille flows strongly favor an orientation inclined by roughly π/8 relative to this plane. This anomalous observation is consistent with at least two previous reports of colloidal rods and dimers of colloidal spheres in Poiseuille flow and therefore appears to be a generic, yet unexplained feature of colloidal transport at low Reynolds numbers.

A high sensitivity and multi-axis fringing electric field based capacitive tactile force sensor for robot assisted surgery

This paper presents a design of multi-axis tactile force sensor using the fringe effect of an electric field between stationary patterned electrodes. The unique configuration of the electrodes consisting of four separate square-shaped sensing electrodes, with each encircled by excitation electrodes, allows to achieve enhanced fringe field effect and hence sensitivity. The proposed sensor can decouple the normal, shear and angular shear applied forces. The sensor is fabricated using low-cost rapid prototyping techniques with flexible Ecoflex 00–30 and silicone rubber RTV-528 as the elastomers for contact with the environment. An analytical model is developed that correlates the nominal capacitance of the sensor with that of the geometric dimensions of the stationary electrodes and air cavity height between the electrodes and elastomer. The force measurement ranges in the normal, shear, and angular axis are 5 N, 1.5 N, and 1 N respectively. The sensor shows a perfectly linear response, repeatability, and a low hysteresis error, thermal stability and robustness to the environmental interferences that makes it suitable to be used for force feedback in minimally invasive robotic surgery.

Optimization matrix method for the determination of the real torsion axis orientation angle

The vertical axis of a multi-story building, at which the rigidity centers of the floors are aligned, is called real torsion axis. In particular, the real torsion axis is characterized as bending; twist; and shear axis, as well. If the local axes of the vertical structural elements are not aligned with the axes X and Y of the global orthogonal coordinate system (O,X,Y,Z), the principal horizontal axes, I and II of the coordinate system defined at the real torsion axis, present an angle, ao, which is usually determined according to axis X. The principal vertical axis III coincides with Z axis. The present paper proposes a new method for the determination of the orientation angle of the real torsion axis. The method refers to single-story and special classes of multi-story buildings, which possess a real torsion axis, in contrast with the majority of the multi-story buildings, at which an optimum torsion axis is usually sought. Firstly, the stiffness matrix of the building is determined at the location of the real torsion axis. Secondly, the rotation matrix around the vertical axis is determined and the rotated stiffness matrix is determined, as well. Three new criterions are proposed in order to define the critical rotation angle, at which the rotated stiffness matrix receives a diagonal form, and therefore, the critical angle defines the orientation of the two principal bending planes I,III and II,III. The optimization matrix method can be easily implemented in any programming language. Numerical examples are presented. Their results satisfy the three characteristic axis properties of the real torsion axis and are in complete agreement with the results of other researchers.

Transverse deformation zonality values and palinspastic reconstructions of Carpathians on the base of structural analysis of folding

On the basis of the structural analysis of folds the complex deformation profile in the Hust—Ivano-Frankivsk (central part of Ukrainian Carpathians) transsection is constructed. It characterises distribution of non-coaxial flow deformation on a spectrum of parameters: angles of an axis of compression and simple shear, sizes of horizontal compression and deformational ellipses. Horizontal shortening shows a series of peaks over more or less levelled general background of double compression. The most intensive deformation, expressed in the maximum sizes of horizontal and general compression (to 4 times), is dated for area of Internal Nappes (basically the Dukljansky zone) and to the termination of the Krosnensky zone. There are also indications on growth of deformation in back of Internal Nappes and in front of Skibovaya zone. Deformation as a whole goes down to the central part of a profile occupied by Krosnensky zone where conditions of almost horizontal main compression are marked also. Reconstruction of the primary sizes of structural zones along of Hust—Ivano-Frankivsk profile in the interval of Porkuletsky—Skibovoj zones as a result of returning in a initial condition before deformation of non-coaxial flow has increased in 2.4 times, having reached 183 km that it is necessary to consider as the bottom estimation of initial width which should be increased at the expense of components of bend folding. Possibilities which are given by model of non-coaxial flow for reconstruction on the scale of full deep crossing of Carpathians are short estimated for what approach of homogeneous deformation on depth has been used: 2-time size of horizontal reduction, and also angle of an axis of compression 20є are accepted as averages. Obtained contours of the Krosnensky zone of profile DOBRE-3 shows convergence with results of application of a method of the balanced cross-sections.

A model of hard-magnetic soft curved beams at large deformation

<p indent="0mm">Magnetic-activated soft materials have shown their considerable advantages such as quick response, remote and reversible control, and programmable shape-shifting, making them promising in functional designs of bionic robots, bionic sensors, grippers, valves and metamaterials. Magnetoactive elastomers (MAEs) (also referred to as magnetic polymer composites (MPCs) or magnetorheological elastomers) are a kind of soft active composites that can respond to magnetic field excitation, which are generally composed of micrometer-scale magnetizable particles (e.g., NdFeB particles) embedded in a soft matrix (e.g., silica gel, hydrogel and shape memory polymer). The matrix acts as a continuum medium transmitting the internal force, while the magnetic particles have the interaction among themselves and with the external magnetic field. Compared with soft magnetic materials which are difficult to achieve robust programming, hard-magnetic materials hold residual magnetic flux density vector that does not change with the external magnetic field. After saturation of magnetization, the interaction with the external magnetic field produces micro torque, and programming the micro torque distribution generated by hard-magnetic particles can further form complex shapes. Owing to the intricate interplay between inherent electromagnetic coupling and geometric nonlinearity, it is still a challenge to model and predict the mechanical behaviors of hard-magnetic soft materials. Most of existing models of hard-magnetic elastomers are based on the assumption that the remanence direction is along the axis, which limits the diversification degree of deformation to some extent. In addition, most hard-magnetic beam models are based on Euler-Bernoulli hypothesis (normal remains normal) by neglecting shear deformations. When the beam becomes thick, the effect of shear deformation may turn out to be significant and cannot be ignored. Here, we develop a nonlinear curved beam model to predict large deformations of hard-magnetic soft elastica. The model follows Timoshenko’s first-order shear deformation theory, by accounting for axis elongation and the constitutive law of hard-magnetic elastomers. A set of ordinary differential governing equations containing seven basic unknowns are deduced theoretically. The model can thus describe shear deformation, axis elongation and curvature change of hard-magnetic soft beams upon large deformation. Combined with boundary conditions, the model can be efficiently solved by using shooting methods. In order to verify the accuracy of our hard-magnetic soft beam model, we compare it with the experiments, finite element simulations, and the Euler-Bernoulli hypothesis-based beam model in the literature, for different directions of applied magnetic field. The results verify and highlight the accuracy and universality of our hard-magnetic soft curved beam model which has higher accuracy and wider application range (applicable to thick beams, thin beams and curved beams) compared to the hard-magnetic thin beam model based on Euler-Bernoulli hypothesis (only considering bending deformations). Besides, we explore the bending and buckling deformations of hard-magnetic soft beams with different length-thickness ratios, under different applied magnetic fields. We reveal that the decrease of length-thickness ratio and of applied magnetic fields can enhance shear effects on deformations of hard-magnetic soft beams. Our model could be used not only to analyze geometrically nonlinear behaviors of hard-magnetic elastomers, but also to guide rational designs of ferromagnetic slender structures and soft continuum robots.

On the generalized Clausen problem

AbstractWe analyze the classical problem of finding the shape of the column that optimizes certain criteria. The new formulation proposed here may be stated as: given the critical buckling load F of the column and the length L, find cross‐sectional area A, such that the volume W of the column attains minimal value. This is a classical Clausen problem. However, in this work we shall use the generalized constitutive equations of the column that allows for shear deformation and axis compressibility. This, as well as the novel use of the first integral, are the main novelties of our work. We will formulate a nonlinear boundary value problem for post critical deformation of optimally shaped rod. Finally we show that optimally shaped rod exhibits pitchfork supercritical bifurcation at critical buckling load.

Variable shearing holography with applications to phase imaging and metrology

We report variable shear interferometers employing liquid-crystal-based geometric-phase (GP) gratings. Conventional grating-based shear interferometers require two lateral shifts of the gratings to enable phase-shifting capabilities in x- and y- direction and two axial shifts of the gratings to adjust the shear amount in x- and y- direction, i.e., these systems need control of four axes mechanically. Here we show that the GP gratings combined with a pixelated polarization camera give instantaneous-phase shifting so that no mechanical movement is necessary to obtain phase shifts. Furthermore, we show that a single fixed shear with a rotational shear axis provides a more robust selection of shears while requiring the control of only one mechanical axis. We verify this statement using spatial domain and frequency domain criteria. We further show that the resolution of the reconstructed wavefield depends not only on the numerical aperture of the imaging system, the pixel size of the detector, or the spatial coherence of the source but also on the ability to determine the shear amount accurately. To improve this, we report a methodology to accurately detect the shear amounts using the second derivative of the autocorrelation function of the measured holograms, which further relaxes the requirements on mechanical stability.

Brownian systems perturbed by mild shear: comparing response relations

We present a comprehensive study of the linear response of interacting underdamped Brownian particles to simple shear flow. We collect six different routes for computing the response, two of which are based on the symmetry of the considered system and observable with respect to the shear axes. We include the extension of the Green–Kubo relation to underdamped cases, which shows two unexpected additional terms. These six computational methods are applied to investigate the relaxation of the response towards the steady state for different observables, where interesting effects due to interactions and a finite particle mass are observed. Moreover, we compare the different response relations in terms of their statistical efficiency, identifying their relative demand on experimental measurement time or computational resources in computer simulations. Finally, several measures of breakdown of linear response theory for larger shear rates are discussed.

Design formulas for channels subject to combined compression, shear and major axis bending

In this work, analytical formulas are presented for channel design subject to multiple load combinations. Common design procedures found in the North American and Eurocode ignore the rotational and lateral restraints. Furthermore, limited design rules are available to predict buckling of channels subject to combination of compression, shear and major axis bending. The proposed formulas account for rotational and lateral restraints and result in significant weight reduction. Comparisons are made with other numerical procedures to confirm accuracy and suitability of the proposed expressions to use in practice. Influence of channel parameters on buckling behaviour of cold form steel (CFS) channels is also highlighted. It is shown that shear buckling stress (τcr) decreases by increasing (h/b) ratio. The difference in (Δτcr) reaches 14% for (h/D) = 25. Furthermore, much of the decrease in (τcr) values occurs for (h/b) between 2 and 4. It is also shown that a decrease in (τcr) up to 18.2% is attained by fully restraining the web edges against lateral movement.

On the banded texture and nematic elasticity in a thermotropic liquid crystalline polymer. In situ optical microscopy and light scattering

Optical banded texture after cessation of shear was investigated in a semi‐flexible thermotropic liquid crystalline polymer (LCP) by in situ polarized optical microscopy (POM) and small‐angle light scattering (SALS). The LCP is a random copolymer consisting of mesogenic units separated by alkyl spacers. The quiescent state of the nematic phase exhibited a polydomain texture, with microdomains randomly oriented. Upon application of shear the texture aligned along the shear axis. In situ X‐ray scattering demonstrated that the texture alignment corresponded to macromolecular alignment along the shear axis. Above certain shear rate the aligned texture relaxed and produced a banded texture upon cessation of shear. Shearing at higher shear rate further aligned the texture to produce a monodomain. Stopping the shear spatially uncorrelated structures orthogonal to the shear direction were developed with incubation time in the 100 seconds of second. Hence, there is a threshold of texture alignment to produce banded texture. Shear rheometry showed that the liquid crystalline phase is viscoelastic with features akin to entangled linear polymer melts, for example, a minimum in mechanical damping tan δ [=G”/G']. Furthermore, the nematic phase exhibited considerable recoverable strain after creep. The elastic recoil after cessation of flow would be responsible to produce banded texture. Increasing the creep time reduced the recoverable strain, correlating with longer time to produced banded texture. In contrast, wholly aromatic LCPs exhibit much shorter recovery times after creep and shorter incubation time for banded texture formation.

Isogeometric free vibration of sector cylindrical shells with carbon nanotubes reinforced and functionally graded materials

An isogeometric numerical procedure based on non-uniform rational B-splines is applied to solve the free vibration of carbon nanotubes reinforced and functionally graded material sector cylindrical shells. A typical isogeometric analysis cylindrical shell element is introduced to transform curvilinear domain to parametric domain. The effects of the shear deformation, rotary inertia and axis extensibility are taken into consideration. The material properties are estimated by a mixture rule and effective carbon nanotube parameters. The weak form is derived in detail by applying virtual principle. The novelty of this paper is to use the isogeometric finite element method to analyze the dynamic behaviors of sector cylindrical shells with functionally graded material and four types of carbon nanotubes distributed material. By numerical examples, the convergence and accuracy of the current method are validated. Then, a series of natural frequencies and mode shapes are presented to serve as benchmark solutions in future researches. Moreover, the effects of boundary conditions, geometric proprieties as well as material parameters on the frequencies of the carbon nanotubes reinforced and functionally graded material sector cylindrical shells are examined.

Complex dynamics of long, flexible fibers in shear

The macroscopic properties of polymeric fluids are inherited from the material properties of the fibers embedded in the solvent. The behavior of such passive fibers in flow has been of interest in a wide range of systems, including cellular mechanics, nutrient acquisition by diatom chains in the ocean, and industrial applications such as paper manufacturing. The rotational dynamics and shape evolution of fibers in shear depends upon the slenderness of the fiber and the non-dimensional “elasto-viscous” number that measures the ratio of the fluid’s viscous forces to the fiber’s elastic forces. For a small elasto-viscous number, the nearly-rigid fiber rotates in the shear, but when the elasto-viscous number reaches a threshold, buckling occurs. For even larger elasto-viscous numbers, there is a transition to a “snaking behavior” where the fiber remains aligned with the shear axis, but its ends curl in, in opposite directions. These experimentally-observed behaviors have recently been characterized computationally using slender-body theory and immersed boundary computations. However, classical experiments with nylon fibers and recent experiments with actin filaments have demonstrated that for even larger elasto-viscous numbers, multiple buckling sites and coiling can occur. Using a regularized Stokeslet framework coupled with a kernel independent fast multipole method, we present simulations that capture these complex fiber dynamics.

NOVEL STARCH BASED THICKENERS FOR COTTON PRINTING USING VAT DYES

Formic acid was reacted with different kinds of starch to yield O-Formate derivatives. Starches used included corn starch, rice starch, and oxidized corn starch. Thus obtained O-formates derivatives were submitted to assessment for acyl content, the degree of substitution (D.S), solubility and rheological characteristics. The highest%acyl and DS value were obtained with cornstarch and the least values with rice starch while oxidized corn starch stood in Mid-way position. All these starch formate derivatives displayed non-Newtonian thixotropy. Nevertheless, the degree of thixotropy and situation of the rheogram with respect to the rate of shear axis were determined by both natures of the starch before derivatization and storing the time of the paste. The degree of derivatization of starch via O-Formylation expressed as D.S., was a governing factor for the apparent viscosity of the pastes. Color strength (K/S) and fastness of cotton printed using the starch derivatives in question were very comparable, if not higher than those obtained with the conventional British gum thickener. This was observed irrespective of the D.S. of the formate derivatives of starch and time of printing paste storing and advocated current thickeners as good substitutes for conventional printing thickeners.

Experimental and Numerical Study of the Failure Behavior of Intermittent Rock Joints Subjected to Direct Shear Load

Two series of intermittent rock joints containing three joints arranged along the central shear axis were considered in this study. The failure behavior under direct shear loads was investigated by means of both physical tests and numerical simulations. The cracking behavior was found to be distinctly associated with the joint arrangement. Several types of main and secondary cracks were identified. The variation trends of the crack initiation stress ratio with inclination angle were analyzed and found to be partly different for the two series of intermittent joints. The whole fracturing process was characterized by three phases. Not all samples have to experience all three phases. The second phase is alternative and can be reflected by the shearing curve. Hence, two types of shearing curves, including single and double peaks, were identified. The double peak is due to the extrusion or sawteeth cutting in the second phase. Moreover, the numerical micromechanical analysis was performed to explain the shear behavior using the contact force and microcrack within the specimen. Based on the numerically measured local stresses, maximum and minimum principal stresses around the middle joint at crack initiation stress and peak shear stress were analyzed.

Extremely Small Sizes for Faint z ∼ 2–8 Galaxies in the Hubble Frontier Fields: A Key Input for Establishing Their Volume Density and UV Emissivity

Abstract We provide the first observational constraints on the sizes of the faintest galaxies lensed by the Hubble Frontier Fields (HFF) clusters. Ionizing radiation from faint galaxies likely drives cosmic reionization, and the HFF initiative provides a key opportunity to find such galaxies. However, we cannot assess their ionizing emissivity without a robust measurement of their sizes, since this is key to quantifying both their prevalence and the faint-end slope to the UV luminosity function. Here we provide the first size constraints with two new techniques. The first utilizes the fact that the detectability of highly magnified galaxies as a function of shear is very dependent on a galaxy’s size. Only the most compact galaxies remain detectable in high-shear regions (versus a larger detectable size range for low shear), a phenomenon we quantify using simulations. Remarkably, however, no correlation is found between the surface density of faint galaxies and the predicted shear, using 87 high-magnification ( –100) –8 galaxies seen behind the first four HFF clusters. This can only be the case if faint ( mag) galaxies have significantly smaller sizes than more luminous galaxies, i.e., mas or 160–240 pc. As a second size probe, we rotate and stack 26 faint high-magnification sources along the major shear axis. Less elongation is found even for objects with an intrinsic half-light radius of 10 mas. Together, these results indicate that extremely faint –8 galaxies have near point-source profiles (half-light radii &lt;30 mas and perhaps 5–10 mas). These results suggest smaller completeness corrections and hence shallower faint-end slopes for the –8 LFs than derived in some recent studies (by –0.3).