Partial Slippage Research Articles

Biomechanics of the finger pad in response to torsion.

Surface skin deformation of the finger pad during partial slippage at finger-object interfaces elicits firing of the tactile sensory afferents. A torque around the contact normal is often present during object manipulation, which can cause partial rotational slippage. Until now, studies of surface skin deformation have used stimuli sliding rectilinearly and tangentially to the skin. Here, we study surface skin dynamics under pure torsion of the right index finger of seven adult participants (four males). A custom robotic platform stimulated the finger pad with a flat clean glass surface, controlling the normal forces and rotation speeds applied while monitoring the contact interface using optical imaging. We tested normal forces between 0.5 N and 10 N at a fixed angular velocity of 20° s-1 and angular velocities between 5° s-1 and 100° s-1 at a fixed normal force of 2 N. We observe the characteristic pattern by which partial slips develop, starting at the periphery of the contact and propagating towards its centre, and the resulting surface strains. The 20-fold range of normal forces and angular velocities used highlights the effect of those parameters on the resulting torque and skin strains. Increasing normal force increases the contact area, the generated torque, strains and the twist angle required to reach full slip. On the other hand, increasing angular velocity causes more loss of contact at the periphery and higher strain rates (although it has no impact on resulting strains after the full rotation). We also discuss the surprisingly large inter-individual variability in skin biomechanics, notably observed in the twist angle the stimulus needs to rotate before reaching full slip.

Unsteady Dean flow formation in an annulus with partial slippage: A riemann-sum approximation approach

Abstract This paper investigates time-dependent Dean Flow of an incompressible fluid under homogeneous slip, non-homogeneous slip, and no-slip boundary conditions. The fluid flow is due to the sudden application of an azimuthal pressure gradient. The general solutions of the governing momentum equations are obtained using a two-step approach called Laplace transformation and Riemann-sum approximation method of Laplace inversion. The velocity and skin friction are determined exactly in the Laplace domain and inverted back to time domain using a numerical approach known as Riemann-sum approximation. The steady-state solutions for the velocity and the skin friction are obtained for the validation of the method employed. Graphs are plotted for analysis and numerical values are tabulated for comparison of the Riemann-sum approximation and the exact solution at large values of time. From the analysis, it is observed that the velocity profile of the fluid is higher at the wall with the highest slip coefficients. Finally, the influence of the dimensionless time ( T ) and the slip coefficients is also discussed with the aid of graphical illustrations.

Large dunes on the outer shelf off the Zambezi Delta, Mozambique: evidence for the existence of a Mozambique Current

The existence of a continuously flowing Mozambique Current, i.e. a western geostrophic boundary current flowing southwards along the shelf break of Mozambique, was until recently accepted by oceanographers studying ocean circulation in the south-western Indian Ocean. This concept was then cast into doubt based on long-term current measurements obtained from current-meter moorings deployed across the northern Mozambique Channel, which suggested that southward flow through the Mozambique Channel took place in the form of successive, southward migrating and counter-clockwise rotating eddies. Indeed, numerical modelling found that, if at all, strong currents on the outer shelf occurred for not more than 9 days per year. In the present study, the negation of the existence of a Mozambique Current is challenged by the discovery of a large (50 km long, 12 km wide) subaqueous dune field (with up to 10 m high dunes) on the outer shelf east of the modern Zambezi River delta at water depths between 50 and 100 m. Being interpreted as representing the current-modified, early Holocene Zambezi palaeo-delta, the dune field would have migrated southwards by at least 50 km from its former location since sea level recovered to its present-day position some 7 ka ago and after the former delta had been remoulded into a migrating dune field. Because a large dune field composed of actively migrating bedforms cannot be generated and maintained by currents restricted to a period of only 9 days per year, the validity of those earlier modelling results is questioned for the western margin of the flow field. Indeed, satellite images extracted from the Perpetual Ocean display of NASA, which show monthly time-integrated surface currents in the Mozambique Channel for the 5 month period from June–October 2006, support the proposition that strong flow on the outer Mozambican shelf occurs much more frequently than postulated by those modelling results. This is consistent with more recent modelling studies comparing the application of slippage and non-slippage approaches—they suggest that, when applying partial slippage, a western boundary current can exist simultaneously with the southward migrating eddies. Considering the evidence presented in this paper, it is concluded that a quasi-persistent, though seasonally variable Mozambique Current does exist.

Supracondylar “V” osteotomy for postrachitic genu valgum in children: A case series

Objectives: Among the various options available for correction of genu valgum deformities, supracondylar “V” osteotomy is a sparsely used technique. We used the technique for correction of postrachitic deformity in late childhood and adolescence and report the outcome achieved. Patients and Methods: Our operative criteria were age range between 10 and 12 years, a normal metabolic profile, and genu valgum deformity with a standing radiological tibiofemoral angle ≥15°. Patients who had gross collateral ligament instability, any restriction of knee range of motion, genu recurvatum, predominant tibial deformity component, epiphyseal irregularities, active metabolic disease were excluded from the study. Correction was undertaken using “V” osteotomy technique described by Aglietti et al. and was stabilized by two Kirschner wires. Functional outcome was assessed using Bostman et al. score. Results: Seventeen limbs in nine patients with a mean age of 11 years were operated. All the genu valgum deformities were postrachitic but with healed status. Mean follow-up of patients was 24.8 months. Preoperative radiological tibio-femoral angle had a mean value of 20.2° which improved to a mean of 3.05° postoperatively. Knee score was excellent in 88.8%, good in 11.1%. All patients recovered full range of knee motion within 6 weeks after removal of the cast. Two main complications were deep infection and partial slippage of lower femoral physis in one case each. Conclusions: Supracondylar “V” osteotomy is a viable option for the correction of postrachitic genu valgum deformity in older children and adolescents with limited residual physeal growth not amenable to growth modulation procedures.

Intra parenchymal pericatheter cyst in a patient with cerebral shunt malformation

We report an unusual cause of 12 year female who presented with the features of shuntmalfunction where the ventricular end of the catheter got trapped in the intraparenchymalcyst. We believe that growth of the child resulted in the pull of the catheter outside the ventricleinto the brain parenchyma and partial slippage of the catheter into the brain parenchyma,leading to the leakage of the cerebrospinal fluid into the parenchyma with resultant cystformation and cyst enlargement. The vicious cycle of cyst enlargement and slippage of thecatheter outside the ventricle ultimately resulted in the entrapment of the catheter in theparenchyma leading to the symptoms of shunt malfunction.

Development of a Novel Slip Haptic Display Device Based on the Localized Displacement Phenomenon

Human-in-the-loop task involving soft contact has become common in robotic manipulation research, especially in tele-operation and robotic surgery. Soft contact in this task may include a soft-fingered robot hand gripping a rock, or robotic control of forceps to pick up a tissue sample. In these scenarios, operators normally struggle with controlling the gripping force of the remote robotic hand, so that the grasped object is neither dropped nor damaged. Information about slippage , especially incipient slippage (or preslide), occurring at the contact surface is not properly sensed by the operator through cutaneous tactile feedback. This study aimed to generate preslide sensation on human fingertip for enhancement of slip perception of soft objects. We hypothesized that use of a method that can reproduce localized slippage can enhance human perception of slippage based on our previous study of soft-based contact. We created a grounded slip haptic display device, which can efficiently assess partial slippage on a human fingertip efficiently using a bundle of pins under only one actuation. This letter focuses on the creation of the device, including its theoretical underpinnings and design process, as well as assessing its efficiency in enhancing skin stretching through static and dynamic simulations. The device can be utilized to assess the slide process of a human fingertip, perceiving how and when slippage occurs on the contact surface; and can act as a platform for studies on human tactile perception.

Effects of Partial Slippage and Couple stresses on Entropy Generation in a porous Channel filled with Highly Porous Medium

This work investigates the influence of slip condition and couple stresses on entropy generation rate in a steady flow of an incompressible viscous fluid through a porous channel occupied by a highly porous medium with suction/injection. It is assumed that the “no-slip” condition at one of the walls of the channel is no longer valid for both velocity and temperature. Also the porous medium is the non-Darcian type known as the Darcy-extended Brinkman-Forchheimer model. Semi-Analytical solutions of the dimensionless momentum and energy equations are obtained using Differential transform method (DTM). The approximate solutions for velocity and temperature are used to compute the Entropy generation rate, Bejan number and the Irreversibility distribution ratio in the flow field. The variation of the velocity and temperature fields are examined for various values of couple stresses parameter, slip parameter, Brinkman number, entropy generation number, Darcy number, Nusselt number, skin fiction and other parameters. It is found that each of these parameters has significant effect on the velocity, temperature and Entropy generation rate profiles.

Contact adaptability upon the coulomb friction of elastic bodies

We consider the phenomenon of bodies adaptation upon contact interaction, when after several initial loading cycles partial slippage ceases and adherence spreads over the area of contact. The conditions for applying theorems of contact adaptability are analyzed. The results from finite-element numerical simulations verifying and refining the conditions for achieving complete or partial contact adaptability with the dry friction of elastic bodies are presented. The contact adaptability theorem is generalized for the interaction of many bodies.

Full and partial boundary slippage effect on squeeze film bearings

Simple experiments were carried out to illustrate the effect of the boundary slippage on the load capacity of a squeeze film. The surface energy of the bearing surface was modified using laser excimer (UV laser). It was found that the load capacity can be reduced if the surfaces are modified to be hydrophobic. The boundary slippage effect on squeeze film was further studied theoretically to get more insight. The paper presents a mathematical model with a critical shear-stress criterion of slippage to describe the squeeze film effect. Three types of slippage, i.e. single zone partial slippage, single zone full slippage, and double zone partial slippage, are modeled. The analytical solution shows that the pressure distribution is a piecewise parabolic curve, where the pressure gradient can be discontinuous at the border of the slip and no-slip regions. Parametric studies illustrate the variations of the pressure and the boundary slippage under different conditions. It is demonstrated that with the increase of the length of the hydrophobic region, the maximum pressure does not increase continuously. Similar to the classical squeeze film bearing, the pressure decreases with the increase in the film thickness or the decrease in the approach velocity. The influences of the critical shear stress are also explored, and are found to significantly affect the squeeze behavior.

Visco-elastic flows at macro-, micro- and nano-scales

We demonstrate how to model non-Newtonian fluids showing a dependence of the viscosity from the local strain by means of the Lattice Boltzmann Model (LBM). We first consider rheological descriptions of visco-elastic fluids relying on an explicit parameterization of the viscosity in terms of the strain: a) Power-Law Model ; b) Carreau-Yasuda Model. Those models have a number of free parameters that can be used to fit experimental data with an accuracy depending on the range of values of the strain taken into account. We show that their implementation in the LBM scheme is possible and the influence on the resulting simulation is quite relevant, arising both in bulk properties and in boundary conditions. In particular, we investigate the transport properties in micro-channels with non-Newtonian flows in presence of slip properties at the wall. It is known that partial slippage or even total slippage (free shear) may strongly influence mass throughput in micro-devices. Here we show that in presence of non-Newtonian effects, heterogeneous boundary conditions may introduce even more complex behavior in the overall micro-device response. We study the case of both shear thinning and shear thickening fluids. The tests are carried on single component, single phase fluids [1].

Development of a Direct Simple Shear Apparatus for Peat Soils

Abstract This paper discusses the design and development of a new direct simple shear (DSS) apparatus for testing peat soils. The apparatus has been designed to test peat at low effective stresses, representative of its in situ condition and allow the deformation of the specimen to be monitored. This device uses particle image velocimetry (PIV) image analysis techniques to monitor the side of the peat specimen and provide an insight into the behavior of peat during shearing. A set of comparative tests on reconstituted clay have been conducted with another widely used DSS apparatus and has shown both to yield similar undrained strength ratios (su/σvc′) for a range of stress levels. Application of the apparatus to peat soils is demonstrated by a set of tests on a high water content blanket bog peat. Analysis of these tests using the PIV technique reveals the complex shear strain and volumetric strain behavior of peat undergoing shearing. Identification of partial slippage of a specimen is also shown through these analyses.

Flow in Confined Geometry Introduced by Dewetting of Ultrathin Polystyrene Films

By making use of dewetting, the flow of polystyrene (PS) in confined geometry of ultrathin films is investigated as a function of the boundary conditions. Four different surface treatment procedures have been applied to silicon (Si) substrates to realize small changes of the oxide surfaces. Atomic force microscopy and surface-sensitive scattering experiments show a change in the mass transport of PS. A slowing down in comparison to the well-known slip and no-slip conditions is observed, except in the case of binodal dewetting mechanisms, which obeys a partial slippage. In addition to the changed kinetic behavior, the final states show big differences in the contact angle of the drops. Our results are explained within a model, which includes changes of the short-ranged part of the wall potential due to different oxide layer thicknesses, introduced by the treatment processes.

The wear contact problem with partial slippage

A method of analysing the variation in the stress state and shape of wearable bodies, subjected to the action of an oscillating shear load with partial slippage of the surface in the contact area is proposed. The method is based on the introduction of two time scales: the time of a single cycle of variation in the shear load and the time corresponding to a specified number of cycles. To estimate the shape variation of the surface due to wear a linear relation between the wear rate and the contact pressure and velocity of relative slippage is used. Cases of complete or partial removal of the wear particles from the friction zone are considered. As an example, the kinetics of the variation in the stress state in the contact of an elastic indentor, having a flat base and rounded edges, with an elastic half-space of the same material, is investigated. Analytical expressions for calculating the asymptotic values of the stresses and shape of the worn surface are obtained.

Displaying Partial Slippage for Virtual Grasping

We display partial slippage in human precision gripping. Partial slippage provides important information for gripping because we control grasping by detecting expansion in partial slippage. Displaying partial slippage makes it easier for remote controlled mechanical hands to grasp objects, regardless of the friction coefficient between the mechanical hand and object. To display partial slippage, we analyzed finger deformation in contact with a rigid plate using a finite element model. We analyzed finger model deformation in contact with the display of partial slippage. Analysis confirmed the possibility of displaying partial slippage using a tactile display that stimulates the finger at three points. Finally, we confirm the model’s effectiveness.

Assessment of knot security in continuous intradermal wound closures

The traditionally used square knot used for commencement and termination of continuous wound closures is bulky, requiring a minimum of four to six throws to form a secure knot with most suture materials and sizes. This study evaluates the security of self-locking knots, which are significantly smaller in volume than the traditionally applied square knot, for the intradermal closure of standardized wounds in porcine skin. Porcine skin samples with standardized wounds were closed in one of five patterns with 3/0 PDS suture. Wounds were harvested and tested to failure on a materials testing machine. Load at failure, ultimate elongation, wound stiffness, and mode of failure was determined for each sample. Wound closures incorporating the chain stitch knot performed as well as closures incorporating the conventional square knot for load to failure, elongation, and stiffness. Partial slippage or complete knot failure of 4/40 (10%) of the square knots used in closures was observed. 0/20 (0%) of the chain stitch knots displayed slippage. The half-blood knot performed similarly to the square and chain stitch knot in load to failure, elongation, and stiffness, however, 16/20 (80%) of these knots displayed slippage or complete knot failure. The chain stitch knot is as secure as the traditionally used square knot when used for termination of a continuous intradermal wound closure. This knot displays characteristics such as smaller knot volume and ease of applications that may make it a superior knot to the square knot in many clinical situations.

Photoelastic Investigation of Friction and Residual Stress in Shrink-Fitted Shafts and Hubs

This paper describes initial investigations into the use of frozen-stress photoelasticity to study the development of slippage within shrink-fitted shaft/hub pairs, with the aim of studying the residual stresses remaining after partial slippage has occurred. Results to date show the feasibility of measuring the shear stresses along the partially-slipping interface between shaft and hub.

Growth of Holes in Liquid Films with Partial Slippage

We derive an expression for the temporal development of circular holes formed spontaneously in dewetting liquid films. Our formula is shown to interpolate between the known limiting cases of perfect sticking (purely viscous dissipation) and full slippage of the film on the substrate. Good agreement between experiment and theory is found. By fitting the theroetical curves to the data, we can derive the relative importance of slip in the dewetting process.

Continent jejunal reservoir (Kock pouch) for urinary diversion in dogs.

Urinary diversion by transplantation of both ureters into a reservoir constructed from 60 cm of jejunum was performed in six clinically normal dogs. The reservoir was connected to a stoma on the abdominal wall through a valve constructed from a short segment of intussuscepted bowel to provide continence. The reservoir was emptied three times daily by catheterization. One dog did not survive the surgical procedure and two dogs died within 1 week of surgical complications. The postoperative capacity of the reservoir in surviving dogs was 100 to 200 mL; it increased during the first month to 600 to 750 mL. Continence was excellent in two dogs. One dog was continent until month 2, when partial slippage of the intussusception occurred. A reversible hyponatremic, hypochloremic, hypokalemic metabolic acidosis developed. Bacteriuria was not responsive to systemic or local instillation of antibiotics. Ascending pyelonephritis, hydroureter, and hydronephrosis occurred in two dogs. Struvite urinary calculi formed in one dog. The procedure as described would be unsuitable for clinical use in dogs.

Compliance of coated elastic bodies in contact

A model is constructed to analyze the effects or normal and tangential loading on elastically identical coated spheres. The solution for a tangential displacement applied to a circular patch on the coated surfaces, including the occurrence of micro-slip (either full or partial slippage), is derived. If it is assumed that the slip region is a circular annulus of inner radius c, then the following two sets of approximations can be made: a “stiff” approximation that satisfies the zero micro-slip condition exactly for the inner circle and a “soft” approximation that satisfies the Amontons-Coulomb frictional law exactly for the slip region. It is concluded that the “soft” approximation gives an accurate value for the symmetric traction component, 1/2 ½[τzr1(1)−τzθ1(1)], induced by the normal and tangential loads.

Complications of Rigid Anterior Chamber Implants

Despite accurate lens sizing, 100 eyes with rigid anterior chamber implants showed a high incidence of lens-related trauma postoperatively: pigment dispersion (pseudoguttata), angle recession, peripheral anterior synechiae, iris erosion/atrophy, iris holes from stretching, angle fibrosis, haptic tip erosion into sclera and iris, neovascularization of peripheral iris and angle, lens rotation through iridectomy and into ciliary body, lens tilting with corneal endothelial touch, high refractive cylinder with long intraocular lenses, pigment proliferation onto iris surface, partial slippage of the intraocular lens into vitreous following intracapsular procedure, and pupillary-block glaucoma. Vision results were good. Glaucoma and cystoid macular edema rates were low. Bullous keratopathy and retinal detachment didn't occur. High endothelial cell loss was associated with those lenses that “propellered” and those that tilted and touched endothelium. The adverse findings may be static or may represent a continuing process of tissue damage.