Sticking Region Research Articles

CT-scan images preprocessing and segmentation to improve bioprosthesis leaflets morphological analysis

The visualization of bioprosthesis leaflet morphology might help to better understand the underlying mechanism of dysfunction in degenerated aortic bioprosthesis. Because today such visualization of bioprosthesis leaflet morphology is intricate to impossible with other imaging techniques, we hypothesized that the processing of multi-detector CT images would allow better visualization of the prosthetic valve leaflets after biological aortic valve replacement. The purpose of our study was to prospectively evaluate patients with a degenerated aortic bioprosthesis, waiting for reoperation, by using 64-slice CT to evaluate prosthetic leaflets morphology. A semi-automatic segmentation of pre-operative tomodensitometric images was conducted, using 2 different implementations of the region growing algorithm. Here we report all segmentation steps (selection of the region of interest, filtering, segmentation). Studied degenerated aortic bioprostheses were represented by two Carpentier-Edwards Supra Annular Valve (porcine leaflets), one Edwards Perimount (pericardial leaflets) and one Medtronic Mosaic (porcine leaflets). Both segmentation methods (Isotropic Region Growing and Stick Region Growing) allowed a semi-automatic segmentation with 3D reconstruction of all bioprosthetic components (stent, leaflets, degeneration/calcifications). Explanted bioprosthesis CT images were also processed and used as reference. Segmentation results were compared by means of quantitative criteria. Semi-automatic segmentation using region growing algorithm seems to provide an interesting approach for the morphological characterization of degenerated aortic bioprostheses. We believe that in the next future CT scan images segmentation may play an important role to better understand the mechanism of dysfunction in failing aortic bioprostheses. Moreover, bioprostheses 3D reconstructions could be integrated into preoperative planning tools to optimize valve-in-valve procedure.

Probing the micromechanics of a multi-contact interface at the onset of frictional sliding

Digital Image Correlation is used to study the micromechanics of a multi-contact interface formed between a rough elastomer and a smooth glass surface. The in-plane elastomer deformation is monitored during the incipient sliding regime, i.e. the transition between static and sliding contact. As the shear load is increased, an annular slip region, in coexistence with a central stick region, is found to progressively invade the contact. From the interfacial displacement field, the tangential stress field can be further computed using a numerical inversion procedure. These local mechanical measurements are found to be correctly captured by Cattaneo and Mindlin (CM)'s model. However, close comparison reveals significant discrepancies in both the displacement and stress fields that reflect the oversimplifying hypothesis underlying CM's scenario. In particular, our optical measurements allow us to exhibit an elasto-plastic-like friction constitutive equation that differs from the rigid-plastic behavior assumed in CM's model. This local constitutive law, which involves a roughness-related length scale, is consistent with the model of Bureau et al. (Proc. R. Soc. London, Ser. A 459, 2787 (2003)) derived for homogeneously loaded macroscopic multi-contact interfaces, thus extending its validity to mesoscopic scales.

The Sticking Region in Three Chest-Press Exercises with Increasing Degrees of Freedom

The purpose was to investigate the effect of 3 chest-press exercises with different degrees of freedom upon the sticking region and muscle activity in maximal attempts. It was hypothesized that, with increasing degrees of freedom, the sticking region (the weakest region during the lift) would be longer because the muscles need to use a part of their ability to control these increasing degrees of freedom during the exercise. Furthermore, the prime movers would have the same muscle activity, but the biceps muscle activity would increase when the degrees of freedom increases because of the enhanced control of the upward movement. Eleven male subjects (age 22.6 ± 1.7 years, body mass 78.6 ± 8.0 kg, stature 1.80 ± 0.07 m) with at least 1 year of bench press training experience participated in this study. Every subject was tested in 1 repetition maximum (1RM) in the 3 chest-press exercises. During the attempts, kinematics and muscle activity were recorded and analyzed in 4 different regions (downward, presticking, sticking, and poststicking). The participants achieved the highest 1RM strength using the free barbell (106.4 ± 15.5 kg), followed by the Smith machine (103.6 ± 14.8 kg) and dumbbells (89.5 ± 13.7 kg). Furthermore, muscle activity differences (electromyographic) between the 3 different exercises and the muscle activation between the 4 different regions were found. The length of the different lifting regions together with muscle activity was different between the exercises. However, the differences found did not follow the line of increasing degrees of freedom that would result in a longer sticking region. Therefore, it is possible to choose to train a particular chest press exercise with the purpose of training a particular muscle more than the others.

A Numerical Approach for Analyzing Three-Dimensional Steady-State Rolling Contact Including Creep Using a Fast Semi-Analytical Method

This article presents a new rolling contact solver using a semi-analytical method (SAM) to analyze three-dimensional steady-state rolling contacts, including the effects of creep. This new solver includes both the normal and tangential contact issues for the pressure and shear tractions, respectively. The accuracy and efficiency of the present method are demonstrated by comparison to existing analytical and numerical solutions. Rolling contact problems for a smooth infinite roller pressed against a half space with either a single asperity or a sinusoidal wave are investigated. The results show the complexity of pressure and shear traction. Asperities produce higher localized pressures, which demand larger local shear tractions to produce slip in such regions. Stick regions are also observed at the trailing edge of the contact.

Is the occurrence of the sticking region the result of diminishing potentiation in bench press?

In this study we investigated if the occurrence of the sticking region was a result of diminishing potentiation (coinciding delayed muscle activation) or the result of a mechanically poor region in which the muscles can produce less force. A regular one-repetition maximum (1RM) free-weight bench press was compared with isometric bench presses performed at 12 different positions. A lower force at the sticking region compared to the other regions in the isometric bench presses would confirm the mechanically-poor-position hypothesis. Twelve resistance-trained males (age 21.7 ± 1.3 years, mass 78 ± 5.8 kg, height 1.81 ± 0.05 m) were tested in 1RM and in isometric contractions in bench press in 12 different positions, indicated by the vertical distance between barbell and sternum, covering the whole range of motion during the concentric phase. Barbell kinematics and muscle activity were registered. In both types of executions a region of lower force output was observed, which supports the mechanically-poor-position hypothesis. Electromyographic activity of four muscles showed the same pattern in the isometric and 1RM attempts. It was concluded that diminishing effect potentiation could not explain the existence of the sticking region.

Three-dimensional transient rolling contact analysis of similar elastic cylinders

Because most fatigue cracks in wheel and rail take place by rolling contact between wheel and rail in railway industry, it is critical to understand the rolling contact phenomena, especially for the three-dimensional situation. In this paper the steady-state and transient rolling contact problem of three-dimensional elastic bodies has been studied. The transient conditions were controlled by the applied relative slip. The variation of tangential traction and stick-slip region on rolling contact surface were obtained using the finite element method. The three-dimensional distribution of tangential traction and contact stresses on the contact surface are investigated. Results show that the distribution of tangential traction and contact stresses on the contact surface varies rapidly as a result of the variation of stick-slip region. The tangential traction is very close in form to Carter's distribution that contact region divided into stick and slip region. The contact stress at the leading edge is greater than at the trailing edge and the transient distance increases with small slip.

Using multiple point constraints in finite element analysis of two dimensional contact problems

Two-dimensional elastic contact problems, including normal, tangential, and rolling contacts, are treated with the finite element method in this study. Stress boundary conditions and kinematic conditions are transformed into multiple point constraints for nodal displacements in the finite element method. Upon imposing these constraints into the finite element system equations, the calculated nodal stresses and nodal displacements satisfy stress and displacement contact conditions exactly. Frictional and frictionless contacts between elastically identical as well as elastically dissimilar materials are treated in this study. The contact lengths, sizes of slip and stick regions, the normal and the shear stresses can be found.

MICRO-SLIP INDUCED DAMPING IN PLANAR CONTACT UNDER CONSTANT AND UNIFORM NORMAL STRESS

The friction between interfaces at bolted joints plays a major role in the damping of structures. This paper deals with the energy losses caused by micro-slips in the joints. The aim of this study is to define in an analytical way these energy dissipation mechanisms which we examine through the analysis of a new benchmark: the flexural vibration of a clamped-clamped beam with original positioning of the interfaces. The joints exhibit the behavior of an interface under constant and uniform normal stress. The stress and strain values are computed at the joints under the assumption of quasi-static motion. This model allows us to understand the evolution of the slip and stick regions along the joint interfaces during the loading process. The expressions of the strain and stress fields during each phase of the loading process are derived. These lead to the quantification of the dissipated energy within the interface. Using this formula, a nonlinear loss factor can then be computed. In the final part of the paper, the dynamic response of the beam is calculated using this nonlinear loss factor.

COMBINED EFFECTS OF FLANK AND CRATER WEAR ON CUTTING FORCE MODELING IN ORTHOGONAL MACHINING—PART II: BAYESIAN APPROACH-BASED MODEL VALIDATION

Flank and crater wear are the primary tool wear patterns during the progressive tool wear in metal cutting. Cutting forces may increase or decrease, depending on the combined contribution from the flank and/or crater wear. A two-dimensional (2D) slip-line field based analytical model has been proposed to model the force contributions from both the flank and crater wear. To validate the proposed force model, the Bayesian linear regression is implemented with credible intervals to evaluate the force model performance in orthogonal cutting of CK45 steels. In this study, the proposed analytical worn tool force model-based predictions fall well within the 75% credible intervals determined by the Bayesian approach, implying a satisfactory modeling capability of the proposed model. Based on the parametric study using the proposed force model, it is found that cutting forces decrease with the increasing crater wear depth but increase with the increasing flank wear length. Also, the predicted cutting forces are affected noticeably by the friction coefficients along the rake and flank faces and the ratio of crater sticking region to sliding region, and better knowledge of such friction coefficients and ratio is expected to further improve worn tool force modeling accuracy. Compared with the finite element approach, the proposed analytical approach is efficient and easy to extend to three-dimensional worn tool cutting configurations.

The Contact Problem in Ultrasonic Traveling-Wave Motors

In this paper the contact mechanism between stator and rotor will be considered in detail, which plays a key role in ultrasonic motors. A planar contact model for the stator-rotor interaction in traveling-wave type ultrasonic motors is derived, including rotor flexibility and differenciating between stick and slip regions in the contact zones. The model analysis shows that depending on the motor’s operating conditions, complicated contact behavior may occur with several stick-slip subzones in each contact zone. The typical nonlinear resonance observed in ultrasonic motors can be explained with the present analysis. Both the stiffness of the contact layer and of the rotor may drastically influence the speed-torque characteristics. The results will contribute to a better understanding of the contact mechanics in ultrasonic motors.

Numerical Method for Solving Contact Problems under Partial Slip Conditions

An elastic contact model for three-dimensional similar and dissimilar materials under coupled normal load and tangential load in the contact plane,with consideration of partial slip effects,is studied. When two surfaces in static contacts are subjected to normal load and tangential load,even only applying a normal load for dissimilar materials,microscopic slip will take place at certain areas of the contact region even though the contacting bodies remain still without macroscopic movement. The semi-analytical method is used to solve the partial contact problems,in which analytical solutions of displacements due to unit pressure or shear tractions are based on green function. The contact pressure and shear tractions are solved by a numerical procedure based on conjugate gradient method and fast Fourier transform technique. The meshes are applied to the positions just in the contact areas of interest,which saves the computing time. The good agreement with the results from Cattaneo-Mindlin's solution validates the numerical method. The analysis is extended to the sinusoidal wave contact to provide a further demonstration for the pressure distributions,shear stress distributions and stick regions. The results show that the stick regions are located at several disconnected areas due to the roughness effects. With the increase of tangential force,the pressure distribution inclines along the opposite direction of tangential force,the value of shear stress τx becomes positive and the stick zones shrink and move opposite to the direction of tangential force.

Effect of Rake Angle on Stress, Strain and Temperature on the Edge of Carbide Cutting Tool in Orthogonal Cutting Using FEM Simulation

Demand for higher productivity and good quality for machining parts has encourage many researchers to study the effects of machining parameters using FEM simulation using either two or three dimensions version. These are due to advantages such as software package and computational times are required. Experimental work is very costly, time consuming and labor intensive. The present work aims to simulate a three-dimensional orthogonal cutting operations using FEM software (deform-3D) to study the effects of rake angle on the cutting force, effective stress, strain and temperature on the edge of carbide cutting tool. There were seven runs of simulations. All simulations were performed for various rake angles of -15 deg, -10 deg, -5 deg, 0 deg, +5 deg, +10 deg, and +15 deg. The cutting speed, feed rate and depth of cut (DOC) were kept constant at 100 m/min, 0.35 mm/rev and 0.3 mm respectively. The work piece used was ductile cast iron FCD500 grade and the cutting tool was DNMA432 series (tungsten, uncoated carbide tool, SCEA = 0; and radius angle 55 deg). The analysis of results show that, the increase in the rake angle from negative to positive angle, causing the decrease in cutting force, effective stress and total Von Misses strain. The minimum of the cutting force, effective stress and total Von Misses strain were obtained at rake angle of +15 deg. Increasing the rake caused higher temperature generated on the edge of carbide cutting tool and resulted in bigger contact area between the clearance face and the workpiece, consequently caused more friction and wear. The biggest deformation was occurred in the primary deformation zone, followed by the secondary deformation zone. The highest stress was also occurred in the primary deformation zone. But the highest temperature on the chip usually occurs in secondary deformation zone, especially in the sliding region, because the heat that was generated in the sticking region increased as the workpiece was adhered by the tool and later it was sheared in high frictional force.

On shakedown and ratchetting of conforming frictional systems

Conforming contact is found on many important areas: materials with cracks, inclusions, layered structures, pinned geometries, etc. Coulomb friction is non-associative i.e. does not satisfy Drucker’s postulates for stability in plasticity theory, and this does not permit to use the classical Melan and Koiter theorems for cyclic loading which however remain obvious necessary conditions. On the other hand, the Coulomb friction cone has a peculiarity, its linear self-similarity, and this permits few general results, quite different but also powerful. For example, we show that for conforming contact, the Bree interaction diagram is open and sectors-shaped, and therefore there is no lower and upper bounds as in plasticity, since there is linear dependence on a load parameter \(\lambda\), and not a limit on \(\lambda\). As there is dependence on initial conditions in general, the Bree diagram doesn’t have the same profound meaning as in plasticity, since multiple steady states are possible. However, there is a complete scaling of the possible states (elastic shakedown, cyclic slip, ratchetting) with load factor \(\lambda\), and hence a worst-scenario can be defined. However, in order to develop residual stresses (which generally will take many cycles of steady cyclic loading), the load cannot go to zero, at least for friction coefficient below the critical value for "wedging". More in general, there needs to be a "permanent stick region" in the steady state.Almost conforming contacts, and in particular, in the case of initial interference, loose the independence on \(\lambda\) at low \(\lambda\) only, but "gain" greater possibilities to develop residual stresses. However, their study can be greatly simplified by developing a master curve approach to study the dependence on \(\lambda\). The theorems can also be considered the extension to cyclic loadings of the Dundurs results for conforming contacts under monotonic loading, in which case the contact area doesn’t vary in time and hence the problem is linear (from which the denomination "receding contacts"). However, here the problems remain fully non-linear, and the contact are not in general receding, nor there is a unique steady state, not even in the case of proportional loading. In the latter case it is nevertheless possible to derive some special results.

Measurement of real contact area and analysis of stick/slip region

The real contact area obtained between a rough rubber hemisphere and a glass plate, under unlubricated conditions, was visualized by white light interferometry. The contacting friction condition of the real contact area in the starting friction process was analyzed using interference intensity. The real contact area was extracted by fitting the intensity histogram of interference images to Gaussian distribution. This was seen to decrease with the increase of the applied tangential force, and it became approximately constant after initiation of macroscopic sliding. Real shear stress increased linearly in the micro-sliding regime and then became constant in the macro-sliding regime with the increase of the glass plate's displacement. The statistical ratio of stick region to contact area was estimated with the use of a differential histogram of the interference image intensity based on a tangential force coefficient of zero. This ratio showed a tendency to be more than a theoretical solution offered by Mindlin. In addition, we performed particle image velocimetry analysis, which assumed real contact spots as chase markers, and succeeded in the mapping of the stick/slip region within the real contact area.

Contact Analysis by Shape Optimization (CASO)#

A new contact analysis algorithm by shape optimization (CASO) has been proposed: A sequence of usual elasticity problems is solved iteratively until the unknown contact and stick regions are converged while minimizing the mismatches in the contact and friction conditions. It is based on the continuous LCP (linear complementarity problem) formulation of the contact. A series of examples with known solutions or without are solved for verification and show simplicity and beauty of the unique method.

Influence of tool roughness and lubrication on contact conditions in skin-pass rolling

The special contact conditions in skin-pass rolling of steel strip are examined by experimental as well as numerical analysis studying plane strain upsetting of thin sheet with low reduction applying long narrow tools with smooth and roughened surfaces under dry friction and lubricated conditions. The influence of friction on the extent of a central sticking region is determined by an elasto-plastic FEM analysis of the plane strain upsetting. The experimental results obtained by measuring the local surface extension using markers made by Micro Vickers indentation verify the FE analysis and show significant influence of tool roughness and lubrication on the contact conditions for varying pressure. The central sticking region was larger for larger friction or tool roughness. At increasing pressure a sudden change in deformation pattern appeared with drastic elongation and sliding in case of lubrication. This deformation pattern is also affected by the tool roughness.

Slippage Degree Estimation by Using Vision-Based Tactile Sensor for Dexterous Handling

In this paper, we present a new slippage degree estimation method, where the vision-based tactile sensor is used to measure multi-dimensional force and moment in contact with an object. We proposed a new method to obtain the stick ratio based on a quantization process of the maximum displacement in the stick region. The stick ratio is useful when we detect macroscopic slippage in advance. We show that the proposed method can be applied to wider situations and obtain more accurate estimation of stick ratio than the previous method. We can use the proposed method for the following situations. First, the applied normal force seriously changes or a certain amount of moment applies to the contact surface. Second, a macroscopic slippage occurs and the sensor surface re-establishs the contact. Third, a complex history of contact makes each local behavior of the surface difficult. The image processing method has been proposed to decrease the data variation of the captured CCD camera image and to cope with the wider situations of contact conditions. The usefulness of the proposed method is confirmed through the experimental results.

Frictional complete contacts between elastically similar bodies subject to normal and shear load

The problem of trapezium shaped punches pressed into a frictional, elastically similar half-plane and subject to sequential normal and shear loading is studied. The initial mix of stick, slip and separation regions is described, together with the steady state response when the shearing force is cycled. Conditions for full stick are established.

Hertzian fracture at finite friction: A parametric study

Friction has a profound influence on Hertzian fracture initiation when dissimilar materials are involved. Experimental studies show that the presence of friction results in higher fracture loads and fracture radii as compared to the frictionless case. It has also been shown recently that the experimental observations concerning Hertzian fracture initiation at unloading may be explained by the effect friction has on a surface tensile stress distribution. Presently a contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been investigated numerically for a wide range of material parameters and contact geometries. Emphasis has been given to the surface tensile stress distribution which is assumed to be a governing parameter for Hertzian fracture initiation. In particular it was found that during loading the contact region divides into invariant stick and inward slip regions and the presence of outward frictional shear tractions reduces the maximum surface tensile stress and shifts it away from the contact contour as compared to the frictionless case. At unloading, the distributions of stick-slip zones were found to be severely history- and geometry-dependent and shear tractions reversed their direction over part of the contact area. Consequently, tensile stresses were found to grow at unloading. Results concerning the influence of the friction coefficient, Dundur's parameter and the specimen's Poisson's ratio on the absolute maximum surface tensile stress obtained at a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation.

MOTION CONTROL OF A NONLINEAR SPRING BY REINFORCEMENT LEARNING

Recent research in vehicle platform stabilization has developed solutions that do not meet the stringent low-energy demands required for widespread general application of stabilizing active suspension. The energy requirement for active platform stabilization can reach up to 40% of the total output of the engine. This power consumption may lead directly to reductions in vehicle performance and fuel economy. The need for low energy consumption is thereby a fundamental requirement for successful active suspension system. Cameron's investigation [1] involves a mechanical system with a positive stiffness in series with a stiffness spring to provide for reducing the power consumption. We aim to control the motion of a horizontally moving vehicle mass on a rail, when it is subject to friction, under the influence of a controlled compressed spring. The compressed behaves as if it has a negative constant over a range of its displacements. The system has three separate stick regions for some values of the parameters, centred on its critical points. Our objective is to control the motion by keeping its displacements in a robust nonstick region that lies between two predetermined neighboring stick zones. We use reinforcement learning control that applies proper control forces to this nonlinear system in an attempt to keep the motion of the body within the targeted nonstick region. We describe a numerical scheme for the model and its learning control algorithm and present a number of computer simulations, with different initial conditions and driving force amplitudes, and frequencies.