Stick-slip Mechanism Research Articles

Flax‐fabric‐reinforced arylated soy protein composites: Brittle‐matrix behavior

AbstractBiocomposites were successfully prepared by the reinforcement of soy protein isolate (SPI) with different weight fractions of woven flax fabric. The flax‐fabric‐reinforced SPI‐based composites were then arylated with 2,2‐diphenyl‐2‐hydroxyethanoic acid (DPHEAc) for 4 h to obtain arylated biocomposites. A new method was proposed to determine the amount of carbon dioxide evolved during the arylation of the soy protein in the presence of DPHEAc. Characterizations of the arylated and nonarylated biocomposites were done by Fourier transform infrared spectroscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis. The results indicate that the arylated soy‐protein‐based composites exhibited mechanical behavior like brittle‐matrix composites, which differentiated them from nonarylated soy‐protein‐based composites, which showed mechanical behavior similar to polymer–matrix composites. In the arylated composites, there was clear evidence of a stick–slip mechanism, which perhaps dominated and, therefore, prevented easy deformation of the reinforced film. Scanning electron microscopy studies revealed cracks in the arylated soy protein composites when they were subjected to tensile tests. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Modeling simulation of deformation in a blocky geomedium during origination of earthquake

The paper focuses on two models of an earthquake—the dilatancy model and the consolidation and stick-slip model. Experimental basis for the research was measurements of stress-strain state in a granular medium with a movable plate that simulated edges and surfaces of a tectonic fault. The dilatancy model showed the lift of the granular material and the respective accumulation of potential energy. The second model showed that a share of the accumulated energy is elastic energy produced in a blocky medium due to sliding resistance on the surface of faults. The curves of shear stresses and displacements, obtained in soft loading of the plate, showed the stick-slip mechanism with displacement discontinuities and partial drops of stresses. The maximum displacement discontinuity and the highest dynamics on the curves correspond to the maximum value of the accumulated elastic energy which is then released on the descending branch of the curve.

Modeling and Simulation of Stick-Slip Motion for Pneumatic Cylinder Based on Meter-In Circuit

For the stick-slip phenomenon encountered in the pneumatic cylinder motion in practical application, the stick-slip mechanism was analyzed and an nonlinear mathematical model based on the improved LuGre model of pneumatic cylinder movement was established. The movement of the piston and the pressure of the rodless chamber in the pneumatic cylinder based on meter-in circuit were obtained through solving the differential equations by four-order variable-step Runge-Kutta method. The comparison between simulation and experimental results shows that the established mathematical model can describe the stick-slip motion of pneumatic cylinder with a relatively good accuracy.

Nanoscale Footprints of Self-Running Gallium Droplets on GaAs Surface

In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001) surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems.

Investigation into the microstructure evolution caused by nanoscratch-induced room temperature deformation in M-plane sapphire

Nanoscratch tests have been conducted at room temperature on ( 1 0 1 ¯ 0 ) M-plane sapphire under a ramp loading condition from 100 μN to 200 mN along a scratch length of 200 μm at a scratch velocity of 1 μm s −1 using a Berkovich nanoindenter XPS system in scratch mode. Plastic deformation features, including short shaving scratch debris, linear surface features along the scratch groove, pile-up, and fish-bone features, indicating a stick–slip mechanism, and brittle deformation features, i.e. microcracking, chipping and tearing, were observed by optical, scanning electron, and atomic force microscopy. Applying the focused ion beam (FIB) technique, site-specific cross-sectional transmission electron microscopy further revealed nanoscratch-induced deformation behavior. Basal twinning was observed in the region below the scratch. The evolution of plastic deformation mechanisms can be summarized as lattice disorder, dislocation loops, stacking faults, dislocation glide and then basal twin formation. The observed features were rationalized using elastic and residual stress field calculations.

Mechanisms of Microstructural Rearrangement on Two-Dimensional Aggregates under Compressive Stress

Two-dimensional (2D) colloidal aggregates of polystyrene microspheres 4 μm were experimentally modeled to study the rearranged mechanisms and compression behaviors at the air-liquid interface. The aggregated models occurred due to the interaction forces between particles. The combination of mechanical testing technique and the digital video microscopy had been developed to quantitatively analyze the compressive deformation of 2D aggregates. When the compressive forces were applied to the cluster, these forces were transmitted trough the aggregated network during compression. Solid-like mechanical properties of 2D aggregated cluster were examined. Deformation mechanisms occurred within the aggregated network which presented the particle rearrangements during yield. Elastic deformation had undergone the compressive elastic stress of the elastic loading. Rearrangement mechanisms found generally were rolling-hinge, sliding mechanisms and tensile failure for a small-scale deformation. Shear failure and stick-slip mechanisms caused a large-scale plastic deformation. However, across the yield point, the tensile failures were dominated. Rearrangement mechanisms of particles affected both elastic and plastic deformations.

A new micromechanics-based scale transition model for the strain-rate sensitive behavior of nanocrystalline materials

An original two-step “three phase” elastic–viscoplastic scale transition model is developed based on the combined self-consistent and Mori–Tanaka schemes. A coated inclusion is embedded within a matrix, wherein the inclusion represents grain interiors and the coating of the inclusion mimics the effects of grain boundaries and triple junctions. The predominant behavior within the grain interiors is captured through dislocation glide, whereas grain boundary (GB) dislocation emission and absorption, as well as thermally assisted GB sliding, describe the deformation processes within the coating describing the GB affected zone. Furthermore, an imperfect interface is assumed between the inclusion and the coating to account for viscoplastic grain boundary sliding along a stick-slip mechanism. Results and discussion focus on the competitive roles of GB sliding, GB dislocation emission/absorption, dislocation sweep in grain cores and collective dislocation plasticity, and the origins of the pronounced strain rate sensitivity of fcc NC materials.

Stick-slip mechanism in a granular medium

The article describes experimental data on an unsteady slip of granular materials under soft shear loading. The common features are established between the obtained discontinuous slip of a granular material and the “stick-slip” model of solid bodies with a rigid contact. The mechanism is specified by reduction in the dry friction force during transition from the rest state to a slip. The author found the area of the shear-force drop depending on the particle slip velocity for quarts sand. The process refers to a slow-motion class and is an intermediate stage in transition from very slow to faster motion.

Stick-slip substructure in rapid tape peeling

The peeling of adhesive tape is known to proceed with a stick-slip mechanism and produces a characteristic ripping sound. The peeling also produces light and when peeled in a vacuum, even X-rays have been observed, whose emissions are correlated with the slip events. Here we present direct imaging of the detachment zone when Scotch tape is peeled off at high speed from a solid surface, revealing a highly regular substructure, during the slip phase. The typical 4-mm-long slip region has a regular substructure of transverse 220 μm wide slip bands, which fracture sideways at speeds over 300 m/s. The fracture tip emits waves into the detached section of the tape at ∼ 100 m/s, which promotes the sound, so characteristic of this phenomenon.

Scratch-induced deformation in fine- and ultrafine-grained bulk alumina

The nanoscratch behavior of two bulk α-alumina samples with 1.3 μm and 290 nm average grain sizes, respectively, was investigated using a nanoindenter in scratch mode, in combination with atomic force and scanning electron microscopy. A ductile to brittle transition was observed in the fine-grained sample, while the ultrafine-grained sample exhibited predominantly ductile deformation with a fish-bone feature indicative of a stick–slip mechanism. These findings suggest that grain refinement can increase the potential for plastic deformation in ceramics.

Fiber bundle model with stick-slip dynamics

We propose a generic model to describe the mechanical response and failure of systems which undergo a series of stick-slip events when subjected to an external load. We model the system as a bundle of fibers, where single fibers can gradually increase their relaxed length with a stick-slip mechanism activated by the increasing load. We determine the constitutive equation of the system and show by analytical calculations that on the macroscale a plastic response emerges followed by a hardening or softening regime. Releasing the load, an irreversible permanent deformation occurs which depends on the properties of sliding events. For quenched and annealed disorder of the failure thresholds the same qualitative behavior is found, however, in the annealed case the plastic regime is more pronounced.

각가속도 변화에 의해 탐지된 슬립에 기반한 주행로봇의 견인력 제어

The common requirements of rough terrain mobile robots are long-term operation and high mobility in rough terrain to perform difficult tasks. In rough terrain, excessive wheel slip could cause an increase in the amount of dissipated energy at the contact point between the wheel and ground or, even more seriously, the robot could lose all mobility and become trapped. This paper proposes a traction control algorithm that can be independently implemented to each wheel without requiring extra sensors and devices compared with standard velocity control methods. The proposed traction algorithm is analogous to the stick-slip friction mechanism. The algorithm estimates the slippage of wheels by angular acceleration change, and controls the increase or decrease state of torque applied to wheels Simulations are performed to validate the algorithm. The proposed traction control algorithm yielded a 65.4% reduction of total slip distance and 70.6% reduction of power consumption compared with the standard velocity control method.

Chasing drops: Following escaper and pursuer drop couple system

We study experimentally six different systems in which Marangoni flow is induced by two chemically different drops on a solid surface in air. In such systems one drop seems to chase away the other. We show that in all the systems studied, the Marangoni flow is induced at the solid–vapor interface as opposed to the air–liquid interface. This is true even for the case of water drop and alcohol drop on a glass surface (which corresponds to the “tears of wine” classical case). Thus we explain the drop motion as a result of an interfacial tension gradient which takes place primarily at the air–surface region and less, if at all, at the two other interfaces in the problem: the liquid–substrate or liquid–air interfaces. Then we follow the motion of drops on surfaces and find that it is discontinuous, i.e. characterized by stops and jumps as in a stick slip mechanism. We explain this behavior by an increase in the Laplace pressure that creates a higher anchoring pinning effect at the front edge of the moving drop. The understanding of this process has implications for passively separating mixed liquids.

Underlying mechanics of active nanocomposites with tunable properties

This paper proposes the development of a new class of nanotube-based piezoelectric polymeric composites with controllable bond expansion and contraction in the interface of nanotube and matrix for use in next-generation structural vibration control systems. It is theoretically shown that through applying external electrical field, the quality of adhesion between nanotube and the matrix at nanoscale can be imparted to result in novel engineered composites at macroscale with tunable mechanical properties ranging from stiffer structure to better damper, the attributes that are essential for structural vibration control. Along this line, two classes of nanotubes; namely, carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs), are investigated. It is demonstrated that BNNTs possess better tunability compared to CNTs due to their outstanding molecular crystalline structure. More specifically, it is shown that mechanical properties of BNNT-based structures are more sensitive to the variation of separation distance in the interphase zone, and the stick-slip mechanism, which is responsible for damping change, can easily occur in BNNT-reinforced piezoelectric polymers.

Biomimetic Core–Shell Fibril for Enhanced Adhesion

Fibrillar adhesive structures in nature are usually terminated by compliant plate-like elements that are critically important. We have fabricated a simple, model, core-shell fibrillar structure by coating an aluminum wire with (poly)dimethylsiloxane (PDMS). By partially etching the core metal, we obtain a compliant annular terminus. Measurements of the force required for this structure to detach from and slide against a glass substrate show that sliding is accommodated by a stick-slip mechanism and that substantial enhancement of adhesion can be achieved. A simple theoretical model, which is in good agreement with experimental data, shows that during the sticking phase the contact reduces in size and the mechanics of this process is controlled by the balance of energy release from the stretched PDMS and adhesion between it and the substrate.

Piezoelectric film-actuated motion platform with high resolution

A piezoelectric film-actuated motion platform with high resolution, which can run in two directions within a horizontal plane, is presented. On the basis of the analysis of the working principle of a stick-slip mechanism, a mathematical model describing its dynamic behavior is set up and simulated. Experiments of the motion performance and carrying ability on the prototype are conducted. Results show that this type of platform has advantages including a simple structure, small volume, light weight, stable step length, and large traveling range. When the driving voltage is less than 30 V, step error is less than 0.5 mm. The carrying ability of the platform is terrific and about 7–8 times its weight.

Identification of mechanisms competing with self-assembly during directed colloidal deposition

For many proposed applications of colloidal crystals it is desirable to obtain arrays with specific geometries. In this contribution, mechanisms competing with self-assembly during area specific deposition are identified and discussed. Specifically, flat chemically patterned substrates are created by micro-contact printing of alkanethiols and silanes. Polystyrene spheres (200–460 nm) are then deposited onto these patterned substrates by evaporative vertical deposition. The presence of a Rayleigh–Plateau instability and a stick–slip mechanism during area specific colloidal deposition are reported. It has also been demonstrated that when using the vertical deposition method, with patterned features of the scale 25–400 μm, difference in surface energy rather than electrostatic interactions dominate the direction of colloidal self-assembly.

Inducing large deformation in wood cell walls by enzymatic modification

It has been shown recently that wood with a high cellulose microfibril angle in the S2-layer, e.g. compression wood, shows permanent plastic deformation without significant mechanical damage to the matrix. This molecular stick-slip mechanism was explained by a gliding of the cellulose fibrils, after a certain shear stress in the matrix was exceeded [1]. Such a material behaviour would be desirable for various applications, for instance, to cover complex geometries with highly deformable veneers as needed in the automotive industry. However, veneers that are typically used for these purposes have a rather brittle failure behaviour, which leads to breakage, and drastic quality and productivity losses. A better deformability of such veneers might be achieved when the underlying deformation principles are conferred by modifying the wood cell wall components, in particular the cellulose fibrils and their matrix coupling. Enzyme treatments were performed on mechanically isolated wood fibres to plastify the entire lignified secondary cell wall. Cellulase Onozuka R-10 from Trichoderma viride (E.C.3.2.1.4) with activity on cellulose and xylan was utilized. Micromechanical tests and FT-IR microscopy studies revealed the change of mechanical properties and nanostructural features of the cell wall. An extended deformability was achieved for two of ten of the modified fibres.

The Predictions of the Fretting Wear between Supporting Grids and Cladding Tubes of Nuclear Fuel Rod

Fretting can be defined as the oscillatory motion with very small amplitudes, which usually occur between two contacting surfaces. Fretting wear is the removal of material from contacting surfaces through fretting action. This fretting wear, which occurs between cladding tubes of nuclear fuel rod and grids, causes in damages the cladding tubes by flow induced vibration in a nuclear reactor. In this paper the fretting wear tests were performed with two types of cladding tubes and three types of supporting grids in water. Fretting wear tests were done using various applied loads. From the results of fretting tests, the wear amounts of tube materials can be predictable by obtaining the wear coefficient using the work rate model. Depending on various normal load, tube materials, and supporting grid shapes, distinctively different wear scar of fretting and stick-slip mechanism can occur.

Determination of dynamic and sliding friction, and observation of stick-slip phenomenon on compacted polymer powders during high-velocity compaction

Dynamic friction, sliding friction, and the stick-slip phenomenon have been studied on compacted polymer powders during high-velocity compaction. It is particularly important from a practical point of view to distinguish the stick-slip mechanism and the sliding mechanism which occur concurrently. A practical experimental system has been successfully developed to study the dry frictional force and to measure the sliding coefficient between the polymer powder particles and the die wall during high-velocity compaction. Two new components have been introduced as relaxation assists to improve the compaction process by reducing the frictional forces. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form with less change in dimensions. The subsequent movement of the particles can be reduced and the powder bed attains a higher density with a minimum total elastic spring-back. The relative time of the stick-slip phenomenon during the compacting stage is also reduced so that the time needed to transfer from an intermittent stick-slip state to a smooth sliding state is reduced and the powder bed slides smoothly. It was found that the dynamic, dry frictional force is intermittent (stick-slip mechanism) at low compaction rates but that at high compaction rates is becomes more smooth (sliding mechanism). Both mechanisms depend on the nature of the powder and on the compaction conditions. At the beginning of the compaction stage, the sliding coefficient decreases due to an increase in the radial to axial stress ratio until the maximum pressure has been reached. During the reorganization stage, more time is needed for large particles to move, rotate and slide due to their relatively large diameter and mass. As a result, the reorganization stage is extended and the stick-slip phenomenon is observed more with increasing particle size. Much better transfer of the pressure throughout the powder bed and less loss of pressure lead to a higher sliding coefficient due to the overall friction during the compaction process. It was found that the sliding coefficient is proportional to the density. A more homogeneous density distribution in the compacted powder and a smaller pressure loss during compaction has a major influence on the sliding coefficient and on the quality of the compacted material.