Interface Friction Characteristics Research Articles

Effect of Process Variables on Interface Friction Characteristics in Strip Drawing of AA 5182 Alloy and Its Formability in Warm Deep Drawing

Warm forming is widely used to enhance the formability of aluminum alloy sheets. In warm deep drawing, the process variables significantly affect frictional characteristics at the tool–blank interface. It has been a conventional approach to use a constant value of friction coefficients in the finite element (FE) simulations. However, this can occasionally result in suboptimal accuracy of the predictions. In the present work, strip drawing tests were carried out on AA5182 aluminum alloy sheets to investigate the effect of important process variables, namely, temperature, contact pressure, and drawing speed, on the friction coefficient in the warm forming temperature range (100–250 °C) under lubricated condition. The results obtained from the strip drawing tests were used for defining the friction conditions in the simulation of warm deep drawing of cylindrical cups incorporating the variation of the friction coefficient with contact pressure and speed at different temperatures. The Barlat89 yield criterion was used to define the effect of anisotropy in the material. The Voce hardening law and Cowper–Symonds model were used to incorporate the effect of strain hardening and strain rate, respectively, in the simulation. Drawability and peak force were compared with the predictions when a constant friction coefficient was assumed. Warm deep drawing experiments were conducted to validate the predicted drawability and load–displacement curves. It is clearly observed that the accuracy of prediction of the limiting drawing ratio and peak load through simulations is improved by incorporating the effect of pressure and speed on friction coefficient as it captures the local variations of friction during warm deep drawing precisely, rather than assuming a constant average friction coefficient at all the tool–blank contact areas.

Analysis of the rolling interface stiffness and friction characteristics of multi-scale rolling mill based on contact probability approximation

Analysis of the rolling interface stiffness and friction characteristics of multi-scale rolling mill based on contact probability approximation

Analysis of the rolling interface stiffness and friction characteristics of multi-scale rolling mill based on contact probability approximation

Analysis of the rolling interface stiffness and friction characteristics of multi-scale rolling mill based on contact probability approximation

Research on the Effect of Particle Size on the Interface Friction between Geogrid Reinforcement and Soil

For projects such as roads and railways, different fillers are often selected, and these also relate to the area where the project is located, so the characteristics of the filling soil should be considered in the design. However, the characteristics of the soil used in geosynthetic-reinforced soil (GRS) structure design are routinely simple soil properties and are not based on testing of soil with reinforcement. In order to study the influence of fillers with different particle sizes on the interface friction characteristics between the geogrid and soil, a self-developed large-scale pull-out testing machine was used. Under the action of a normal static load, pull-out tests were carried out with different fillers, such as sand, silt and gravel. According to the test results, the greater the stress applied in the normal direction, the greater the maximum pull-out force. As for the different fillers, shear stress from material with a larger particle size, such as gravel, was larger than that of sand and silt. Finally, to reveal the pattern of how the soil particles moved during the pull-out test, from a microscopic point of view, and the effect on particle–mesh size ratio, a series of discrete element method (DEM) analyses were conducted by PFC2D. The results indicated that a larger particle is more likely to rotate and move during the test, and this makes the interlocking effect greater between the geogrid and the soil, which leads to a larger pull-out force in the laboratory test.

Study on friction behavior at the interface between prosthetic socket and liner

The friction characteristics at the interface between prosthetic socket and liner have an important influence on the walking function and wearing comfort of amputees. The frictional behavior at the prosthetic socket/liner interface can provide theoretical guidance for the design and selection of prosthetic materials. So it is of great significance to study the friction behavior at prosthetic socket/liner interface. The surface roughnesses of the prosthetic socket and liner materials were measured by a laser confocal microscope. The frictional behavior at the prosthetic socket/liner interface was studied on a UMT TriboLab Tribometer by simulating the reciprocating sliding contact mode. An infrared camera was used to take thermal images and then calculated the temperature increase at the socket/liner interface. The coefficient of friction of the silicon rubber fabric are significantly smaller than that of the foam liner materials. The frictional energy dissipation at the liner/acrylic socket interface is the smallest, while it is greater for 3D-printed socket materials. Meanwhile, the temperature increase has a positive correlation to the coefficient of friction and frictional energy dissipation. The three kinds of 3D-printed materials with high surface roughness have higher interface coefficient of friction and energy dissipation than acrylic material. The stiffness and energy consumption play an important role in the interface friction characteristics of the prosthetic liner materials. The appropriate coefficient of friction at the surface between prosthetic socket and liner is essential. A type of the reinforcement fiber has influence on the friction behavior of the 3D-printed reinforced nylon.

Motion behavior of graphene sheets and friction characteristics between the interfaces of silicon-based materials

The <i>ab initio</i> molecular dynamics method is used to simulate the friction process of the graphene sheet as lubricant added to the silicon-based material interface under the action of compression and shear, and the influence of water molecules and oxidation of graphene surface on the movement behavior of graphene sheet are studied. In a dry environment, the pristine graphene (PG) sheet will slip only when the pressure is high. Owing to the presence of surface functional groups, a strong force is formed between the graphene oxide (GO) sheet and the substrate. The direction of the hydroxyl groups on the surface of the upper slab is consistent as the upper slab moves at a constant speed, resulting in the fact that the force between the GO sheet and the upper slab is greater and the GO sheet slides forward with the upper slab. Owing to the formation of mechanical interlock between the GO sheet and the lower slab surface, the GO sheet no longer slips when the pressure is high. In a humid environment, the interface structure affects the overall distribution and movement state of water molecules. The water molecules between the PG sheet and the upper slab are adsorbed only on the surface of the upper slab and always remain in a “flat” state, and their motion behavior is consistent with the upper slab’s. Comparing with a dry environment, the PG sheet starts to slip only when the pressure is high. Since the hydroxyl orientation angle on the surface of the upper slab is greater than the hydroxyl orientation angle on the surface of the GO sheet, the water molecules gradually change from the "flat" state to the slightly “upright” state as the pressure increases. The change of the orientation of water molecules makes the bonding strength between water molecules and the GO sheet gradually decrease, leading to a relative slip between them. The change in the movement behavior of the graphene sheet causes the shear plane to change. There is a positive correlation between the velocity fluctuation mean square error of the graphene sheet and the friction coefficient as the oxidation rate of graphene sheet increases under different coverages of water molecules, indicating that the motion behavior of the lubricant affects the interface friction characteristics.

Study on the influence of micro-textures on wear mechanism of cemented carbide tools

Wear behavior of micro-textured insert with lubrication was studied. Micro-pits with different diameters (80–200 μm), depths (3–10 μm), and area occupancies (10–30%) were manufactured on the tool rake face near the main cutting edge. Experimental research was conducted to reveal the effect of micro-pits on tool-chip interface friction characteristics. Besides, the texture parameter with better tribological characteristics was selected to study the wear mechanism of textured insert. Scanning electron microscopy analysis was conducted on the worn area of rake face. The results confirmed that the micro-textures can effectively reduce the average shear strength of rake face and actual tool-chip contact length during machining. The best average friction coefficient can be obtained with texture diameter of 170 μm, depth of 7 μm, and area occupancy of 20%. Adhesive wear, diffusion wear, and oxidation wear appeared on the worn area of rake face. The micro-textures can effectively reduce the diffusion wear and suppress the built-up edge (BUE) by improving tool-chip interface friction characteristics. The findings are of significance for enhancing the application of textured insert with excellent tribological characteristics.

Shear strength and interface friction characteristics of expandable foam grout

The deterioration of buried pipes in urban areas leads to the formation of underground cavities, which may induce road subsidence. To fill these cavities, this study investigates the shear strength characteristics of expandable foam grout (EFG) and the interface between EFG and two types of sands. A series of direct shear tests is conducted using EFG specimens prepared under different conditions of curing time and unit weights of sand. After three days of curing, the shear stress curves of EFG and EFG–sand interface obtained at three normal stresses indicate brittle behavior and ductile behavior, respectively. Friction angles of the EFG increase with curing time, while those of the EFG–sand interface remain almost constant. The interface friction angles between the EFG and sands are smaller than or equal to the internal friction angles of the sands. Therefore, the shear strength of the EFG–surrounding soil interface should be given more attention than the high shear strength of the EFG, to fill underground cavities.

Cupronickel B10 and YG6 interface friction characteristics tested on a friction device for metal cutting

Friction behavior is an important component of the metal-cutting mechanism. A simple and effective friction device that can yield the desired friction characteristics is required. In this article, a friction device with a solid–liquid–gas vibration reduction was proposed to research the interface friction characteristics. The interface friction characteristics of cupronickel B10 and YG6 were obtained through the new friction device, including the friction force, friction temperatures, and friction coefficient. The results show that an experimental solid–liquid–gas vibration reduction is feasible and effective to obtain the interface friction characteristics. The relationship between the friction-interface temperature T2 and the measured-point temperature T1 that was obtained by a heat-conduction model is linear. For cupronickel B10 and YG6, the friction coefficient gradually decreases with an increase in friction speed, and increases initially and then decreases with an increasing load. Based on the effect of friction temperature, friction speed, and load, a friction model for the interface friction characteristics of cupronickel B10 and YG6 was obtained.

Seismic fragility of buried steel natural gas pipelines due to axial compression at geotechnical discontinuities

This paper presents an extended set of numerical fragility functions for the structural assessment of buried steel natural gas (NG) pipelines subjected to axial compression caused by transient seismic ground deformations. The study focuses on NG pipelines crossing sites with a vertical geotechnical discontinuity, where high compression straining of a buried pipeline is expected to occur under seismic transient ground deformations. A de-coupled numerical framework is developed for this purpose, which includes a 3D finite element model of the pipe–trench system employed to evaluate rigorously the soil–pipe interaction effects on the pipeline axial response in a quasi-static manner. One-dimensional soil response analyses are used to determine critical ground deformation patterns at the vicinity of the geotechnical discontinuity, caused by the ground shaking. A comprehensive parametric analysis is performed by implementing the proposed analytical framework for an ensemble of 40 recorded earthquake ground motions. Crucial parameters that affect the seismic response and therefore the seismic vulnerability of buried steel NG pipelines namely, the diameter, wall thickness, burial depth and internal pressure of the pipeline, the backfill compaction level, the pipe–soil interface friction characteristics, the soil deposits characteristics, as well as initial geometric imperfections of the walls of the pipeline, are systematically considered. The analytical fragility functions are developed in terms of peak ground velocity at the ground surface, for four performance limit states, considering all the associated uncertainties. The study contributes towards a reliable quantitative risk assessment of buried steel NG pipelines, crossing similar sites, subjected to seismically-induced transient ground deformations.

Interface Friction of Double-Walled Carbon Nanotubes Investigated Using Molecular Dynamics †

The interface friction characteristics of double-walled carbon nanotubes (DWCNTs) are studied using molecular dynamics simulations based on the Tersoff potential. The effects of the DWCNT type, outer shell diameter, and temperature are evaluated. The simulation results show that when an inner shell is being pulled out from a DWCNT, the friction force and normal force between shells increase with increasing the outer shell diameter. The noise of the friction force significantly increases with the increasing temperature. Zigzag@zigzag and armchair@armchair DWCNTs exhibit larger friction forces and smaller normal forces compared to those of chiral@chiral DWCNTs.

Rolling interface friction dynamics of hot strip continuous rolling and its effect on mill chatter

According to the fluid mechanics and rolling theory, the rolling interface friction dynamic characteristics and their influence on rolling speed, rolling load, roller material, rolling temperature and oil properties were studied respectively with lubrication or without lubrication in hot rolling. The two-dimensional Reynolds equation was established for steady and unsteady rolling friction interface. Through the research of rolling interface friction characteristics influence on the mill vibration, we found that when the lubrication film thickness in the roll gap was thicker, the friction coefficient was lower, its damping effect and system stability was worse. And if the rolling speed is greater than a certain value, the rolling interface friction coefficient will fall sharply with the increase of rolling speed and produces the self-excited vibration caused by negative damping. So the contrast test with different rolling interface has been carried out, such as the emulsion is open or close, high chromium cast iron/high speed steel roller is put to use, high chromium cast iron roller is grinded finely or coarsely, rolling speed is normal/reduced. And the results showed that it had an obvious effect on the mill vibration suppression by the adoption of the emulsion close and high speed steel roller.

Pullout Test Research on Interfacial Interaction of Reinforced Band and Gravelly Soil

Taking steel-plastic composite reinforced band (CAT) and gravelly soil as the test materials, the pullout tests of reinforced band in gravelly soil with different water contents have been carried out by the laminated shear test instrument. The interface friction characteristics between reinforced band and gravelly soil are studied, and the influences of water content on the interaction characteristics are also discussed. Results show that (1) the extraction of reinforced band is a gradual process. The anchor end began to move firstly because of the extensibility of reinforced belt itself. As interface friction gradually transfer backward by, the free end start to move onward, then displacement schedule curves of the anchor end and the free end are gradually parallel, the whole movement of reinforced belt happens immediately. (2) Pulling force and displacement curve of the pullout friction test displays obviously nonlinear characteristics. Pulling force of the reinforced band increases greatly with increasing displacement at the beginning of the test, then decrease with the increasing displacement after the peak value is reached, the force-displacement curves generally exhibit strain soften characteristics. But it present strain hardening trend under greater normal stress, and pullout frictional strength increases with the increasing normal stress. (3) The pullout friction coefficient of the interface is sensitive to water content. It decreases linearly with the increasing water content.

Soil-Geomembrane Interface Friction Characteristics

Soil-Geomembrane interface friction characteristics were investigated using direct shear test apparatuses at a normal stress from 0.036 to 0.6kgf/cm2. Two different sizes of interface area were used, which were about 30 and 1000cm2. Then Pull-out tests were also carried varing the length of embedded Geomembrane under normal stress of 0.036kgf/cm2. Testing materials were kinugawa-river sand of which dry-density was 1.79gf/cm3 and High Density Poly-Ethylen with 1mm of thickness. As a results, a sample with larger interface area gave lower friction factor. The pull-out capacities might be estimated appropriately using a friction factor derived from larger apparatus although they were overestimated using a friction factor from smaller one.

Nonlinear Dynamics of Rotor/Blade/Casing Rub Interactions

This paper considers the transient analysis of rub problems in high-speed rotating equipment that involve interactions between the rotor, blades, and casing. Special emphasis is given to ascertaining the participation characteristics of turbine/impeller blades during the overall rub event. To generalize the scope of the work, single and multiple blade rub events are considered including the effect of such system parameters as imbalance magnitude, blade/rotor stiffness, system damping, and rub interface friction characteristics.

Effect of Die Surface Composition on Friction and Adhesion in Deformation Processing

An experimental investigation was carried out to determine interface friction and adhesion characteristics of workpiece and die materials under pressures and temperatures typical of plastic deformation. Evaluations were made using a twist-compression technique, which provided conditions of enforced sliding, and a ring upsetting technique in which sticking friction was predominant. Hot-rolling tests were performed to correlate the results with conventional metalworking practices. Workpiece materials included aluminum, titanium, and molybdenum alloys, low-alloy steel, and a nickel-base superalloy. Tools were made of die steels, tungsten carbide, and diffusion-coated die materials to evaluate the effects of surface chemistry and hardness in unlubricated contact with the workpiece material. Significant variations in friction due to die surface composition were observed, the effects being more marked with forced interface sliding. The most promising die materials were boronized 4140 steel and titanium carbide-coated 4140 steel. The investigation has shown that with the proper choice of die and workpiece material combinations, friction can be reduced and more importantly, adhesion can be minimized thereby avoiding or delaying catastrophic die failure in the event of lubricant breakdown.