New Hypothesis of Friction and Its Application to Design of a Railway Wheelset

Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroud-like contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between slick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response nf a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.

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Effects of Ball’s Rolling, Gyroscopic, and Spin Slide in a Ball Bearing on Raceway’s Stress and Fatigue Life

Journal of Tribology ◽

10.1115/1.4046568 ◽

2020 ◽

Vol 142 (8) ◽

Author(s):

Zhuang Chen ◽

Guanci Chen

Keyword(s):

Fatigue Life ◽

Friction Coefficient ◽

Contact Mechanics ◽

Friction Force ◽

Ball Bearing ◽

Equivalent Model ◽

Element Calculation ◽

Heavy Load ◽

Friction Forces ◽

Bearing Life

Abstract The motions between the ball and raceway in a ball bearing involve rolling, gyroscopic, and spin slide. These complex motions result in the serious distribution of the friction force. Based on the contact mechanics in tribology, the friction force greatly affects stress and fatigue life. Thus, it is necessary to figure out the effects of the motions and its friction force of ball–raceway contact on the fatigue life of a ball bearing. In this paper, first, the equivalent model of ball–raceway contact was studied and established for the convenience of finite element calculation. Second, the contact mechanics considering the friction force with the friction coefficient from 0 to 0.3 was computed. The influences of the motions and its friction forces of ball–raceway contact on the raceway’s stress were analyzed. Third, based on different structure fatigue life algorithms, the raceway’s fatigue life of the cases with the friction coefficient 0, 0.05, 0.1, and 0.3 were studied. The raceway’s fatigue life based on ISO 281-2007 bearing life theory is studied. Results show that the friction force on the contact surface has some influence on the stress and fatigue life to a certain extent. Especially, the ball’s spin has the greatest influence on the stress distribution and fatigue life of the raceway. Thus, for the cases of heavy load and high friction coefficient, the effect of the friction force of ball–raceway contacts cannot be neglected.

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Forced Response of Shrouded Blades With Intermittent Dry Friction Force

Volume 5: Structures and Dynamics, Parts A and B ◽

10.1115/gt2008-51041 ◽

2008 ◽

Author(s):

Weiwei Gu ◽

Zili Xu ◽

Lv Qiang

Keyword(s):

Friction Coefficient ◽

Friction Force ◽

Normal Load ◽

Harmonic Balance Method ◽

Forced Response ◽

Gap Size ◽

Algebraic Equations ◽

Friction Damper ◽

Friction Forces ◽

Contact Points

The gap friction damper model is presented in this paper, which is employed to simulate the friction forces at the contact points of the shroud interface. Using the harmonic balance method (HBM), the friction force can be approximated by a series of harmonic functions. The governing differential equations of blade motion are transformed into a set of nonlinear algebraic equations, which can be solved iteratively to yield the steady-state response. The results show that the forced response is attenuated due to the additional damping introduced by frictional slip. The predicted results agree well with those of the Runge-Kutta method. In addition, the effect of parameters of damping structures such as the gap size, friction coefficient and normal load on the forced response of blades were studied. The results show that increasing the damper gap size causes a increase in resonant response. However, the increment isn’t obvious. In addition, an increase in friction coefficient or normal load decreases the forced response of blade.

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Tribological behaviors of DLC films with hierarchical surface textures under water lubrication: A molecular dynamic simulation

Journal of Micromechanics and Molecular Physics ◽

10.1142/s2424913021500053 ◽

2021 ◽

pp. 2150005

Author(s):

Huan Chen ◽

Guangan Zhang ◽

Zhibin Lu ◽

Xia Li ◽

Narasimalu Srikanth ◽

...

Keyword(s):

Bearing Capacity ◽

Friction Force ◽

Normal Load ◽

Complete Separation ◽

Dynamics Simulation ◽

Water Molecules ◽

Friction Forces ◽

Surface Textures ◽

Tribological Behaviors ◽

Temporary Stabilization

Tribological behaviors of diamond-like carbon (DLC) films with different levels of hierarchical surface textures with lubricant water molecules are investigated through molecular dynamics simulation. The friction forces stabilize at a small value for small normal loads, due to the complete separation between DLC films by water molecules, while friction forces with large normal loads show complicated changes under the cooperation of interfacial evolution and water behaviors. Under large normal loads, friction force increases firstly due to the direct contact of surface textures which are subsequently worn and graphitized, resulting in the temporary stabilization of friction force at a large value. With their further wearing, the amount of interfacial carbon clusters decreases and water molecules distribute evenly at interface, which leads to the gradual decrease and final stabilization of friction force. During the sliding, the water molecules show a restoration in the structure and amount of hydrogen bonds, thus making these molecules play different roles in various stages, i.e., these molecules demonstrate a better diffusion during the friction rise and an enhanced separating effect for DLC films during the friction stabilization. Furthermore, the same amount of water molecules in the one-level hierarchical (L1) model has a larger bearing capacity than that in the two-level hierarchical (L2) model. When the normal load exceeds the bearing capacity of water, the friction force for model L2 is more stable and smaller than that for model L1 after running-in periods due to flattened interfaces and evenly distributed water molecules.

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The Friction Forces Between Si Tip and Multilayer Graphene

Volume 9: Micro- and Nano-Systems Engineering and Packaging, Parts A and B ◽

10.1115/imece2012-87131 ◽

2012 ◽

Author(s):

Yan Zhang ◽

Yingying Wang ◽

Yunfei Chen ◽

Yujuan Wang

Keyword(s):

Friction Force ◽

Graphene Layer ◽

Adhesion Force ◽

Normal Load ◽

Multilayer Graphene ◽

Friction Forces ◽

Layer Number ◽

Si Substrates ◽

Atomic Force ◽

Natural Oxide

Mechanical peeling method is used to prepare multilayer graphene on silicon wafer with natural oxide, and the layer number of graphene is determined through atomic force microsopy (AFM) topography image and optical image. The friction force between Silicon tip and multilayer graphene and SiO2/Si substrates is measured with AFM. It is found that the friction force is reduced with the increase of the graphene layer number and approaches the value between the Si tip and graphite. Through comparing the tip sliding on graphene with different layers, the deformation of graphene is believed to be the main reason causing the decrease of the friction force with the layer number. When the normal load is much larger than the adhesion force, friction force increases with normal load linearly. However, while normal load closes to the adhesion force, friction force is independent of the normal load.

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Non-Linear Signal Analysis Applied to Surface Wear Condition Monitoring in Reciprocating Sliding Testing Machines

Shock and Vibration ◽

10.1155/2006/938951 ◽

2006 ◽

Vol 13 (4-5) ◽

pp. 327-341 ◽

Cited By ~ 1

Author(s):

Francisco Paulo Lépore Neto ◽

José Daniel Biasoli de Mello ◽

Marcelo Braga dos Santos

Keyword(s):

Friction Force ◽

Signal Analysis ◽

Testing Machine ◽

Wear Testing ◽

Friction Forces ◽

Prismatic Body ◽

Linear Path ◽

Elastic Bodies ◽

Non Linear ◽

Linear Signal

When the surfaces of two elastic bodies present relative motions under certain amount of contact pressure the mechanical system can be unstable. Experiments conducted on elastic bodies in contact shown that the dynamic system is self-excited by the non-linear behavior of the friction forces. The main objective of this paper is to estimate the friction force using the vibrations signals, measured on a reciprocating wear testing machine, by the proposed non-linear signal analysis formulation. In the proposed formulation the system global output is the sum of two outputs produced by a linear path associated in parallel with a non-linear path. This last path is a non-linear model that represents the friction force. Since the linear path can be identified by traditional signal analysis, the non-linear function can be evaluated by the global input/output relationships. Validation tests are conducted in a tribological system composed by a sphere in contact with and a prismatic body, which has an imposed harmonic motion. The global output force is simultaneously measured by a piezoelectric and by a piezoresistive load cells. The sphere and prismatic body vibrations are measured by a laser Doppler vibrometer and by an accelerometer respectively. All signals are digitalized at the same time base and the data is transferred to a microcomputer. The non-linear signal analysis technique uses this data to identify the friction force.

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Modeling of Friction Contact and Its Application to the Design of Shroud Contact

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2817082 ◽

1997 ◽

Vol 119 (4) ◽

pp. 958-963 ◽

Cited By ~ 29

Author(s):

B.-D. Yang ◽

C.-H. Menq

Keyword(s):

Friction Force ◽

Normal Load ◽

Harmonic Balance Method ◽

Forced Response ◽

Effective Stiffness ◽

Force Model ◽

Stick Slip ◽

Friction Forces ◽

Friction Joint ◽

Stiffness And Damping

Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroudlike contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between stick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response of a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.

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Influence of Nanoscale Textured Surfaces and Subsurface Defects on Friction Behaviors by Molecular Dynamics Simulation

Nanomaterials ◽

10.3390/nano9111617 ◽

2019 ◽

Vol 9 (11) ◽

pp. 1617 ◽

Cited By ~ 1

Author(s):

Ruiting Tong ◽

Zefen Quan ◽

Yangdong Zhao ◽

Bin Han ◽

Geng Liu

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Friction Force ◽

Copper Substrate ◽

Dynamics Simulation ◽

Textured Surfaces ◽

Friction Forces ◽

Subsurface Structures ◽

Texture Orientation ◽

Subsurface Defects

In nanomaterials, the surface or the subsurface structures influence the friction behaviors greatly. In this work, nanoscale friction behaviors between a rigid cylinder tip and a single crystal copper substrate are studied by molecular dynamics simulation. Nanoscale textured surfaces are modeled on the surface of the substrate to represent the surface structures, and the spacings between textures are seen as defects on the surface. Nano-defects are prepared at the subsurface of the substrate. The effects of depth, orientation, width and shape of textured surfaces on the average friction forces are investigated, and the influence of subsurface defects in the substrate is also studied. Compared with the smooth surface, textured surfaces can improve friction behaviors effectively. The textured surfaces with a greater depth or smaller width lead to lower friction forces. The surface with 45° texture orientation produces the lowest average friction force among all the orientations. The influence of the shape is slight, and the v-shape shows a lower average friction force. Besides, the subsurface defects in the substrate make the sliding process unstable and the influence of subsurface defects on friction forces is sensitive to their positions.

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Experimental Study of Static Friction in a Spherical Elastic-Plastic Contact

Volume 3: Design; Tribology; Education ◽

10.1115/esda2008-59008 ◽

2008 ◽

Author(s):

Andrey Ovcharenko ◽

Gregory Halperin ◽

Izhak Etsion

Keyword(s):

Friction Force ◽

Normal Load ◽

Static Friction ◽

Tangential Displacement ◽

Accurate Identification ◽

Elastic Plastic ◽

Static Friction Coefficient ◽

Wide Range ◽

Material Good ◽

Contact Diameter

The elastic-plastic contact between a deformable sphere and a rigid flat during pre-sliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. It is found that at low normal loads the static friction coefficient depends on the normal load in breach of the classical laws of friction. The pre-sliding displacement is found to be less than 5 percent of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

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Motion of masses with asymmetric and symmetric friction. Application to fault sliding

10.5194/egusphere-egu21-3934 ◽

2021 ◽

Author(s):

Rui Xiang Wong ◽

Elena Pasternak ◽

Arcady Dyskin

Keyword(s):

Frictional Force ◽

Normal Load ◽

Power Spectra ◽

Inertial Force ◽

Friction Reduction ◽

Relative Mass ◽

Hydraulic Fractures ◽

Driving Frequency ◽

Stick Slip ◽

Friction Forces

This study analyses a situation when a geological fault contains a section of anisotropic gouge with inclined symmetry axes (e.g. inclined layering), Bafekrpour et al. [1]. Such gouge in a constrained environment induces, under compression, asymmetric friction (different friction forces resisting sliding in the opposite directions). The rest of the gouge produces conventional symmetric friction. A mass-spring model of the gouge with asymmetric and symmetric friction sections is proposed consisting of a mass with asymmetric friction connected through a spring to another mass with symmetric friction. These masses are set on a base subjected to vibration. A parametric analysis is performed on this system. Two distinct characteristic regimes were observed: recurrent movement resembling stick-slip motion similar to predicted by [2] and sub-frictional movement. Recurrent movement arises when the inertial force is sufficient to overcome frictional force of a block with symmetric friction. Sub-frictional movement occurs when the inertial force is not sufficient to overcome frictional force of an equivalent system with only symmetric friction. The sub-frictional movement is produced by the force in the connecting spring increased due to the movement of the asymmetric friction block in the direction characterised by low friction. We formulate the criterion at which sub-frictional movement occurs. The occurrence of sub-frictional depends upon the relative mass of the symmetric and asymmetric friction sections, as well as the amplitude and driving frequency of the excitation. Power spectra of the produced vibrations are determined for both regimes. The results can shed light on mechanisms of sliding over pre-existing discontinuities and their effect on seismic event generation and propagation of hydraulic fractures in the presence of discontinuities.[1] Bafekrpour, E., A.V. Dyskin, E. Pasternak, A. Molotnikov and Y. Estrin (2015), Internally architectured materials with directionally asymmetric friction. Scientific Reports, 5, Article 10732.[2] Pasternak, E. A.V. Dyskin and I. Karachevtseva, 2020. Oscillations in sliding with dry friction. Friction reduction by imposing synchronised normal load oscillations. International Journal of Engineering Science, 154, 103313.Acknowledgement. AVD and EP acknowledge support from the Australian Research Council through project DP190103260.

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