Microstructure and Tribological Properties of TPU/Fluoropolymer Composites

2020 ◽  
Vol 35 (5) ◽  
pp. 415-421
Author(s):  
K. Rohm ◽  
M. Amirkhosravi ◽  
I. Manas-Zloczower
Keyword(s):  
Shear Stress ◽  
Coefficient Of Friction ◽  
Solid Phase ◽  
Thermoplastic Polyurethane ◽  
Stress Transfer ◽  
Interfacial Area ◽  
Melt Mixing ◽  
Molded Part ◽  
The Matrix ◽  
The Coefficient Of Friction

Abstract A network of poly(tetrafluoroethylene) (PTFE) microfibers in a thermoplastic polyurethane (TPU) was prepared by melt mixing the TPU with solid PTFE particles. The effect of rotor speed on the fiber dimensions was investigated. Higher shear stress was found to be the critical parameter for producing thinner PTFE fibers, rather than the shear rate imposed by the mixer. Shear stress transfer from the melt to the PTFE crystal results in solid phase plastic deformation, and the efficiency of the deformation depends on the shear stress in the matrix. All of the PTFE fiber/TPU composites show lower coefficients of friction compared with the neat TPU. The magnitude of the coefficient of friction was found to correlate with the interfacial area between PTFE and TPU generated by the microfiber network. However, for macroscale PTFE agglomerates, the reduction in the coefficient of friction is mostly affected by the uneven distribution of PTFE in the bulk and on the molded part surface.

THE INFLUENCE OF GLASSY CARBON AND ITS FORMS ON TRIBOLOGICAL PROPERTIES OF ALUMINIUM MATRIX COMPOSITES

Tribologia ◽  
2019 ◽  
Vol 285 (3) ◽  
pp. 79-87 ◽  
Author(s):  
Jerzy MYALSKI ◽  
Andrzej Posmyk ◽  
Bartosz HEKNER ◽  
Marcin GODZIERZ
Keyword(s):  
Coefficient Of Friction ◽  
Tribological Properties ◽  
Glassy Carbon ◽  
Amorphous Structure ◽  
Matrix Composites ◽  
Alloy Matrix ◽  
Entire Volume ◽  
Carbon Particles ◽  
The Matrix ◽  
The Coefficient Of Friction

Carbon with an amorphous structure was used as a component to modify the tribological properties of engineering plastics. Its construction allows the formation of carbon-based wear products during friction, adhesively bonded to the surface of cooperating machine parts, acting as a solid lubricant. The work compares the tribological properties of two groups of composites with an aluminium alloy matrix in which glassy carbon appeared in the form of particles and an open cell foam fulfilling the role of strengthening the matrix. The use of spatial structures of reinforcement provides, in comparison with the strengthening of particles, homogeneity of carbon distribution in the entire volume of the composite. The tests carried out on a pin-disc tester showed that the use of spatial carbon structures in the composite ensures a greater coefficient of friction stability than when reinforcing with particles, and the coefficient of friction with a small proportion of carbon foams (about 1 wt%) is comparable with the coefficient of friction in the contact with composites containing 5-10% carbon particles in granular form.

The Influence of the Coefficient of Friction on the Elastic Stress Concentration Factor for a Pin-Jointed Connection

1962 ◽  
Vol 13 (1) ◽  
pp. 17-29 ◽  
Author(s):  
T. H. Lambert ◽  
R. J. Brailey
Keyword(s):  
Shear Stress ◽  
Stress Concentration ◽  
Coefficient Of Friction ◽  
Stress Concentration Factor ◽  
Elastic Stress ◽  
Maximum Shear Stress ◽  
Interference Fit ◽  
Stress Load ◽  
The Coefficient Of Friction ◽  
Very High

SummaryThe benefit to be obtained by using an interference fit between the pin and plate in a pin-jointed connection has already been established. An examination of the published results shows that some non-linearity occurs in the mechanism of load transference from the pin to the plate since, except at very high initial interference, doubling the load on the joint more than doubles the maximum shear stress in the plate. An examination of the stress-load relationship shows a distinct discontinuity, the load at which this discontinuity occurs being dependent upon both the initial interference and the coefficient of friction between the pin and the plate. It is shown that the results hitherto published correspond to a coefficient of friction between the pin and the plate of 0.3 and results for lower and higher coefficients are given.

A Contribution to the Theory of Friction and Wear and the Relationship between them

1976 ◽  
Vol 190 (1) ◽  
pp. 477-488 ◽  
Author(s):  
J. Halling
Keyword(s):  
Shear Stress ◽  
Coefficient Of Friction ◽  
Interfacial Shear Stress ◽  
Failure Criteria ◽  
Elastic Behaviour ◽  
Total Load ◽  
Perfectly Plastic ◽  
The Coefficient Of Friction ◽  
Wear Law ◽  
The Relationship

The nature of the interaction between a rigid spherical asperity and an asperity governed by the stress/strain law [Formula: see text] is studied. The interfacial shear stress is defined by f τmax where 0 < f < 1, τ maxbeing the maximum allowable shear stress at the contact. By integrating the total effect of a population of such surface asperities expressions for the total frictional forces, and the total load are derived. The value of the coefficient of friction is thus obtained and the special conditions for perfectly plastic and elastic behaviour are considered. In both cases the friction coefficient is seen to contain a term defined by the deformation and dependent on surface roughness and a term totally defined by f. Using the same model a fatigue type failure criteria is introduced to predict the volume of wear. It is then possible to produce a wear law which is consistent with experience and which includes the relationship between the wear and the coefficient of friction.

Experimental investigation of the dynamic properties of natural cartilage under reciprocating sliding at two typical rubbing pairs

2019 ◽  
Vol 233 (9) ◽  
pp. 1318-1326 ◽  
Author(s):  
Shanhua Qian ◽  
Liguo Liu ◽  
Zifeng Ni ◽  
Yong Luo
Keyword(s):  
Coefficient Of Friction ◽  
Solid Phase ◽  
Dynamic Properties ◽  
Surface Characteristics ◽  
High Water ◽  
Sampling Frequency ◽  
High Water Content ◽  
Data Systems ◽  
The Coefficient Of Friction ◽  
Contact Displacement

Natural cartilage is a multiporous viscoelastic biological material with extremely high water content and a macroscopically curved surface. Due to the sampling frequency limitations of typical data systems, the dynamic properties of the contact of cartilage against other surfaces, including rubbing surface characteristics and coefficient of friction, is still not completely understood. In this study, cartilage samples were retrieved from 18- to 24-month-old bovine femora. Contact displacement and coefficient of friction of two typical rubbing pairs of for cartilage-on-glass and cartilage-on-cartilage were recorded using a UMT-2 testing rig using a high sampling frequency data system. A five-point sliding average method was adopted to analyze the experimental data. The results showed that contact displacement comprised cartilage deformation and nominal rubbing profile. Cartilage deformation increased nonlinearly with time while nominal rubbing profile was associated with the rubbing configuration and appeared to be a factor in the low surface sample configuration. Higher cartilage deformation resulted in more load being carried by the solid phase and coefficient of friction with the time as a whole, but the surface characteristics played a role in determining the coefficient of friction in the cartilage-on-cartilage configuration but a lesser role for cartilage-on-glass. Therefore, surface characteristics have a clear role in defining the dynamic properties of natural viscoelastic soft biological materials and these research results will help to evaluate in future the frictional properties of artificial cartilage biomaterials.

Junction growth in metallic friction: the role of combined stresses and surface contamination

1959 ◽  
Vol 251 (1266) ◽  
pp. 378-393 ◽  
Keyword(s):  
Shear Stress ◽  
Tangential Stress ◽  
Coefficient Of Friction ◽  
Tangential Force ◽  
Critical Shear Stress ◽  
Surface Contamination ◽  
Combined Stresses ◽  
The Coefficient Of Friction ◽  
True Contact ◽  
Metallic Friction

This paper extends earlier work on the adhesion mechanism of friction and considers in particular the growth in area of contact as the tangential force is increased to the point at which gross sliding occurs. The earlier studies assumed that the area of true contact A is the same as that produced under static loading so that A = W / p 0 where W is the normal load and p 0 the plastic yield pressure of the metal. If the junctions have a specific shear strength s , the friction F , that is the force to shear them, will be F = As and the coefficient of friction becomes μ = s / p 0 (Bowden & Tabor 1954). Recent studies, however, show that as the tangential stress is applied the area of true contact increases according to a relation of the type p 2 + αs 2 = p 2 0 where p is the normal and s the tangential stress in the contact region and α an appropriate constant. With thoroughly outgassed metals, junction growth generally proceeds until practically the whole of the geometric area is in contact and coefficients of friction of the order of 50 or more are observed (Bowden & Young 1951). If the interface is contaminated, the stresses transmitted through it cannot exceed the critical shear stress of the interface. The new point developed in this paper based on the work of Courtney-Pratt & Eisner (1957), is that until the shear stress reaches this value junction growth occurs as for clean metals. Beyond this point, however, further junction growth is impossible and gross sliding occurs within the interfacial layer itself. The analysis given here shows that if the interface is only 5% weaker than the bulk metal, junction growth ceases and gross sliding occurs when the coefficient of friction is of the order of unity. This corresponds to the experimental observation that minute amounts of oxygen or air reduce the friction of thoroughly clean metals from extremely high values to values of about 1. In the presence of a lubricant film the transmissible stresses are so small that little junction growth can occur before sliding takes place. The expression for the coefficient of friction now reduces to a form resembling that given by the earlier simpler theory, namely μ = s i / p 0 , where s i is the critical shear stress of the lubricant layer. The present treatment thus incorporates the effect of combined stresses and surface contamination into a more general theory of metallic friction.

Synthesis of Polymeric Nancocomposites by Infiltration. Applications in 3D (Fused Filament Molding) Printing

MRS Advances ◽  
2018 ◽  
Vol 3 (63) ◽  
pp. 3793-3798 ◽  
Author(s):  
Kevin Riberi ◽  
Jesica Yanina Pereyra ◽  
Gabriel A. Planes ◽  
Silvestre Bongiovanni Abel ◽  
Diego F. Acevedo ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Functional Properties ◽  
Coefficient Of Friction ◽  
Solid Lubricant ◽  
Thermoplastic Polyurethane ◽  
Solvent Mixtures ◽  
Test Pieces ◽  
The Coefficient Of Friction

ABSTRACTThe generation of filaments constituted by nanocomposites allows printing pieces with functional properties. A method is proposed for incorporating nanoparticles in plastic filaments (thermoplastic polyurethane, PU) by diffusion in the swollen material. The nanoparticles must be dispersed in solvents (or solvent mixtures) in which the polymer swells but does not dissolve. Nanoparticles are incorporated mainly at the surface as revealed by SEM/EDS mapping. The thermal properties (studied by DSC and TGA) of the PU are only slightly affected by the presence of NPs. Test pieces successfully are printed using the modified filaments. Incorporation of solid lubricant (MoS2) nanoparticles decreases the coefficient of friction of the printed test samples.

CREATION OF COMPOSITE BRONZES REINFORCED BY STEEL DENDRITES

2018 ◽  
pp. 68-76
Author(s):  
B. A. Potekhin ◽  
A. S. Khristolyubov ◽  
A. Yu. Zhilyakov
Keyword(s):  
Wear Rate ◽  
Coefficient Of Friction ◽  
Cross Sections ◽  
Sliding Friction ◽  
Casting Process ◽  
New Class ◽  
Friction Units ◽  
The Matrix ◽  
The Coefficient Of Friction ◽  
Order Of Magnitude

The paper studies the group of composite bronzes, BrFNCA 9-4-1-1, BrFNA 12-7-1 and others where brittle Cu3Sn intermetallics are «replaced» by steel dendrites. The mass transfer of Fe, Ni, Co, Al between the matrix and dendrites in these bronzes is investigated. Dendrite dispersion depending on the methods used to produce these bronzes can be increased by a factor of 10, for example, in the vacuum casting process. The mechanical properties of BrFNCA samples (σв = 372 МPа, δ = 25 %, ψ = 42 %) are higher as compared with the BrO10 prototype: by 50 % in terms of σв hardness, and by 4–5 times in terms of δ and ψ plasticity. The coefficient of friction is lower than that of BrO10 by 20–30 %, and wear resistance is higher by an order of magnitude. The fact of a significant effect of the dendritic component dispersion on the BrFNA bronze wear rate is found. Thus, the wear rate for 1 μm and 10 μm dendrite cross sections is 0,002 and 0,025, respectively, and the coefficient of friction remains unchanged, i.e. it does not depend on dendrite dispersion. The whole set of mechanical, processing and service properties makes it possible to consider that the semicommercial tests of this new class of BrFNCA composite bronzes reinforced with H12C7A maraging dendrites for sliding friction units are justified and promising.

Friction and Wear Behavior of Graphite-Carbon Short Fiber Reinforced Al–17%Si Alloy Hybrid Composites

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
C. S. Ramesh ◽  
T. B. Prasad
Keyword(s):  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Hybrid Composite ◽  
Friction And Wear ◽  
Hybrid Composites ◽  
Matrix Alloy ◽  
Short Fiber ◽  
Wear Rates ◽  
The Matrix ◽  
The Coefficient Of Friction

Graphite and carbon short fiber (copper coated) reinforced (2 wt %) hypereutectic Al–17%Si alloy composites were prepared by liquid metallurgy route. Room temperature friction and wear properties of as-cast hypereutectic Al–Si alloy reinforced with copper coated graphite and short carbon fibers were investigated. Friction and wear tests were conducted using a pin-on-disk machine under dry sliding conditions. The loads (contact pressure) and sliding velocities have been varied from 10 N to 50 N (contact pressure of 0.12–0.60 MPa) and 0.3 m/s to 1.2 m/s, respectively. The results reveal that the coefficient of friction and the wear rate of the hybrid composite are lower than that of the matrix alloy. The coefficient of friction of the matrix alloy and its hybrid composite decreased with increased load of up to 30 N and increased beyond this load. The wear rates of both the matrix alloy and its hybrid composite increased with the increasing load. However, at all the loads and sliding velocities studied, the developed hybrid composite exhibited a lower coefficient of friction and wear rates when compared with the matrix alloy.

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