Experimental measurement and numerical simulation of the plastic strain during indentation and scratch tests on polymeric surfaces

2009 ◽  
Vol 24 (3) ◽  
pp. 1184-1196 ◽  
Author(s):  
Hervé Pelletier ◽  
Christian Gauthier ◽  
Robert Schirrer
Keyword(s):  
Friction Coefficient ◽  
Plastic Strain ◽  
Strain Field ◽  
Contact Radius ◽  
Polymeric Surfaces ◽  
Testing Conditions ◽  
First Approximation ◽  
Scratch Tests ◽  
Tip Radius ◽  
Plastic Strain Gradient

For elastic–plastic contacts, we propose a complete description of the plastic strain field beneath the indenter during indentation and scratch with a spherical indenter (with R, the tip radius), as a function of the testing conditions, defined by the geometrical strain, noted a/R (with a, the contact radius), and the local friction coefficient μloc. The main parameter of the description is the level of the plastic deformation imposed during test into amorphous polymeric surfaces, related in first approximation to the ratio a/R. An equivalent average plastic strain, noted (εp)av, is calculated over a representative plastically deformed volume, both for indentation and scratch tests. The equivalent average plastic strain (εp)av, is observed to increase with the ratio a/R, as predicted by the empirical Tabor's rule, but also with the local friction coefficient μloc for a given ratio a/R, especially during scratching. The plastic zone dimensions and the plastic strain gradient developed beneath the moving tip are shown to depend both on the geometrical strain a/R and also on the friction coefficient μloc.

Thermal Oxidation Behavior of TiAlCrSiN and AlCrTiN Films on HastelloyX

2012 ◽  
Vol 486 ◽  
pp. 400-405 ◽  
Author(s):  
K. Tuchida ◽  
Kessaraporn Wathanyu ◽  
S. Surinphong
Keyword(s):  
Thermal Oxidation ◽  
Oxidation Behavior ◽  
Oxide Scales ◽  
Surface Appearance ◽  
Turbine Engine ◽  
Testing Conditions ◽  
Working Temperature ◽  
Fuel Nozzle ◽  
Higher Temperature ◽  
Scratch Tests

In this paper, the thermal oxidation behavior of TiAlCrSiN and AlCrTiN films coated on hastelloyX substrate, typically used for fuel nozzle in gas turbine engine application, have been studied. The thermal oxidation behavior at 950, 1050 and 1150 °C in controlled atmosphere were investigated. The surface appearance, microstructure, chemical composition and adhesion of films were investigated. The thermal oxidations were observed in all testing conditions showing oxide films at the surface with thicker oxide film at higher temperature. However, spalling of oxide scales was found in both coated and uncoated specimens at 1150°C suggesting the maximum working temperature of < 1150 °C for turbine engine applications. The critical loads corresponding to the full delamination of the thermal oxidation coated specimens were found to be higher than the non-thermal oxidation specimens. The effect of thermal oxidation on damage patterns during scratch tests, i.e. less chipping and cracking for thermal oxidation specimen, were also observed.

Gradient of Soil Constitutive Model

2010 ◽  
Vol 168-170 ◽  
pp. 1126-1129
Author(s):  
Wen Xu Ma ◽  
Ying Guang Fang
Keyword(s):  
Plastic Strain ◽  
Strain Gradient ◽  
Soil Analysis ◽  
Natural Material ◽  
Flow Rule ◽  
The Finite Element Method ◽  
Gradient Effect ◽  
Non Local ◽  
Associated Flow Rule ◽  
Plastic Strain Gradient

For the soil is a very complex natural material, significant strain gradient effect exist in soil analysis. Based on the "gradient" phenomenon, we add the plastic strain gradient hardening item into the traditional Cambridge yield surface. By using the consistency conditions and associated flow rule, we get the explicit expression of plastic strain gradient stiffness matrix. And the finite element method of plastic strain gradient is also shown in this article. Plastic strain gradient is actually a phenomenological non-local model containing microstructure information of the material. It may overcome the difficulties in simulating the gradient phenomenon by traditional mechanical model.

scholarly journals Microstructure Evolution and Nanotribological Properties of Different Heat-Treated AISI 420 Stainless Steels after Proton Irradiation

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1736 ◽  
Author(s):  
L.Y. Dai ◽  
G.Y. Niu ◽  
M.Z. Ma
Keyword(s):  
Stainless Steel ◽  
Friction Coefficient ◽  
Wear Rate ◽  
Proton Irradiation ◽  
Energy Proton ◽  
Aisi 420 ◽  
Transmission Electron ◽  
Heat Treated ◽  
Nanoscale Friction ◽  
Scratch Tests

In this paper, low-energy proton irradiation experiments with different cumulative fluences were performed on samples of AISI 420 stainless steel that were either annealed or tempered at 600 or 700 °C. The effects of the cumulative proton irradiation fluence on the evolution of the microstructure of AISI 420 were studied by transmission electron microscopy (TEM). Scratch tests were performed using a Tribo Indenter nanomechanical tester, in order to investigate the effects of the cumulative fluence on the tribological properties of the AISI 420 stainless steel. The results indicate that the dislocation density of the microstructure near the surface of the AISI 420 stainless steel increases with higher cumulative proton irradiation fluences. Under the same load, the nanoscale friction coefficient and wear rate both decreased with increasing cumulative proton irradiation fluence. This indicates that the surface hardening effect induced by proton irradiation can diminish the nanoscale friction coefficient and wear rate.

scholarly journals Equivalent plastic strain gradient enhancement of single crystal plasticity: theory and numerics

2012 ◽  
Vol 468 (2145) ◽  
pp. 2682-2703 ◽  
Author(s):  
Stephan Wulfinghoff ◽  
Thomas Böhlke
Keyword(s):  
Plastic Strain ◽  
Strain Gradient ◽  
Equivalent Plastic Strain ◽  
Plasticity Theory ◽  
Strain Gradient Theory ◽  
Local Algorithm ◽  
Alternative Formulation ◽  
Element Discretization ◽  
Gradient Enhancement ◽  
Plastic Strain Gradient

We propose a visco-plastic strain gradient plasticity theory for single crystals. The gradient enhancement is based on an equivalent plastic strain measure. Two physically equivalent variational settings for the problem are discussed: a direct formulation and an alternative version with an additional micromorphic-like field variable, which is coupled to the equivalent plastic strain by a Lagrange multiplier. The alternative formulation implies a significant reduction of nodal degrees of freedom. The local algorithm and element stiffness matrices of the finite-element discretization are discussed. Numerical examples illustrate the advantages of the alternative formulation in three-dimensional simulations of oligo-crystals. By means of the suggested formulation, complex boundary value problems of the proposed plastic strain gradient theory can be solved numerically very efficiently.

A Laboratory Method to Comprehensively Evaluate Abrasion, Traction and Rolling Resistance of Tire Tread Compounds

2007 ◽  
Vol 80 (4) ◽  
pp. 580-607 ◽  
Author(s):  
M. Heinz ◽  
K. A. Grosch
Keyword(s):  
Friction Coefficient ◽  
Laboratory Test ◽  
Rolling Resistance ◽  
Limited Range ◽  
Slip Angle ◽  
Testing Conditions ◽  
Side Force ◽  
The Road ◽  
Wide Range ◽  
On The Road

Abstract A laboratory test method has been developed which allows the evaluation of diverse properties of tire tread compounds on the same sample. The laboratory test instrument consists of a rotating abrasive disk against which a rubber sample wheel runs under a given load, slip angle and speed. All three force components acting on the wheel during the tests are recorded. By changing the variable values over a wide range practically all severities encountered in tire wear are covered. The well-known fact that compound ratings depend on the road testing conditions is verified. Most compounds are only significantly distinguishable against a control over a limited range of testing conditions. Using a road test simulation computer program based on the laboratory data shows that not only ratings correspond to practical experience but also calculated absolute tire life times do. Tests on surfaces of different coarseness and sharpness indicate that sharp coarse surfaces give the best results with road tests, which of necessity are mostly carried out on public roads of differing constitution. The abrasive surface can be wetted with water at different temperatures and hence either the friction force at a locked wheel or the side force at a slipping wheel can be measured over a wide range of temperatures and speeds. At small slip angles the side force is dominated by dynamic cornering stiffness of the compound, at large slip angles by the friction coefficient. In this case, too, good correlations to road experience exist over a limited range of testing conditions. Low water temperatures and low slip speed settings in the laboratory produce side force ratings, which correlate closely with ABS braking on the road High and higher slip speeds give ratings in close agreement with locked wheel braking on the road. A heatable/coolable disk enables traction measurements on ice and newly abrasion measurements on surfaces at elevated surface temperature. Ice surface temperatures between −5 °C and −25 °C are possible. Friction measurements show that the difference in compound rating between summer and winter compounds is maintained over the whole temperature range. New investigations show not only a differentiation between different winter tire treads qualities but also an excellent correlation between tire and laboratory results. As a new topic side force measurements on dry surfaces highlight the correlation to dry handling of tires. The tire tread compound contributes to this performance through its shear stiffness and its friction coefficient. The shear stiffness contributes to the response of the tire in directional changes. The friction coefficient determines the maximum force, which can be transmitted. A simple operation possibility for evaluation of determined side forces is demonstrated. In addition to antecedent investigations the rolling resistance of the rubber wheel can be measured over a range of loads and speeds with the slip angle set at zero. Again for these new results good correlations are achieved with practical experience. In particular, the dependence of the rolling resistance on the velocity and loads are pointed out. Ultimately a good correlation between tire test and laboratory test results was demonstrated.

scholarly journals Micromechanical Gurson-based continuum damage under the context of fretting fatigue: Influence of the plastic strain field

2020 ◽  
Vol 125 ◽  
pp. 235-264 ◽  
Author(s):  
C.F.B. Sandoval ◽  
L. Malcher ◽  
F.A. Canut ◽  
L.M. Araújo ◽  
T.C.R. Doca ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Strain Field ◽  
Fretting Fatigue ◽  
Continuum Damage

Scratching of Elastic∕Plastic Materials With Hard Spherical Indenters

2008 ◽  
Vol 75 (6) ◽  
Author(s):  
Shane E. Flores ◽  
Michael G. Pontin ◽  
Frank W. Zok
Keyword(s):  
Friction Coefficient ◽  
Normal Force ◽  
Scaling Relations ◽  
Elastic Plastic ◽  
Plastic Materials ◽  
Finite Element Calculations ◽  
Plastic Analysis ◽  
Elastic Plastic Materials ◽  
Scratch Tests ◽  
Theoretical Results

A mechanistic framework has been developed for interpreting scratch tests performed with spherical indenters on elastic∕plastic materials. The pertinent scaling relations have been identified through a plastic analysis and the model has been subsequently calibrated by finite element calculations. The results show that the ratio of scratch force to normal force (or apparent friction coefficient) can be partitioned into two additive components: one due to interfacial friction and another associated with plastic deformation. The plastic component scales parabolically with the normal force and depends only weakly on the true (elastic) friction coefficient. A simple formula for the scratch force, based on the plastic analysis and the numerical results, has been derived. Finally, experimental measurements on two material standards commonly used for nanoindenter calibration have been used to verify the theoretical results.

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