Scratch-tip-size effect and change of friction coefficient in nano / micro scratch tests using XFEM

2018 ◽  
Vol 120 ◽  
pp. 398-410 ◽  
Author(s):  
Kwangmin Lee ◽  
Karuppasamy Pandian Marimuthu ◽  
Chang-Lae Kim ◽  
Hyungyil Lee
Keyword(s):  
Friction Coefficient ◽  
Size Effect ◽  
Scratch Tests

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

Numerical Investigation of Size Effect on Dry Friction Behavior in Micro Upsetting Process

2014 ◽  
Vol 997 ◽  
pp. 321-324
Author(s):  
Wei Zheng ◽  
Guang Chun Wang ◽  
Bing Tao Tang ◽  
Xiao Juan Lin ◽  
Yan Zhi Sun
Keyword(s):  
Friction Coefficient ◽  
Size Effect ◽  
Dry Friction ◽  
Normal Pressure ◽  
Friction Model ◽  
Strain Hardening Exponent ◽  
Forming Process ◽  
Friction Behavior ◽  
Initial Yield Stress ◽  
Coulomb’S Friction

After modifying the Wahime/Bay friction model, a new friction model suitable for micro-forming process without lubrication is established. In this model, it is shows that the friction coefficient is a function of strain hardening exponent, the normal pressure and the initial yield stress of material. Based on the experimental data, the micro-upsetting process is simulated using the proposed friction model. The simulation results are used to investigate the size effect on the dry friction behavior. It is found that the Coulomb’s friction coefficient is dropping with miniaturization of specimens when the amount of reduction is not too large.

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.

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.

The size effect of hexagonal texture on tribological properties under mixed lubrication

2018 ◽  
Vol 70 (9) ◽  
pp. 1798-1805 ◽  
Author(s):  
Long Zheng ◽  
Yihang Gao ◽  
Yinghui Zhong ◽  
Guolong Lu ◽  
Zhenning Liu ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Size Effect ◽  
Tribological Properties ◽  
Equivalent Stress ◽  
Mixed Lubrication ◽  
Groove Width ◽  
Area Density ◽  
Content Type ◽  
Simulated Distribution ◽  
Similar Area

Purpose The purpose of this study is to elucidate the size effect (groove width, unit length and area density) of the hexagonal texture on tribological properties under lubrication. Design/methodology/approach The tribological properties of nine hexagonal textures with different hexagon lengths and groove widths have been investigated under mixed lubrication to elucidate the size effect. Findings Overall, the friction coefficient decreases as the groove width increases within the examined range, whereas the hexagon length shows an optimal value around 3 mm. In particular, one hexagonal texture (3 × 3 mm) exhibits lower friction coefficients and less wear losses than the others. Interestingly, two hexagonal textures of similar area density (1 × 1 mm and 3 × 3 mm) yield the worst and best tribological performances, respectively, which can be explained by the simulated distribution of equivalent stress. Originality/value The tribological properties of nine hexagonal textures are examined under lubrication. The 3 × 3 texture exhibits lower friction coefficient and wear loss than the others. Two textures of similar area density yield the worst and best tribological performances. The results agree with the simulated distribution of equivalent stress.

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.

Lattice Discrete Particle Modeling of Size Effect in Slab Scratch Tests

2020 ◽  
Vol 88 (2) ◽  
Author(s):  
Lin Han ◽  
Madura Pathirage ◽  
Ange-Therese Akono ◽  
Gianluca Cusatis
Keyword(s):  
Fracture Mechanics ◽  
Size Effect ◽  
Mixed Mode ◽  
Brittle Materials ◽  
Mixed Mode Fracture ◽  
Compressive Behavior ◽  
Fracture Properties ◽  
Mode Fracture ◽  
Discrete Particle ◽  
Scratch Tests

Abstract For a long time, geomechanicians have used scratch tests to characterize the compressive behavior and hardness of rocks. In recent years, this test has regained popularity in the field of mechanics, especially after a series of publications that highlighted the potential capability of the scratch test to determine the fracture properties of quasi-brittle materials. However, the complex failure mechanisms observed experimentally in scratch tests led to scientific debates and, in particular, raised the question of the size effect. This article intends to provide a better understanding of the problem by using numerical tools and fracture mechanics considerations. To narrow the investigation area, this study focuses on slab scratch tests of quasi-brittle materials and adopts two different numerical methods: (i) the lattice discrete particle model (LDPM) that includes constitutive laws for cohesive fracturing, frictional shearing, and nonlinear compressive behavior, and (ii) the meshless method based on Shepard function and partition of unity (MSPU) implementing linear elastic fracture mechanics (LEFM). The numerical results are further analyzed through Bažant’s size effect law (SEL) with an appropriate mixed-mode fracture criterion. Fracture properties are then calculated and compared to the results of typical notched three-point bending tests. The results show that mixed-mode fracture considerations are of paramount importance in analyzing the fracture process and size effect of scratch tests.

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