The Role of Indentation Depth on the Measured Hardness of Materials

1993 ◽  
Vol 308 ◽  
Author(s):  
Melissa Shell De Guzman ◽  
Gabi Neubauer ◽  
Paul Flinn ◽  
William D. Nix
Keyword(s):  
Strain Hardening ◽  
Amorphous Materials ◽  
Indentation Depth ◽  
Density Of Dislocations ◽  
Real Material ◽  
Dislocation Densities ◽  
Indentation Tests ◽  
Micro Indentation ◽  
Measured Hardness

ABSTRACTUltra micro-indentation tests on Ni and Cu samples showed increasing hardness with decreasing penetration depth over a range from 200 to 2000 nm. The results suggest increased strain hardening with decreased indentation depth. To establish that this is a real material effect, a series of tests were conducted on amorphous materials, for which strain hardening is not expected. The hardness of Metglas® was found to be independent of depth. A simple model of the dislocation densities produced under the indenter tip describes the data well. The model is based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness. At large depths, the density of geometrically necessary dislocations is sufficiently small to have little effect on hardness, and the measured hardness approaches the intrinsic hardness of the material.

Influence of Substrate Hardness on the Response of W–C–Co-coated Samples to Depth-sensing Indentation

2000 ◽  
Vol 15 (8) ◽  
pp. 1766-1772 ◽  
Author(s):  
J. V. Fernandes ◽  
A. C. Trindade ◽  
L. F. Menezes ◽  
A. Cavaleiro
Keyword(s):  
Indentation Depth ◽  
Critical Value ◽  
The Other ◽  
Differential Analysis ◽  
Depth Sensing ◽  
Indentation Tests ◽  
Influence Of Substrate ◽  
Film Substrate ◽  
Substrate Hardness ◽  
Measured Hardness

Depth-sensing indentation tests were used to determine the hardness of amorphous W–C–Co coatings deposited on different steel and copper substrates. The hardness of the film, Hf, was chosen to be always greater than the hardness of the substrate Hs and within the range Hf/Hs = 2 to 18.5. The influence of the ratio Hf/Hs on the ratio (t/hD)C between the film thickness t and the critical value of the indentation depth (hD)C, for which the substrate starts to deform plastically, was studied. Two independent methods were used to determine (hD)C values. One utilized the differential analysis of the loading part of the indentation curve, and the other was based on the plot of (Hc – Hs)/(Hf − Hs) versus t/(hD), Hc being the measured hardness of the film/substrate composite at a given indentation depth (hD). A good correlation between both methods was found.

Further analysis of the size effect in indentation hardness tests of some metals

1995 ◽  
Vol 10 (11) ◽  
pp. 2908-2915 ◽  
Author(s):  
M. Atkinson
Keyword(s):  
Size Effect ◽  
Strain Hardening ◽  
Indentation Size Effect ◽  
Plastic Hinge ◽  
Small Scale ◽  
Indentation Hardness ◽  
Vickers Indentation ◽  
Indentation Size ◽  
Hardness Tests ◽  
Indentation Tests

The variation of apparent hardness observed in previously reported Vickers indentation tests of metals is reexamined. Common deseriptions of the effect are shown to be inaccurate: the variation of apparent hardness is monotonic but not simple. The effect is consistent with varying size of a previously postulated “plastic hinge” at the perimeter of the indent. This complexity confers uncertainty on the estimation of characteristic macrohardness from small scale tests. Association of the indentation size effect with friction and with strain hardening is confirmed.

ELASTO-PLASTIC PROPERTIES OF Mo-MODIFIED Ti DEDUCED FROM INDENTATION TESTS AND FINITE ELEMENT ANALYSIS

2019 ◽  
Vol 26 (07) ◽  
pp. 1850225
Author(s):  
YONG MA ◽  
ZHAO YANG ◽  
SHENGWANG YU ◽  
BING ZHOU ◽  
HONGJUN HEI ◽  
...  
Keyword(s):  
Finite Element ◽  
Surface Treatment ◽  
Load Capacity ◽  
Indentation Test ◽  
Element Analysis ◽  
Plastic Properties ◽  
Polynomial Expression ◽  
Indentation Tests ◽  
Graded Material ◽  
Micro Indentation

The aim of this paper is to establish an approach to quantitatively determine the elasto-plastic parameters of the Mo-modified Ti obtained by the plasma surface alloying technique. A micro-indentation test is conducted on the surface under 10[Formula: see text]N. Considering size effects, nanoindentation tests are conducted on the cross-section with two loads of 6 and 8[Formula: see text]mN. Assuming nanoindentation testing sublayers are homogeneous, finite element reverse analysis is adopted to determine their plastic parameters. According to the gradient distributions of the elasto-plastic parameters with depth in the Mo-modified Ti, two types of mathematical expressions are proposed. Compared with the polynomial expression, the linear simplified expression does not need the graded material to be sectioned and has practical utility in the surface treatment industry. The validation of the linear simplified expression is verified by the micro-indentation test and corresponding finite element forward analysis. This approach can assist in improving the surface treatment process of the Mo-modified Ti and further enhancing its load capacity and wear resistance.

scholarly journals Role of capillary adhesion in the friction peak during the tacky transition

Friction ◽  
2021 ◽  
Author(s):  
Tianyan Gao ◽  
Jiaxin Ye ◽  
Kaisen Zhang ◽  
Xiaojun Liu ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Indentation Depth ◽  
Normal Force ◽  
Normal Load ◽  
Pdms Film ◽  
Capillary Adhesion ◽  
Static Contact ◽  
Van Der Waals Attraction ◽  
Contact Experiments

AbstractThe friction peak that occurs in tire-road sliding when the contact changes from wet to dry was previously attributed to capillary cohesion, van der Waals attraction, and surface roughness, but the detailed mechanisms have yet to be revealed. In this study, friction and static contact experiments were conducted using a custom-built in situ optical microtribometer, which allowed us to investigate the evolution of the friction, normal load, and contact area between a polydimethylsiloxane (PDMS) film and a silicon nitride ball during water volatilization. The friction coefficient increased by 100%, and the normal force dropped by 30% relative to those in the dry condition during the wet-to-dry transition. In static contact experiments, the probe indentation depth increased, and the normal load decreased by ∼60% as the water evaporated. Combining the friction and static contact results, we propose that the large friction peak that appeared in this study can be attributed to the combined effects of increased adhesive capillary force and increased plowing during the wet-to-dry transition.

Effects of strain hardening and residual stress in impression on the instrumented indentation technique

2006 ◽  
Vol 21 (7) ◽  
pp. 1680-1686
Author(s):  
L.Z. Liu ◽  
Y.W. Bao ◽  
Y.C. Zhou
Keyword(s):  
Residual Stress ◽  
Strain Hardening ◽  
Energy Analysis ◽  
Maximum Load ◽  
Contact Theory ◽  
Elastic Contact ◽  
Instrumented Indentation ◽  
Indentation Technique ◽  
Indentation Tests ◽  
Elastic Loading

Finite element analyses were carried out to simulate the loading, unloading, and reloading processes of indentation tests. It was found that the validity of applying the elastic contact theory to the indentation unloading process is strongly related to the strain hardening and residual stress in impression. It is the combination of strain hardening and residual stress that causes the unloading or reloading curves to show elastic loading in the range from zero to the maximum load whereas the reloading curve on the impression without strain hardening and residual stress shows elastic–plastic loading in the same range. These computations indicate that applying the elastic contact theory to the unloading or reloading processes, the fundamental prerequisite of the instrumented indentation technique, is valid because of the existence of strain hardening and residual stress. The mechanism of this hardening effect is discussed through energy analysis.

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