Technical Brief

Strengthening Effect of Soft Thin Coatings

[+] Author and Article Information
R. Goltsberg

Department of Mechanical Engineering,
Haifa 32000, Israel
e-mail: goltsberg.roman@gmail.com

S. Levy, Y. Kligerman, I. Etsion

Department of Mechanical Engineering,
Haifa 32000, Israel

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received September 11, 2017; final manuscript received April 24, 2018; published online May 21, 2018. Assoc. Editor: Wang-Long Li.

J. Tribol 140(6), 064501 (May 21, 2018) (5 pages) Paper No: TRIB-17-1356; doi: 10.1115/1.4040115 History: Received September 11, 2017; Revised April 24, 2018

A finite element analysis was used to study the onset of plasticity of a coated sphere compressed by a rigid flat. This was done for soft coatings on a harder substrate. Generally, the results agree very well with the findings in the literature for the opposite case of an indentation of a rigid sphere into a coated flat, with a soft coating. In this case, a weakening prevails over the entire range of coating thicknesses, resulting in critical loads (at yield inception) lower than the critical load of the uncoated contact. However, a surprising strengthening effect was discovered, in this study, for very thin coating thicknesses resulting in a higher resistance to plasticity, compared to an uncoated sphere. This phenomenon resembles a mirror image of the opposite weakening effect which was reported for very thin hard coatings. These results may suggest that when very thin coatings are to be applied in a spherical contact, a softer, rather than harder, coating should be considered in order to increase the contact's resistance to plasticity inception.

Copyright © 2018 by ASME
Topics: Coatings , Stress , Plasticity
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Grahic Jump Location
Fig. 1

Typical axisymmetric cross section of (a) flattening and (b) indentation approaches

Grahic Jump Location
Fig. 2

Critical load Pc of coated substrate as a function of the dimensionless coating thickness t/R. The critical loads for hard coating and soft coatings systems are marked by squares and triangles, respectively (Adapted from Ref. [6]).

Grahic Jump Location
Fig. 3

Maximum strengthening case for the dimensionless critical load Pc/Pc_su as a function of the dimensionless thickness t/R for Esu/Ysu=200, Esu/Eco=1.1 and Ysu/Yco=1.1

Grahic Jump Location
Fig. 4

Dimensionless equivalent von Mises stress distribution along the axis of symmetry for different dimensionless thicknesses t/R for the case presented in Fig. 3

Grahic Jump Location
Fig. 5

The dimensionless critical load Pc/Pc_su as a function of the dimensionless thickness t/R for Esu/Eco=1.1,  Ysu/Yco=1.1 and various Esu/Ysu values

Grahic Jump Location
Fig. 6

Dimensionless coating thickness of maximum strengthening (t/R)MS as a function of the ratio Esu/Ysu for Esu/Eco=Ysu/Yco=1.1



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