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Research Papers: Applications

# Study of a Brittle Transparent Disk Under Dry RCF Conditions

[+] Author and Article Information
Arthur Francisco

Laboratoire de Mécanique des Solides, Université de Poitiers, UMR CNRS 6610, 4, Avenue de Varsovie, 16021 Angoulême Cedex, Francearthur.francisco@univ-poitiers.fr

Houssein Abbouchi, Bernard Villechaise

Laboratoire de Mécanique des Solides, Université de Poitiers, UMR CNRS 6610, 4, Avenue de Varsovie, 16021 Angoulême Cedex, France

J. Tribol 132(3), 031101 (Jul 21, 2010) (8 pages) doi:10.1115/1.4001785 History: Received January 14, 2009; Revised May 06, 2010; Published July 21, 2010; Online July 21, 2010

## Abstract

Despite the numerous experimental works on rolling contact fatigue, dealing with two-disk contacts, some phenomena still remain badly understood. Most of the test benches, used for that purpose, impose the rotational speeds to the disks: global slipping occurs and the tangential force is measured. Even if this configuration is found in some mechanical contacts, it does not reflect situations, where only microslipping occurs with high tangential loads. For these reasons, an original bench has been designed: a specimen disk rotates a braked stainless steel disk under a normal load $N$. The tangential load $T$, due to the braked disk, is set below the global slipping value; the specimen disks are transparent for the cracks observation and brittle to avoid any plasticity complication. A typical run consists in carrying out a succession of steps of increasing the number of cycles. Each step ends with several measurements on the cracks: their counting and their width and depth measurements. The results are divided in two categories: general observations and quantitative results. The most evident observation concerns the crack shape since it propagates along an ellipse on the contact path. Furthermore, the direction of propagation inside the disk is perpendicular to the surface. Lastly, a regular primary network of well-defined cracks is observed with cracks less marked. Concerning the effects of varying loads, the higher the $T$, the faster the cracks initiate and propagate because of a higher tensile stress state. However, these effects can be partly overridden by $N$ beneath the contact path. As the disk material is brittle, the crack behavior is quite similar to the one observed on metallic specimens. Even if the results are obtained in an epoxy resin, a reasonable transposition is possible. The disk transparency makes it possible to quantify the cracks growth and to propose original 3D photographs of the cracks.

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## Figures

Figure 1

Stick and slip regions in the contact

Figure 2

Effect of the crack orientation on its propagation

Figure 3

The RCF bench

Figure 4

Disk geometrical properties

Figure 5

Optical microscope bench

Figure 6

Microscope bench degrees of freedom

Figure 7

Optical resolution target

Figure 8

Microscope positioning for width and depth measurements

Figure 9

Contact overview

Figure 10

A 3D view of the cracks

Figure 11

Crack layout: at 1E6 (a) and 4E6 cycles (b)

Figure 12

Numerical model characteristics

Figure 13

Maximum principal stress (MPa) for three different crack depths

Figure 14

Effect of the cracks interdistance on Sxx

Figure 15

Repeatability test, mean number of cracks

Figure 16

Repeatability test, widths and depths

Figure 17

Normal load influence, number of cracks

Figure 18

Figure 19

Crack progression with regards to the contact width

Figure 20

Figure 21

Tangential load influence, number of cracks

Figure 22

Crack network at 5E5 cycles

Figure 23

Crack depth effect on Sxx(i=0.5 mm)

Figure 24

Figure 25

## Errata

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