PSI - Issue 36

Iakov Lyashenko et al. / Procedia Structural Integrity 36 (2022) 394–400 Iakov Lyashenko, Vadym Borysiuk / Structural Integrity Procedia 00 (2021) 000 – 000

396

3

In the studied case we use the lightening developed for previous version of the device (Popov et al. (2017)). The enlarged contact area between indenter (4) and elastomer (5) is shown in the right panel of Fig. 1. Elastomer consists of three layers of rubber TARNAC CRG N0505 (total thickness of the elastomer is 15 mm), which is almost absolutely transparent for visible light and thus contact area can be observable through the digital camera (8) with physical resolution 1600 x 1200 pixels. Similar apparatus was used in our previous studies of the adhesive contact where various factors, such as surface roughness, impurities, indenter velocity, chemical inhomogeneity of the surface, tangential shift of the indenter etc. were taken into account (Lyashenko et al. (2021), Popov et al. (2021)).

Fig. 1. (left panel) general view of the setup; (right panel) photo of the contact area between the elastomer surface (5) and the indenter (4).

In the performed experiments indenter (4) was indented into elastomer (5) at depth d and then it was shifted upward in normal direction until the total disappearance of contact. During the movement, normal component of the contact force was measured, and the contact area was photographed every 1 s. All the devices described above were controlled through the computer program that was developed in the LabVIEW software. The usage of transparent elastomer gives the advantage of the direct observation of the contact area. Moreover, from the obtained photos of the contact, its area can be estimated and average contact pressure can be calculated. 3. Experimental results We performed series of experiments concerning the indentation of different indenters (with mirror polished surface before the experiment) into the rubber layer, produced by Japan manufacturer TARNAC CRG N0505. This rubber has excellent transparency, so the evolution of the contact area can be directly observed. Rubber sample consists of three layers with thickness of each layer 5 mm (total thickness 15 mm). Diameter of the rubber substrate was equal to 45 mm. As rubber is not containing water the corrosion interaction is absent in the system and reversible results are observed in all indentation cycles. Obtained in experiments results are shown in Fig. 2. For cylindrical indenter only one experiment on indentation was performed, while for spherical indenters five cycles of indentation were performed and all related load curves are shown in the plots. As it can be seen from the figure, all five cycles are almost overlapping, however slight differences are present, that is why curves in the Fig. 2 b and Fig. 2 c are look “bolder” than in the panel a . In our experiments indenter was shifted with relatively small velocity v = 0.5 µm/s, therefore, contact can be considered as quas i-static.