Contact area determination in indentation testing of elastomers

Abstract

To evaluate mechanical properties by means of nanoindentation, information on the contact area is crucial. However, the contact area is not directly accessible in experiments and is usually calculated according to the Oliver and Pharr procedure, which turned out to be unsatisfying when applied to viscoelastic materials like polymers. In this study, complementary in situ indentation testing and finite element analysis (FEA) were performed on silicone elastomers. Through this combination of techniques, several individual error sources in the conventional contact area determination have been identified and quantified. For shallow penetrations, contact areas after Oliver and Pharr were up to 40% smaller than the in situ testing results; for larger penetrations, the contact size was overestimated by approximately 6%. The deviations of the resulting mechanical properties were approximately 10%. Viscoelastic effects could be captured if dynamic indentation testing was performed.

Interfacial damage on fatigue‐loaded textile–rubber composites

“…The values measured in this study by nanoindentation are then more than 20 times higher. This fact could be explained by viscoelastic creep effects or an underestimation of the contact area, as attractive forces between the RFL and the diamond Berkovich tip are neglected here . It could also be explained by the different RFL formulations investigated here and/or chemical diffusions from rubber to RFL, occurring during molding.…”

The compensational boundary method to calculate the projected contact area of nanoindentation in atomistic simulations

“…The nanoindentation was performed on the (111) surface of a single crystal with dimensions of 13 as shown in Fig. 1a, where a is the lattice constant, 3.615 Å for Cu and 4.09 Å for Ag.…”

“…H and bou IT H can be characterized by: O-P bou bou O-P O-P bou max c max c c c IT IT IT bou O-P ma c IT x c = ( ) P A P A A A H H H P A H A − = ∆ − − = (13) Fig. 9 shows that the values of ΔHIT fall over an interval of 0.12-0.32 for Cu(111), 0.10-0.30 for Ag(111), indicating that O-P…”

“…The AFM can be used to directly measure the area function, rather than the actual contact area due to the elastic recovery of tested materials during withdrawal of the indenter [7,8]. Additional corrections must be made for the evaluation of the PCA due to the imperfect indenter geometry, the tilt and surface defects of samples, and the pile-up/sink-in behaviour of tested materials [9][10][11][12][13].…”