INSTRUMENTED INDENTATION OF MODEL SOFT ELASTOMERS AND ADHESION EFFECTS

摘要

IIT and JKR measurements were conducted on a series of model PDMS samples ranging in elastic modulus from 106 to 10~5 Pa. JKR experiments verified that the inherent adhesion of these soft materials caused the IIT instrument to overestimate the elastic modulus. This was because adhesive forces increase the true area of contact between the indenter and the sample. The Hertzian contact analysis used by the IIT instrumentation is unable to account for the adhesion effects. In addition it was observed in the 5 wt % sample that the instrument does not give a clean measure of the contact stiffness. Instead the instantaneous slope of the load versus displacement provides a better measurement of contact stiffness. Elastic modulus determined from IIT accounting for adhesion effects results in better agreement with bulk rheology techniques.