Open Access

Christian Müller, Martin Müser

• We present an approximate, analytical treatment for the linearly elastic response of a film with arbitrary Poisson's ratio ?, which is indented by a flat cylindrical punch while resting on a rigid foundation. Our approach is based on a simple scaling argument allowing the vast changes of the elastomer?s effective modulus E? with the ratio of film height h and indenter radius a to be described with a compact, analytical expression. This yields exact asymptotics for large and small reduced film heights h/a, whereby it also reproduces the observation that E?(h/a) has a pronounced minimum for ?>0.49 at h/a≈1.6. Using Green?s function molecular dynamics (GFMD), we demonstrate that the predictions for E?(h/a) are reasonably correct and generate accurate reference data for effective modulus and pull-off force. GFMD also reveals that the nature of surface instabilities occurring during stable crack growth as well as the crack initiation itself depend sensitively on the way how continuum mechanics is terminated at small scales, that is, on parameters beyond the two dimensionless numbers h/a and ? defining the continuum problem.