Strain shielding and confined plasticity in thin polymer films: Impacts on thermomechanical data storage

Substrate constraints and interfacial boundary layers in thin polystyrene films are explored with high strain rate indentations characteristic of thermomechanical terabit data storage operations. Under these impact-like conditions, the coupling of strain-rate and inertial effects leads to large plastic deformations relative to quasi-static indentations. Strain shielding is present when the plastic deformation radius exceeds 65% of the film thickness. Thereafter, deformation is restricted by the rigid substrate, giving rise to elevated rim heights and interfacial shearing. The shielding effects were alleviated with use of a modulus-matched buffer layer between the polymer film and the substrate. A non-monotonic rheological gradient in the polymer films leads to the distribution of contact pressures between two asymptotic scenarios: (i) a compliant surface with a rigid sub-surface and (ii) a rigid surface with a compliant sub-surface.