Indentation of Polytetrafluoroethylene (PTFE) Thin Film: Simulations by Using Continuum Damage Mechanics

Thin compliant films on relatively hard substrates have a wide range of applications. In this work, continuum damage mechanics is used to simulate indentation of a 10-μm-thick polytetrafluoroethylene (PTFE) film deposited on glass for different load levels by finite element analysis. The results, compared to experiments, are useful in investigating the mechanics of wear and friction of soft thin films. The material model is elastic–plastic before damage initiation and includes linear damage progression thereafter. The effects of ductile and shear damage criteria and two parameters pertinent to the damage model, the equivalent plastic strain for damage initiation and the bulk fracture toughness, on the indentation are investigated. It is shown that the shear damage model is more suitable to characterize the indentation of the PTFE thin film. The bulk fracture toughness has greater significance with regard to damage compared to equivalent plastic strain at the onset of damage initiation. Comparison of simulation and experimental results shows that bulk fracture toughness of the thin PTFE film is approximately 20 J/m². This value is lower than that for the bulk PTFE, and the difference is attributed to the thin-film nature of the case considered here.