Abstract: Flexibility factor analysis was proposed for exploring the indentation size effect (ISE) of viscoelastic polymers，and the influencing factors of ISE were analyzed by dynamic nanoindentation for PMMA and thermoplastic polyurethane (TPU).It was found that the carrier load was the key factor of ISE of linear viscoelastic materials in dynamic nanoindentation using Berkovich tip，and the harmonic load control methods have little influence on ISE. The viscoelastic performances by dynamic nanoindentation agree with the dynamic mechanical analysis(DMA)results as the carrier displacement was larger than the critical value.

Key words: nanoindentation, viscoelasticity, dynamic, indentation size effect