The use of nano- and micro-instrumented indentation tests to evaluate viscoelastic behavior of poly(vinylidene fluoride) (PVDF)

Nano-load (n-IIT) and micro-load (mu-IIT) instrumented indentation tests (Ifs) were used to characterize elastic modulus and hardness in a semicrystalline polymer. The tests were conducted with loading rates ranging from 4.9 to 317 mN.min(-1) for n-IIT and from 300 to 10000 mN.min(-1) for mu-IIT. A decrease in the elastic modulus was observed as the load rate increased for the n-IIT process, and the elastic modulus increased as the load rate increased for the mu-IIT process. This behavior was explained by two-flow volume control under the indenter and the corresponding shear stress, which can influence the state of stress. The effect of holding time on the elastic modulus and hardness was also investigated for mu-IIT. E decreased with increasing holding time up to 30 s and became constant from there on. Hardness, however, decreased for all holding times evaluated. The steady state creep was only reached after 90 s, which is significantly higher than the time for elastic modulus stabilization. (C) 2013 Elsevier Ltd. All rights reserved.