A detailed study of nanoindentation in Continuous Stiffness Mode (CSM) on a family of aromatic thermosetting polymers is carried out to identify the causes for the large variability in the extracted values of the elastic modulus of organic polymer films.
It is shown that the variation of parameters determining the dynamics of the force application such as the CSM frequency, the actual strain or load rate, and the duration of the waiting time segments can lead up to 20% difference in the estimated elastic modulus. The reason for this is related to creep, more specifically to viscoelastic behaviour, typical of organic films. On the other hand, pile-up is shown to have a negligible effect on the extraction of the elastic modulus from indentation depths below 50% of the film thickness, even for films with hardness as low as 0.13GPa. It is also concluded that neither pile-up nor creep phenomena can account for the overestimation of the elastic modulus with nanoindentation as compared to the values extracted with the surface acoustic waves technique.