Characterization of viscoelastic materials by quasi-static and dynamic indentation

Abstract

This paper describes the experimental measurements of the elastic modulus and hardness of viscoelastic materials under quasi-static and dynamic depth-sensing indentation using a homemade tribology probe microscope (TPM). The indentation measurements were performed using a sapphire sphere tip under various conditions. Materials such as polytetrafluoroethylene, styrene rubber and nitrile rubber were tested in both quasi-static and dynamic experiments. In quasi-static mode, the loading and unloading force curves were obtained from these specimens, and the results show a significant load effect on the measured hardness and elastic modulus. The dynamic indentation tests were conducted under a range of loading forces with various frequencies. The values of storage modulus, loss modulus and damping factor were determined by dynamic indentation. To get an accurate measurement, the stiffness and damping of the instrument were rigorously analyzed. Using dynamic indentation, it was confirmed that the variation in the frequency of the oscillation force has a significant effect on the measured results of the materials. Comparing the results obtained from the quasi-static and dynamic indentations, for the viscoelastic properties, dynamic indentation offers an advantage over the quasi-static method. Collectively, these results clearly demonstrate the capability of our homemade TPM facility to determine the constitutive behavior of viscoelastic solids in the frequency domain.