Measurement of quasi-static and dynamic mechanical properties of soft materials based on instrumented indentation using a piezoelectric cantilever

Abstract

Instrumented indentation is a powerful in-situ mechanical characterization method and has been intensively investigated in recent years. In this work, we proposed an instrumented indentation method for soft materials based on a piezoelectric bimorph cantilever where the indentation force (F) is measured by a strain gauge and the indentation depth (h) is monitored by a piezoelectric motor driven displacement platform. The quasi-static mechanical properties of the soft samples are obtained by using the F-h curve and the dynamic properties are extracted from the contact resonance curve of the piezoelectric cantilever which is measured by using electromechanical impedance (EMI). Firstly, the working principle of this indentation method for quasi-static and dynamic mechanical property measurement is presented. Then, both the quasi-static and dynamic indentation testing were conducted on a silica gel sample, and the testing results fit well with that obtained using tensile testing. Later, the viscoelastic properties of a Polydimethylsiloxane (PDMS) sample was tested which is strongly dependent on the indentation force. Finally, modulus imaging was conducted on a silica gel sample containing a stiffer elastomer sphere using the local contact stiffness (LCS) as the indicator, and the elastomer can be clearly revealed. The proposed piezoelectric cantilever based instrumented indentation method is very convenient for mechanical characterization of soft materials and may be widely used in near future.