Characterising the frequency‐response of ultra‐soft polymers with the Virtual Fields Method

Aaron Graham,Clive Siviour

doi:10.1111/str.12386

Abstract

AbstractThis paper presents a novel apparatus, combined with application of the Virtual Fields Method (VFM) for the high frequency characterisation of the mechanical response of ultra‐soft materials. The viscoelastic response is characterised under harmonic deviatoric loading at a range of frequencies using the dynamic VFM in the frequency domain. Obtaining useful high rate data on soft materials is challenging using typical test methodologies, as the low speed of sound in the material makes stress equilibrium difficult to obtain; additionally, the low stiffness results in small stresses and weak measurement signals. This novel apparatus and analysis method have been shown capable of obtaining important material characterisation data that would be impossible to access using currently existing test techniques.

Highlights

Soft materials may be defined as materials that have low mechanical stiffness and strength and include polymers, foams, and biological tissues.[1]
Two materials were tested in this set of experiments, as previously described: the stiffer polymer was used in order to validate the new apparatus against Dynamic Mechanical Analysis (DMA) rheometry data
While this apparatus was designed to operate above 100 Hz, some experiments were conducted at frequencies as low as 10 Hz in order to probe the lower limits of the apparatus's operating envelope

Summary

Introduction

Soft materials may be defined as materials that have low mechanical stiffness and strength and include polymers, foams, and biological tissues.[1] These materials are widely used in applications in which large amplitude dynamic or impact deformations are experienced; there is a paucity of data on their properties at high strain rates and frequencies when compared to metals and ceramics. One reason for this is that they are challenging to characterise under these loading conditions.[1,2,3,4]. The use of semi-conductor strain gauges and very thin

Methods

Results

Conclusion