Comparison of frequency and strain-rate domain mechanical characterization

Abstract

Indentation is becoming increasingly popular to test soft tissues and (bio)materials. Each material exhibits an unknown intrinsic “mechanical behaviour”. However, limited consensus on its “mechanical properties” (i.e. quantitative descriptors of mechanical behaviour) is generally present in the literature due to a number of factors, which include sample preparation, testing method and analysis model chosen. Viscoelastic characterisation – critical in applications subjected to dynamic loading conditions – can be performed in either the time- or frequency-domain. It is thus important to selectively investigate whether the testing domain affects the mechanical results or not. We recently presented an optomechanical indentation tool which enables both strain-rate (nano-) and frequency domain (DMA) measurements while keeping the sample under the same physical conditions and eliminating any other variability factor. In this study, a poly(dimethylsiloxane) sample was characterised with our system. The DMA data were inverted to the time-domain through integral transformations and then directly related to nano- strain-rate dependent results, showing that, even though the data do not perfectly overlap, there is an excellent correlation between them. This approach indicates that one can convert an oscillatory measurement into a strain-rate one and still capture the trend of the “mechanical behaviour” of the sample investigated.

Frequency dependent viscoelastic properties of porcine brain tissue

“…A linear viscoelastic model was adopted to model biological tissues under cyclic loading, characterised by the storage and loss moduli. Further, methods to convert data from the frequency domain to time-domain are reported in literature [62]; further, the maximum strain rate in this study ranges approximately between 7-14 /s. Based on this approach, the frequency dependent values presented in this paper could be used to fit viscoelastic constitutive models such as through Prony series representations following adaptation of the storage and loss moduli obtained to represent the mechanical behaviour of brain tissue.…”

Viscoelastic Properties of Crosslinked Chitosan Films

“…Strain hardening from preloading can be avoided with strain-rate measurements which negate the use of a trigger force before the measurements. Bartolini et al [54] studied the viscoelastic response of nano-indented poly(dimethylsiloxane) strips and found that the apparent elastic moduli of previously strained samples were lower than non pre-strained samples.…”

Preparation and Behavior of Bamboo Fiber-Reinforced Polydimethylsiloxane Composite Foams during Compression

“…Rate-dependence of elastic response in polymer systems is well known and has been explained on the basis of different molecular motions at various time regimes [24]. Recent studies have reported dependence of elastic moduli on strain rate for virgin and prestrained pristine PDMS [25]. With its emergence as a leading material for flexible pressure sensors, the strain-rate dependence of mechanical properties of carbon-filled PDMS have been reported [14].…”