Abstract
Characterising the mechanical response of ultra-soft materials is challenging, particularly at high strain rates and frequencies [1]. Time Temperature Superposition (TTS) can sometimes be used to mitigate these limitations [2], however not all materials are suitable for TTS. Biological tissues are particularly difficult to test: in addition to the extreme softness, challenges arise due to specimen inhomogeneity, sensitivity to boundary conditions, natural biological variability, and complex post-mortem changes. In the current study, a novel experimental apparatus and methodology was developed and validated using low modulus silicone elastomers as model materials. The full field visco-elastic shear response was characterised over a wide range of deformation frequencies (100-1000+ Hz) and amplitudes using Digital Image Correlation (DIC) and the Virtual Fields Method (VFM). This methodology allows for the extraction of fullfield material properties that would be difficult or impossible to obtain using traditional engineering techniques.
Highlights
Soft materials have low mechanical stiffness and strength, and include polymers, foams, and biological tissues
Whilst soft materials are widely used in applications where they experience high rate loading, there is a paucity of data on their properties at high strain rates and frequencies when compared to metals and ceramics
A further limitation of standard engineering test methodologies is the assumption of specimen homogeneity: material inhomogeneity or specimen strain localisation is not detected by traditional engineering tests; a form of full field measurement is needed
Summary
Soft materials have low mechanical stiffness and strength, and include polymers, foams, and biological tissues. A primary reason for this is the challenges inherent in testing soft materials under these loading conditions. A further limitation of standard engineering test methodologies is the assumption of specimen homogeneity: material inhomogeneity or specimen strain localisation is not detected by traditional engineering tests; a form of full field measurement is needed. Precise control of specimen boundary conditions is critical when testing soft materials using traditional methods, and any deviation from the assumed deformation state can lead to large errors. 3. The VFM can be setup to take advantage of the full-field measurements provided by DIC, and give a full-field measurement of the material properties. The VFM can be setup to take advantage of the full-field measurements provided by DIC, and give a full-field measurement of the material properties This allows for the testing of heterogeneous materials. Properties that would be impossible to access using currently existing techniques are directly measured
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