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Mechanical and structural characterization of the poroviscoelastic properties of natural and synthetic biocomposites
Rubber-like insect cuticle is a light fibrous composite which exhibits great deformability and long range elasticity due to the presence of a large amount of the elastomeric protein resilin. The presence of resilin in specific locations in the insect body leads to the assumption that its main function is loss-free storage of energy. The composition of the cuticle reveals the presence of a resilin matrix in which chitin fibers are embedded. Nanoindentation testing was used to study the differences in the mechanical properties of the structure between genders and wing morphs of the sand field cricket, Gryllus firmus. The results provide insight into the structure-function relations associated with the properties of insect rubber-like cuticle from different morphs and genders. An understanding of this relationship is of great importance if synthetic bio-inspired loss-free composites are to be manufactured. Inspired by the rubber-like cuticle, a synthetic composite was made of the elastomeric protein elastin in which polycaprolactone fibers were embedded. Nanoindentation testing was used to investigate the differences in the mechanical properties of the synthetic rubber-like composite between materials crosslinked for different time periods (2, 4, and 6 hours). Furthermore, the characterization of the viscoelastic properties of the synthetic composite by nanoindentation reveals the composite crosslinked for 4 hours as an optimized strain energy storage material when employed at low frequency load cycles. Also, investigating the microstructure of the synthetic composite shows the presence of pores which, under deformation, are responsible for the generation of a simultaneous mechanical response to viscoelasticity which is known as poroelasticity. Thus in this dissertation a methodology is developed to decouple the viscoelastic and the poroelastic behavior by combining the nanoindentation technique with finite element simulations. With this approach, it is possible to quantify measurements of the poroviscoelastic properties of these rubber-like composites. Such techniques are expected to find broader applications for quantifying the influence of crosslinking density and environmental factors on the nanoscale mechanical properties of many other similar composites.
Hayot, Celine M, "Mechanical and structural characterization of the poroviscoelastic properties of natural and synthetic biocomposites" (2013). ETD collection for University of Nebraska - Lincoln. AAI3590980.