Bioinspired Structure Design for Strain-rate Dependent Properties of Composites: Investigation, Prototyping, and Mechanical Modeling

Description

A wide range of industrial applications such as aviation/aerospace, marine, and automobile rely  on the development of advanced composite materials, which have benefitted from unitizing  bioinspired designs for high performance under constant loading rates. However, a practically-important  but rarely-recognized route is bioinspired structure design for superior mechanical  properties under varying loading rates (strain-rate dependent behaviors), the real loading  condition of these composites. The strain-rate dependency of composites has been mostly  ascribed to material attributes, e.g., viscoelasticity and/or viscoplasticity, while effects from  structure design remain unclear, despite abundant literature on strain-rate dependent properties  of biological and engineering composites (as the material and structure are fixed). Nevertheless,  an intriguing finding from the applicant reveals that keratinous materials with similar chemical  keratin constituents but different structures show different strain-rate dependent properties (450%  difference in strain-rate sensitivity index from whale baleen to human hair). This opens a new  avenue for such an initiative. Also, our preliminary studies showed that a bioinspired tubular  structure exhibits elastic strain-rate stiffening 10% higher, inelastic strengthening 42% higher,  and average strain energy density 10% higher than its counterpart of fiber-matrix structure.  This project hypothesizes that structure can enhance strain-rate stiffening and toughening  synergistically and restrict damage-induced weakening of composites through optimizing the  spatial organization of constituents. In an aim to answer (i) how structure affects strain-rate  dependent behaviors, (ii) what effective bioinspired structures for high strain-rate dependent  performance to be extracted, and (iii) how to quantify and evaluate the structure-caused strain-rate  dependent properties, we will (1) correlate different strain-rate dependent properties with  different structures by investigating keratinous materials, (2) extract and test effective structure  features for strain-rate dependent properties through prototyping, and (3) formulate into original  theories by mechanical modeling with examples of validation.  By completion of this project, we will be able to establish a novel scheme of bioinspired  structure design for high strain-rate stiffening and toughening composites. New bioinspired  structures will be brought forth that could outperform conventional composites in superior  strain-rate stiffening and toughening. Furthermore, a new theoretical framework will be built  that solves structure-related parameter functions to quantify strain-rate effects and explains  important structural mechanisms in dominating strain-rate dependent properties.