Nanomechanics of nanocomposite systems: Experimental studies in bone, seashells and synthetic nanocomposites using nanoindentation and atomic force microscopy

Since last couple of decades, scientists and engineers are turning towards nature for material design lessons. Considerable efforts have been made to decode the design rules found in natural biological materials, which can be used to develop next-generation nanocomposite materials. The reason for these efforts lies in the extraordinary properties of biological materials that are not found in synthetic materials. Nacre and bone are two such materials designed nature through billions years of evolution. Both of these materials are nanocomposites having unique microstructures and exhibiting remarkable mechanical properties. In this work, several nanocomposite systems of biological and synthetic origin are investigated for nanomechanical properties and also the methodology for their nanomechanical property measurement. Unique experiments in quasistatic and dynamic nanoindentation that shed light on both novel experimental routes to evaluate mechanics at the nanoscale as well as methodology to evaluate nanomechanical data are undertaken.;Nacre is the shiny inner layer of many molluskan shells. Its exceptional mechanical properties have been the inspiration for material scientists for several decades. We have described the nanomechanical properties of nacre using quasistatic and dynamic nanoindentation. Our results indicate that the aragonite platelet in nacre is viscoelastic in nature. We have also investigated the nanomechanics of protein-aragonite in nacre using atomic force microscopy and have estimated the force of adhesion between the organic and inorganic phase.;Compact or cortical bone is the major load-bearing hard tissue in most living organisms which is optimized by nature to perform multiple functions. Bone exhibits unique mechanical properties depending on its hierarchical structure that spans from nanoscale to macroscale. We have studied the nanoscale mechanics of bone using nanoindentation. The results indicated that the microstructure and/or composition changes along the thickness of bone.;Also investigated are nanomechanical properties in synthetic nanocomposites composed of nanoclays and polymers (nylon 6). The novel experiments conducted in this work describe quantitatively the extent of the alteration zone of polymers around nanosized clays to be about 25 nm using phase imaging in atomic force microscopy. These experiments provided valuable input for the development of multiscale models of polymer clay composite systems.