SUMMARY

Nanoindentation has a high load resolution, depth sensing capabilities, and can be used to characterize the local mechanical behavior in material systems with heterogeneous microstructures thereby extracting useful stress-strain curves. To be able to apply the indentation stress-strain methods to polymer composites, we have to first develop analysis techniques that will work for materials that exhibit viscoelasticity. In a lot of current research the viscoelastic material properties are extracted after the material has been deformed enough to initiate plasticity and in some cases the time dependence of the deformation is ignored. This does not give an accurate representation of the material properties of the undeformed sample. This dissertation develops analysis protocols to extract stress-strain curves and viscoelastic properties from the load-displacement data generated from spherical nanoindentation on materials exhibiting time-dependent response at room temperature. Once these protocols are developed they can then be applied, in the future, to study viscoelastic and viscoplastic properties of various mesoscale constituents of composite material systems, including both interior regions as well as those near interfaces. These new protocols will be developed and demonstrated through selected case studies on a range of materials that include commercial polymers and the bio-polymer chitosan.