A review of key developments and pertinent issues in nanoindentation testing of fibre reinforced plastic microstructures

In recent decades, nanoindentation has emerged as a useful experimental technique for characterising the in situ properties of fibrous composite constituents. However, the elastic theory used by the nanoindentation technique assumes that the substrate is a stress-free single-phase homogeneous continuum. Therefore, the application of nanoindentation theory to inhomogeneous composite materials composed of discrete regions with distinct material properties has proven to be problematic in certain scenarios. In this paper, a review of the key developments and pertinent issues reported by authors in relation to the nanoindentation of polymer matrix composites is presented. The effects of sample preparation, neighbouring constituents, residual stress, pile-up, time-dependent deformation and hydrostatic stress on the important nanoindentation parameters and properties are highlighted. The review also details the use of numerical simulations to gain greater insight into the stress and deformation fields produced during the nanoindentation of FRP microstructures, and includes recommendations regarding the standardisation of nanoindentation protocols for composite and polymeric materials.