Recent advances in nanomechanical and in situ testing techniques: Towards extreme conditions

•Continuous stiffness measurement and direct in situ observation facilitate significant experimental advances.•Novel measurement possibilities enable investigation of elastic modulus, material damping and fracture characteristics of micron sized volumes.•Rate dependent flow curves can be assessed by spherical nanoindentation.•Extreme environments and operando conditions can be probed by advanced nanoindentation and in situ deformation set-ups. Nanoindentation based techniques were significantly enhanced by continuous stiffness monitoring capabilities. In essence, this allowed to expand from point-wise discrete measurement of hardness and elastic modulus towards advanced plastic characterization routines, spanning the whole rate-dependent spectrum from steady state creep properties via quasi static flow curves to impact or brittle fracture. While representing a significant step forwards already, these techniques can tremendously benefit from additional or complementary input provided by in situ or operando experiments. In fact, by combining and merging these approaches, impressive advances were made towards well controlled nanomechanical investigations at various non-ambient conditions. Here we will discuss some novel experimental avenues facilitated by deliberate extreme environments, and also indicate how future improvements and enhancements will potentially provide previously unseen insights into fundamental material behavior at extreme conditions.