| dc.description.abstract | Over the last decade mechanical size effects have been recognised as a real phenomenon in which
a material appears stronger when the volume of material under stress is reduced to dimensions of
less than a micrometre. These size effects in the plastic deformation result from microstructural
features in the material, such as crystal size or object spacing, or from the stressed volume
imposed during nanomechanical tests. Plasticity size effects are particularly evident in materials
that deform by dislocation plasticity, such as metals and some semi-conductor and ceramic
materials. The relationships between test scale and internal microstructural features were
examined for pure copper and the precipitation-hardened alloy copper-chromium-zirconium. A
variation in test scale was achieved using spherical nanoindentation with a range of tip radii, as
well as Berkovich indentation. The microstructural length-scales considered were Cr precipitate
spacing, grain size, and nano-scale defects due to proton irradiation.
The work has implications in the application of small-scale test techniques such as nanoindentation.
Understanding size effects is important for interpreting the results of such tests and for
exploiting the size effect as a new strengthening mechanism in materials. For the nuclear power
generation industry small-sized test samples have significant advantages; reduced volumes of
material have lower levels of radioactivity, and non-destructive test methods enables continued
structural monitoring using the same witness sample. An understanding of the size effects will
also assist in adoption of these test methods in the nuclear power and other critical industries. | en_US |
