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Figures, from the top to bottom (simulated Fe at 300K with cylindrical indenter RI=20nm):
* Initial stage of indentation – dislocation generation.
* Dislocation-dislocation interaction with creation of sessile triple-node that defines the maximum stress during deformation.
* Closer view of the sessile triple node. |
New View of Nanoindentation: Experiment and Modeling
Nanoindentation is a powerful tool for investigating the basic mechanical properties of materials and is successfully used in coupling of high-resolution experiments with large-scale atomistic modeling. Localized indenters create localized deformation that defines the properties of a small volume of the material imposing a quite specific mode of deformation. Atomic-scale modeling of such process demonstrate the localized character of such deformation and cannot be compared directly with bulk experiments due to, at least, one to two orders of magnitude in scale difference. We expand this technique by applying indenters extended in one dimension, i.e. having cylindrical or wedge shapes. This creates an extended and crystallographically-controlled deformation mode that involving many dislocations, their motion and interaction with each other and pre-existing material’s microstructure.
The new technique permits investigation of particular mechanisms of work-hardening (due to dislocation-dislocation reactions), matrix hardening (due to dislocation-internal obstacle interactions) as well as more complicated mechanisms related to secondary dislocation sources (internal interfaces) and, potentially, plastic instability (high stress sources generating dislocations creating localized shear bands).
Specially designed nano-indentation experiments and high-resolution microstructure characterization techniques will be coupled with large-scale atomistic modeling to investigate particular mechanisms which can be then parameterized in terms of continuum dislocation dynamics models and used for prediction of mechanical property changes in materials subjected to various treatment such as thermal, mechanical and irradiation with energetic particles. |
