Abstract
The micron components or structures with characteristic sizes ranging from a few hundred nanometres to several micrometres, have been widely applied in various advanced areas, such as optics, biomedical engineering, electronics, etc. In the past two decades, the micro- and nano-manufacturing technologies have been continuously developed as powerful tools to produce high-quality micron components/structures with specifically designed functionalities. When the size of machined materials is close to sub-micron/micron, it is recognized that the well-established conventional machining mechanism cannot fully explain the material deformation behaviours during micromachining, because the mechanical properties of crystal materials at submicron/micron scale distinctly differ from their bulk counterparts. Therefore, to achieve a more reliable fabrication of sub-micron/micron products, it is necessary to gain an indepthunderstanding of the mechanical properties of materials at sub-micron/micron
scales.
This thesis reports the systematic investigations on the mechanical deformation of crystal materials at sub-micron/micron scales under the most common engineering tests, including sub-micron pillar compression, nanoindentation, and nano-scratch. Firstly, a multiscale simulation framework based on discrete continuous method (DCM) was developed. The implementation details, such as the initial setting of discrete dislocation dynamics (DDD) module and the strain regularization, are presented. Besides, compression tests of aluminium sub-micron pillars were performed. The simulation results were compared to other modelling results to validate the developed model. The results show that the developed simulation framework successfully captures the sample size effect. The intermittent plastic deformation of sub-micron pillars is closely related
to the evolution of dislocation density.
Then, both experiment tests and numerical simulations have been performed to
investigate the mechanical properties of aluminium under nanoindentation. The
experiment results show that the indentation hardness increases with decreasing
indentation depth. A three dimensional (3D) crystal plasticity finite element method (CPFEM) nanoindentation simulation model has been developed to determine the effects of crystallographic orientation and the shape of indenters on the material nanoindentation responses. The simulation results show the crystalline orientation and the shape of indenter have significant effects on the material nanoindentation behaviours. The consistency between the shear strain and surface pile-up directly demonstrates the formation of material pile-ups is related to the activation of slip systems.
Next, the effects of crystallographic orientation, indenter orientation and scratch
direction on the nanoscratch behaviours of single crystal copper have been investigated by CPFEM simulations. The (001)-orientated sample is with the worst wear resistance as its plastic deformation prefers to extend along the indented surface. The activation of the slip systems strongly depends on the indenter orientation and scratch direction. The lattice rotation and activation of slip systems are two ways to moderate the deformation caused by the penetration of indenter during nano-scratch.
Finally, further research, such as the development of physics-based simulation models and experimental investigation, are proposed.
| Date of Award | 8 Sep 2022 |
|---|---|
| Original language | English |
| Supervisor | Jane Jiang (Main Supervisor) & Zhen Tong (Co-Supervisor) |