Abstract
From understanding the effect of manufacturing processes on the mechanical properties of a component to micro-structural defects affect the macroscopic behavior of a material, it is crucial to accurately characterize stress and strain fields at the micro-scale. Such fields impact the macroscopic behavior and properties of mechanical components, and their correct understanding can make the difference between the failure of an emerging technology and the successful optimization of a mechanical design. It is therefore paramount to have accurate and accessible characterization techniques for strains stresses at the micro-scale.Metrology methods based on Electron Back Scatter Diffraction (EBSD) have seen important advancements in the last decades. A variation of this technique, named High Resolution Electron Back Scatter Diffraction (HR-EBSD) makes it possible to capture microscopic relative strain fields with very high levels of sensitivity (~e−4). HR-EBSD relies on the acquisition of a map of EBSD patterns and the correlation of said patterns to one that is selected to be the reference. However, recent research in the field faces the following recurring obstacle: the resulting strain and stress measurements, are relative to the state of the reference EBSD pattern.
The following thesis presents a new method to accurately measure absolute strains and stresses at the micro-scale with HR-EBSD by combining it with a semi-destructive relaxation technique: FIB ring-core milling. This technique consists of milling a ring of around 10um in diameter such that the surface of the pillar within it is free to deform back to its unstrained state. In theory, if this relaxation is successfully achieved, an EBSD pattern taken from the surface of the ring-core’s pillar may be used as a strain-free reference for absolute strain measurements. In this work, the method is validated with single-crystal silicon and a custom-made bending stage for in-situ experiments. Practical issues from using FIB ring-core milling are considered and a solution is proposed. Ultimately, absolute strain and stress measurements are obtained and compared to analytical and numerical predictions for the expected loading conditions.
| Date of Award | 20 Apr 2022 |
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| Original language | English |
| Supervisor | Johan P.M. Hoefnagels (Supervisor 1) |