- Title
- Neutron diffraction and micromechanical modelling for elastic constant and stress determination in polycrystals
- Creator
- Zhang, JianFeng
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2014
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Micromechanics has been a popular scientific topic since the late 19th century. The anisotropic mechanical properties of crystals and the complexity of the interaction across grain boundaries were obstacles for revealing a rigorous connection between macroscopic and microscopic stresses and strains. The development of neutron and synchrotron diffraction enables practitioners to accurately measure the internal strains for certain groups of crystallites with the same orientation. This provides us experimental possibilities for analysing the micromechanical response of individual grains to external load. Eshelby's study on ellipsoidal inclusions in a matrix material gave us the theoretical foundation of how the individual grains interact with the surrounding material. By considering the polycrystalline material as an isotropic or transversely isotropic medium in terms of the macroscopic scale, it is possible to determine the internal stress and strain under an external load. Incorporated with the in situ loading neutron diffraction, the relationship between the measured strains as a reaction to the external load can be quantitatively analysed. This helps us to understand the micromechanical state of polycrystalline materials. The initial objective of this research was the micromechanical analysis for determining the single crystal elastic constants (SCEC) from polycrystals. Inspired from the hypothesis that ductile materials are more Reuss-like whilst brittle materials are more Voigt-like, we started research from the background and literature review, experimental methods and quantitative texture analysis. Following this a practical method was analytically developed for quantifying the micromechanical stress for individual groups of grains. Based on this method, a few differently categorised materials (e.g. alumina, MAX phases and metal alloys) were studied in order to determine the SCEC from the experimentally measured microscopic strains. Eventually, we concluded that the method developed based on Eshelby's theory and the self-consistent micromechanical model is capable of determining the micromechanical state for a material without any non-elastic deformation under external load. Anelastic deformation plays a significant role in determining the micromechanical state of a material therefore the proper precautions must be taken in order to apply the method developed to applications such as determination of SCEC from polycrystals or residual stress analysis.
- Subject
- micromechanical analysis; neutron diffraction; single crystal elastic constant; diffraction elastic constant; crystallographic texture determination; stress analysis; Eshelby's solution
- Identifier
- http://hdl.handle.net/1959.13/1040282
- Identifier
- uon:13762
- Rights
- Copyright 2014 JianFeng Zhang
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Abstract | 352 KB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Thesis | 5 MB | Adobe Acrobat PDF | View Details Download |