Dong Liu
My PhD project focussed on the measurements of residual stresses and mechanical properties in environmental and thermal barrier coatings (TBC). Non-destructive approaches such as Raman spectroscopy and Photo-stimulated luminescence piezo-spectroscopy were employed for stress measurement in coatings and oxides. The multi-scale mechanical properties of the coatings are evaluated by bending micro-scale cantilever beams, typically 2x2x10 micrometres in size, which is a novel method independently developed in Bristol and was applied to TBC first here.
My post-doc project is on quasi-brittle fracture, the model materials are nuclear graphite and cement paste that has been tailored to various porosity. Micro-scale fracture in the process zone is the key. The fracture behavior and mechanical properties of the materials are investigated in a multi-scale approach.
Address: Department of Materials, Oxford University, Oxford OX1 3PH
My post-doc project is on quasi-brittle fracture, the model materials are nuclear graphite and cement paste that has been tailored to various porosity. Micro-scale fracture in the process zone is the key. The fracture behavior and mechanical properties of the materials are investigated in a multi-scale approach.
Address: Department of Materials, Oxford University, Oxford OX1 3PH
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Papers by Dong Liu
aggregates, the lattice strain is not expected to change 1:1 with the externally bulk strain applied to macroscale specimen. Deformation of the material containing pores and flaws causes localisation of strains and, hence, initiation of inelastic damage. The length-scale at which the localised damage develops during
loading can be characterised by the lattice strain in a bulk volume of material. Therefore, in situ neutron diffraction on a Gilsocarbon graphite bend geometry test specimen has been undertaken at the ENGIN-X, ISIS facility. It was found that lattice strain changes linearly with applied bulk strain but with reduced magnitude. The results are discussed with respect to the evolution of characteristic process zones, as deformation is increased, and the associated of microcracking.
Gilsocarbon graphite. The test geometry adopted has a ‘five-point’ bending configuration, i.e. a cruciformshaped
specimen that creates a tensile biaxial stress on the surface. This allows the effect of changing the
biaxial ratio on the load-displacement and fracture characteristics to be considered. An acoustic emission
(AE) technique has been applied to monitor and identify the occurrence of acoustic events and their locations
in specimens loaded either monotonically to failure or via several progressively increasing load-unloading
cycles. It was found that the fracture path changes with biaxial ratio. AE events occurred from low load in
all loading modes, and increased progressively with the increase of applied load. The total number of AE
events and the sum of the cascade energy from the AE measurements were similar for specimens fractured
at the same load under a particular loading condition.
mechanisms. For each test, an example using a particular specimen geometry is given and discussed with respect to the particular mechanical property evaluated and compared with macro-scale data. Nano-indentation was carried out as a conventional approach to validate and assist the understanding of the mechanical properties obtained via other small scale tests. The use of small scale test specimens offers benefits when handling irradiated reactor core graphite. The results are discussed with respect to the potential benefits, difficulties and
value of small scale mechanical tests for this particular application.
temperatures or improve surface properties. Residual stress generated in these multi-layer systems is one of the main causes of coating delamination and eventual failure. Systematic
measurement and monitoring of the residual stresses are a vital basis for integrity evaluation and remaining life prediction. Raman spectroscopy has been recognised as one of
the most important approaches to measure the stress in films and coatings. This review considers the measurement of stresses in films and coatings using Raman spectroscopy. It
addresses the following questions: what is Raman spectroscopy, why is stress important for films and coatings, how is strain/stress derived from Raman spectra and what confidence do we have in this technique and the limitations. To elucidate specific issues related to the application of the Raman technique for stress measurement, despite the wide
range of coatings available, important films and coating are chosen as representative examples.
aggregates, the lattice strain is not expected to change 1:1 with the externally bulk strain applied to macroscale specimen. Deformation of the material containing pores and flaws causes localisation of strains and, hence, initiation of inelastic damage. The length-scale at which the localised damage develops during
loading can be characterised by the lattice strain in a bulk volume of material. Therefore, in situ neutron diffraction on a Gilsocarbon graphite bend geometry test specimen has been undertaken at the ENGIN-X, ISIS facility. It was found that lattice strain changes linearly with applied bulk strain but with reduced magnitude. The results are discussed with respect to the evolution of characteristic process zones, as deformation is increased, and the associated of microcracking.
Gilsocarbon graphite. The test geometry adopted has a ‘five-point’ bending configuration, i.e. a cruciformshaped
specimen that creates a tensile biaxial stress on the surface. This allows the effect of changing the
biaxial ratio on the load-displacement and fracture characteristics to be considered. An acoustic emission
(AE) technique has been applied to monitor and identify the occurrence of acoustic events and their locations
in specimens loaded either monotonically to failure or via several progressively increasing load-unloading
cycles. It was found that the fracture path changes with biaxial ratio. AE events occurred from low load in
all loading modes, and increased progressively with the increase of applied load. The total number of AE
events and the sum of the cascade energy from the AE measurements were similar for specimens fractured
at the same load under a particular loading condition.
mechanisms. For each test, an example using a particular specimen geometry is given and discussed with respect to the particular mechanical property evaluated and compared with macro-scale data. Nano-indentation was carried out as a conventional approach to validate and assist the understanding of the mechanical properties obtained via other small scale tests. The use of small scale test specimens offers benefits when handling irradiated reactor core graphite. The results are discussed with respect to the potential benefits, difficulties and
value of small scale mechanical tests for this particular application.
temperatures or improve surface properties. Residual stress generated in these multi-layer systems is one of the main causes of coating delamination and eventual failure. Systematic
measurement and monitoring of the residual stresses are a vital basis for integrity evaluation and remaining life prediction. Raman spectroscopy has been recognised as one of
the most important approaches to measure the stress in films and coatings. This review considers the measurement of stresses in films and coatings using Raman spectroscopy. It
addresses the following questions: what is Raman spectroscopy, why is stress important for films and coatings, how is strain/stress derived from Raman spectra and what confidence do we have in this technique and the limitations. To elucidate specific issues related to the application of the Raman technique for stress measurement, despite the wide
range of coatings available, important films and coating are chosen as representative examples.