Strain fields measurements to study the nonlinear mechanical behaviour of refractory materials

Abstract : The present thesis aimed to apply digital image correlation (DIC) used for kinematic fields’ measurements as a support for the experimental characterization of refractory materials with specific non-linear behaviour. Model and industrial materials with different degrees of flexibility were studied. The first type of materials was a single phase model flexible aluminium titanate material (AT VF) developed for academic purposes by improving the grain growth. Its non-linear mechanical behaviour was obtained thanks to the thermal expansion mismatch of its grains according to the different crystallographic axis. The second one is multi-phased magnesia based industrial materials, whose flexibility is less accentuated, and for which the non-linear mechanical behaviour is obtained thanks to the thermal expansion coefficients mismatch between spinel aggregates and magnesia matrix. In order to apply the optical methods on these materials which exhibit lower strain-to-rupture, it was necessary to optimize the accuracy of these techniques by improving experimental conditions.In the case of AT VF, DIC and mark tracking method have been applied on four-points bending test at room temperature to underline the material asymmetric mechanical behaviour which induces a significant shift of the neutral fibre and to evaluate the relative displacement of rolls. The application of DIC has been extended to other experimental testing method such as Brazilian and Wedge Splitting test using the multi-phased magnesia based materials. This highlighted fracture mechanisms (crack occurrence and propagation) and the presence of crack branching phenomenon promoted thanks to an initial micro-cracks network voluntary introduced by thermal expansion mismatch between the different phases so as to improve their thermal shock resistance. From displacement experimentally obtained by DIC, a finite element method updating (FEMU-U) has been developed to determine material properties.
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Younès Belrhiti. Strain fields measurements to study the nonlinear mechanical behaviour of refractory materials. Materials. Université de Limoges, 2015. English. ⟨NNT : 2015LIMO0128⟩. ⟨tel-01362983⟩

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