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Investigation of the Thermomechanical Properties and Fracture Behaviour of Magnesia-Based Materials by Using a Refined Digital Image Correlation Method

Wednesday, February 03, 2021

Magnesia-spinel and magnesia-hercynite bricks for thermal shock applications often show an enhanced crack propagation resistance due to an engineered microstructure design. In these materials, microcrack networks resulting from the thermal expansion mismatch between magnesia matrix and spinel/hercynite aggregates promote the activation of energy dissipating mechanisms within the so-called Fracture Process Zone (FPZ) during loading.

Fracture behaviour of magnesia-based model materials was investigated by coupling a refined Digital Image Correlation method (2P-DIC) with theWedge Splitting Test (WST). Despite the rather similar elastic and dilatometric properties of spinel and hercynite single constituents, peculiar microcracking patterns were observed, especially in magnesia-hercynite. Extensive diffusion between magnesia and hercynite during sintering led to the formation of spinel solid solutions around hercynite aggregates. These solid solutions contributed to create numerous fine microcracks confined within the diffusion zone. Initially present within the microstructure, microcrack networks promote an increase of specific fracture energy during WST experiments. Strain fields measured by 2P-DIC revealed extensive crack branching for magnesia-hercynite materials. The 2P-DIC and WST measurements showed that microcrack networks promoted the development of the FPZ, which in turn induced higher fracture energies.

Keywords: digital image correlation, magnesia spinel, thermomechanical behaviour, fracture