TY - THES

T1 - Mechanical response of textured alumina-based ceramics after Hertzian contact damage

AU - Stücklberger, Fabian

N1 - no embargo

PY - 2023

Y1 - 2023

N2 - Mimicking biological materials (i.e. nacre) has been established as effective approach to enhance the mechanical properties of advanced ceramic. The design of layered multi-material ceramic architectures with strong interfaces introduces alternating in-plane residual stresses, caused by the thermal mismatch after cooling down from sintering temperature. In so-called damage-tolerant designs, the embedded layers with in-plane compressive residual stresses in a multilayer system (laminate) can be used for providing a barrier against crack propagation. Furthermore, microstructure ¿texturing¿ through template grain growth has been demonstrated to further increase the fracture resistance of laminates through crack deflection mechanisms within the textured layer. The combination of texturing and in-plane compressive residuals stresses in a multilayer architecture may be used to improve contact resistance in ceramics. In recent research, the effectiveness of layered alumina ceramics against Hertzian crack initiation has been demonstrated, as a combination of sub-surface micro-crack formation and crack deflection within the textured layers. The question raises whether such architecture containing textured alumina (nacre-like) layers with elongated grains can be also effective against the further propagation of contact cracks. In this thesis, the mechanical response of textured alumina-based layered ceramics after Hertzian contact damage is investigated. Layered designs and monolithic samples are fabricated using tape casting method. Uniaxial bending tests are performed on laminates after spherical contact loading. Two orientations, parallel and perpendicular to the casted layers are tested. Results are compared to the mechanical response of equiaxed and textured monoliths, taken as a reference. Fractographic analyses are carried out to understand the fracture process.

AB - Mimicking biological materials (i.e. nacre) has been established as effective approach to enhance the mechanical properties of advanced ceramic. The design of layered multi-material ceramic architectures with strong interfaces introduces alternating in-plane residual stresses, caused by the thermal mismatch after cooling down from sintering temperature. In so-called damage-tolerant designs, the embedded layers with in-plane compressive residual stresses in a multilayer system (laminate) can be used for providing a barrier against crack propagation. Furthermore, microstructure ¿texturing¿ through template grain growth has been demonstrated to further increase the fracture resistance of laminates through crack deflection mechanisms within the textured layer. The combination of texturing and in-plane compressive residuals stresses in a multilayer architecture may be used to improve contact resistance in ceramics. In recent research, the effectiveness of layered alumina ceramics against Hertzian crack initiation has been demonstrated, as a combination of sub-surface micro-crack formation and crack deflection within the textured layers. The question raises whether such architecture containing textured alumina (nacre-like) layers with elongated grains can be also effective against the further propagation of contact cracks. In this thesis, the mechanical response of textured alumina-based layered ceramics after Hertzian contact damage is investigated. Layered designs and monolithic samples are fabricated using tape casting method. Uniaxial bending tests are performed on laminates after spherical contact loading. Two orientations, parallel and perpendicular to the casted layers are tested. Results are compared to the mechanical response of equiaxed and textured monoliths, taken as a reference. Fractographic analyses are carried out to understand the fracture process.

KW - Kontaktschädigung

KW - Aluminiumoxid

KW - Laminate

KW - texturiertes Gefüge

KW - Fraktographie

KW - Eigenspannungen

KW - contact damage

KW - alumina

KW - laminates

KW - textured microstructure

KW - fractography

KW - residual stresses

M3 - Master's Thesis

ER -