document: The second stress state is a tri-axial tensile stress designed to represent the zone ahead of an advancing crack tip. Micro-scale lateral cracks have been observed in the oxide layer, and appear to form very close to or at the metal–oxide interface (Fig. 1). Finite element analysis by Parise et al. indicated that these cracks form as a result of localised tensile stresses above peaks in the metal–oxide interface roughness [31]. These cracks are considered separate to any nano-scale cracks that might result from the tetragonal to monoclinic phase transformation. An assumption is made here that whether the micro-scale lateral cracks form via fracture of the oxide or by de-bonding at the interface a triaxial tensile stress state will still be present. In manufactured partially stabilised zirconia cracks would be expected to destabilise the tetragonal phase. This is simulated by applying tensile stress in direction 1, 2 and 3. As this the maximum stress at the crack tip is not known, the applied tensile stresses cover a range from 0.1GPa up to a maximum stress value of 2.2GPa as it is approximately equal to three times the fracture strength of bulk fracture strength for manufactured stabilized zirconia [34]. For the biaxial compressive and triaxial tensile stress states it is the trends in behaviour rather than the absolute values that are considered of greatest importance for this work.
doc_bio_tags: O B I I O O B I I O O O O O O O O B I I O O B O O O O O B O O O O O O O O O O O B I O O B I I O O O O O O O B O O O O O B I I O O O O B I O O O B O O O O O O B O O O O O B I I I I O O O O O O O O O O B O O B O O B O O O O O O O B I I O O O O O O B I I I B O O O O O O B I O O O O B I I O O O O O O O O O B I O O O O O O O O B I I O O O O O O O O B I O O O O O O O O O O O O B O O O B O O B I I O O O B I I I I I I O O O O O O O O O O O O O O O O O O O O
extractive_keyphrases: advancing crack tip applied tensile stresses applying tensile stress biaxial compressive and triaxial tensile stress states cracks finite element analysis fracture localised tensile stresses manufactured partially stabilised zirconia manufactured stabilized zirconia maximum stress metal–oxide interface oxide second stress state tetragonal phase tetragonal to monoclinic phase transformation triaxial tensile stress
abstractive_keyphrases: de-bonding oxide layer simulated by applying tensile stress in direction 1, 2 and 3 tri-axial tensile stress