TY - BOOK

T1 - New methods for the mechanical characterisation of ceramic rolling elements

AU - Strobl, Stefan

N1 - no embargo

PY - 2014

Y1 - 2014

N2 - In high performance hybrid bearings the raceways are made of steel, and the rolling elements – e.g. balls or rollers – are made of ceramic materials. In comparison to steel, ceramic materials have some outstanding properties, which are beneficial for such hybrid bearings under special loading conditions or applications. Due to the brittle material behaviour of ceramics, the reliability of the ceramic components in rolling contact is mainly determined by fracture toughness as well as by the surface finish, i.e. one single defect may lead to catastrophic failure of the whole bearing. Therefore, easily interpretable component tests are needed for the assessment of the surface quality of the original rolling elements. This can be characterised by the surface strength that is typically affected by defects at or slightly below the surface (such as cracks or grinding scratches). These defects are caused by the specific surface finishing process (i.e. grinding and polishing). Moreover, the fracture toughness is strongly related to the microstructure, which may vary with details of the production route used. Hence, it is also important to determine the fracture toughness directly at the component. In this dissertation new methods – applicable to the original components – are presented for the determination of the surface strength and the fracture toughness. They are also suitable for small rolling elements with diameters down to 3 mm. Examples are the “Notched Roller Test” or the recently standardized “Notched Ball Test” for strength testing. Among others, these strength testing methods are further modified by using artificial (and well-defined) surface cracks for the determination of fracture toughness. This dissertation focuses on the mechanical properties of rolling elements made of the state-of-the-art bearing material, i.e. silicon nitride ceramic. In addition, the feasibility of the developed procedures is also demonstrated for other structural ceramics.

AB - In high performance hybrid bearings the raceways are made of steel, and the rolling elements – e.g. balls or rollers – are made of ceramic materials. In comparison to steel, ceramic materials have some outstanding properties, which are beneficial for such hybrid bearings under special loading conditions or applications. Due to the brittle material behaviour of ceramics, the reliability of the ceramic components in rolling contact is mainly determined by fracture toughness as well as by the surface finish, i.e. one single defect may lead to catastrophic failure of the whole bearing. Therefore, easily interpretable component tests are needed for the assessment of the surface quality of the original rolling elements. This can be characterised by the surface strength that is typically affected by defects at or slightly below the surface (such as cracks or grinding scratches). These defects are caused by the specific surface finishing process (i.e. grinding and polishing). Moreover, the fracture toughness is strongly related to the microstructure, which may vary with details of the production route used. Hence, it is also important to determine the fracture toughness directly at the component. In this dissertation new methods – applicable to the original components – are presented for the determination of the surface strength and the fracture toughness. They are also suitable for small rolling elements with diameters down to 3 mm. Examples are the “Notched Roller Test” or the recently standardized “Notched Ball Test” for strength testing. Among others, these strength testing methods are further modified by using artificial (and well-defined) surface cracks for the determination of fracture toughness. This dissertation focuses on the mechanical properties of rolling elements made of the state-of-the-art bearing material, i.e. silicon nitride ceramic. In addition, the feasibility of the developed procedures is also demonstrated for other structural ceramics.

M3 - Doctoral Thesis

ER -