Proof test of hybrid shrink fits with ceramic hub

Abstract

Advanced ceramic machine components are required in many applications because of their specific material properties like high hardness, resistance to chemicals, corrosion and wear, low specific weight etc. The most suitable shaft-hub connection to ceramics is an interference fit assembly because it is free of geometrical notches and transmission of forces takes place in a large area. Such a shrink fit is rated for endurance strength when the stress intensity factor is below the specific value KI0 where no crack growth occurs. The total component suddenly fails, when the stress intensity factor exceeds the KIC value. The load to the press fit during the joining process, caused by the interference of the assembly, could be regulated by ambient conditions. In case of undetected material defects or microcracks in the ceramic and if the stress intensity is below KIC, the ceramic will not fail but a crack could grow. Thus, the joining process only seems to be a proof test. When the load during operation leads to a stress intensity that remains higher than KI0 the crack grows until the whole ceramic component fails. This effect was verified in tests at the Institute for Engineering Design and Industrial Design.