INVESTIGATION OF THE MECHANICAL-BEHAVIOR OF SILICON-NITRIDE IN A SPHERE-ON-PLATE CONTACT

Silicon nitride is recently used as a material for full ceramic roller bearings. The reasons for this are the specific material properties l ike the high chemical resistance, the low specific weight and the high strength, even at high temperatures. Nevertheless, there is only litt le experimental and theoretical experience in the field of full cerami c roller bearings with respect to load capacity and lifetime of these components. This lack of information is the motivation for the investi gations on the mechanical behaviour of a gas pressured sintered silico n nitride (GPSN) in a sphere-on-plate contact, where fracture or plast ic deformation can occur. The load-displacement curves and the load ne cessary to cause fracture or plastic deformation are determined as a f unction of sphere radius. The initiation of fracture at natural defect s is described by fracture mechanics. The fracture mechanical model is based on independently measurable material constants like young's mod ulus, poisson's ratio and fracture toughness K-Ic. The plastic deforma tions are described within a Finite-Element calculation with an elasti c-ideal plastic material law according to von Mises. The results form the starting point for further investigations in the field of design a nd lifetime calculations for ceramic roller bearings.