Fatigue Resistant Silicon Nitride Ceramics Due TO Anelastic Deformation and Energy Dissipation
To investigate the link between internal friction and fatigue resistance of sintered silicon nitride at elevated temperatures, uniaxial tension-compression and impulse excitation tests were performed and the results compared with those of previously reported torsion pendulum tests. AN internal friction peak associated with the glass transition of amorphous intergranular phases is observed at low stress-amplitudes. This peak occurs near the operating temperature of combustion engine valves and thus is considered to be one of the reasons for earlier reported enhanced vibration fatigue resistance and acoustic quality of silicon nitride valves. High-amplitude internal friction measurements have revealed a new and much larger internal friction effect than previously could be expected from low-amplitude test results. Rheological analysis has revealed that the underlying deformation is truly anelastic. Within the investigated stress-amplitude-range the damping is shown to be linearly dependent on the stress-amplitude. As a consequence, energy dissipation in a cyclically loaded component will increase locally at stress concentrations such as crack tips. This inevitably results in an increased crack propagation resistance. Thus, the anelastic deformation behaviour explains earlier observations of a positive fatigue effect in sintered silicon nitride at high temperatures.
Bibliographic Reference: Paper presented: International conference on Internal Friction and Ultrasonic Attenuation in Solids, Buenos Aires (AR), 19-23rd July (1999)
Availability: Available free of charge from the Public Relations and Publications Unit, Ispra (IT)
Record Number: 200011833 / Last updated on: 2000-02-25
Original language: en
Available languages: en