Effect of nodularity on resonant vibration fracture behavior in upper bainitic and ferritic cast irons

This work examines resonant vibration fatigue fracture behavior. According to those results, the region I section of the D-N curve (deflection amplitude vs number of vibration cycles) declined with decreasing graphite nodularity or a changing of the matrix to a bainitic structure. Resonant vibration fatigue cracks were often initiated at graphite particles on the surface and grew into the body of the specimen. Initiation and propagation of these cracks were promoted by lowering the graphite nodularity, but no significant difference in deflection amplitude was observed with a bainitic or ferritic matrix microstructure. Bainitic cast iron speciments proved to have a higher initial deflection amplitude and would simply drop almost without displaying region I as the cycle numbers of vibration increased.