Shell-core bond spalling can only occur on duplex rolls and results in catastrophic spalling of the roll barrel. It can be identified as a large area of fracture through the shell layer where fracture flow can be traced back only to the interface between the shell and the core material. This type of fracture is typically symmetrical in appearance with an exposed area of the core material at the centre.
As ribbon fatigue spalling can also exhibit similar features as described above (discussed in Section III.A), it is important to fully inspect the fracture face visually as well as the surrounding area of the barrel using ultrasonic inspection before determining what fracture mechanism occurred. Shell-core bond spalling will show no evidence of surface initiated fatiguing (fatigue ribbon that can be traced back to the surface) either visually on the fracture face or ultrasonically in any areas surrounding the fracture face.
EXAMPLES
Example 1
Spalling that