What I wanted you to look at in the photo, Figure 15, Page 21, was the fracture surface near the forward face of the disc (golden color) very close to the bore. enlarge it. Look at the stepped lines that have been created in that area and the directional orientation. It could be these lines represent plastic deformation (slips). You answered the question correctly, Heat and stress (rpm's) combined. It is the only way the drive arm could bend that much without snapping. Also, there is no sign of rubbing on the IPT disc rim, meaning this portion of the disk, at least did not contact the stator ID band behind it. My thought is the disk tore out of its fastening mechanism, at the 580 power drive arm bolt holes because of plastic deformation (stretching). Also, it seems there were 4 fractured pieces of the disc. The three that were not found went out over or under the fuselage to the right according to the exit trajectory sketch in the report. The found disc piece came out of the engine to the left based on where it was found according to the labeled map.