Barit1
I'll propose another scenario - which may/may not be pertinent to the RB.
The fact that the IP SHAFT is sheared is very worrisome - and in fact that may be the initiating event. If this occured first, then the IPT is suddenly unloaded and very quickly overspeeds, since the N3 system continues to run and provide the gas flow. The overspeeding N2 turbine will at some point fail - and it's possible that the next part to break will be the IPT blade roots. The release of all the blades could rip open the case and the cowl, but then leave the IPT disc without a driving torque, so it does not burst (a very, very good thing!)
Maybe someone more familiar with specific knowledge of RB failure modes can comment
Not sure what RB stands for
I do agree that the shaft separation is troubling, more so because the visible unbalance of the IP rotor looks unlikely to to put much of a load on its drive shaft (chicken-egg question)
The battered off LP blades sure look secondary to the IP debris, while the empty blade roots in the IP suggest either severe overspeed or fire and stretching of the disk.
Sucessful design if the shaft was primary and the rotor disk remained intact
