TurbineD, bearfoil
Quote:
The seperation, Disc from Arm, would not be in any way orderly, and an imbalance (a certainty) would impart an elliptical and irregular orbit to the Wheel.
The problem I see with this is that it would completely wipe out the bearing structure below it and because the IP shaft is so close the the LP shaft, we would see rubbing or damage to the LP shaft. Based on the photos of the pulled LPT module (ASTB Report) there isn't any damage to the LPT shaft.
there is no damage at the end bearings (roller) but the damage may be seen closer to front bearings, where the IP shaft splines are located
what bothers me is the way the drive arm of the IP turbine disk if bent (fig 15 from preliminary report) - outward as if the disk was forced
first into the axis of rotation and only afterwards has flown away - but would it has enough place to move like this?
How about such alternative explanation:
separation of the IP disc from the shaft has happened longitudinally when the IP shaft has moved rearwards significantly enough to break out the mentioned drive arm with its 580 bolts instantly. Still this would require the IP disk to stay fixed longitudinally to enable the forced break-out. Roller bearing do enable such shaft movement easily as long as the traveled distance stays within the width of the raceway (here the raceways could be estimated at around 1 inch). To
press out (break out) the IPT from the shaft it would need to move backwards by less than 15mm resulting from 2mm gap between the IPT and following vanes fixture plane and some distance to impose enough force to break the disk (for a rigid structure like IPT i guess it could be 5..10mm).
This could happen only if the IP midshaft (splines) connection would got loose or separated. Suddenly free front end of the rear shaft, not supported by the roller bearings anymore, would wobble and move rearvards driven by the IPT. But than what would break the disk from the shaft? Two possibilities: (1) high energy from the rotating disk (2) significant longitudinal force coming from the screw used to keep splined shafts together. If the splines get loose, two parts of the IP shaft start rotating against each other, front part stays fixed by the roller bearing but the the rear part of IP shaft presses the IP turbine against anything available to slow it a little just enough to get shafts unscrew from one another (4..5 full rotations would be enough) to
press-break-out the IP turbine disk drive arm from the IP shaft. Disc goes free to speed up and fly away. No roller bearing get damaged except the bearing supporting the IP shaft which has to support wobbling shaft .
how the splines could have separated - easily if splines are worn out on outside diameter - fire in the bearing box would suddenly heat up the external surface of the shaft which would thermally increase diameter enough to splines get free - no need for Oldham razor here
does it make sense?