Dr. Ronald Frishmuth,
P.O. Box 690626
Houston, TX 77269-0626
Voice (281) 807-0203
FAX: (281) 807-9134
For further information:
| Fracture Analysis
This experimental turbine disk failed during a
spin pit test at a speed of 46,000 RPM. Failure investigation revealed
that the likely origin of the failure was a defect oriented transverse
to the tangential stress in a thin section of the disk below the blade
dovetail grooves and near the disk surface.
Material testing, finite element analysis and fracture mechanics
calculations were performed. It was demonstrated that a surface defect
of semi-circular shape with a surface length of 0.010 inch would be
critical at the stress level imposed on the disk at 46,000 RPM.
An investigation into the history of the disk revealed that no fracture
mechanics analysis had been done during the design. It was further
found that the disk was ultrasonically inspected in the pancake forged
condition and passed. However, no additional inspection was apparent in
the records. It was concluded that, if fracture analysis had been done
during the design phase and careful inspection had been performed
during manufacture, this failure could have been avoided.