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Frishmuth Consulting Services, LLC
Dr. Ronald Frishmuth, P.E.
P.O. Box 690626
Houston, TX 77269-0626
Voice (281) 807-0203
FAX: (281) 807-9134
For further information:
info@applied-mechanics.net
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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.
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