Engineering Appraisal of Southwest Research Institute Magnetic Crack Definer Applied to CH47 Rotor Blades,
Abstract
The Magnetic Crack Definer (MCD), a nondestructive evaluation device recently developed at Southwest Research Institute, was evaluated to determine the applicability for detecting fatigue cracks in CH-47 helicopter rotor blade spars (AISI 4340) in the fully assembled blade. For test purposes, fatigue cracks were produced by cyclically stressing several sheet specimens cut from a spar from a scrap blade. Several different probe configurations and other system parameters of the MCD were investigated, and after optimizing overall design, cracks as small as 0.3-inch long by 0.025-inch deep were reliably detected under the major adverse conditions associated with the blade, namely: varying lift-off up to 0.10-inch; and different types of overlaying materials, including stainless steel, fiberglass, mastic and adhesive. Additional investigations are recommended to determine the capability for detecting fatigue cracks under the ferromagnetic steel doubler plates, and to determine possible sources of false alarms. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1973
- Accession Number
- AD0769068
Entities
People
- C. Gerald Gardner
- J. Robert Birchak
- John R. Barton
- Robert R. King
Organizations
- Southwest Research Institute