Characterization and Measurement of Defects in the Vicinity of Fastener Holes by Nondestructive Inspection
Abstract
This report describes a program designed to develop advanced nondestructive inspection testing and signal processing techniques that can be used to improve the capability and reproducibility of detection of defects associated with fastener holes. Metallurgical and mechanical characteristics associated with flaws in the vicinity of straight shank fastener holes that would influence their detectability were investigated. Two NDI procedures were used: shear wave ultrasonics and eddy current. The results show that crack size, local stresses, width of the crack and material within the crack are primary factors influencing their detectability, with the crack size, crack orientation, and local stress being the dominating factors, particularly with ultrasonic techniques. Eddy current technique are particularly sensitive to crack size and crack width, but relatively insensitive to local stresses and orientation. The influence of stress level used to grow the defect was also found to be a factor in its detectability, providing no other stresses were applied. A technique using the concept of a transfer function Tr(s) and corresponding Bode plots has been developed that allows recognition of and detection of small 0.030 inch cracks anywhere within the bolt hole scan region. For normal conditions this means that minimum of two scans must be made for each bolt hole. The sensitivity of this technique decreases as the angle of the normal of the crack to the plane of the shear wave increases, i.e. when the crack is perpendicular to the plane of the wave the sensitivity is highest.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1975
- Accession Number
- ADA029524
Entities
People
- J. M. Larsen
- Paul F. Packman
- R. M. Stockton
Organizations
- Vanderbilt University