Rapid Detection of Falsely Marked Bolts and Large Screws

摘要

Falsely marked steel fasteners are of concern, particularly SAE grade 5.2threaded fasteners marked as grade 5 and grade 8.2 threaded fasteners marked as grade 8. The object of this research was to determine if an electromagnetic nondestructive test method could be used to detect falsely marked fasteners. The proposed test method consisted of measuring the impedance of a probe at two test frequencies and two magnetic field levels when in close proximity to the fastener head. Test frequencies explored ranged from 1 khz to 2 MHz. Magnetic fields ranged up to 12 kG. The 8-dimension state vector generated by this type of measurement was insufficient to sort fastener grades. The reason for this inability to sort is not because of differences in plating, but is due to the relative insensitivity of the steel electrical conductivity and magnetic permeability to fastener grade. (r.h.)