Residual stress measurements in metal objects using four coils

Details Residual stress measurements in metal objects using four coils Residual stress measurements in metal objects using four coils

1997-11-25

1999-04-27

Strecker, Gerard

Electricity: measuring and testing

Magnetic

Stress in material measurement

324232, 324233, 324234, 324657, 324725, G01R 3312, G01R 1710, G01B 724, G01N 2772

Patent

active

058983023

ABSTRACT:
A device for measuring residual stress in ferromagnetic and non-ferromagnetic metal objects. The device having four electrically identical induction coils which form a four terminal alternating current bridge circuit. There is a fine wire shield formed of fingers for shielding the coils from stray capacitance. The bridge having four coil terminals. Two diagonally opposite coil terminals are connected to a variable frequency constant voltage generator. The other two diagonally opposite coil terminals are connected to a low noise broad band preamplifier. The preamplifier amplifies any unbalance in the bridge. There is a double pole double throw switch connected to two coil terminals which are diagonally opposite each other. Connected to the preamplifier is an amplifier. The amplifier is connected to a phase detector which is connected to a computer. The phase detector detects in phase and quadrature component signals. The computer has software for determining changes in differential resistivity as a function of frequency, and for converting resistivity differences into residual stress using an algorithm.

REFERENCES:
patent: 2370845 (1945-03-01), Davis
patent: 3132299 (1964-05-01), Hochschild
patent: 4107605 (1978-08-01), Hudgell
patent: 4893079 (1990-01-01), Kustra et al.
patent: 5017869 (1991-05-01), Oliver
patent: 5329230 (1994-07-01), Viertl
patent: 5610515 (1997-03-01), Soules

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