HF response fault detection in metal workpieces - exposing cracks or faults deep inside workpiece by monitoring frequency against voltage drop characteristic

摘要

A method of detecting faults or cracks deep inside metallic workpieces, using a h.f. voltage drop response technique, in which this characteristic is altered by any such faults in the workpiece, is presented. Faults which lie deep in the workpiece can be exposed by this technique, in contrast to X ray and ultrasonic methods which can detect those lying relatively near a surface. Basically, the voltage drop against frequency response of the workpiece up to a frequency of 1 GHz is plotted automatically on a pen recorder, using a variable frequency signal generator and an amplitude measurement network. A fault in the workpiece produces a non-linear characteristic due to the additional surfaces present in the workpiece producing skin effects additional to those in the fault free workpiece.