Stress measurement in a body by detecting magneto-acoustic emission

摘要

A method and an apparatus are provided for measuring stress in a steel pipe or rail utilizing magneto-acoustic emission (MAE). A piezoelectric transducer (24) detects the ultrasonic MAE in a steel rail (12) subjected to a low amplitude modulating field and to a steady magnetic field. The steady field is either sufficient almost to saturate the rail, or is almost zero; and the ratio between the MAE signals under these two circumstances is dependent on the stress in the rail while being substantially unaffected by its microstructure. Both the steady field and the modulating field are aligned parallel with the direction of the expected stresses. The steady field is supplied by a d.c. fed electromagnet 14 and the modulating field is generated by series-connected air-cored windings 28. The transducer 24 is connected to a signal processor and store 32. The device may be vehicle-mounted, e.g. for traversing the bore of a tube. IMAGE