Field emissions caused by fracture and yielding

Two effects, magnetic and electric emission, have been observed and used in fracture tests to detect and analyse onset and progress of plastic deformation and fracture. While magnetic emission (ME) occurs only in ferromagnetic materials, electric emission (EE) can be found with any material, metals as well as plastics, ceramics, glass, and others. In ferromagnetic materials the two effects supplement each other. In steel, for example, electric emission is produced by plastic deformation but not by fracture; magnetic emission, on the other hand, is produced by fracture but not by plastic deformation. This paper describes the effects, demonstrates their application in Charpy tests, and shows how to derive fracture parameters, for instance the instants of the onset of plastic deformation and fracture. ME and EE, therefore, yield an attractive, inexpensive and fast supplement to conventional fracture test methods.