Comparative measurement of residual stresses with the method based on the magnetic Barkhausen noise and the relaxation method
For an efficient prediction of residual stresses in a material or a machine part the non-destructive method based on the magnetic Barkhausen noise is, among others, employed in practice. An experimental system developed at home and including measuring and assessment units has proved to be very efficient in various applications of surface hardening or cold hardening, and heat treatment.
The Determination of Microhardness and Residual Stress of Machined Ferromagnetic Components by Using the Barkhausen Effect
Strengthening of the surface boundary layer expressed by microhardness and residual stress have been found as essential characteristics of surface integrity. It has been proved that the Barkhausen effect is of great advantage for a contactless measuring of these quantities as slight structural changes clearly effect the magnetic properties of the materials. Also the Barkhausen noise voltage can readily be processed as an electrical signal. By appropriate arrangement of the sensors both microhardness and residual stress can be determined in case of ferromagnetic components. The paper deals with the investigations on the selection of the proper magnetizing frequency and the air gap influence as well as the dependence of noise voltage difference of microhardness and residual stress. Specially the influence of feed and material on microhardness and residual stress has been proved by this method. The technique can be used in research and for quality control.
A New Surface Transducer for Generating and Detecting Magnetic Field Transients in
A new surface transducer is described for gen- erating and detecting magnetic field transients or magnetiza- tion discontinuities in ferromagnetic materials ( 81. The sensing is based on searching for transients of the magnetic poten- tials which would be likely to occur on the surface of the specimen. A coil core of high-frequency ferrite is used for this. The sensor theory presented shows the coaxial geometry of the coil core to be that which is more practicable for limiting detection to a compact volume of the specimen to be analyzed. The fundamental noise and disturbance analyses performed show adequate margins for wideband noise and external stray field disturbances. The transducer electronics for generating the varying external magnetic field in the specimen and for detecting the occurring field transients are described with a view to the optimization of the electrical circuits, and the resulting specifications are discussed. The surface transducer constructed is widely applicable for study- ing the magnetization characteristics of different ferromag- netics nondestructively in conjunction with stochastic-ergodic analyzers such as a pulse-height analyzer or a digital correlator through a punch-tape recorder or in on-line connection with a computer (7).