The role of residual stresses in the failure of metallic components and the need to determine such stresses is well recognised. Magneto-acoustic emission (MAE) is a relatively new non-destructive detection technique and its working principle is based on Barkhausen discontinuities or noise and magnetostriction when a ferromagnetic material is subjected to a varying magnetic field. MAE is being used to characterise the stress state of a ferritic stainless steel (AISI 430). Other stress measurement techniques; X-ray diffraction (XRD), magnetic Barkhausen noise (MBN) have also been used to confirm / support the results achieved using MAE. A new measurement parameter has been developed for stress characterisation called MAE absolute energy and has proved to be a useful quantitative method in MAE waveform measurement. I can't seem to get to grips with this last sentence. When you say stress characterisation, what do you mean? INTRODUCTIONHigh stress corrosion resistance and relatively low production costs are the main reasons for the increasing applications of AISI 430 ferritic stainless steels [1]. But problems such as loss of ductility and toughness when exposed to elevated temperatures, for instance during welding, is a main concern [2]. The heat of welding leads to grain coarsening in the heat effected zone and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferrite phase without any intermediate phase transformation [2][3]. The use of a non-destructive evaluation technique to characterise the post-welding microstructural state of a material, could be of use in determining the optimal levels of heat input and welding speeds.For characterisation, ferritic stainless steel (AISI 430) samples were plastically deformed and heat treated to various degrees and measured using Barkhausen sensing techniques. In a ferromagnetic material, Barkhausen noise (BN) is generated by the discontinuous movement of irreversible domains walls. This movement can be induced by applying a time varying magnetic field across the sample. This noise can be detected in the form of acoustic noise (electrical energy) or in the form of voltage pulses which are induced in a coil placed near the surface of the material. Magnetic Barkhausen noise (MBN) results from the reversible and irreversible displacement of 180º and non-180º domain walls, or by abrupt rotation of domain magnetisation vectors at higher magnetic fields. Acoustic Barkhausen noise, measured by magneto-acoustic

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&&ax. The onset of dissipation in the I-V characteristics of granular YBa2Cu307shows clear evidence for a finite critical current. At currents above critical, dissipation in the weak links is only slightly field-and temperaturedependent.

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