Amorphous Glass-Coated Microwires for Using as Embedded Stress Sensors in Functional Materials
Contactless measurement of the internal stress distribution in composite materials is of high importance in the structural health monitoring. Considerable efforts are made to develop the embedded stress-sensor approaches. In the present work it is proposed to utilize the soft-magnetic amorphous microwires with a stress-sensitive magnetization process as the sensors embedded into a polymer matrix. The microwire of a diameter of 10-50 microns is covered by glass and is compatible with the structural glass or carbon fibers. Because of an amorphous state, the main source of the anisotropy is the magnetostrictive interaction, so the wire magnetization processes may be highly sensitive to stress. When a bistable microwire is remagnetized a sharp voltage surge is induced which is characterized by high frequency harmonics. The amplitude of these harmonics sensitively depends on the various stresses. This property can be used for the stress monitoring inside composite materials. In wires with the axial anisotropy which is induced by the combination of positive magnetostriction and frozen-in internal tensile stress the remagnetization takes place by axial domain propagation, which generates the sharp voltage signal producing higher harmonics. The harmonic amplitude depends on external parameters, such as stress, strain and temperature. Enhanced stress sensitivity is seen in the case when the magnetostriction constant can change a sign under the stress effect as was demonstrated in the present paper. Therefore these wires are perspective as the wireless sensors with remote interrogation and can be placed on the surface or inside materials. We have demonstrated that the ratio of harmonic amplitude may also sensitively depend on tensile and torsion stress which can be used directly for the structural health monitoring.