Desarrollo de composites magnetostrictivos de FeAl y FeGa para su aplicación en sensores de deformación

Abstract

The control of stresses and deformations in the hull of a ship is vitally important for the safety of navigation as well as for its proper functioning. Currently, the control of the good condition of the ship's structure is carried out by the Classification Societies during the regular reviews of the ships, based on the reports prepared by the on-board personnel after visual examinations in all accessible parts of the ship. In some cases, mainly in tanker vessels, this control is carried out through the use of strain gauges. However, this procedure is not very suitable due to the marine environmental conditions that affect the proper functioning of strain gauges. In the present work a study of the effect of reverse magnetostriction on Fe-Al/polyester, Fe-Al/silicone and Fe-Ga/silicone composites is carried out for its subsequent use as a sensor element of a magnetostrictive sensor, which may allows us to measure the stresses and deformations. The magnetic particles of the composites have been obtained by grinding, in an Attritor mill, and another in a Planetarium mill, of ribbons of the same composition obtained by melt spinning technique. The reason for using these ribbons is that, as indicated in the literature and as we have verified so, the Fe-Al ribbons obtained by melt spinning have a high magnetostriction. The first results we have obtained indicate that there are two effects that affect inverse magnetostriction (Villari effect) which are: a magnetic one, due to the dipole-dipole interaction of the magnetic particles, and another mechanical one, due to the easy deformation of the elastomeric materials. It has been found that when the isotropic composites (random orientation of the magnetic particles) undergo a magnetic field of 1T, the composites continue to have an isotropic distribution but remain in a state of magnetic remanence. This has allowed us to obtain a signal of the Villari effect without the need to apply a magnetic field in the measurement process. This fact is of the utmost importance when developing a magnetostrictive sensor using these composites as a sensor element, since it avoids the use of the primary coil. Due to the different origins of magnetostriction in these materials, it is very complex to develop a model that explains the results of the Villari effect. In Fe75Ga25 / silicone composites we have verified that the variation of the magnetic flux due to the tension in the sample, is caused by the variation of the cross-section of the composite when subjected to a tension. A simple model based on this variation has been developed and it explains the results obtained. We have also verified that this model does not explain the results in other composites. However, the influence of mechanical properties on the Villari effect is checked. The Young's modulus of the composites has been measured by microindentation (P-h curves) and the results obtained show the close relationship between the Young's modulus and the Villari effect. Finally, a proof of concept has been carried out to verify the suitability of magnetostrictive sensors based on these composites for the measurement of deformations in the structure of a ship. For this reason, a sensor prototype has been developed, which has been applied to naval steels of different thicknesses that had been deformed by a tensile tests. The measurements obtained show the suitability of this prototype and are very promising to develop a definitive sensor model.