Investigation of Martensitic Transformation Induced by Cyclic Plastic Deformation in Austenitic Steels

The main goal was to demonstrate the possibility of investigating martensitic transformation induced by plastic strain, especially including the kinetics of this transformation, using selected cross effects. It is commonly known that this type of transformation is a basic “mechanism” occurring in shape memory materials and metastable austenitic steels strengthened with martensite separations. The motivation behind the research was also to follow and visualise the transformation on line, during cyclic loading (fatigue process), without the necessity to use, for example, roentgenographic (destructive) or microscopic methods. The application of the magneto-mechanical effect (the Villari effect) and the thermomechanical effect (the Kelvin/Thomson effect) turned out to be particularly useful because they significantly change with martensite initiation and then accumulate in austenite. Therefore, the goal was to develop the non-destructive methods of investigating martensite transformation, which could then be used on real constructions made of metastable austenite steel. In the case of the magneto-mechanical method, the goal was to additionally visualise the magnetic field transformations along a sample in the function of a loading cycle and the index of this period. To achieve this, high-resolution phase maps were used, which also allowed image processing methods known from machinery visioning (MV) or digital image correlation (DIC) techniques to be used

Electromagnetic measurements of steel phase transformations

This thesis describes the development of electromagnetic sensors to measure the phase transformation in steel as it cools from the hot austenite phase to colder ferritic based phases. The work initially involved investigating a variety of sensing configurations including ac excited coils, C-core arrangements and the adaptation of commercial eddy current proximity sensors. Finally, two prototype designs were built and tested on a hot strip mill. The first of these, the T-meter was based on a C-shaped permanent magnet with a Gaussmeter measuring the magnetic field at the pole ends. Laboratory tests indicated that it could reliably detect the onset of transformation. However, the sensor was sensitive to both the steel properties and the position of the steel. To overcome this, an eddy current sensor was incorporated into the final measurement head. The instrument gave results which were consistent with material property variations, provided the lift off variations were below 3Hz. The results indicated that for a grade 1916 carbon- manganese steel, the signal variation was reduced from 37% to 2%, and the resulting output was related to the steel property variations. The second of these prototypes was based on a dc electromagnetic E-core, with Hall probes in each of the three poles. 'Cold' calibration tests were used to decouple the steel and the lift-off. The results indicated that there was an error of 3-4% ferrite/mm at high ferrite fractions. At lower fractions the error was higher due to the instrument’s insensitivity to lift-off. The resulting output again showed a relationship with varying steel strip properties. ft was also shown that a finite element model could be calibrated to experimental results for a simple C-core geometry such that the output was sensitive to 0.2% of the range. This is required to simulate the sensor to resolve to 10% ferrite

Towards ferrite based rare-earth free permanent magnets: from model systems to new technological applications

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física la Materia Condensada y Nanotecnología. Fecha de lectura: 19-12-2017Esta tesis tiene embargado el acceso al texto completo hasta el 19-06-2019Permanent magnets are essential in many applications of very relevant technological areas (transport, communications technology, energy) and are present in virtually all smart devices. However, they are not without controversy and have generated in recent years serious economic and political problems, as well as having important repercussions on the environment. In 2012 the global alarm was raised due to the monopoly derived from the strategic geographical situation of the so-called rare earths, fundamental constituent elements of these materials. Advances in nanoscience and nanotechnology are key in the search for alternatives to permanent magnets based on rare earths. In this sense, and in a general way, this thesis work combines fundamental studies in nanomagnetism with energetically efficient technological processes in order to be able to develop permanent magnets free of competitive rare earth of last generation, as well as to implement new technological applications. To this end, the objectives set out in the present study have included: 1) The study of rare earth-free magnetic systems exploiting anisotropy, shape and microstructure in both model systems (epitaxial layers and manganese nanowires) and in isotropic ferrite powders. 2) The search for general relations to improve / enhance the magnetic properties of rare earthfree materials based on nanostructured ferrites by effective, reproducible and scalable methods. 3) Understanding and controlling the microstructural effects on the magnetic properties of treated and refined ferrite isotropic powders. 4) The development of new methodologies to enhance the properties of permanent magnets based on isotropic ferrite powder, and the prototyping of new applications making use of the permanent magnets free of developed rare earths. From the scientific point of view, it is necessary to highlight the microscopic determination of the magnetization reversal processes in model systems as well as the experimental demonstration of the generic effects induced by engineered microstructure (tensions and grain size) on the magnetic properties in processed isotropic powders. From the technological point of view, to review the development of an efficient, reproducible and scalable methodology to produce isotropic powder with improved magnetic properties (coercivity and / or (BH)max product) as well as the design and prototyping of new technological applications.

Dynamical systems : mathematical and numerical approaches

Proceedings of the 13th Conference „Dynamical Systems - Theory and Applications" summarize 164 and the Springer Proceedings summarize 60 best papers of university teachers and students, researchers and engineers from whole the world. The papers were chosen by the International Scientific Committee from 315 papers submitted to the conference. The reader thus obtains an overview of the recent developments of dynamical systems and can study the most progressive tendencies in this field of science

Conference Proceedings: 1st International Conference on Nanofluids (ICNf2019), 2nd European Symposium on Nanofluids (ESNf2019)

Conference proceedings of the 1st International Conference on Nanofluids (ICNf2019) and 2nd European Symposium on Nanofluids (ESNf2019), 26-28 June 2019 in Castelló (Spain), organized by Nanouptake Action (CA15119) and Universitat Jaume

Determination of the Location and Magnetic Moment of Ferromagnetic Objects Based on the Analysis of Magnetovision Measurements

This article is concerned with the localization of ferromagnetic objects on the basis of magnetovision measurement analysis. In the presented case, the concept of localization is understood as the indication of the x, y, and z coordinates of the magnetic moment of the sought object. Magnetovision measurement provides a much simpler, two-dimensional localization of magnetic anomalies compared to existing active and passive mobile devices, largely based on operator knowledge and experience. In addition, the analysis of the obtained magnetovision measurement, by fusing data with a mathematical model, enables a quantitative assessment of the position of an object in space and the determination of the value and spatial orientation of its magnetic moment vector. The detection and localization method was verified using the certified magnetic moment standard. An additional novelty is the inclusion of the influence of the constant gradient of the external field in the model, which corresponds to disturbing the measurement by the influence of large, but distant, objects. The proposed three-dimensional magnetovision measurement method and its analysis enable the determination of the x, y, and z coordinates; the angular position; and the magnetic moment values of unknown magnetic dipoles in real conditions (effects of disturbances generated by other distant objects and background noise), thus precisely detecting and locating the ferromagnetic object