Barkhausen Magnetic Noise (MBN) and Magnetic Acoustic Emission (MAE) are phenomena that occur in ferromagnetic materials which undergo changes in their magnetization. These phenomena are very sensitive to changes on microstructure and residual stresses. The MBN and MAE can be applied as monitoring techniques to detect plastic deformation in materials subjected to thermomechanical processes, such as machining and manufacturing processes. In this work, the plastic deformation in samples subjected to uniaxial tensile tests is investigated through MBN and MAE. Twelve stainless steel test pieces of two different materials (AISI 430 and AISI 441A), were tested. As a first step, in order to obtain their mechanical properties, two test pieces of each material cut in different directions with respect to the rolling direction, were tested up to rupture. The others were deformed in four stages on plastic deformation. After each stage, MBN and MAE measurements were made, in order to obtain a correlation with the strain and the magnetic situation of the materials. We present here the microstructural analyses, the study of MBN and MAE signals, correlating them with the state of deformation of the specimens.
RESUMENLa adición de fibras a la matriz cementicia, dando lugar a los hormigones reforzados con fibras, tiene por objeto mejorar la baja ductilidad que se observa en la respuesta mecánica del hormigón frente a distintos tipos de solicitación, particularmente bajo esfuerzos de tracción directa. En este trabajo, se estudia el proceso de fisuración y degradación mecánica de elementos de hormigón utilizando la técnica de emisión acústica, con el objetivo de analizar la incidencia de la acción de altas temperaturas sobre el comportamiento de falla de vigas de hormigón de alta resistencia con y sin fibras. Se presentan resultados de un plan experimental que incluye distintos ensayos mecánicos sobre especímenes de hormigón con y sin adición de una combinación híbrida de fibras de acero y de polipropileno. La incorporación de las fibras de polipropileno tiene por objeto mejorar el comportamiento del hormigón frente a temperaturas elevadas. Se analiza la evolución de las emisiones acústicas registradas durante los ensayos de flexión y su relación con la respuesta mecánica. Se observa que frente a la exposición a una temperatura de 600°C, las propiedades del hormigón reforzado con fibras fueron relativamente menos afectadas que las del hormigón sin fibras, conservando cierta capacidad de absorber energía en el pos-pico. Asimismo, se confirma que la técnica de monitoreo utilizada tiene una correlación directa con el proceso de degradación del hormigón.Palabras clave: Hormigón de alta resistencia, Hormigón reforzado con fibras, Emisión Acústica, Alta temperatura, Ensayo de flexión de tres puntos. ABSTRACTThe addition of fibers to the cementitious matrix, giving rise to fiber-reinforced concrete, aims to improve the low ductility observed in concrete mechanical response under different load scenarios, particularly under direct tension. In this work, cracking and mechanical degradation processes of concrete elements using acoustic emission technique are examined, with the objective of analyzing the incidence of high temperatures on the failure behavior of high-strength concrete beams with and without fibers. Results of an experimental campaign including different mechanical tests on concrete specimens with and without the addition of a hybrid combination of steel and polypropylene fibers are presented. The incorporation of polypropylene fibers is intended to improve the behavior of concrete against elevated temperatures. The evolution of acoustic emission measurements during bending tests and its relation with the mechanical response is analyzed. It is observed that after being exposed to a temperature of 600°C, properties of fiber reinforced concrete were relatively less affected than those of plain concrete, retaining some capacity to absorb energy in the post-peak regime. It is also confirmed that the monitoring technique used, has a direct correlation with the degradation process of concrete.
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