Estudio teórico experimental de la resistencia a fatiga de uniones soldadas a tope considerando la influencia de la geometría de la unión y el ciclo térmico de enfriamiento
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Hernández Laguna, Edgar David
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Resumen: Se realizó un estudio teórico experimental mediante la caracterización de la resistencia a fatiga en uniones soldadas a tope considerando la geometría y el ciclo térmico de enfriamiento. Se utilizó el proceso de soldadura manual por arco eléctrico (SMAW) en unión soldada a tope, con acero estructural ASTM A36 tipo placa de espesor 6 mm como metal base, y electrodo revestido E6013. En los ensayos de fatiga uniaxial se seleccionaron 8 réplicas por cada tratamiento para un total de 32 probetas. En el arreglo experimental se consideraron dos niveles tanto para el sobreespesor del cordón, como para la intensidad del medio de enfriamiento utilizando, un enfriamiento lento (aire tranquilo) y un enfriamiento rápido (inmersión en agua). Se relacionaron las propiedades mecánicas y fractomecánicas de las zonas de la unión soldada (zona de fusión, zona afectada térmicamente y material base) con la propagación de grietas por fatiga, con base en el conteo de microestriaciones y ensayos experimentales como: tensión uniaxial, dureza por microindentación, energía de impacto Charpy y análisis metalográfico para cada uno de los tratamientos bajo estudio. En el análisis teórico se parametrizó el sobreespesor del cordón y el radio del borde de soldadura, para ello se realizó un diseño experimental a tres niveles. La geometría de un grupo de cordones de soldadura reales es digitalizada y emulada en la construcción de los modelos de sólido 3D, definiendo una grieta semielíptica superficial en el borde de la soldadura. Mediante el Método de los Elementos Finitos se obtuvieron ecuaciones analíticas para el factor de agnificación por soldadura (Mk). Entre los resultados inicialmente se destacó la marcada influencia del sobreespesor del cordón en la vida de fatiga, un mayor sobreespesor significa una reducción en la redicción de vida de fatiga de hasta un 42% para la unión soldada considerada; y en segundo lugar se obtuvo el factor de intensidad de esfuerzos en el vértice del perímetro de la grieta a medida que incrementa su tamaño. Lo anterior provoca que la grieta durante su propagación estable se torne cada vez más alargada y estrecha. Las ecuaciones analíticas obtenidas para Mk pueden ser utilizadas en modelos de gestión de vida para este tipo de unión soldada.
Abstract: An experimental and theoretical investigation through of the characterization of fatigue strength in butt welded joints, considering the geometry and the cooling rate was carried out. ASTM A36 structural steel as the base metal in the SMAW process, with welding electrode E6013 was used. For the uniaxial fatigue tests, 8 replicates were selected for each treatment for a total of 32 specimens. In the experimental analysis, two levels were considered for both the weld reinforcement and the intensity of the cooling medium using, slow cooling (quiet air) and fast cooling (immersion in water). Mechanical properties and fractomechanical properties of the weld joint zones (fusion zone, heat affected zone and base metal) were correlated with the fatigue crack growth, based on the counting of fatigue microstriations and experimental tests such as: uniaxial tension test, microindentation hardness test, Charpy V-notch impact test and metallographic analysis in each of the study treatments. For the theoretical analysis, a three-level experimental design was carried out, in which the weld reinforcement and the weld toe radius were parameterized. The geometry of a group of real weld beads is digitized and emulated in the construction of 3D solid models, defining a semi-elliptical surface crack at the weld toe radius. Through the Finite Element Method, we obtain analytical equations for the weld toe magnification factor (Mk). Among the results, initial the marked influence of the welding reinforcement in the fatigue life is emphasized, a greater welding reinforcement means a reduction in the prediction of fatigue life of up to 42% for the considered welded joint; And secondly the variation of the stress intensity factor at the vertex of the crack perimeter, which causes of the crack during its the stable crack growth to become more and more elongated and narrow. The analytical equations obtained for Mk can be used in life management models for this type of welded joint.
Abstract: An experimental and theoretical investigation through of the characterization of fatigue strength in butt welded joints, considering the geometry and the cooling rate was carried out. ASTM A36 structural steel as the base metal in the SMAW process, with welding electrode E6013 was used. For the uniaxial fatigue tests, 8 replicates were selected for each treatment for a total of 32 specimens. In the experimental analysis, two levels were considered for both the weld reinforcement and the intensity of the cooling medium using, slow cooling (quiet air) and fast cooling (immersion in water). Mechanical properties and fractomechanical properties of the weld joint zones (fusion zone, heat affected zone and base metal) were correlated with the fatigue crack growth, based on the counting of fatigue microstriations and experimental tests such as: uniaxial tension test, microindentation hardness test, Charpy V-notch impact test and metallographic analysis in each of the study treatments. For the theoretical analysis, a three-level experimental design was carried out, in which the weld reinforcement and the weld toe radius were parameterized. The geometry of a group of real weld beads is digitized and emulated in the construction of 3D solid models, defining a semi-elliptical surface crack at the weld toe radius. Through the Finite Element Method, we obtain analytical equations for the weld toe magnification factor (Mk). Among the results, initial the marked influence of the welding reinforcement in the fatigue life is emphasized, a greater welding reinforcement means a reduction in the prediction of fatigue life of up to 42% for the considered welded joint; And secondly the variation of the stress intensity factor at the vertex of the crack perimeter, which causes of the crack during its the stable crack growth to become more and more elongated and narrow. The analytical equations obtained for Mk can be used in life management models for this type of welded joint.
Abstract
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Unión soldada a tope; grieta semielíptica superficial; tasa de enfriamiento; intensidad de esfuerzos; fractura elástica lineal; gestión de vida a fatiga; Butt weld joint; fatigue crack growth; semi-elliptical surface crack; stress intensity factor; linear elastic fracture mechanics; fatigue life management