Publication: Estudio numérico de la propagación de fisuras en ejes rotativos mediante XFEM
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2014-06
Defense date
2014-07-10
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Abstract
El campo de la Mecánica de Fractura ha adquirido en los últimos años un papel fundamental en el diseño y desarrollo de elementos mecánicos, que se ven sometidos a esfuerzos cíclicos y en los cuales el fenómeno de la fatiga supone el principal
requisito de diseño. Tener la capacidad de predecir el crecimiento de las fisuras presentes en estos elementos, resulta fundamental para garantizar la seguridad durante su
vida útil, así como para alargar esta última.
El nacimiento y posterior desarrollo de los métodos numéricos de cálculo han
permitido el avance en este campo. Poco a poco se han ido desarrollando nuevas
técnicas que permitieran un estudio cada vez más preciso de los mecanismos de fractura. Una de las más novedosas es el Método de los Elementos Finitos eXtendido, también conocido como XFEM.
Con esta novedosa técnica es posible estudiar la creación y desarrollo de fisuras sin importar la complejidad geométrica tanto de la pieza o de la fisura. Todo ello
permite superar las limitaciones que presentaba el MEF tradicional. La complejidad de
esta nueva técnica es considerable, no solo por la dificultad de alcanzar la convergencia en algunas ocasiones sino también por la necesidad de conocer profundamente los mecanismos de fractura.
En este Trabajo Fin de Grado se ha desarrollado por primera vez un modelo
numérico tridimensional que, mediante XFEM, permite estudiar la propagación de fisuras en ejes giratorios en condiciones cuasiestáticas. Además, para simplificar lo máximo
posible el proceso de modificación de variables en el modelo, se ha realizado una
aplicación en el entorno de Abaqus que permite automatizar este proceso. En última
instancia se han comparado los resultados obtenidos con los ofrecidos por la literatura.
Además se comparan entre sí las dos alternativas que ofrece el código Abaqus para
este tipo de problemas: la de los modelos cohesivos CZM, y la que se basa en la
Mecánica de Fractura Elástico Lineal LEFM.
The field of Fracture Mechanics has played in recent times a vital role in the design and development of mechanic elements which have to withstand cyclic forces and thus making fatigue to be the main design requirement. Hence, being able to predict the growth of the crack located in these elements, turns out to be essential in order to ensure safe operation during its service life along with enhance service life itself. The very founding and the further development of numeric methods has enabled the constant breakthrough of this field. Little by little, new techniques have been developing thus allowing increasingly accurate studies as to the fracture mechanisms to be performed. The latest is the eXtended Finite Element Method, better known as XFEM. This novel method gives us the possibility to study not only the onset but also the growth of cracks however complex the geometry both the cracked body and the crack itself is. All this enable to overcome the limitations of FEM when it comes to this issue. The complexity of this new technique is huge. Not only is it difficult to make the problem to converge and get proper results but also a deep understanding and knowledge about the fracture mechanism is required in order to solve the problems that arise through the process. Within this Project, a 3D XFEM numeric model has been developed from scratch so as to study the growth of cracks in rotary shafts in quasistatic conditions. Besides, for the sake of simplicity when it comes to modify the big amount of parameters involved, a custom application within Abaqus environment has been built which automates the whole process and thus helping save time. Eventually, the results have been discussed in contrast to the ones appearing in other researches. In addition to this, the two alternatives, the first one based on the Linear Elastic Fracture Mechanics and the second one based on the Cohesive Zone Model, within Abaqus have been compared.
The field of Fracture Mechanics has played in recent times a vital role in the design and development of mechanic elements which have to withstand cyclic forces and thus making fatigue to be the main design requirement. Hence, being able to predict the growth of the crack located in these elements, turns out to be essential in order to ensure safe operation during its service life along with enhance service life itself. The very founding and the further development of numeric methods has enabled the constant breakthrough of this field. Little by little, new techniques have been developing thus allowing increasingly accurate studies as to the fracture mechanisms to be performed. The latest is the eXtended Finite Element Method, better known as XFEM. This novel method gives us the possibility to study not only the onset but also the growth of cracks however complex the geometry both the cracked body and the crack itself is. All this enable to overcome the limitations of FEM when it comes to this issue. The complexity of this new technique is huge. Not only is it difficult to make the problem to converge and get proper results but also a deep understanding and knowledge about the fracture mechanism is required in order to solve the problems that arise through the process. Within this Project, a 3D XFEM numeric model has been developed from scratch so as to study the growth of cracks in rotary shafts in quasistatic conditions. Besides, for the sake of simplicity when it comes to modify the big amount of parameters involved, a custom application within Abaqus environment has been built which automates the whole process and thus helping save time. Eventually, the results have been discussed in contrast to the ones appearing in other researches. In addition to this, the two alternatives, the first one based on the Linear Elastic Fracture Mechanics and the second one based on the Cohesive Zone Model, within Abaqus have been compared.
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Keywords
Método de los Elementos Finitos eXtendido (XFEM), Mecánica de Fractura Elástico Lineal (LEFM), Elementos mecánicos, Fatiga