Projecte llegit
Títol: Study of a simplified friction joint for the identification of the contact stiffness
Estudiants que han llegit aquest projecte:
- RODRÍGUEZ GAUXACHS, IRENE (data lectura: 17-07-2020)
- Cerca aquest projecte a Bibliotècnica
Director/a: ROJAS GREGORIO, JOSEP IGNASI
Departament: FIS
Títol: Study of a simplified friction joint for the identification of the contact stiffness
Data inici oferta: 01-03-2020 Data finalització oferta: 01-03-2020
Estudis d'assignació del projecte:
- GR ENG SIST AEROESP
Tipus: Individual | |
Lloc de realització: ERASMUS | |
Supervisor/a extern: Prof. Christian Maria Firrone | |
Institució/Empresa: Politécnico di Torino | |
Titulació del Director/a: PhD in Machine Design | |
Paraules clau: | |
numerical analysis; experimental analysis; joints; turbine; turbojet; engine; contact stiffness | |
Descripció del contingut i pla d'activitats: | |
El objetivo del TFG es estudiar el comportamiento de las
articulaciones de una turbina de un motor turborreactor, en diferentes situaciones de contorno (cuando están cerca de entrar en resonancia, por ejemplo). El estudio constará de una parte de simulación numérica (usando Ansys y Matlab) y una parte experimental (ensayos en laboratorio). El plan de actividades del proyecto consta de las siguientes fases: 1. en primer lugar, se realizará una búsqueda y análisis de documentación relevante; 2. en segundo lugar, se realizará una formación en los equipos experimentales a utilizar y en los paquetes de software relevantes (Ansys y Matlab); por ejemplo: a. se empezará haciendo ejemplos/tutoriales fáciles en Ansys para que la estudiante se familiarice con el programa y lo entienda bien; y b. luego, se pasará a ejemplos sobre Static analysis, Model/Modal analysis, y Harmonic analysis que están más relacionados con el tema a tratar en el TFG; 3. en tercer lugar, se empezará la simulación en Ansys con una articulación simple y luego se pasará a hacer la prueba experimental de la articulación estudiada. Lo más probable es que los resultados obtenidos no concuerden con los de la simulación, ya que en la simulación se habrá utilizado una articulación simple; 4. a continuación, se realizará otra simulación con una articulación mucho más compleja y realista, y se volverá a hacer la prueba experimental. En este caso, los resultados deberían parecerse más, por la mayor sofisticación del modelo numérico; y 5. finalmente, se elaborará la memoria y la presentación para la defensa final del TFG. |
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Overview (resum en anglès): | |
Turbine blades normally use mechanical joints to attach themselves to turbine disks. In this kind of joints, contact problems are very common. They are called contact problems because they occur where two localized surfaces are in contact. In these cases, peculiar behaviours with respect to the global behaviour of the structure due to high stresses and friction-related effects occur. In some cases, the specific contact behaviour can affect the global behaviour of the structure and it cannot be neglected: from the static point view possible stress intensifications can lead to failure, while from the dynamic point of view the joint may act as a constraint. Therefore, the contact might affect natural frequencies of the structure and associated normal modes. Thus, it is necessary to characterize the contact behaviour in terms of stiffness and damping associated to friction forces. To do so, usually three parameters are used: the normal contact stiffness, the tangential contact stiffness, and the friction coefficient between the surfaces.
In this project, a method to estimate the contact stiffness between two flat punches with rounded edges is investigated. To do so, numerical simulations will be performed using Ansys, using the finite element analysis (FEA) and the solution of non-linear equations since contact elements are used. As a consequence, a numerical equation solver and a solution method will be defined. To perform a numerical simulation, the finite element is defined in Ansys using a parametric construction of the model. The model will be meshed to obtain more precise results in specific areas close to the contact, but the mesh might affect the results of the contact simulation when a preload is applied. Therefore, before obtaining contact stiffness results, a mesh validation study will be developed comparing the numerical and analytical results for normal pressure distribution of a specific geometry to select the adequate mesh that will provide robust numerical results similar to the ones obtained with the analytical formulation. Then, the stiffness of the joint characterized by a flat punch will be obtained, first applying only a normal displacement to the top surface of the flat punch to calculate an equivalent normal contact stiffness and then applying a normal and a tangential displacement in the same location to calculate an equivalent tangential contact stiffness. Attention to the results is paid if the numerical results depend on the mesh (mesh-dependency). Therefore, a way to define a contact stiffness that is mesh-independent will be provided in order to find the pattern that the local stiffness of the joint (affected by the material property and the geometry of the punch) follows along the body. In detail, it will result smaller near the contact surface because of the specific geometry of the flat punch geometry: for a given force, the relative displacements and therefore the elastic strain will be larger close to the contact surface. |