Ponencias (Ingeniería Mecánica y de Fabricación)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/11374

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Walking dynamics from mechanism models to parameter optimization
(Elsevier, 2011) Schiehlen, Werner; García Vallejo, Daniel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla. TEP111: Ingenieria Mecanica
The paper deals with the historical development of human body dynamics, and it presents results received for simple models by parameter optimization. The scientific research on human walking dynamics started already in the 19 th century and was later promoted by the physicist and physiologist Otto Fischer who published in 1906 his fundamental book. Fischer used the mechanism theory for modeling and analysis of human walking. His research was based on the barycenters of the corresponding reduced mechanisms. By the end of the 20th century computational multibody dynamics provided more complex models which were applied to human body dynamics, too. More recently parameter optimization has been used to deal with the overactuation of biomechanical systems still a very active research topic in biomechanics. As an example a gait disorder simulation is presented showing that even today mechanism models, muscle group selection, inverse dynamics approaches and parameter optimization techniques using energy and aesthetics criteria are essential tools.
Modelo multiaxial de fatiga por fretting considerando la trayectoria de la grieta
(Sociedad Española de Integridad Estructural – Grupo Español de Fractura, 2021) Erena Guardia, Diego; Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP111: Ingeniería Mecánica
Este trabajo se basa en un modelo de predicción de vida a fatiga, previamente desarrollado por los autores, donde se combinan las fases de iniciación y propagación sin definir a priori donde termina una y empieza la otra. Para mejorar dicho modelo se han incluido nuevas variables del problema. Estas nuevas variables se introducen gracias al método de elementos finitos extendido (XFEM). El modelo puede clasificarse como uno de longitud de iniciación de grieta variable: las fases de iniciación y propagación de la grieta se calculan en función de la longitud de iniciación y la orientación de la grieta. Entre todas las grietas posibles, la combinación de la vida de iniciación y propagación que produce el valor mínimo se considera como la vida a fatiga. Además, en esta nueva propuesta la dirección de la grieta se determina automáticamente mediante un criterio basado en el parámetro de fatiga multiaxial de Smith-Watson-Topper en ambas fases de la grieta. El modelo se aplica a una campaña experimental de ensayos de fatiga por fretting, y se obtiene una excelente correlación con las vidas de fatiga por fretting y las trayectorias de grieta.
Caracterización de la aleación Scalmalloy y comparación entre fabricantes
(Sociedad Española de Integridad Estructural - Grupo Español de Fractura, 2023) Erena Guardia, Diego; Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Junta de Andalucía; Universidad de Sevilla. TEP111: Ingeniería Mecánica
Con respecto a los métodos tradicionales, el uso de la fabricación aditiva en componentes metálicos ofrece ventajas en cuanto a geometrías realizables y ahorro de material, lo que la hace muy atractiva para el diseño y construcción de piezas. Sin embargo, a día de hoy esta técnica tiene dos importantes inconvenientes. En primer lugar, durante el proceso de fabricación en el interior de las piezas aparecen poros que dan lugar a una menor resistencia a fatiga en comparación con piezas fabricadas de la manera tradicional. Por otro lado, el comportamiento a fatiga de piezas realizadas mediante fabricación aditiva depende notablemente de los parámetros seleccionados para su fabricación, siendo el número de estos parámetros bastante alto y algunos de ellos inherentes al equipo de fabricación utilizado. En relación a esta variabilidad en el comportamiento, este trabajo va a analizar una serie de probetas de Scalmalloy® hechas por tres fabricantes distintos, pero que durante el proceso de fabricación aplicaron el mismo espesor de capa y posterior tratamiento térmico. En este análisis se compararán la resistencia a fatiga y a tracción, la microestructura resultante, forma y causa de la rotura en los ensayos de fatiga, etc.
Fatiga por fretting con Inconel 718 a baja y alta temperatura
(Sociedad Española de Integridad Estructural - Grupo Español de Fractura SEMF-GEF, 2023-06) Moreno-Rubio, María; Erena Guardia, Diego; Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla. TEP111: Ingeniería Mecánica
La fatiga por fretting es un tipo de daño superficial producido en contactos mecánicos que se encuentran sometidos a cargas que varían con el tiempo. Este tipo de fallo es un problema muy frecuente en componentes mecánicos, con especial relevancia en el mundo aeronáutico como, por ejemplo, en las uniones álabe-disco en turbinas de gas. En este estudio, se analiza el daño producido por fatiga por fretting a baja y a alta temperatura. Para ello una probeta del tipo “dog-bone”, de sección rectangular, se presiona contra unos elementos de contacto de superficie cilíndrica. El montaje se realiza en lo que habitualmente se denomina “puente de fretting”. El material utilizado para la fabricación de todos los elementos es la superaleación de base Níquel-Cromo, Inconel 718. Material que a altas temperaturas posee excelentes propiedades mecánicas y una gran resistencia ante la corrosión y la oxidación. Los ensayos se realizaron tanto a temperatura ambiente como a una temperatura de 650ºC; todo ello con el objetivo de cuantificar el comportamiento frente a la fatiga por fretting del material en ambos casos, pudiendo observar cómo la vida a fatiga por fretting es inferior a fatiga simple.
Numerical analysis of flanging using tailored rubber pad forming on AA7075-O sheets
(Material Research Forum LLC, 2024) Borrego Puche, Marcos; Palomo Vázquez, David; Morales-Palma, Domingo; Martínez Donaire, Andrés Jesús; Rosa-Sainz, Ana; Centeno Báez, Gabriel; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Ciencia, Innovación y Universidades. España; Agencia Estatal de Investigación. España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP111: Ingeniería Mecánica
The flanging of metal sheets is extensively used in the automotive and aeronautical industries to provide rigidity or support for subsequent assembly. Flanging by rubber pad forming is one of the most common processes for small and medium batch production. Flanges with nonlinear bending lines are exposed to severe conditions that significantly hinder our comprehension of the geometrical, material, and process factors associated with flange formability (i.e., flangeability). This work presents a numerical study of the flanging process by a tailored rubber pad of hollow AA7075-O parts with continuous concave and convex flanges. The flangeability limits, the geometric capabilities of the forming process, and the deformation mechanisms of stretched and shrunk flanges as well as in the transition zone between them are analysed.
Formability analysis of incrementally hole-flanged parts using different tool sizes
(Material Research Forum LLC, 2024) Borrego Puche, Marcos; Palomo Vázquez, David; Morales-Palma, Domingo; Martínez Donaire, Andrés Jesús; Centeno Báez, Gabriel; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Ciencia, Innovación y Universidades. España; Agencia Estatal de Investigación. España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP111: Ingeniería Mecánica
This contribution analyses the formability of incrementally hole flanged parts using different tool radii (10, 20 and 47.9 mm). The smallest radius (10 mm) can induce full incremental benefits in the hole-flanged specimen, whereas the biggest one generates a formability behaviour closer to a conventional press forming. In the first case, the necking process is clearly delayed, being the development of a fracture in the middle of the wall flange the mechanism that controls the failure of the specimen. In contrast, in the second case, failure is governed by the appearance and development of a neck at the edge of the flange, which ends in material fracture. The intermediate tool radius (20 mm) shows midway features between a conventional and a fully incrementally formed specimen. The location and fracture mode of the flanged parts with different tool sizes are experimentally analysed and discussed within the Forming Limit Diagram (FLD) using the optical strain measurement system ARGUS®.
About kinematic consistency in the inverse dynamics problem in biomechanics
(2015) Ojeda Granja, Joaquín; Martínez Reina, Francisco Javier; Mayo Núñez, Juana María; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Economia, Industria y Competitividad (MINECO). España; Universidad de Sevilla. TEP111: Ingeniería Mecánica
The inverse dynamic analysis is used in the study of the human gait to evaluate the reaction forces transmitted between anatomical segments and to calculate the net joint moments resulting from the muscle activity in each joint. There are two approaches well defined. In the clinical field reconstruction techniques are often applied. The errors caused, mainly, by the relative movement of the skin over the bones make that the joint centres localized in two adjacent segments do not place the same position in the space. Velocities and accelerations are obtained through numerical derivation of the position. Finally, joint moment are calculated to balance the equilibrium equations. On the other hand, the engineers employ multibody models. They apply techniques to reduce the measurement errors and to obtain kinematically consistent data up to the acceleration level and calculate reaction and driving actions by means of the Lagrange multipliers. There is no agreement about which approach provides better results. The first procedure presents errors due to the skin motion which are avoid in the second method introducing errors inherent to the model. In this work, the two approaches were compared. Dynamic residuals defined to balance the Newton's equations were used as a measure of the model goodness. A discussion about the effect of the kinematically inconsistent data on the second approach was carried out. Results highlighted that the addition to the recorded motion of kinematic constrains according to a multibody model could lead to worse results in the inverse dynamic problem.
Automatic grading of student-specific exercises in large groups of the subject theory of machines and mechanisms
(Springer, 2019) Chamorro Moreno, Rosario; García Vallejo, Daniel; Martínez Reina, Francisco Javier; Reina Romo, Esther; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. TEP111: Ingeniería Mecánica
This study establishes an already defined and tested method to grade exercises of kinematics and dynamics within the course entitled “Theory of Machines and Mechanisms” of the Industrial Technologies Engineering Degree at the Seville School of Engineering (Spain). Particular emphasis is made on the automation of grading and personalization of the exercises, due to the large number of students enrolled in this course. The former is made through a teaching platform available at the University of Seville and called Doctus, whilst the latter is achieved by defining the input data of the exercises and the requested results as a function of the digits of the student’s ID. The students must face and solve a personalized problem by their own with the knowledge and competences acquired during the academic course. This paper describes the exercises and the tools used to grade them and shows the satisfactory results obtained with these exercises after three academic courses.
On the combination of geometrically nonlinear models and substructuring for multibody simulation of wind turbine blades
(ASME, 2022-11) Jensen, Christian Sigurd L.; Pedersen, Rasmus B. E.; Blanco, Blas; Escalona Franco, José Luis; Balling, Ole; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; European Union (UE). H2020; Universidad de Sevilla. TEP111: Ingeniería Mecánica
This study develops a geometrically nonlinear model of a wind turbine blade utilizing finite strain theory for the calculation of elastic forces. The model is based on the floating frame of reference (FFR) formulation, which is a common choice in the modeling of long and flexible wind turbine blades. To model the nonlinear deformation of blades, the FFR formulation divides the structure into several substructures, which involves a significant increase of the system degrees of freedom. In the presented model, a nonlinear description of the elastic forces is introduced to achieve the convergence of the dynamic blade model at a lower number of substructures. The nonlinear elastic forces are formulated according to the Euler-Bernoulli beam theory, and they account for third-order terms of the potential elastic energy, the so-called geometric stiffness. The developed blade model is formulated in two dimensions and tested in a blade of 44.8 m length, which corresponds to a 2.75 MW wind turbine. Firstly, the results show that linear models do not accurately represent tip blade transverse displacement, and the substructuring technique becomes necessary to account for geometric nonlinearity. Secondly, using nonlinear elastic models significantly reduces the number of substructures needed to achieve convergence of the solution.
Preliminary study on the use of 3D printed biodegradable polymeric sheet for the manufacturing of medical prostheses by SPIF
(Elsevier, 2022) García Romeu, María Luisa; Ferrer Real, Inés; Pasotti, C.; Coma, J.; Rosa-Sainz, Ana; Centeno Báez, Gabriel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Girona; Ministerio de Educación. España; Agencia Catalana de Gestión de Ayudas Universitarias y de Investigación; Universidad de Sevilla. TEP111: Ingeniería Mecánica
Incremental Sheet Forming (ISF) and Fused Deposition Modelling (FDM) of polymers have both an edge over conventional manufacturing by their ability to directly get complex structures without the need of a mold or a die. Obtaining biocompatible polymer blanks for ISF is not always as easy as it could be expected. Concerning nowadays FDM offers a good opportunity to print biocompatible polymer sheets as blanks to next be formed by ISF. Exploring the combination of FDM and ISF for two biodegradable polymers (Polylactic acid (PLA) and Polycaprolactone (PCL)) is the objective of this work. An analysis of the initial printed sheets in terms of thickness uniformity and surface roughness was carried out. Truncated cone shape with fixed slope angle geometries in a CNC machine were formed. The ISF process parameters modified were the traditional: step down, feed rate and spindle speed. As saved outputs there are: Forming Forces, Maximum Temperature, Surface Integrity, Surface Roughness and Shape Accuracy. After this first approach, a good feasibility process window was established for being used on prosthesis manufacturing of PCL. On the contrary, the feasibility window for PLA is limited because of its low formability. The first results of the combination of both additive manufacturing processes are interesting and deserve further studies to evaluate more in depth the behaviors and the forming mechanism of these materials.
Numerical Modelling of Conventional and Incremental Forming of Thin-Walled Tube
(Trans Tech Publications Ltd., 2022) Suntaxi, C.; Centeno Báez, Gabriel; Rosa-Sainz, Ana; Morales-Palma, Domingo; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía; Universidad de Sevilla. TEP111: Ingeniería mecánica
This study presents a numerical analysis of the tube expansion process by conventional tube-end forming versus single point incremental forming (SPIF) using DEFORM. The work includes the assessment of the strain paths within the principal strain space of these processes with respect to the formability limits as well as their evaluation within the equivalent strain versus stress triaxiality space. The results obtained demonstrated that the mechanics of tube flaring process in conventional and incremental forming are substantially different. This analysis of formability in the light of the accumulated equivalent strain and the average stress triaxiality allowed a better understanding of the differences between both processes in terms of the fracture limit strains.
Preliminary Study on the Onset of Necking Detection Using DIT in Tensile Tests
(Trans Tech Publications Ltd., 2022-07-22) Palomo Vázquez, David; Martínez Donaire, Andrés Jesús; López Fernández, José Andrés; Borrego Puche, Marcos; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP111: Ingeniería mecánica
The experimental detection of localized necking is an important issue in sheet metal forming. Today, the most common and extended techniques are strain-based methods using digital image correlation (DIC). The present work discuses a thermal methodology to detect the onset of necking in metals based on the analysis of the temperature gradient using digital infrared thermography (DIT). A series of tensile tests of H240LA-O3 high-strength steel of 1.2mm thickness is analysed using DIC and DIT techniques. It is proposed that necking initiates when the temperature difference at a reference distance from the necking point reaches a critical value, which allows identifying the necking time and estimating the limit strains from the visible images using circle grid analysis.
Design for FDM of flexible tooling for manufacturing aeronautical components by incremental sheet forming
(IOP Publishing, 2021) Flores, G.; Palomo Vázquez, David; Martínez Donaire, Andrés Jesús; Borrego Puche, Marcos; López, J.A.; Morales Palma, Domingo; Centeno Báez, Gabriel; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla; Ministerio de Ciencia e Innovación (MICIN). España; Cátedra Aeroespacial AIRBUS (Universidad de Sevilla); Junta de Andalucía
Nowadays, industrial production is required to reduce industrialization times and development costs for new products while maintaining high quality standards. In this context, the development of new flexible manufacturing technologies has gained relevance in the last few years. The use of Fused Deposition Modelling (FDM) additive technique has been recently proposed in different industrial sectors for manufacturing rapid tooling (dies) to be used in conventional sheet metal stamping or stretching processes with a significant decrease in costs and time savings. On the other hand, Incremental Sheet Forming (ISF) technology is characterized by an enhanced formability of the parts thus manufactured as well as for the need of a small number of tooling, reducing costs compared to conventional processes such as hydroforming or stamping. In particular, its simplest variant, Single-Point Incremental Forming (SPIF) requires the use of backing plates, which do not require tight tolerances as their only function is to collaborate in the deformation process acting as a support point. Furthermore, the strength requirements are also not a limitation since the forces involved in SPIF are very small given the local nature of the deformation. In this context, the main objective of this work is the design of a modular tooling system, manufactured using the FDM additive technique, that allows the flexible manufacturing of different aeronautical components by SPIF.
Numerical analysis of necking in stretch-bending based on modified maximum force criteria
(IOP Conference Series: Materials Science and Engineering, 2021) Morales, D.; Borrego Puche, Marcos; López, J. A.; Martínez Donaire, Andrés Jesús; Centeno Báez, Gabriel; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Ministerio de Ciencia e Innovación (MICIN). España
The necking criteria based on the maximum force principle, such as the Swift and Hill necking models, have been extensively used in the past to study sheet formability. Many extensions or modifications of these criteria have been proposed to improve necking predictions under only stretching conditions. Recently, the authors proposed two approaches to predict necking under stretch-bending conditions: a generalisation of classical maximum force criteria to stretch-bending; and a necking criterion based on critical distance concepts, suggesting that necking is controlled by the damage of a critical material volume located at the inner side of the sheet. Both approaches were evaluated with analytical models and the failure was successfully predicted in different materials, such as steel, brass and aluminium. This work presents a numerical study of the proposed necking criteria in stretch-bending processes with different punch radii. The simulations are validated with experimental tests over H240LA steel sheets.
Experimental and numerical analysis of fatigue cracks emanating from internal defects in Ti6Al4V SLM
(Elsevier, 2021) Aguado Montero, Santiago; Navarro Pintado, Carlos; Vázquez Valeo, Jesús; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. TEP111: Ingeniería mecánica
In the present work a series of fatigue tests on Ti6Al4V SLM parts are analyzed via both SEM and confocal microscopy. On the one hand, fracture surfaces are studied, and a common pattern is found, formed by a series of different textures which show the complex crack front evolution from crack initiation in a particular internal defect to complete failure. On the other hand, fatigue strength is observed to highly depend on the defect where initiation takes place, so experimental observation of that critical entity is carried out. Both defect location within the specimen and shape are studied, considering the crack-like or blunt feature of every defect. Once experimental analysis is complete, numerical simulation is attempted. By making use of critical defect and residual stress measurements obtained experimentally, both fatigue strength and crack front evolution are estimated.
Rolling effect in fretting fatigue test at the crack initiation stage
(Elsevier, 2022) Erena Guardia, Diego; Martín, Vicente; Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. TEP111: Ingeniería mecánica
The aim of this work is to perform a detailed analysis of the cracks paths obtained in fretting fatigue tests with cylindrical contact but taking into account the presence of an unavoidable (due to the fretting device’s stiffness) small oscillatory rolling. In order to obtain the crack paths crack surfaces were measured with a confocal microscope after the tests. Besides, the contact area and the surface crack initiation location were obtained by means of an optical microscope. The measurements indicate that the contact area is substantially larger than the theoretical one according to Hertz´s theory, contrary to tests done with only static normal load, in which both theoretical and experimental areas match perfectly. This observation means, that, due to the surface contact pad’s geometry (cylindrical) and the stiffness of the test setup, rolling is occurring during tests when tangential loading is developed. To reproduce this phenomenon, a 2D FEM model is developed. Stress/strain fields along the fretting cycle are analysed, noticing a substantial change of the contact surface hot-spot point and surface contact stress distribution, when compared with the non-rolling case. To predict the initial crack path, a previously developed model, based on a critical plane parameter, is applied using FEM stress/strain results. The results obtained show a better prediction of the surface hot-spot point and initial crack orientation estimation, when compared with the non-rolling case, and considering as a reference the experimental crack paths measured via confocal microscope.
Influencia de la longitud de iniciación en las predicciones de vida a fatiga por fretting
(Grupo español de fractura, 2001) Navarro Pintado, Carlos; Muñoz, Sergio; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
En fatiga se suelen distinguir dos fases en el proceso de desarrollo de una grieta: iniciación y propagación. Para la determinación de la vida a fatiga de un elemento existen numerosos modelos que combinan ambas fases, determinando la vida total como la suma de los números de ciclos ocupados en iniciación, Ni, y en propagación, Np. Para la aplicación de estos modelos es necesario definir la longitud de la grieta en el instante en que se considera que termina la iniciación y comienza la propagación: longitud de iniciación, ai. Generalmente esta longitud se suele definir a priori, ya sea en función del tamaño de grieta más pequeño detectable, de cómo esté definida la curva S-N, escogiendo la longitud de iniciación que mejor ajuste los resultados experimentales, etc. El objetivo de este artículo es analizar la influencia de dicha longitud de iniciación sobre la vida a fatiga estimada. Para definir el número de ciclos necesario para iniciar una grieta de longitud ai, el modelo utilizado emplea una curva S-Ni obtenida a partir de una curva S-N a la que se le resta el número de ciclos de propagación desde la longitud de iniciación definida. Este modelo se aplica a un conjunto de resultados experimentales de fatiga por fretting obtenidos con contacto esférico.
Influencia del coeficiente de rozamiento en fretting
(Grupo español de fractura, 2004) Muñoz, Sergio; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
En este artículo se analiza el efecto que una modificación del coeficiente de rozamiento tiene sobre la vida a fatiga en un ensayo de fretting. Para ello se ha realizado una serie de ensayos de fretting con contacto esfera-plano. El material empleado ha sido la aleación de aluminio 7075-T651. En estos ensayos se ha medido el coeficiente de rozamiento usando dos métodos distintos. Los ensayos se han realizado a distintas frecuencias y se ha estudiado cómo afecta dicho parámetro al coeficiente de rozamiento. A raíz de los resultados obtenidos, se ha analizado la influencia del coeficiente de rozamiento en las tensiones en la zona de contacto en varias situaciones distintas: (i) variando el tamaño de la zona de contacto (ii) variando la relación entre las cargas tangencial y normal. Este estudio se realiza tanto para condiciones de deslizamiento parcial como global. Por último, mediante un modelo analítico, se estudia la influencia de dichas variaciones del coeficiente de rozamiento en la vida a fatiga estimada
Comportamiento del shot y laser peening frente a la fatiga por fretting
(Asociación Española de Ingeniería Mecánica, 2010) Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras
El objetivo de este artículo es mostrar el efecto que tienen los tratamientos de shot y laser peening en la fatiga por fretting en la aleación de aluminio Al 7075-T651. Uno de los principales beneficios que aportan estos tratamientos superficiales es debido a que introducen un campo de tensiones residuales de compresión en las cercanías de la superficie, zona donde en la fatiga por fretting aparecen altos valores de las tensiones como consecuencia del contacto. Para analizar el comportamiento del shot y laser peening en estas circunstancias, se han realizado una serie de ensayos de fatiga por fretting sobre probetas a las que se les han aplicado este tipo de tratamientos. Para completar este estudio y tener un mejor conocimiento de cómo influyen ambos tratamientos, se ha medido el campo de tensiones residuales, la relajación de las tensiones residuales por la acción de las cargas cíclicas, el coeficiente de fricción, la rugosidad superficial y la dureza del material.
A New Algorithm for the Evaluation of the Elastic Forces in the Absolute Nodal Coordinate Formulation
(Eccomas Proceedia, 2004) García Vallejo, Daniel; Mayo Núñez, Juana María; Escalona Franco, José Luis; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras
The use of the Absolute Nodal Coordinate Formulation (ANCF) to model flexible multibody systems leads to a system of equations in which the mass matrix is constant. Among other advantages of the ANCF, as the simplicity of the formulation of joint constraint, the constancy of the mass matrix is specially useful since it implies that the mass matrix is calculated once before the analysis and stored as a invariant quantity. On the other hand, the evaluation of the elastic forces has been considered as a difficult task since they result in large nonlinear functions. Both linear and nonlinear formulations based on either Continuum Mechanics or Timoshenko/Euler-Bernoulli approaches have been supposed to lead to the same level of complexity of the elastic force function. The evaluation of the elastic forces when using a nonlinear Continuum Mechanics approach requires, as presented in the literature, the integration over the volume of the element. However, it can be shown that this integration can be avoided for every evaluation since there is a closed form of the elastic force function that can be obtained before the simulation. Finite elements based on ANCF have such a large number of nodal coordinate (24 and 48 for three-dimensional beams and plates, respectively) that the search for a closed form of the elastic force function becomes difficult and costly. This paper presents a set of constant matrices that are integrated in advance (before simulation) and allows the evaluation of the elastic forces without the integration over the volume of the element suggested in the literature. In addition, the amount of data that has to be stored in order to evaluate the function is reduced. These constant matrices together with the mass matrix complete the set of invariants of the ANCF that allows an acceleration of simulations. Numerical simulations comparing CPU time and number of arithmetic operations carried out when these invariant matrices are used with those carried out when they are not used, support the convenience of their use.

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