Tesis (Ingeniería Mecánica y Fabricación)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/11375

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Numerical Models of cell Mechanobiology oriented to organic Vascularization
(2025-05-23) Carrasco Mantis, Ana; Sanz Herrera, José Antonio; Reina Romo, Esther; Mecánica de Medios Continuos y Teoría de Estructuras; Ingeniería Mecánica y Fabricación
In the investigation of the role of mechanical cues in biology, i.e., mechanobiology, in silico modeling is used to complement in vivo and in vitro models, guided by the development of computers and algorithms that make it possible to apply engineering tools to living beings. Rather than the ambitious goal of predicting the evolution of a biological system, like a disease, many of them without a therapeutic treatment, in silico modeling tries to identify elements that may be important in the development of such problems and provides tools to measure and quantify magnitudes that would be very difficult to obtain through experiments. In this thesis, 3D in silico models of some important cellular processes in mechanobiology are constructed. To this end, this thesis begins by studying the evolution of spheroids, particularized for a type of brain cancer, Glioblastoma Multiforme (GBM). This approach allows for the replication of key phenomena, such as cellular communication mechanisms, nutrient gradient effects and the formation of realistic 3D biological structures. The primary aim of this research is to connect the evolution of spheroids to the mechanical activity of cells, integrating nutrient diffusion, consumption and the resulting cellular dynamics of growth and death through a 3D continuum mechanobiological model that is qualitatively validated with own experiments. The model offers a novel explanation for diverse scenarios, such as spheroid growth and shrinkage, behavior attributed to the mechanical interactions among cells, guided by their evolutionary dynamics. Subsequently, it is analyzed how the extracellular matrix (ECM) passively stimulates vascularization. Vasculogenesis, the process of forming new blood vessels, is influenced by numerous factors, biochemical and biomechanical. Nevertheless, the biomechanical factors that impact the shape, organization, and structure of vascular networks remain poorly understood and require further study. A 3D agent-based model (ABM) of vasculogenesis is developed to explore how the mechanical properties of the ECM influence this process. To achieve this goal, a growing domain containing different endothelial cell types is modeled: tip cells, that sense the chemotactic gradient and lead the growth at the ends of the vessels, and stalk cells, which form the interior of the vascular network. The ECM is represented as particles surrounding the developing vascular structure. Various forces are incorporated depending on the cell type, including chemotactic, mechanical, random, and viscoelastic forces, among others. The network is analyzed and updated iteratively at each time step using a mechanically-driven proliferation rule. Through in silico simulations, the impact of various biomechanical factors, such as ECM stiffness and viscoelasticity, is investigated. Several indicators, including the number of cells, branches, tortuosity, and anisotropy, are defined throughout the algorithm to assess topological variations in the vascular network during vasculogenesis under different ECM conditions. The results are qualitatively compared with findings from other related studies in the literature. Finally, a hybrid model is developed, combining both continuum and discrete formulations, to simulate the vascularization process in an organoid, a model similar to the spheroid but with a more complex structure, in an attempt to study in silico the lack of vascularization that limits the usefulness of this type of in vitro models. Organoids replicate hierarchical functions, acting as miniature versions of living tissues and providing a reliable representation of cellular mechanisms. The model combines a finite element and agent-based frameworks to incorporate the mechanical stimulation through a laminar and stationary flow and the main biophysics within the organoid. It analyzes parameters such as fluid velocity and nutrient consumption along the organoid evolution, whose results agree qualitatively.
New Process designs for the Assessment of the shear fracture forming Limit for thin-walled Tube
(2024-11-20) Suntaxi, C.; Vallellano Martín, Carpóforo; Centeno Báez, Gabriel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación
Components manufactured from thin-walled tubes by plastic deformation are de-mand in various industries, such as automotive, aerospace, medical devices, air conditioning, and chemical industry, among others. The formability of sheet metal is a widely studied topic, and the methods to assess the forming limits are well known. In contrast to the case of sheet metal, a route to study the formability of tubes and the characterization of mode II fracture has recently begun to be established. This thesis combines the finite element method and experimentation to de-termine the shear fracture forming limit line (SFFL) of 6061-T4 aluminum tubes that characterizes fracture mode II of fracture mechanics. Numerical analysis has allowed to propose two specimens suitable to obtain strain loading paths leading to obtain the strain fracture strains by shear stress. Experimentation has made it possible to observe the shear failure mechanism in more detail and to overcome the limitations of the numerical model. With this work, it has been possible to determine: the instant, the location of the crack initiation point, other failure modes, the strain load paths and the shear fracture strains. By plotting the different pairs of shear fracture strains in the space of principal strains, the shear fracture forming limit was obtained. The finite element model was further updated with experimental results to be validated in terms of strains. Apart from the analysis of the principal deformations, the evolution of the triaxiality is analyzed to compare the results of the proposed methods with the results of the incremental expansion of tubes by SPIF. In this incremental process, stress states close to shear stress have been observed in the final stages. The characterization of the tube fracture limit in mode II of fracture mechanics with the two test specimens allows to obtain the SFFL curve in a simple and effective way by combining experimentation and numerical analysis.
Nonlinear Multibody Modelling and Optimal Control Techniques for E-sail Dynamics
(2024-11-25) Pacheco Ramos, Guillermo; García Vallejo, Daniel; Vázquez Valenzuela, Rafael; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos
This dissertation investigates the dynamics and control of Electric Solar Wind Sails (E-sails), a promising propellantless propulsion system for deep-space exploration. The E-sail utilizes a network of long, electrically charged tethers to extract momentum from the solar wind, enabling continuous thrust without consuming any propellant. While this concept offers significant advantages for long-duration missions, it presents several challenges related to complex multibody dynamics, solar wind variability, and the development of efficient control strategies. This research addresses these challenges by developing and analyzing two dynamic models of the E-sail. First, a simplified analytical model, based on a Lagrangian approach and considering rigid tethers, provides a fundamental understanding of the E-sail’s dynamic characteristics in simple operational scenarios, such as coning motion and steady-state operation. This model serves as a benchmark for validating a more detailed multibody model. The second model, developed using the Absolute Nodal Coordinate Formulation (ANCF) and Natural Coordinates (NC), offers a high-fidelity representation of the E-sail dynamics, considering both rigid and flexible elements. This model incorporates nonlinear bending stiffness, structural damping, and damping at tether anchor points, capturing the complexity of tether motion and its interaction with the central vehicle in free-flight operation. The dissertation further investigates the application of linear and nonlinear control techniques for E-sail regulation and transition between steady-states. For the simplified model, both Linear Quadratic Regulator (LQR) and nonlinear Model Predictive Control (MPC) are implemented and validated for the fully-actuated and under-actuated scenarios, respectively. The results demonstrate the effectiveness of these control schemes in stabilizing the E-sail in steady-state operation and compensating for disturbances, such as solar wind fluctuations and initial condition errors. The study then focuses on planning and tracking stable transitions between different steady states. The transition maneuver is formulated as an optimal control problem using the direct transcription method, and the results provide both optimal planning for the states and an open-loop optimal control law. Subsequently, tracking of the optimal trajectory is investigated using a finite-horizon LQR for the fully-actuated scenario and a Shrinking Horizon MPC (SHMPC) for the under-actuated case. This approach allows for the efficient planning and precise tracking of the maneuver, mitigating the impact of disturbances and uncertainties. The insights gained from this work contribute to a deeper understanding of E-sail dynamics and control, paving the way for the development and implementation of robust control strategies for this innovative propulsion system. The dissertation also highlights the potential of employing simplified models for preliminary analysis and the need for more detailed models to capture the complex interactions between flexible tethers and the central vehicle, particularly in non-null sailing angle configurations. The findings serve as a valuable foundation for further research, particularly in the areas of robust control design, multi-physics considerations, and the exploration of new applications for E-sail technology in future space missions.
Development of a wearable exoskeleton (exosuit) for lower limb assistance based on simulations
(2024-03-22) Bermejo García, javier; Romero Sánchez, Francisco; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
In the upcoming years, there will be a significant increase in the world’s older adult population. This demographic shift, combined with rising cases of spinal cord injuries, stroke or cerebral palsy, will result in a greater number of individuals affected by walking-related conditions. Therefore, the development of assistive walking devices is essential to enhance the autonomy of people with reduced mobility. Generally, the design of customised devices for each pathology is complex and expensive. This means that the need to use tools that facilitate the selection of the number of actuators providing external assistance to reduce the manufacturing costs of these devices and simplifying their usability for patients are essential objectives. Under this premise, this doctoral thesis presents the framework to analyse and simulate gait using a cable-assisted exoskeleton (Exosuit) to support the gait of older adults. For customizing the device, a study of the main differences between the gait patterns of young adults and older adults is carried out. For the design of the exosuit, a study of the effect on the neuromuscular system is proposed through the simulation of cable-assisted gait. These simulations provide information on how muscle activations vary during assisted gait based on inverse dynamic analysis and dynamic optimization. The results obtained in this doctoral thesis have allowed for a preliminary design of a functional prototype of an exosuit for walking assistance within the context of the National and Regional Research Projects in which this thesis has been developed. The proposed methodologies have been used to design a wearable exoskeleton to assist in walking for the elderly.
Modelling and linear stability analysis of highly mobile nonholonomic multibody systems
(2023-11-10) García-Agúndez Blanco, Alfonso; Freire Macías, Emilio; García Vallejo, Daniel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. Departamento de Matemática Aplicada II (ETSI)
This PhD thesis aims to develop a methodology that contributes to the modelling of nonholonomic multibody systems, the study of their linear stability and the design of linear feedback controllers. The ultimate objective is on single-person nonholonomic vehicles, particularly in terms of safety in urban transportation. By understanding how critical design parameters affect stability, it will be possible to carry out design modifications that result in safer vehicles and reduce accidents. These modifications will also cater to a wider range of potential users, including elderly and physically impaired individuals. From a regulatory perspective, understanding stability conditions will play a crucial role in formulating rules for the use of these vehicles within cities. Moreover, advancements focused on enhancing safety will promote the adoption of electric single-person vehicles, leading to a reduction in environmental degradation and aiding in the accomplishment of pollution reduction objectives. The methodology consists of the following phases. First, multibody models of a class of nonholonomic systems are developed. Subsequently, in order to carry out the linear stability analyses of these multibody systems, efficient and accurate linearization approaches are required. To this end, novel linearization procedures, for multibody systems with holonomic and nonholonomic constraints, are proposed. The correctness of the linearization approaches is validated with the linear stability results of a well-acknowledged bicycle benchmark. The results show that the procedures are completely accurate, efficient, valid for any multibody system (regardless of its complexity) and powerful, obtaining the linearized equations of motion along an arbitrary reference solution as a function of the design parameters of the multibody system. Next, by varying these parameters over a wide range of values, a detailed sensitivity analysis of the eigenvalues can be performed to assess the linear stability of the multibody system. Lastly, linear feedback controllers can be designed by using the linearized equations of motion. These linearization approaches are applied to study the linear stability of several nonholonomic systems. First, linear time-invariant (LTI) systems are addressed. In particular, the linear stability of the steady forward motions of classical nonholonomic systems, as the skateboard or the rolling hoop, and highly mobile nonholonomic multibody systems, such as the bicycle, the waveboard and the electric kickscooter, is assessed. Next, the case of periodic linear time-varying (LTV) systems is studied, including a detailed linear stability analysis of the circular steady motion of the rolling toroidal wheel. Another application is the use of the linearization procedures in multiphysics scenarios, and, in particular, with hydraulically actuated multibody systems. Finally, the approaches are applied in the design of linear feedback controllers for nonholonomic multibody systems. As an example of application, the optimal control of the well-known ball-plate system, using a Linear-Quadratic Regulator (LQR), is shown.
Ontology-based engineering supporting the conceptual design of reconfigurable manufacturing systems in the aerospace industry
(2023-11-20) Arista Rangel, Rebeca Rubí; Más Morate, Fernando; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
This doctoral dissertation focuses on enhancing the manufacturing system design process in the aerospace industry by exploring two key research areas: Reconfigurable Manufacturing Systems (RMS) design and Ontology-based Engineering (OBE) systems supporting the collaborative design process. While RMS principles can enhance the manufacturing system resilience and reduce costs, their implementation in aerospace is constrained by industry-specific requirements, not sufficiently addressed by current RMS design methods. Additionally, the lack of digital tools for collaborative design and knowledge capitalization within it, prevent a true integration of manufacturing system requirements during product development. To overcome these challenges, the thesis investigates the design of RMS tailored to aerospace industry characteristics and collects this design knowledge using OBE techniques, to shift the cognitive processes from the designers to the digital design tools. The combination of these approaches enables informed decision-making, trade-offs between design scenarios, and facilitates manufacturing system reconfiguration. The dissertation includes a systematic literature review, the development of different ontologies part of a single knowledge base, and the demonstration of use in realistic aerospace design cases. The research contributes to advancing collaborative design processes and promoting the adoption of RMS in the aerospace industry.
Formability and failure of polymeric sheets: experimental assessment and medical applications
(2023-06-02) Rosa-Sainz, Ana; Centeno Báez, Gabriel; Silva, María Beatriz; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
Durante las últimas décadas, el paradigma de la Industria 4.0, que se dirige hacía procesos flexibles, de baja-media producción, y orientados hacía la personalización del producto, ha provocado grandes cambios en los procesos de fabricación, ejemplo de esta evolución es el avance que ha tenido la fabricación aditiva en los últimos años. Otro claro ejemplo de esta evolución se ha visto en el proceso denominado conformado incremental mono-punto o SPIF (por sus siglas en inglés), que permite gran flexibilidad de proceso, ahorro de utillaje y permite la fabricación de productos customizados. Recientemente, la aplicación de SPIF a materiales poliméricos se ha visto incrementada, debido a que además de las ventajas del proceso mencionadas anteriormente, se han realizado verificaciones experimentales de que las deformaciones alcanzadas mediante SPIF se encuentran por encima de la curva límite de conformado por estricción o FLC (por sus siglas en inglés), sin fallo. Sin embargo, cabe señalar que en el caso de las láminas poliméricas no existe un procedimiento sistemático para construir el diagrama límite de conformado o FLD como está bien definido para chapa metálica. En este contexto, la primera parte de esta tesis doctoral tiene el objetivo de proporcionar procedimientos para obtener la curva límite de conformado por estricción (FLC por sus siglas en inglés) y por fractura en modo I de mecánica de fractura (FFL por su siglas en inglés), y con ello, obtener el diagrama límite de conformado (FLD) de materiales poliméricos. Las láminas poliméricas escogidas fueron tres polímeros termoplásticos ampliamente utilizados: policarbonato (PC por sus siglas en inglés), polietileno de alto peso molecular (UHMWPE por sus siglas en inglés) y polieteretercetona (PEEK por sus siglas en inglés). Por otro lado, esta tesis doctoral establece un marco de estudio de distintos parámetros de proceso en SPIF, con el objetivo de asentar una base experimental sobre la afectabilidad de estos parámetros de proceso a los tres materiales poliméricos mencionados anteriormente. El estudio se realiza en términos de deformaciones dentro del diagrama límite de conformado de cada material polimérico obtenido independientemente mediante procesos convencionales. La tercera parte de esta tesis aborda la fabricación de aplicaciones médicas mediante los dos polímeros biocompatibles, UHMWPE and PEEK, con el objetivo de demostrar factibilidad de fabricar mediante SPIF implantes médicos a temperatura ambiente.
Test bike bench design for 3d kinematic and kinetic optimisation in cycling
(2023-04-19) Martín-Sosa, Ezequiel; Ojeda Granja, Joaquín; Mayo Núñez, Juana María; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
The main objective of this thesis was to solve the 3D inverse dynamic problem during cycling. For this purpose, the procedures used for motion capture using videogrammetry were adapted to the practice of cycling. In addition, modifications were made to a commercial bicycle in order to measure the forces applied to it. In order to achieve the objective, the first of the studies carried out in this thesis was the 3D lower body movement analysis during pedalling. The complexity of accurately measuring movements outside the sagittal plane (plane parallel to the bicycle frame), caused the number of studies focusing on 3D kinematic analysis of cycling to be limited. The studies that opt to analyse kinematics outside the sagittal plane tended to use marker protocols from gait analysis, which did not take into account the cycling particularities. Due to the lack of a specific marker protocol for cycling, one of the aims of this thesis was to develop and evaluate a new marker protocol with which to carry out a 3D kinematic analysis in cycling at the level of position, velocity and acceleration in a simple way and without affecting the comfort of the participant. Because there is no gold-standard of 3D pedalling kinematics accepted by the scientific community, the results obtained have been evaluated by physiological and comparative analysis with previous works. The results obtained were similar to those in the literature, with low intra-subject variability in the sagittal and transverse planes and a high repeatability of the order of that reported by other protocols for gait analysis. Velocity and acceleration results outside the sagittal plane suggested their importance when considering them in the resolution of the inverse dynamic problem. To solve the inverse dynamic problem in the lower body, in addition to the movement of this, the 3D force applied to the pedals had to be known. To obtain this force, the most commonly used equipment tended to focus only on the components contained in the sagittal plane, which means that one of the components of the force was disregarded. On the other hand, equipment intended to measure all three components of force tended to be bulky and heavy, which could affect the naturalness of pedalling. In this work an equipment capable of measuring the three components of the force applied to both pedals, with a reduced mass and size, has been developed and evaluated. The results obtained when measuring the pedalling forces were similar to those shown in the literature. The correct estimation of the lateral-medial direction force was of great interest to assess possible joint overload. The temporal evolution of the total power over the pedalling cycle was also estimated with values also similar to the literature. Once a procedure for obtaining the 3D motion of the cyclist and calculating the three components of the force applied to the pedals was available, the 3D dynamics analysis during pedalling was possible. In the literature, most of the works that carry out a dynamic analysis of pedalling focused on the sagittal plane. Few studies performed a 3D dynamic analysis and those that carried it out, did not study all the joints that form the lower body. In this thesis, the 3D inverse dynamic problem was solved for the three joints that make up the lower body using the bottom-up methodology. In order to carry out this study, the marker protocol designed in this thesis and the force measurement equipment installed in both pedals were used. Additionally, a process had to be designed to synchronise the kinematic data and the forces applied to the pedals. As a result, joint moments and forces and joint-specific powers were obtained, but they could only be partially evaluated due to the limited information available for data outside the sagittal plane. Those results that could be compared showed significant similarities with the published results. The study of cycling dynamics showed that the pedalling ability of the participants analysed had a notable effect on the results obtained. In addition to the main objective, this thesis also carried out other types of studies applying the knowledge obtained in the processes described above. One of these studies was the analysis of the asymmetries in the forces applied to the pedals by both legs. This study was important because the asymmetries may affect the performance of the cyclist or prevent the occurrence of injuries. Studies focused on analysing asymmetries in forces tend to consider only the effective force, disregarding the three-dimensional nature of the force. Another characteristic of these studies was that they tend to analyse asymmetries using significant scalar data, such as the maximum value of the force or the range. This way of operating can also hide information. Therefore, in this thesis the analysis of the asymmetries for the three components of the force evaluated at all the instants of the pedalling cycle was carried out using the normalised symmetry index and the cross-correlation coefficient. The combination of both indices not only made possible to detect if there were asymmetries, but also the possible cause of these asymmetries: differences in force levels and/or time lags in the temporal evolutions of the forces applied by each leg. Forces in the sagittal plane showed a high level of symmetry. The lateral-medial force presented the highest level of asymmetry due to the difference in the magnitudes of the applied forces by both legs and the existing time shift between the two force patterns. Another application of the knowledge obtained in this thesis was the analysis of the effect of pedalling power on joint angles, forces and moments and joint-specific powers. This type of study has been carried out in the literature focusing on the sagittal plane and using scalar variables (ranges, maximum or minimum values). This way of working causes loss of information, as well as not identifying in which instants or phases of the cycle the pedalling power used has the greatest effect. In this thesis, the effect of using different pedalling powers on the variables mentioned above was analysed using three different pedal powers (170 W, 240 W and 310 W). All the variables were analysed in a 3D way and throughout the whole pedalling cycle (vector variables). The study of the effects of power was carried out by analysis of variance using the statistical parametric mapping methodology. From these statistical analyses the conclusion was that pedalling power did not affect kinematics. Joint moments and forces were the variables most sensitive to pedalling power, while the knee was the joint that showed the greatest sensitivity to changes in pedalling power. For joint moments, significant differences were obtained for all three anatomical planes. Similarly, joint forces also showed significant differences in the three directions of space. For both variables, the instants where the greatest differences occurred were near the top or bottom dead centre or the zone of maximum force application. As a final part of this thesis, the conclusions reached were presented together with the limitations presented in the different studies carried out. Additionally, the contributions of this thesis to scientific journals and congresses were listed together with the future lines of research.
A Novel Synergy-Based Approach for the Design of Cable-Driven Exosuits for Walking Assistance
(2022-11-02) Rodríguez Jorge, Daniel; Alonso Sánchez, Francisco Javier; Herrera Navarro, Ignacio; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
The growing tendency of worldwide societies, but particularly in the West, to aging leads to a growing number of individuals that might require any kind of walking assistance. Life expectancy in Spain, for instance, has doubled in barely four generations. As such, there exist numerous solutions, among which exoskeletons must be highlighted as wearable devices with rigid elements that assist, generally driven by motors, human gait in any way. As an alternative to these devices, a new variant, much lighter and cheaper for the user has been proposed: wearable exoskeletons, or exosuits. They, made only of textile elements aside from the actuation system, offer a more comfortable and economic solution to those who can walk, but need an assistive device or, alternatively, wish to increase their motion capabilities: the lack of rigid elements forces the subject to sustain themselves, yet at the same time does not restrict or impede their natural gait in any way. A common variety of exosuits consists of an actuation system, including the motors and the power transmission system, generally included in a backpack and transmitting force via cables anchored to the joints in the so-called anchor points, in most cases textile elements located at the joints that will be actuated. A motor might be required for each target joint and leg: if all hip, knee, and ankle are to be actuated, six motors will be required, which will be the main contributors to the overall system weight and price. This work arises from the need of reducing such weight and price, as well as increasing the wearability of walking-assistance exosuits. The document focuses on the development of a new design approach for exosuits that allows a heavy reduction in the number of actuators required to provide the desired assistance and, thus, offers a much more affordable solution, at the reach of many more potential users. The thesis is, thus, supported by two main cornerstones. On one side, the development of an inverse-dynamics model capable of predicting the forces and torques to be produced by the system to assist human gait, establishing a base for the system design and for its control. On the other side, stands the detailed description of the novel design approach that provides the desired improvements, serving as a guide for future exosuit designs for the lower limb. The latter is where lies the main contribution of this work, which will try to improve current technology with regards to cost and weight: the mechanical design based on synergies. Statistical analysis of human gait demonstrates a rather evident fact: as opposed to other movements, such as grasping an object or holding it, walking has a cyclic nature and presents clear similarities between several of its parameters. A kinematic study performed on the joint flexion-extension angles for hip, knee, and ankle, among others, yields a notable degree of similarity between them. The same happens in the cable forces during gait required to provide a certain fraction of the total joint torque, or in the cable extensions themselves. These similarities make it possible to approach, by statistical means, a dimensionality reduction problem while keeping a high degree of correspondence with the original variables. In other words, the number of required actuation curves, thus the number of required motors, can be significantly reduced, as much as the problem's dimensions. Therefore, a design allowing the actuation of six simultaneous degrees of freedom (up to three joints per leg) has been proposed with only one motor. All of it leads to the main contribution of the work to the current walking-assistance exosuits design: the detailed, rigorous, and mathematical description of a novel method of design targeting the significant reduction in the weight and price of these devices, while also improving their wearability and making them more accessible.
Mechanobiology of bone regeneration: distraction osteogenesis and tissue engineering
(2022-10-21) Blázquez Carmona, Pablo; Domínguez Abascal, Jaime; Reina Romo, Esther; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
Bone regeneration is the natural process of bone reconstruction during the continuous adult remodeling, fracture healing, or complex clinical treatments of bone defects. In this biological problem, the role of engineering is essential for several aspects, including the control of the callus mechanical environment, predicting the complex mineralization phenomena, or designing materials and structures to optimize angiogenesis. The aim of this thesis is to find mechanical solutions to current challenging limitations in this field: the current mechanical incompatibility between brittle implants and external fixations in load-bearing models; the insufficient knowledge of the surrounding soft tissues’ mechanics during the elongation; the lack of understanding of the mechanical environment that promotes mineralization; or the need of quantitative tools for better clinical control of the processes. Distraction osteogenesis and tissue engineering experiments were carried out on merino sheep. A flexible Ilizarov-type external fixator was initially implanted in their right-back metatarsus. The distraction group underwent an osteotomy in a middle cross-section of the bone that, after a latency period of 7 days, was elongated to a final length of 15 mm (distraction rate of 1 mm/day). By cons, the tissue engineering group had 15 mm of bone directly replaced with a porous bioceramic scaffold biologically enhanced with cancellous bone autograft. Animals were slaughtered at different time-points of the consolidation phase. Before surgeries, an instrumented external fixator was devised to control bone formation through mechanical parameters indirectly. By working with a low-cost and size-optimized real-time wireless acquisition system, they reported promising results in estimating callus forces and stiffening. The resulting versatile system offers mechanobiological comparisons of the evolutions of different treatments. Concerning the scaffold design, a standardized optimization problem was defined and applied to optimize their inner architecture by covering biological parameters (porosity, pore size, and surface area) and mechanical constraints to ensure its structural integrity in vivo. During the distraction phase, higher viscoelastic forces with a similar relaxation rate were quantified compared to other distraction processes without limb elongation. After applying rheological models to the raw data, the mechano-structural changes suffered by this bone callus and its surrounding soft tissues were estimated. The contribution of these tissues to the distraction forces was limited to elongations above 4% of the original length when anatomical changes were evidenced. Likewise, the quantified elastic callus stiffening was mathematically modeled to elucidate the mechano-structural phenomena behind the callus accommodation-to-mineralization. It was based on ex vivo confocal imaging data applied to non-mineralized callus samples. The continuous collagen reorientation, densification and maturation seemed to control this problem. In the consolidation stage, several in vivo monitoring techniques were employed to build an exhaustive comparison between processes: gait analysis, internal force distribution, callus stiffening, x-rays, and CT imaging. All the parameters analyzed tended to healthy values in both groups but at different rates. In the short-term, the bone callus recovered its loading capacity and it exponentially increased its stiffness, being faster in the tissue engineering group. The healthy callus mineral density and limb bearing capacity were reached around 5-6 months after surgery. However, the recovery time of this last parameter seems to have been influenced by the walking conditions acquired by the animals due to pain and low confidence in the treated limb in the early stages. Finally, both the apparent geometry of the callus and its trabecular microstructure seemed to recover in the long remodeling phase.
Stretch and shrink flanging of AA2024-T3 sheet by single point incremental forming
(2021-10-07) López Fernández, José Andrés; Centeno Báez, Gabriel; Vallellano Martín, Carpóforo; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
Flanging is a forming process widely used to increase the sti ness of sheet parts in industrial applications such as the production of aircraft and automobile components. Flanges are usually formed by rubber forming or using a punch and a die, as these processes are fast and economical for producing a large number of parts. However, there is increasing interest in the manufacturing of anges using nonconventional processes, such as single point incremental forming (SPIF), that allow cost savings due to their exibility and low tooling. This thesis studies the manufacturing of open stretch and shrink anges of AA2024-T3 sheets by SPIF for a wide range of process parameters, including the ange principal radius, spindle speed and tool diameter. In this context, an experimental campaign was performed for each type of ange, classifying the principal modes of failure in the sheet and assessing its formability within the forming limit diagram (FLD). For stretch anging, FE modelling in combination with a theoretical framework based on Barlat's 89 anisotropic yield criterion was used to evaluate the formability in the stress triaxiality space. The fracture forming limit (FFL) obtained for proportional loading and the evolution of the anges were compared in the average stress triaxiality versus equivalent strain space, showing that this space might be the most appropriate for making failure predictions in SPIF. A geometry analysis of shrink anges obtained by SPIF was carried out to evaluate their formability in terms of their tendency to develop wrinkling. The elastic recovery in successful and failed is also studied. Finally, a new approach based on the analysis of compression stresses was proposed to predict the onset of failure in this type of ange. In this regard, it was shown that there exists a stress limit at which the anges analysed fail by wrinkling.
Fast-Ion Transport and Acceleration Induced by Edge Localized Modes in MAST Upgrade and ASDEX Upgrade
(2021-07-16) Rivero Rodríguez, Juan Francisco; García Vallejo, Daniel; García Muñoz, Manuel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. Departamento Física Atómica, Molecular y Nuclear
La fusión nuclear se esboza como una fuente de energía sostenible, de bajas emisiones y que aportará potencia de base al mix eléctrico. Los tokamaks son los dispositivos más avanzados para la obtención de energía mediante fusión nuclear y operan en condiciones cercanas a las de las futuras centrales nucleares. Hoy en día, los tokamaks existentes tienen como objetivo resolver los desafíos científicos y técnicos que plantean las futuras plantas de fusión nuclear. En los tokamaks, los iones rápidos, -- aquellos iones cuya energía es superior a la del resto del volumen de plasma --, se emplean para aumentar la temperatura del plasma hasta energías donde la fusión se hace patente. Los iones rápidos pueden perder el confinamiento debido a interacciones con perturbaciones electromagnéticas de diversa naturaleza, siendo esto un riesgo para el rendimiento del plasma y para la integridad del reactor. En el modo de operación de alto confinamiento, conocido por H-mode, aparecen de forma repetitiva inestabilidades magnetohidrodinámicas (MHD) explosivas localizadas en el borde, conocidas como Edge Localized Modes (ELMs). Los ELMs liberan una gran cantidad de energía y momento hacia las paredes del plasma, cuyo efecto se estima intolerable en futuros tokamaks. Además, investigaciones recientes en el tokamak ASDEX Upgrade han observado un aumento en las pérdidas de iones rápidos a energías por encima de su energía de inyección, que aparecen relacionadas con la actividad de los ELMs. Estas observaciones sugieren que existe una interacción entre los ELMs y los iones rápidos, que resulta en la aceleración y pérdida de estos últimos. Este trabajo tiene como objetivo de estudio las pérdidas de iones rápidos inducidos por ELMs. Para conseguir este objetivo, la tesis ha abarcado el desarrollo de herramientas numéricas y el diseño de diagnósticos experimentales. En el aspecto numérico, se han utilizado códigos de seguimiento de órbitas como ASCOT5 y se han implementado perturbaciones electromagnéticas 3D que evolucionan en el tiempo. Esto ha permitido investigar los principales mecanismos de transporte y aceleración planteados para esclarecer la pérdida de iones rápidos inducida por ELMs. En el ámbito experimental, durante esta tesis se ha diseñado el primer detector de pérdidas de iones rápidos (FILD) en el tokamak esférico MAST-U. El diagnóstico está montado sobre un mecanismo de rotación y traslación que permite adaptar la sonda a diferentes orientaciones [0o, 90o] y posiciones radiales [1.40 m, 1.60 m]. Los primeros datos experimentales del FILD de MAST-U se esperaban obtener a lo largo de esta tesis. Sin embargo, distintos retrasos en el comienzo de la campaña experimental de MAST-U han impedido poner el diagnóstico en funcionamiento. Por este motivo, los planes experimentales y numéricos han tenido que seguir distintos planteamientos. Los experimentos, que se han realizado en ASDEX Upgrade, han tenido como objetivo expandir el alcance de las observaciones de pérdida de iones rápidos inducidas por ELMs, llevando a cabo nuevos rastreos para detectar los parámetros que más afectan en la interacción entre los iones rápidos y los ELMs. Con respecto al modelado, se busca realizar un modelado que permita reproducir las principales observaciones experimentales en ASDEX Upgrade y revele los mecanismos básicos de transporte y aceleración de iones rápidos durante los ELMs. Además, el modelado en MAST-U ha permitido preveer la señal de FILD, que se ha podido comparar con la señal en ASDEX Upgrade.
Spatial Distribution of Fast Ion Loss Detectors in the ASDEX Upgrade Tokamak
(2021-07-08) González Martín, Javier; Domínguez Abascal, Jaime; García Muñoz, Manuel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
To ensure heating efficiency and device integrity in future fusion reactors, suprathermal (fast) ions need to be confined for a sufficient time so that their energy is transferred to the bulk plasma via Coulomb collisions. In order to understand the mechanisms responsible for the loss of fast-ion confinement, fast-ion loss detectors (FILD) provide velocity-space measurements at the reactor wall. These measurements are nevertheless spatially localized and do not provide enough information to characterize the spatial distribution of the losses required to fully understand (and therefore mitigate) the loss mechanism induced by MHD instabilities and externally applied 3D magnetic perturbations. In order to characterize the spatial distribution of the fast-ion losses, in the frame of this thesis, the FILD suite of the ASDEX Upgrade (AUG) tokamak is upgraded with two new fast-ion loss detectors, being both located below the tokamak midplane. One of these diagnostics, labelled FILD5, is installed right above the lower divertor, between two saddle coils. The other new detector, known as FILD4, is an in-situ probe consisting of an in-vessel coil that, when externally energized, creates a magnetic dipole that tries to align with the existing tokamak toroidal magnetic field, generating the torque required to move the probe head back an forth. The equations governing the coil dynamics and motion of the probe head are derived and linearized to optimize the coil parameters for fast-retraction. A multibody model is applied to estimate the induced stresses on the more sensitive components and the effect of friction on the diagnostic trajectory. The mechanical stresses induced by thermal expansion on the probe head under convective heat loads is analyzed to optimize the measurement cycle. A programmable power supply is employed to energize the magnetic coil, enabling real-time retraction when overheating is detected on the probe head. These new detectors enabled simultaneous measurements of multiple FILDs in quiescent plasmas and in the presence of MHD instabilities such as toroidicity induced Alfvén eigenmodes (TAEs) and magnetic islands. Moreover, the insertion of the magnetically-driven FILD4 is rapidly scanned during plasma discharges, enabling unprecedented radially-resolved velocity-space measurements of escaping ions generated by ICRH and NBI. The light-ion beam probe technique is employed to these scans to radially resolve the internal structure of MHD instabilities. The impact of the poloidal spectrum of the applied 3D magnetic perturbations on fast-ion losses and TAEs amplitude is investigated experimentally. The hybrid kinetic-MHD MEGA code is employed to model these experiments. The plasma response to the externally applied 3D perturbations is modelled using the MEGA code for the first time. The observed TAEs are reproduced in both axisymetric and 3D equilibriums, finding a phase-space overlap of the TAE fast-ion drive and the edge resonant transport layer induced by the 3D fields.
Nuevo método de medición de geometría de la vía con un sistema embarcado en un vehículo comercial
(2021-06-07) Briales Palacios, Eduardo; Escalona Franco, José Luis; Valverde García, Juan Sebastián; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. Departamento de Matemática Aplicada II (ETSI)
Esta Tesis presenta la utilización de un conjunto de sensores inerciales, sistemas de visión artificial y un sistema de odometría para obtener las irregularidades de alta longitud de onda de la geometría de una vía ferroviaria (ancho de vía, peralte, alineación y nivelación) a partir de datos adquiridos desde un equipo compacto embarcado en un vehículo ferroviario comercial. La variedad de sensores utilizados convierte esta Tesis en un desarrollo multidisciplinar: se plantea como base la cinemática de sistemas multicuerpo para integrar los diferentes resultados de visión artificial, datos de la geometría ideal, algoritmos de fusión de sensores y un sistema de odometría preciso con el objetivo último de reconstruir la geometría de la vía. Cada vez es más frecuente encontrarse con medios de transporte sobrecargados debido al creciente número de desplazamientos de personas que se producen de manera diaria en ciertos núcleos urbanos, y en particular en las grandes ciudades, a lo largo de todo el mundo. Se tiende entonces al transporte público para descongestionar las vías principales, siendo uno de los medios de transportes urbanos más frecuentados el transporte ferroviario. Esta tendencia ocasiona que los operadores y mantenedores de instalaciones ferroviarias deban incrementar la disponibilidad de sus servicios mientras que controlan los costes de operación y mantenimiento, misión cada vez más difícil. El sistema y la metodología que se presenta en este documento busca ayudar a los operadores y mantenedores ferroviarios a reducir los costes de operación y mantenimiento mediante la aplicación de la tecnología que se desarrolla en esta Tesis a la inspección y medición de vías. Aún en la actualidad, la inspección de los carriles sigue siendo un reto. Las opciones disponibles son muy costosas (trenes laboratorio) o excesivamente invasivas, lentas al medir (carros auscultadores). Esto deriva en un número de inspecciones de la vía poco frecuente. Al no realizarse mediciones con suficiente frecuencia, es difícil elaborar modelos de evolución del daño de la vía precisos, lo que finalmente imposibilita la implementación de la gestión preventiva del mantenimiento que ha ido incrementando su popularidad en numerosas industrias en los últimos años. Metro de Sevilla permitió el uso de sus instalaciones para desarrollar diferentes experimentos para medir la longitud total de sus instalaciones (36 km de vía) y comparar los resultados del sistema embarcado (medidas propuestas) con aquellas obtenidas con un carro auscultador (medida de referencia). Una vez se realizaron estas mediciones, la comparativa entre medida propuesta y de referencia se utiliza para validar la nueva metodología mostrada en este documento. Gracias al buen acuerdo que se consigue como resultado se sientan las bases de un cambio importante en los modelos de mantenimiento ferroviario de vías actuales.
Análisis del efecto de tamaño y forma de la entalla en componentes sometidos a fatiga
(2020-09-24) Balbín Molina, José Antonio; Navarro Robles, Alfredo; Chaves Repiso, Víctor Manuel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación
Materiales sinterizados de aluminio aleado mecánicamente
(2002-09) Fuentes, José Jesús; Herrera Luque, Enrique J.; Rodríguez-Ortiz, José Antonio; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
Se ha llevado a cabo un estudio experimental encaminado a conseguir la consolidación de polvo de aluminio aleado mecánicamente (AL AM) mediante un proceso original de prensado en frío y sinterización al vacío. A este fin, se ha mejorado la comprensibilidad del polvo de AL AM por ablandamiento, conseguido por tratamiento térmico de recocido en vacío, así como su sinterabilidad, por adición de pequeñas cantidades de polvo de silicio, cobre o magnesio, respectivamente, previamente al procesado de consolidación. Los aditivos empleados facilitan la sinterización por formación de fases líquidas durante el calentamiento. Los resultados obtenidos son muy prometedores, respecto a la posibilidad de fabricar industrialmente grandes series de piezas pequeñas de este material por un procedimiento de prensado en frío y sinterización.
Wheel-rail contact force measurement. A comparison between distance laser and strain gauges measuring technology
(2019-12-13) Urda Gómez, Pedro; Escalona Franco, José Luis; Muñoz Moreno, Sergio; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
The development of this PhD thesis is focus on the wheel/rail contact force measurement on a 1 : 10 scaled railway vehicle. To that end, the author has designed and manufactured a dynamometric wheelset instrumented with several sensors for the direct measurement of forces applied on the instrumented wheel. Two di erent technologies have been used for the wheelset instrumentation: On the one hand, a set of strain gauges measure the radial strains experienced by the wheel-web when a lateral load is applied on the wheel. On the other hand, three high precision lasers have been installed on the axel that measure the lateral de ection experienced by the wheel due to the applied lateral loads. Normal contact forces are measured independently throughout the de ection experienced by the primary suspension. This is also measured with laser distance sensors. After being instrumented, the wheelset has been submitted to a calibration process. A calibration test bench where controlled loads can be applied to the wheelset has been also designed and manufactured. Finally the instrumented wheelset has been installed on the scaled vehicle and tested on a 5 inches wide scale track. The force measurements obtained in the experiments with both set of sensors have been compared with numerical results drawn from a computational model of the vehicle. A novel procedure to measure the track irregularities applied to the scaled track has been also include as part of this thesis.
Paliativo frente a la fatiga por fretting y análisis del proceso de fatiga en cordones metálicos
(2019) Erena Guardia, Diego; Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
El fallo de cables de acero es comúnmente producido por el fenómeno de la fatiga. Para analizar el fallo por fatiga en este tipo de elementos, un nuevo equipo de ensayos ha sido diseñado, fabricado y validado. Uno de los principales aspectos de este nuevo útil de ensayos, es la capacidad de aplicar al cable tanto cargas axiales como de flexión simultáneamente. Además, ambas cargas pueden ser estáticas o variables con el tiempo. El primero de los objetivos fue evitar el fallo del cable en la zona de sujeción, y de este modo producir el fallo debido únicamente a las tensiones globales producidas por las fuerzas externas aplicadas y las tensiones inducidas por el contacto entre hilos. Durante el desarrollo de este primer objetivo y tras el análisis numérico de diferentes tipos de elementos de sujeción para evitar fretting en los mismos, surge la idea de un nuevo concepto de paliativo, extensible al fenómeno de la fatiga por fretting en general. La idea básica consiste en realizar orificios debajo de las superficies en contacto y cerca de las zonas en las que se inician las grietas por fretting. Con la introducción de dichos orificios se consigue que la distribución de presiones sea menor en los bordes de contacto y también la tensión axial que provoca la iniciación de grietas. En base a ello se realiza un trabajo complementario, en el que se analiza el efecto producido por estos orificios en un par de contacto básico, como es el contacto cilíndrico. Los análisis numéricos con este tipo de geometrías producen resultados muy satisfactorios que marcan una guía para el uso de un nuevo tipo de paliativo frente al fretting. El segundo de los objetivos, y volviendo al análisis de la rotura en cables de acero, es diseñar un equipo de ensayos versátil, de forma que sea posible ensayar diferentes combinaciones de cargas, así como diferentes configuraciones de cables. El tipo de fallo esperado, será producido por una combinación de tensiones globales (axiales y de flexión) y de contacto, dependiendo fuertemente del tipo de configuración del cable ensayado y por tanto del tipo de contacto. Una vez diseñado el equipo se realiza una amplia batería de ensayos con la configuración de cables más básica de las comúnmente empleadas, un cordón de x acero inoxidable de siete hilos. El cordón ha sido sometido a diversas combinaciones de fuerzas axiales y de flexión. Una vez llevados a cabo los ensayos de fatiga, y con el objetivo de analizar las zonas de iniciación de grietas, así como su propagación y determinar el fenómeno que provoca el fallo, las superficies de fractura de los cables ensayados fueron analizadas mediante microscopia electrónica. Debido al tamaño de los hilos que conforman el cordón ensayado, la medición de tensiones y deformaciones in situ es compleja o casi imposible. Por ello y con el objetivo de conocer los campos de tensiones y deformaciones que aparecen en el cordón, se han realizado diversas simulaciones numéricas mediante dos modelos de elementos finitos de formulación implícita. Un primer modelo complejo en el que se ha modelado un cordón completo con el objetivo de reproducir fielmente los ensayos llevados a cabo y un segundo modelo simplificado realizado con el objetivo de una aplicación rápida y práctica. Por último, se han aplicado diversos métodos de predicción de vida a fatiga en función de los resultados experimentales y numéricos obtenidos. En base a ambos resultados se llega a la conclusión que, debido a la geometría de cordón empleada, y por tanto al tipo de contacto que de forma inherente aparece entre hilos, el fallo es producido debido a las tensiones globales aplicadas al cordón y no al fenómeno de fretting, que aunque también se observa en el contacto entre hilos, no es determinante. En base a estos resultados se concluye con un método simple, pero efectivo, para la predicción a fatiga de cordones de acero de siete hilos sometidos a cargas axiales y de flexión.
Análisis del shot peening como paliativo en fatiga por fretting
(2019-06-11) Martín Rodríguez, Vicente; Navarro Pintado, Carlos; Vázquez Valeo, Jesús; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
La fatiga por fretting es un tipo especial de fatiga que se produce en las superficies de contacto de uniones mecánicas tales como uniones atornilladas, uniones roblonadas, álabes de turbinas, uniones de ejes, cables metálicos trenzados o rotores de generadores. Con la intención de aumentar la vida de estos componentes bajo el efecto de la fatiga por fretting, en la industria es bastante usual aplicar el tratamiento superficial de shot peening sobre estos componentes mecánicos. Esto es debido a que durante la fatiga por fretting se producen unas altas tensiones y deformaciones en las superficies en contacto y que además presentan altos gradientes (variación muy rápida con respecto a la profundidad). Este tratamiento introduce tensiones residuales de compresión y transforma la microestructura del material en las cercanías de la superficie, además de producir un importante aumento de la rugosidad superficial. Los altos valores de tensiones y deformaciones producidos por la fatiga por fretting dan lugar a una pronta nucleación/iniciación de grietas tanto en la superficie como internamente y su posterior propagación hasta la rotura completa de la pieza. Además, se producen daños superficiales tales como el desgaste de la capa superficial y la oxidación del material. En ocasiones estas distribuciones de tensiones llegan a profundidades similares a aquellas en donde se produce la máxima tensión de compresión debida al tratamiento de shot peening. Por este motivo el shot peening es un buen paliativo de la iniciación o propagación de pequeñas grietas e incluso elimina la aparición de estas en algunas condiciones. Así, una pieza con este tratamiento puede alcanzar vidas a fatiga por fretting mucho más altas que sin él, incluso no romper. Además de estas tensiones residuales de compresión, el shot peening, tiene otras consecuencias como la alteración y modificación de las características microestructurales haciendo el que material se endurezca en la zona afectada por el shot peening. Otra de las consecuencias es la alteración de la rugosidad superficial de las probetas tratadas. Estos aspectos, que aun influenciando enormemente en el comportamiento frente a la fatiga por fretting, no se han estudiado en profundidad en la bibliografía. Por ello en esta tesis se estudia el efecto producido por el shot peening en una serie de ensayos de fatiga por fretting. Estos ensayos se hicieron con contacto cilíndrico, donde se tiene una alta concentración de tensiones en el borde de dicho contacto con un alto gradiente de tensiones en función de la profundidad. Anteriormente en el grupo de investigación al que este proyecto pertenece, se han realizado exhaustivos estudios sobre fatiga por fretting con contacto esférico y el efecto de las tensiones residuales generados por diferentes tratamientos superficiales tales como es el shot peening y el láser peening. Para estudiar el efecto causado por el tratamiento superficial de shot peening en fatiga por fretting con contacto cilíndrico se realizaron una serie de ensayos de fatiga por fretting en las que algunas probetas estaban tratadas con shot peening y otras no. El material empleado en la fabricación de las probetas para los ensayos fue el Al-7075-T651 de amplio uso en la industria aeroespacial. Se realizaron ensayos con diferentes combinaciones de cargas que crean distintos estados tensionales. De esta forma se puede ver con qué combinaciones de carga es más o menos efectivo el tratamiento de shot peening. Por otra parte, estudios previos realizados en este grupo de investigación, mostraron que ante una situación de fatiga por fretting, superficies con una cierta textura o rugosidad pueden producir mejoras sustanciales en la vida a fatiga por fretting. Para comprobar este supuesto se han realizado una serie de ensayos específicos, dos tipos de ensayos en probetas sin tensiones residuales inducidas por el shot peening donde a las probetas de uno de los tipos de ensayo se les alteraba la rugosidad superficial para reproducir la rugosidad producida por el shot peening. Otros dos tipos de ensayos eran en probetas con shot peening donde a las probetas de uno de estos tipos de ensayos se eliminaba la rugosidad por pulido. Al igual que la rugosidad, en esta tesis se estudian y cuantifican los efectos causados por la relajación de tensiones residuales, hecho que afecta a la vida a fatiga por fretting debido a que esta relajación de tensiones residuales puede llegar a alcanzar hasta un 50% según estudios anteriores. Una vez finalizados los ensayos se han analizado las superficies de fractura, grietas y huellas marcadas por los contactos en todas las probetas ensayadas. Así, se han ver los daños producidos durante un ensayo, evaluarlo y compararlo con diferentes probetas ensayadas. Todo este se ha realizado como paso previo para continuar y estudiar nuevos métodos de predicción de vida en fretting fatiga.
Monitorización de estructuras aeroespaciales y análisis de técnicas de integración de sensores de BRAGG.
(2018-12-19) Fernández Valderas, Rosario; Domínguez Abascal, Jaime; Lasagni, Fernando Adrián; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
La presente tesis doctoral tiene como objetivos el estudio y desarrollo de la tecnología de los sensores de Bragg para la monitorización estructural, evaluando sus principales limitaciones y deficiencias que impiden su aplicación en elementos reales en entonos industriales. Con este fin, se ha trabajado en diversas líneas de investigación, elaborando metodologías y proponiendo soluciones a dichos puntos débiles. La validez de las redes de Bragg para medir cargas térmicas se ha demostrado a través de numerosos ensayos, tanto estáticos como dinámicos. La correcta medida de la temperatura hace posible la monitorización del curado de estructuras de material compuesto, permitiendo el análisis y la caracterización tanto de su proceso de fabricación como de su vida en servicio. Aunque las múltiples ventajas de los FBGs son ampliamente conocidas en el ámbito industrial, su uso se encuentra restringido a aplicaciones de laboratorio bajo condiciones controladas, a consecuencia de su reducida tasa de supervivencia. Diversas soluciones se han desarrollado, permitiendo elaborar procedimientos robustos y sencillos de integración de sensores de fibra óptica en estructuras reales bajo condiciones de operación. Las mejoras y herramientas desarrolladas en las diferentes líneas se han aplicado a demostradores representativos de la industria civil y aeroespacial, campos de especial relevancia para la tecnología de las redes de Bragg, donde su implementación mejora de forma significativa los procesos actuales de monitorización estructural y de mantenimiento. Finalmente, un nuevo método de integración de sensores de Bragg en componentes metálicos se ha propuesto, el cual permite crear estructuras con sensores integrados en los puntos de interés. Dicho procedimiento es factible gracias al empleo de las tecnologías de fabricación aditiva.

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