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Spherical gear couplings are characterized by their high capacity to transfer power between rotating shafts in highly misaligned conditions. They are usually small because of space restrictions and require a high amount of longitudinal crowning, which sometimes leads to undercutting profiles. These issues have been solved recently with analytical models for the generation of tooth surfaces that consider the hob thread surface, however, they are not experimentally validated. Likewise, it has been numerically concluded that the number of teeth in contact in high misalignment conditions decreases, and thus may fail by tooth root breakage. Nevertheless, published experimental tests for such high misalignment angles are scarce. This paper presents test techniques to study highly crowned spherical gear couplings, together with a test rig design adapted to high misalignment angles. The tooth surface geometry, maximum misalignment, stiffness, and contact pattern are compared. The results demonstrate that the analytical and numerical models employed accurately represent the mechanical behavior of spherical gear couplings working at high misalignment applications.

Spherical gear couplings are commonly used mechanical components to transmit power between highly misaligned rotating shafts. For that, gear couplings are manufactured with high longitudinal crowning and are usually small due to space restrictions, with the probability to contain undercutting sections. High misalignment angles cause the number of teeth in contact to decrease drastically, resulting in the failure of the component by tooth root fatigue breakage. This paper investigates the load distribution and the tooth root stress of highly crowned spherical gear couplings working at high misalignment angles using a finite element model. Moreover, a deep understanding of the bending tooth root stresses in terms of the operating conditions is presented, which is novel for such high misalignment angles (). Results show that different mechanical behaviors are observed at low or high misalignment angles since teeth in the pivoting position lose contact. This results in a tooth root stress history change from a sinusoidal cycle to a pulsating cycle. Finally, this study shows evidence that current sizing methods are not suitable, and underlines the need for further research to determine the spherical gear coupling life to tooth root bending fatigue.

Spherical gear couplings are machine elements that enable power transmission between highly misaligned shafts. The highly crowned tooth surfaces and the presence of undercut sections, have been a matter of disagreement between existing geometry generation methods available in the scientific literature. The main reason for this, are the geometry variations which arise in the generated parts, and consequently, the effect of such variations on the contact point location and clearance distribution. In this paper the influence of the main design parameters of spherical gear couplings (namely, the crowning ratio, the pitch diameter, the pressure angle, etc.), on the geometrical properties of the gear tooth surfaces are investigated. An algorithm to calculate the maximum misalignment angle is proposed, which is one of the most crucial design parameters. It shows that the values obtained with models existing in the literature are not applicable to highly crowned spherical gear couplings. Finally, design criteria are described to help the designer choose proper spherical gear coupling tooth geometry parameters to fit in a certain space and achieve a given maximum misalignment angle without further geometrical issues (undercut or pointed teeth).

This article presents an innovative energy recovery shock absorber system for motorcycles. The shock absorber is named synchronous pulley - energy harvesting shock absorber (SP-EHSA). The SP-EHSA is the first system specifically designed to maximize the energy recovery of motorcycles without compromising their dynamic behavior. Throughout the article, the theoretical design, computer modeling, optimization, design, and testing of the system are presented. The article results in a validated computer model of the SP-EHSA shock absorber. The validation is done by manufacturing and testing a physical prototype on a test bench. A study of the energy recovery potential for different road profiles at speeds between 20 and 100 km/h was carried out, obtaining in a typical type B road at 60 km/h an estimated 19.68 W average power. Finally, the effect of energy management (i.e., battery's state of charge) on the dynamic behavior of the vehicle is analyzed.

Radial fretting is defined as the damage caused by the relative motion of a ball under a variable normal load. The conducted experimental tests proved the existence of this damage even in contacting bodies with similar ma-terials and elastic properties; however, the reviewed analytical methods do not predict damage under these conditions, and the numerical methods are time-consuming, especially when the investigation requires the analysis of several loading cases or during large number of cycles. The main objective of this work was to develop a fast analytical method to analyse radial fretting wear. For this purpose, a novel formulation for contact dis-placements under a normal variable load was built and merged to different contact mechanic formulas. For validation purposes, false brinelling in thrust bearings was used as a representative industrial example. The results were compared with a FEM model showing a relative difference under 9% and a massive reduction of the calculation time of more than 30 000 times, moreover experimental tests were carried out, showing a good agreement between the density of friction energy and the obtained fretting damage what endorse the use of this formulation for the analysis of a large number of cycles and loading cases.

Load distribution in ball screws is a representation of the ball contact stress, and it is fundamental to understanding the behavior of these machine elements. This work aims to conduct a multi-variable analysis of the load distribution in ball screws. For this purpose, a numerical tool is developed for the generation and calculation of ball screw finite element (FE) models, which has been validated against the state of the art. This tool is based on the combination of an analytical contact model and the use of high-order FE models for the analysis of the load distribution of ball screws and stands out for its accuracy (less than 1% error against high-order FE models), adaptability, versatility (models are generated with more than 20 design variables and they can be introduced as components in larger models) and efficiency (being the computational time 1.25% of that of a high-order FE models) with respect to other existing models. Many different design variables (number of start threads, pitch, contact angle, ball size, slenderness and load arrangement) are studied in order to obtain a general characterization of the morphology of the load distribution in ball screws. Among them, the most influential variables on the load distribution and therefore on the structural behavior of ball screws are, load arrangement (with ratio r variations of up to 25% on the same ball screw) and slenderness (with ratio variations of up to 13% on ball screws with two turns of difference). The two most characteristic features, the non-uniformity at a local and global level are identified, along with as the possible causes of their appearance and the consequences that they may cause.

Debido a las dimensiones de los vehículos actuales, la baja tasa de ocupación de los mismos y el aumento de la población mundial, los fabricantes de vehículos están desarrollando diseños compactos orientados a la movilidad personal (1-2 personas). Además de la reducción de espacio es requisito indispensable mantener unos valores mínimos de confort y seguridad en el vehículo. Es por ello, por lo que el presente trabajo pretende desarrollar, fabricar y testear un mecanismo de ancho de vía variable para un vehículo de tres ruedas (2 delante y 1 detrás). De esta forma, dicho mecanismo permitirá al usuario aparcar en un tercio del espacio requerido por un vehículo convencional. En primer lugar, se muestra el desarrollo del mecanismo de variación de ancho de vía del eje delantero del vehículo incluyendo suspensiones y dirección. Para asegurar el correcto funcionamiento de todos los componentes diseñados, se ha desarrollado un modelo multi-cuerpo (MBS) del vehículo de tres ruedas. En el mismo, se ha definido un caso de carga crítico para la obtención de cargas transmitidas desde el neumático hasta el chasis del vehículo. Debido a la iteración necesaria entre el mecanismo de ancho de vía y el vehículo, se ha definido una lógica de control para el mecanismo, el cual controla de forma instantánea el ancho de vía del vehículo en función de la velocidad y aceleración del vehículo. Para poder testear todos los componentes desarrollados, se ha empleado un banco de suspensiones de cuarto de vehículo, donde han sido testeadas las suspensiones, y una estructura diseñada específicamente para el testeo del mecanismo de ancho de vía, donde se han mantenido las mismas condiciones de contorno y carga que en el vehículo en cuestión.

Residual Stress (RS) pattern changes considerably depending on the width of the plates and the welding parameters, having effect on the fatigue strength. Most of the standards do not consider them and in some works, yield stress is taken as residual stressvalue. It results in a very conservative estimation of fatigue life. Authors developed recently a numerical model to predict more properly the value of RS pattern depending on the plate thickness. In a welded joint, considering the RS and alternating axial loads, the evolution of the stresses is multiaxial, becoming necessary its study. Therefore, the aim of this work is to analyse different fatigue indicator parameters (Smith-Watson-Topper, Fatemi-Socie, and Critical Plane implementation of the Basquin equation) in order to predict the fatigue behaviour of butt-weld components. For that purpose, the numerical model to predict the RS pattern in welded joint developed by this research group is used.

Due to the actual vehicle dimensions, low occupancy rates and the increase of world population, a trend to develop new vehicle concepts with smaller dimensions is seen. The objective of this trend is to reduce traffic congestion and park ability related issues in overpopulated areas. Not only footprint reduction is necessary, but also maintaining actual vehicle safety and comfort metrics is a must. Therefore, first of all, a mechanism to reduce wheel track to the third of the space required for a conventional car for low speed and parking situations is designed and developed. Once the track variation mechanism is completely defined, several suspensions and steering mechanism are analysed, concluding with a design of an unconventional front independent suspension and steering systems which are detailed in the present manuscript. By using MBS (Multi-body System) model, loads transmitted from tyre through mechanism joints to the vehicle chassis are computed. Special attention has been paid to the maximum peak loads that mechanism will suffer from road irregularities in extreme conditions. These load values are also used to evaluate the components that compose the track variation mechanism. Continuing with the actuation of the system, an electronic control strategy is created and virtually tested, with what vehicle track position and vehicle speed and acceleration conditions are instantaneously controlled and related with the wheel track variation system. Finally, the complete track width variation mechanism is manufactured, assembled and tested in a test rig.

Gas metal arc welding (GMAW) is one of the most used joining method in the industry. However, one of the main problems of this process is the generation of residual stresses which have direct impact on the fatigue life of welded components. Nevertheless, residual stress pattern prediction is complex and requires the simulation of the welding process. Currently, there are different numerical methods to predict the residual stresses generated in GMAW process, being Goldak’s method one of the most widely used model. However, the main limitation of these methods is that they require defining many parameters experimentally and, consequently, this method is not valid during design process. Alternatively, in this work, it is developed a procedure where the heat source is defined based on the welding physics for spray transfer welding. The developed procedure has been validated for a spray transfer multipass butt weld case. Results have shown good correspondence with an average deviation of 9.16 % in thermal field and 42 MPa in the final residual stress field. Thus, the developed procedure has been validated as a cost-effective alternative method to estimate residual stress pattern in spray transfer multipass welding. Furthermore, the developed method does not require any welding experimental characterization once the efficiency of the used welding machine is defined. The proposed method can be used as a valid tool to optimize the welding process in order to minimize the residual stress field and, consequently, improve the fatigue life.

En la presente tesis doctoral se estudia la deformación de la aleación de magnesio AZ31B a altas velocidades de deformación y diferentes temperaturas. En un primer apartado, se ha caracterizado el comportamiento mecánico de chapas laminadas de dicha aleación de Mg mediante ensayos de tracción uniaxial, empleando técnicas de caída de dardo y de barra Hopkinson además de los métodos convencionales de ensayo. Con el propósito de conocer los mecanismos de deformación causantes de las diferencias durante la deformación plástica, se ha analizado la microestructura y la estructura cristalográfica mediante técnicas de difracción de neutrones y EBSD. A altas velocidades de deformación, para todo el rango de temperaturas ensayado, se observa una mayor tensión de fluencia como consecuencia del aumento de maclado así como la ausencia de recristalización dinámica. En un segundo apartado, se aborda el conformado electromagnético (EMF) a diferentes temperaturas. Se constata que mediante el empleo del EMF se consigue un aumento de la conformabilidad del material estudiado. Asimismo, se desarrollan modelos de simulación numérica acoplada de los campos electromagneto-termo-mecánicos.