Nuevas metodologías docentes para la enseñanza de estructuras aeronáuticas.

La asignatura “Estructuras Aeronáuticas” está orientada a completar los conocimientos del análisis de estructuras del futuro ingeniero aeronáutico. La organización y programación de la asignatura está pensada para transmitir los conocimientos necesarios para el cálculo de estructuras laminares mediante métodos clásicos y modernos, como el basado en el Análisis con Elementos Finitos (AEF), de manera que el alumno posea una perspectiva amplia de la problemática asociada al diseño de estructuras laminares como las que integran una aeronave. Ello se lleva a cabo mediante clases teóricas, clases de problemas, clases prácticas de estructuras por ordenador y trabajos prácticos. En este trabajo se presentan nuevas metodologías docentes implementadas e introducidas en el esquema docente de dicha asignatura con objeto de satisfacer las líneas prioritarias del Plan Propio de la Universidad de Sevilla sobre metodologías docentes. De esta forma se llevan a cabo diferentes frentes de actuación: estudio y experimentación de nuevas metodologías didácticas como la enseñanza virtual, usando plataformas virtuales tipo WebCT, la elaboración de clases por transparencias PowerPoint y animaciones a partir de material específico, y la promoción del trabajo en equipo mediante la realización de un proyecto en grupo de AEF de un ala de una aeronave de recreo. El modelado mediante elementos finitos se realizará empleando el software comercial NASTRAN ® y PATRAN ® , de extensa aplicación en el sector aeronáutico

Influence of micromechanics in composite panels buckling loads

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.In-plane compression loads may cause buckling of fiber-reinforced composite panels. An accurate knowledge of these critical buckling loads is essential for structural design. In all cases of buckling of panels, critical loads increases with the increase in the thickness of the panel, however, more economical solutions can be obtained by keeping the thickness of the plate as small as possible and increasing the stability by considering micromechanical aspect such as: fiber orientation relative to axial direction, fiber aspect ratio or fiber volume fraction. This paper presents some parametric studies to study the influence of micromechanics in the critical buckling load of fiber-reinforced plates and curved panels

Innovación y mejora docente en el ámbito de la enseñanza de estructuras metálicas.

La asignatura “Estructuras Metálicas” está orientada a completar los conocimientos del análisis de estructuras del futuro ingeniero industrial con su aplicación práctica al diseño de estructuras metálicas. La organización y programación de la asignatura está pensada para transmitir los conocimientos necesarios para el cálculo de elementos estructurales simples, de manera que el alumno posea una perspectiva amplia de la problemática asociada al diseño de estructuras metálicas complejas. Ello se lleva a cabo mediante clases teóricas, clases de problemas, clases prácticas de estructuras por ordenador, prácticas de laboratorio, y trabajos prácticos. Este trabajo presenta nuevas metodologías docentes, de acuerdo con las líneas prioritarias del Plan Propio de la Universidad de Sevilla, para mejorar los diferentes frentes de docencia que la asignatura posee. Para ello se profundiza en el estudio y experimentación de nuevas metodologías didácticas como la enseñanza virtual, usando plataformas virtuales tipo WebCT, la elaboración de clases por transparencias PowerPoint y animaciones numéricas realizadas mediante elementos finitos, todo ello basadas en la normativa vigente actual y bibliografía referente actualizada. Además se fomenta el trabajo en equipo mediante la realización de prácticas de campo y un proyecto en grupo, y se desarrollan nuevas prácticas de laboratorio y actividades de manera que el alumno contemple la visión práctica de los conocimientos adquiridos

Formulación numérica de la interacción mecánica entre superficies de sólidos 3d

En líneas generales, los temas que aborda la Tesis se reparten por capítulos de la siguiente forma: ... ily: 'Times New Roman','serif'">En el Capítulo 2 se realiza la formulación fuerte del problema de contacto y rodadura, a partir de la definición del

Subsurface stress evolution under orthotropic wear and frictional contact conditions

This work presents a computational framework to study the evolution of the subsurface stresses in 3D solids under orthotropic frictional contact and wear conditions. The formulation is based on the influence coefficients methodology to relate the discrete elastic response (i.e., displacements and stresses) to the sampled excitation (i.e., surface contact tractions). The proposed methodology is validated by solving several benchmark problems and is applied to analyze how the subsurface stress distribution (i.e. maximum value and its location) – and its evolution – caused by orthotropic wear conditions are clearly affected not only by the considered wear problems (i.e., sliding wear or fretting wear) but also by the friction coefficient values and the sliding direction angle — relative to the tribological axes. Several numerical examples are presented to show the importance of these last two aspects when orthotropic wear conditions are considered. In other case, we could over- or underestimate the maximum values of the subsurface stresses during the wear process

Subsurface stress evolution under orthotropic wear and frictional contact conditions

This work presents a computational framework to study the evolution of the subsurface stresses in 3D solids under orthotropic frictional contact and wear conditions. The formulation is based on the influence coefficients methodology to relate the discrete elastic response (i.e., displacements and stresses) to the sampled excitation (i.e., surface contact tractions). The proposed methodology is validated by solving several benchmark problems and is applied to analyze how the subsurface stress distribution (i.e. maximum value and its location) – and its evolution – caused by orthotropic wear conditions are clearly affected not only by the considered wear problems (i.e., sliding wear or fretting wear) but also by the friction coefficient values and the sliding direction angle — relative to the tribological axes. Several numerical examples are presented to show the importance of these last two aspects when orthotropic wear conditions are considered. In other case, we could over- or underestimate the maximum values of the subsurface stresses during the wear process

Wear and Subsurface Stress Evolution in a Half-Space under Cyclic Flat-Punch Indentation

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Wear is a tremendously important phenomenon, which takes place on the surfaces of two solids in contact under cyclic loads and constitutes one of the most-significant ways of failure for mechanical elements. However, it is not the only source of failure in contacting solids. The subsurface stresses should also be considered, due to the fatigue and crack initiation problems. Nevertheless, these stresses (i.e., their maximum values and distributions) evolve with the solids’ surface wear (i.e., with the load cycles) and also depend on the friction intensity. Therefore, their evolution should be properly computed to predict failures in mechanical elements under wear conditions. This work focused on the study of the evolution of the surface wear and the subsurface stress distributions generated—in an elastic half-space—by a cylindrical flat-ended punch, under cyclic indentation loading (i.e., radial fretting wear conditions). Based on a numerical scheme recently presented by the authors, this is the first time that, for this contact problem, the surface wear and subsurface stress distribution (i.e., maximum value and its location)—and its evolution—were simultaneously analyzed when orthotropic friction and fretting wear conditions were considered. The studies presented in this work were developed for purely elastic contact assumptions

CNT-polymer nanocomposites under frictional contact conditions

The unique intrinsic physical properties of Carbon NanoTubes (CNTs) suggest that they are ideal fillers for high-performance composites. Although some experimental studies have revealed the potential of these nanoparticles to tailor the tribological properties of polymer-based composites, the number of theoretical studies on the characterization of their frictional behavior is still very low. This paper is aimed at filling this lacuna by addressing the theoretical analysis of the indentation response of CNT-polymer nanocomposites. To do so, it is first necessary to compute the overall mechanical properties of CNT-polymer composites. Secondly, these properties must be used to evaluate the macroscopic indentation response of the composites. In this work, an extended Mori-Tanaka approach is used to extract the constitutive properties of CNT-polymer nanocomposites. On the basis of ad hoc Eshelby's tensors accounting for particular wavy filler geometries, along with a two-parameter agglomeration model, the homogenization process is performed considering the coupled effect of fillers' waviness and agglomeration. Afterward, a 3D boundary element formulation for contact modeling is applied to study the indentation response of these nanocomposites. The main objective of this paper focuses on analysing the influence of micromechanical features such as fiber content, orientation, waviness, and dispersion on the indentation response of CNT-polymer nanocomposites. Detailed parametric analyses are presented to characterize this phenomenon under frictional contact conditions. The numerical results demonstrate that fillers' waviness and agglomeration have a coupled detrimental effect on the macroscopic response of CNT-reinforced composites.Ministerio de Ciencia e Innovación DPI2014-53947-RMinisterio de Ciencia e Innovación DPI2017-89162-

MWCNT/epoxy strip-like sensors for buckling detection in beam-like structures

Buckling of slender structures constitutes a hazardous failure mechanism that can yield partial or total collapses. Nonetheless, given that buckling failure is characterized by a highly non-linear and sudden loss of stability, most off-the-shelf monitoring systems fail to detect buckling and very few research works in the literature can be found in this regard. Recent advances in the field of Nanotechnology have fostered the development of innovative composite materials with multifunctional properties, offering vast possibilities in the field of Structural Health Monitoring. Along these lines, the present work proposes a novel concept of smart beams for buckling detection applications. This consists of the deployment of carbon nanotube-reinforced epoxy strip-like sensors on the upper and bottom faces of a beam-like structure. Carbon nanotube-reinforced composites exhibit strain self-sensing capabilities, that is to say, these composites provide measurable variations in their electrical properties under the action of mechanical strains. In this way, the proposed sensing strips not only act as mechanical reinforcements, but also confer self-diagnostic properties to the system. The failure detection principle of the proposed smart beams consists of the assessment of the bending-induced variations of the normal strains during buckling. To do so, the electrical resistance of the sensing strips is continuously monitored through a two-probe resistivity measurement scheme. The present research furnishes detailed numerical parametric analyses to investigate the effectiveness of the proposed smart beams to detect buckling under uniaxially compression, as well as to evaluate the influence of design parameters such as filler volume fraction, boundary conditions and electrodes layouts. The macroscopic behaviour of the smart beams is simulated by a micromechanics-based piezoresistivity model and a multiphysics finite element code. The numerical results demonstrate that the buckling failure can be tracked through sudden disturbances in the electrical output of the smart strips.Ministerio de Economía y Competitividad DPI2014-53947-RMinisterio de Economía y Competitividad DPI2017-89162-

Bending and free vibration analysis of functionally graded graphene vs. carbon nanotube reinforced composite plates

Carbon-based nanomaterials have drawn the attention of a large section of the scientific community in recent years. Most research has focused on carbon nanotubes after some experimental studies reported outstanding enhancements of the mechanical properties of polymeric matrices doped with small filler concentrations. Nevertheless, some limiting factors such as high manufacturing cost and difficulty in obtaining adequate uniform dispersions still remain an obstacle to the extensive manufacturing of these composites. Conversely, recent investigations demonstrate the superior properties of graphene, as well as better dispersion and relatively low manufacturing cost. Although these recent findings have begun to turn the attention towards graphene, the number of publications dealing with the theoretical analysis of graphene-reinforced structural elements is rather scant. In this context, the present work reports the bending and vibrational behavior of functionally graded graphene- and carbon nanotube-reinforced composite flat plates. The macroscopic elastic moduli of the composites are computed by means of the Mori–Tanaka model. The results demonstrate superior load bearing capacity of graphene-reinforced composite plates for both fully aligned and randomly oriented filler configurations. In addition, defects in the microstructure stemming from agglomeration and restacking of graphene sheets into graphite platelets are also analyzed.Ministerio de Economía y Competitividad DPI2014-53947-RJunta de Andalucía P12-TEP-254