1,251 research outputs found

    Multiscale Modeling of Curing and Crack Propagation in Fiber-Reinforced Thermosets

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    Aufgrund ihres Leichtbaupotenzials bei relativ geringen Kosten gewinnen glasfaserverstärkte Polymere in industriellen Anwendungen zunehmend an Bedeutung. Sie verbinden die hohe Festigkeit von Glasfasern mit der Beständigkeit von z.B. duroplastischen Harzen. Bei der Verarbeitung von faserverstärkten Duroplasten kommt es zu einer chemischen Reaktion des Harzes. Die chemische Reaktion geht mit einer chemischen Schrumpfung einher. In Verbindung mit der thermischen Ausdehnung kann das Material bereits beim Herstellungsprozess beschädigt werden. Auch wenn das Komposit nicht vollständig versagt, kann es zu Mikrorissbildung kommen. Diese Schäden können die Blastbarkeit des Bauteils und damit seine Lebensdauer beeinträchtigen. Faserverstärkte Duroplaste enthalten Strukturen auf verschiedenen Längenskalen, die das Verhalten des Gesamtbauteils beeinflussen und daher für eine genaue Vorhersage der Rissbildung berücksichtigt werden müssen. Das Verständnis der Mechanismen der Rissbildung auf den verschiedenen Längenskalaen ist daher von großem Interesse. Auf der Grundlage von Molekulardynamiksimulationen wird ein Harzsystem zusammen mit einer Faseroberfläche und einer Schlichte auf der Nanoskala betrachtet und ein systematisches Verfahren für die Entwicklung eines ausgehärteten Systems vorgestellt. Eine zweistufige Reaktion, eine Polyurethanreaktion und eine radikale Polymerisation, wird auf der Grundlage eines etablierten Ansatzes modelliert. Anhand des fertig ausgehärteten Systems werden Auswertungen über gemittelte Größen und entlang der Normalenrichtung der Faseroberfläche durchgeführt, was eine räumliche Analyse der Faser-Schlichtharz-Grenzfläche erlaubt. Auf der Mikrolängenskala werden die einzelnen Fasern räumlich aufgelöst. Mit Hilfe der Kontinuumsmechanik und der Phasenfeldmethode wird das Versagen während des Aushärtungsprozesses auf dieser Längenskala untersucht. In der Materialwissenschaft wird die Phasenfeldmethode häufig zur Modellierung der Rissausbreitung verwendet. Sie ist in der Lage, das komplexe Bruchverhalten zu beschreiben und zeigt eine gute Übereinstimmung mit analytischen Lösungen. Dennoch sind die meisten Modelle auf homogene Systeme beschränkt, und nur wenige Ansätze für heterogene Systeme existieren. Es werden bestehende Modelle diskutiert und ein neues Modell für heterogene Systeme abgeleitet, das auf einem etablierten Phasenfeldansatz zur Rissausbreitung basiert. Das neue Modell mit mehreren Rissordnungsparametern ist in der Lage, quantitatives Risswachstum vorherzusagen, wo die etablierten Modelle eine analytische Lösung nicht reproduzieren können. Darüber hinaus wird ein verbessertes Homogenisierungsschema, das auf der mechanischen Sprungbedingung basiert, auf das neuartige Modell angewandt, was zu einer Verbesserung der Rissvorhersage selbst bei unterschiedlichen Steifigkeiten und Risswiderständen der betrachteten Materialien führt. Zudem wird zur Erzeugung digitaler Mikrostrukturen, die für Aushärtungssimulationen im Mikrobereich verwendet werden, ein Generator für gekrümmte Faserstrukturen eingeführt. Anschließend wird die Verteilung mechanischer und thermischer Größen für verschiedene Abstraktionsebenen der realen Mikrostruktur sowie für verschiedene Faservolumenanteile verglichen. Schließlich wird das neue Rissausbreitungsmodell mit dem Aushärtungsmodell kombiniert, was die Vorhersage der Mikrorissbildung während des Aushärtungsprozesses von glasfaserverstärktem UPPH-Harz ermöglicht

    Biomedical and Pharmacological Applications of Marine Collagen

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    Biomimetic polymers and materials have been widely used in a variety of biomedical and pharmacological applications. Particularly, collagen-based biomaterials have been extensively applied in various biomedical fields, such as scaffolds in tissue engineering. However, there are many challenges associated with the use of mammalian collagen, including the issues of religious constrains, allergic or autoimmune reactions, and the spread of animal diseases. Over the past few decades, marine collagen (MC) has emerged as a promising biomaterial for biomedical and pharmacological applications. Marine organisms are a rich source of structurally novel and biologically active compounds, and to date, many biological components have been isolated from various marine resources. MC offers advantages over mammalian collagen due to its water solubility, low immunogenicity, safety, biocompatibility, antimicrobial activity, functionality, and low production costs. Due to its characteristics and physicobiochemical properties, it has tremendous potential for use as a scaffold biomaterial in tissue engineering and regenerative medicine, in drug delivery systems, and as a therapeutic. In this Special Issue, we encourage submissions related to the recent developments, advancements, trends, challenges, and future perspectives in this new research field. We expect to receive contributions from different areas of multidisciplinary research, including—but not restricted to—extraction, purification, characterization, fabrication, and experimentation of MC, with a particular focus on their biotechnological, biomedical and pharmacological uses

    Mechanical characterization, constitutive modeling and applications of ultra-soft magnetorheological elastomers

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    Mención Internacional en el título de doctorSmart materials are bringing sweeping changes in the way humans interact with engineering devices. A myriad of state-of-the-art applications are based on novel ways to actuate on structures that respond under different types of stimuli. Among them, materials that respond to magnetic fields allow to remotely modify their mechanical properties and macroscopic shape. Ultra-soft magnetorheological elastomers (MREs) are composed of a highly stretchable soft elastomeric matrix in the order of 1 kPa and magnetic particles embedded in it. This combination allows large deformations with small external actuations. The type of the magnetic particles plays a crucial role as it defines the reversibility or remanence of the material magnetization. According to the fillers used, MREs are referred to as soft-magnetic magnetorheological elastomers (sMREs) and hard-magnetic magnetorheological elastomers (hMREs). sMREs exhibit strong changes in their mechanical properties when an external magnetic field is applied, whereas hMREs allow sustained magnetic effects along time and complex shape-morphing capabilities. In this regard, end-of-pipe applications of MREs in the literature are based on two major characteristics: the modification of their mechanical properties and macrostructural shape changes. For instance, smart actuators, sensors and soft robots for bioengineering applications are remotely actuated to perform functional deformations and autonomous locomotion. In addition, hMREs have been used for industrial applications, such as damping systems and electrical machines. From the analysis of the current state of the art, we identified some impediments to advance in certain research fields that may be overcome with new solutions based on ultrasoft MREs. On the mechanobiology area, we found no available experimental methodologies to transmit complex and dynamic heterogeneous strain patterns to biological systems in a reversible manner. To remedy this shortcoming, this doctoral research proposes a new mechanobiology experimental setup based on responsive ultra-soft MRE biological substrates. Such an endeavor requires deeper insights into the magneto-viscoelastic and microstructural mechanisms of ultra-soft MREs. In addition, there is still a lack of guidance for the selection of the magnetic fillers to be used for MREs and the final properties provided to the structure. Eventually, the great advances on both sMREs and hMREs to date pose a timely question on whether the combination of both types of particles in a hybrid MRE may optimize the multifunctional response of these active structures. To overcome these roadblocks, this thesis provides an extensive and comprehensive experimental characterization of ultra-soft sMREs, hMREs and hybrid MREs. The experimental methodology uncovers magneto-mechanical rate dependences under numerous loading and manufacturing conditions. Then, a set of modeling frameworks allows to delve into such mechanisms and develop three ground-breaking applications. Therefore, the thesis has lead to three main contributions. First and motivated on mechanobiology research, a computational framework guides a sMRE substrate to transmit complex strain patterns in vitro to biological systems. Second, we demonstrate the ability of remanent magnetic fields in hMREs to arrest cracks propagations and improve fracture toughness. Finally, the combination of soft- and hard-magnetic particles is proved to enhance the magnetorheological and magnetostrictive effects, providing promising results for soft robotics.Los materiales inteligentes están generando cambios radicales en la forma que los humanos interactúan con dispositivos ingenieriles. Distintas aplicaciones punteras se basan en formas novedosas de actuar sobre materiales que responden a diferentes estímulos. Entre ellos, las estructuras que responden a campos magnéticos permiten la modificación de manera remota tanto de sus propiedades mecánicas como de su forma. Los elastómeros magnetorreológicos (MREs) ultra blandos están compuestos por una matriz elastomérica con gran ductilidad y una rigidez en torno a 1 kPa, reforzada con partículas magnéticas. Esta combinación permite inducir grandes deformaciones en el material mediante la aplicación de campos magnéticos pequeños. La naturaleza de las partículas magnéticas define la reversibilidad o remanencia de la magnetización del material compuesto. De esta manera, según el tipo de partículas que contengan, los MREs pueden presentar magnetización débil (sMRE) o magnetización fuerte (hMRE). Los sMREs experimentan grandes cambios en sus propiedades mecánicas al aplicar un campo magnético externo, mientras que los hMREs permiten efectos magneto-mecánicos sostenidos a lo largo del tiempo, así como programar cambios de forma complejos. En este sentido, las aplicaciones de los MREs se basan en dos características principales: la modificación de sus propiedades mecánicas y los cambios de forma macroestructurales. Por ejemplo, los campos magnéticos pueden emplearse para inducir deformaciones funcionales en actuadores y sensores inteligentes, o en robótica blanda para bioingeniería. Los hMREs también se han aplicado en el ámbito industrial en sistemas de amortiguación y máquinas eléctricas. A partir del análisis del estado del arte, se identifican algunas limitaciones que impiden el avance en ciertos campos de investigación y que podrían resolverse con nuevas soluciones basadas en MREs ultra blandos. En el área de la mecanobiología, no existen metodologías experimentales para transmitir patrones de deformación complejos y dinámicos a sistemas biológicos de manera reversible. En esta investigación doctoral se propone una configuración experimental novedosa basada en sustratos biológicos fabricados con MREs ultra blandos. Dicha solución requiere la identificación de los mecanismos magneto-viscoelásticos y microestructurales de estos materiales, según el tipo de partículas magnéticas, y las consiguientes propiedades macroscópicas del material. Además, investigaciones recientes en sMREs y hMREs plantean la pregunta sobre si la combinación de distintos tipos de partículas magnéticas en un MRE híbrido puede optimizar su respuesta multifuncional. Para superar estos obstáculos, la presente tesis proporciona una caracterización experimental completa de sMREs, hMREs y MREs híbridos ultra blandos. Estos resultados muestran las dependencias del comportamiento multifuncional del material con la velocidad de aplicación de cargas magneto-mecánicas. El desarrollo de un conjunto de modelos teórico-computacionales permite profundizar en dichos mecanismos y desarrollar aplicaciones innovadoras. De este modo, la tesis doctoral ha dado lugar a tres bloques de aportaciones principales. En primer lugar, este trabajo proporciona un marco computacional para guiar el diseño de sustratos basados en sMREs para transmitir patrones de deformación complejos in vitro a sistemas biológicos. En segundo lugar, se demuestra la capacidad de los campos magnéticos remanentes en los hMRE para detener la propagación de grietas y mejorar la tenacidad a la fractura. Finalmente, se establece que la combinación de partículas magnéticas de magnetización débil y fuerte mejora el efecto magnetorreológico y magnetoestrictivo, abriendo nuevas posibilidades para el diseño de robots blandos.I want to acknowledge the support from the Ministerio de Ciencia, Innovación y Universidades, Spain (FPU19/03874), and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 947723, project: 4D-BIOMAP).Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial por la Universidad Carlos III de MadridPresidente: Ramón Eulalio Zaera Polo.- Secretario: Abdón Pena Francesch.- Vocal: Laura de Lorenzi

    Nonlinear and Linearized Analysis of Vibrations of Loaded Anisotropic Beam/Plate/Shell Structures

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    L'abstract è presente nell'allegato / the abstract is in the attachmen

    A machine learning-based viscoelastic–viscoplastic model for epoxy nanocomposites with moisture content

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    In this work, we propose a deep learning (DL)-based constitutive model for investigating the cyclic viscoelastic-viscoplastic-damage behavior of nanoparticle/epoxy nanocomposites with moisture content. For this, a long short-term memory network is trained using a combined framework of a sampling technique and a perturbation method. The training framework, along with the training data generated by an experimentally validated viscoelastic-viscoplastic model, enables the DL model to accurately capture the rate-dependent stress–strain relationship and consistent tangent moduli. In addition, the DL-based constitutive model is implemented into finite element analysis. Finite element simulations are performed to study the effect of load rate and moisture content on the force–displacement response of nanoparticle/epoxy samples. Numerical examples show that the computational efficiency of the DL model depends on the loading condition and is significantly higher than the conventional constitutive model. Furthermore, comparing numerical results and experimental data demonstrates good agreement with different nanoparticle and moisture contents

    Additive Manufacturing and Physicomechanical Characteristics of PEGDA Hydrogels: Recent Advances and Perspective for Tissue Engineering

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    In this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices

    Micromechanical modelling of ductile damage: from single crystals to polycrystals

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    Mención Internacional en el título de doctorFor more than six decades, improving the strength and ductility of industrially important materials has been in the focus of research. Besides economic reasons, safety issues have driven research and development in this field. For the purpose of safety, it is imperative to understand the failure behaviour of ductile materials, as ductile materials are commonly used in protective structures. It is well known that major failure mode for ductile materials is through void nucleation, growth and void coalescence. In structural ductile materials voids nucleate at inclusions and second-phase particles by decohesion of the particle–matrix interface or by particle cracking. The presence of voids can have drastic implications at the macroscopic level including strong material softening and incipient fracture. Significant efforts have been made over the years to describe the plastic behavior of isotropic and anisotropic ductile materials. Numerous investigations, in the last decades, have been dedicated to the study of ductile failure, leading to a deeper knowledge on the factors influencing the ductile process. This doctoral thesis contributes to the understanding of the key role played by material anisotropy and stress state on the growth of voids in single crystals, bi-crystals and polycrystals using numerical and experimental methods. Using a numerical approach, void growth and morphology evolution in fcc single crystals and bi-crystals are investigated using crystal plasticity finite element method. For that purpose, representative volume element of single crystals and bi-crystals are considered in the analysis. Fully periodic boundary conditions are prescribed in the representative volume element and macroscopic stress triaxiality and Lode parameter are kept constant during the whole deformation process. Simulations are performed to study the implications of triaxiality, Lode parameter and crystallographic orientation on slip mechanism, hardening and hence void evolution. In the bi-crystal case, a void at the grain boundary is considered in the analysis. Grain boundary is assumed initially perpendicular/coaxial with the straight sides of the cell. Three different pairs of crystal orientations characterized as hard-hard, soft-soft and soft-hard has been employed for modelling the mechanical response of the bi-crystal. The impact of void presence and its growth on the heterogeneity of lattice rotation and resulting grain fragmentation in neighbouring areas is analysed and discussed. On the other hand and using an experimental approach, void growth behaviour in pure Aluminium polycrystals with pre-drilled holes are investigated in this work. By varying the hole diameter and position of the holes, three different types of specimens are defined and considered for investigation. Using in-situ tensile test coupled with scanning electron microscope, uni axial tensile tests are performed at constant low strain rate. The specimens are analysed with the help of EBSD, DIC and high resolution SEM images. Interrelation between hole diameter, distance between holes, local orientation of the grains and grain size on void growth and final failure of the material are analysed and discussed.The research leading to the results reported in this doctoral thesis has received funding from the European Union's Horizon2020 Programme (Excellent Science, Marie Skłodowska-Curie Actions) under REA grant agreement 675602 (Project OUTCOME).Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial por la Universidad Carlos III de MadridPresidente: Francisco Javier Llorca Martínez.- Secretario: Kim Lau Nielsen .- Vocal: Stanislaw Stupkiewic

    Additive manufacturing and physicomechanical characteristics of PEGDA hydrogels: recent advances and perspective for tissue engineering

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    In this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices

    Synthesis of Polymer/Graphene Oxide Nanocomposites via Aqueous Emulsion-Based Approaches and Evaluation of Their Properties

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    Graphene-based polymeric nanocomposites have attracted great interest due to significant property enhancement, and have been extensively studied and developed for various advanced applications. However, the synthesis of graphene-based polymeric nanocomposites is usually associated with significant filler aggregation, which might significantly affect the final properties of nanocomposite materials. Among graphene-based nanomaterials, graphene oxide (GO), which comprises oxygen-containing functional groups in the structure, offers a straightforward and feasible approach to fabricating graphene-based polymeric nanocomposites. Moreover, GO can be further reduced to its oxidized state called reduced graphene oxide (rGO) to impart electrical conductivity. In this thesis, facile and eco-friendly strategies, namely miniemulsion polymerization and physical mixing, have been employed to prepare colloidally stable waterborne polymer/GO latexes. The synthesized polymer/GO latexes were drop-cast on substrates and exhibited film formation at ambient temperature before thermal treatment to obtain electrically conductive nanocomposite films. Particularly, the influences of three different factors - polymer matrices, in situ surfactants and high GO concentrations - have been systematically investigated. Firstly, polymer matrices comprising vinyl monomers of low polarity resulted in higher colloidal stability polymer latexes and higher electrical conductivity of the resulting nanocomposite films. Secondly, droplet nucleation was the primary mechanism in the miniemulsion polymerization of polymer/GO nanocomposites using in situ surfactants. Compared to SDS systems, nanocomposite films comprising in situ surfactants showed significantly lower electrical conductivity due to the inhibition of the formation of continuous conductive pathways. Interestingly, higher concentrations of in situ surfactants had less or no effect on the mechanical properties of nanocomposite films. Lastly, higher GO concentrations were successfully exploited to prepare polymer/GO nanocomposites via both miniemulsion polymerization and physical mixing method. Although higher GO loadings led to lower monomer conversion, they strongly influenced the intrinsic properties of the nanocomposite films. The obtained polymer/(r)GO nanocomposite films have shown promising enhancements in properties, which have potential for various applications, especially electrically conductive coatings
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