Rheology and Processing of Polymers

This book covers the latest developments in the field of rheology and polymer processing, highlighting cutting-edge research focusing on the processing of advanced polymers and their composites. It demonstrates that the field of rheology and polymer processing is still gaining increased attention. Presented within are cutting-edge research results and the latest developments in the field of polymer science and engineering, innovations in the processing and characterization of biopolymers and polymer-based products, polymer physics, composites, modeling and simulations, and rheology

Structural analysis and multidisciplinary design of flexible fluid loaded composite canard

Mechanical performance of a composite canard subject to static aerodynamic loads was numerically studied in the present research. The canard was modeled as a symmetrically laminated curved panel, consisting of 8 plies of T300/5208 graphite/epoxy composite laminate. Modeling of this structure-fluid interaction system involves the coupling of two formulations: the solid classically treated in FEM formulation, and the fluid described by potential panel method in CFD. A structure-fluid iterative loop was implemented to simulate the relationship between the deformed aircraft wing and aerodynamic load. The outcome of the structural analysis indicated that the ply orientation have a significant effect on the mechanical performance of the composite laminates such that various design objectives can be achieved just by selecting the proper arrangement of ply orientation and thickness. Three numerical optimization techniques were applied respectively in the structural optimization design which aims at achieving the best structural performance and material efficiency while satisfying certain constraints. Gradient-based CONMIN converged quickly but only provided local optimum values. Probabilistic algorithm GA was capable of achieving the global/near-global optimums but the searching process was time-consuming. HYBRID, an automated hybridization process which combined GA and CONMIN together, has been implemented so that a single run of the algorithm gives a global optimum at reasonable computational cost. A structurally optimized design of the composite canard with lighter weight and higher stiffness has been obtained. A morphing design was performed on this structurally optimized composite panel to improve its maneuverability. An advanced design of composite canard with high structural efficiency and good maneuverability has been obtained by adjusting the ply angles. The strain energy of the host structure decreased which helps reduce the mechanical energy loss and improve the performance of the embedded or bonded actuators/sensors. The improved mechanical performance of the advanced design indicates that the adaptive laminated composite structures enhance the possibility of achieving a multi-functional structure for high performance structural applications

Biofabrication of Electrospun Scaffolds for the Regeneration of Tendons and Ligaments

Tendon and ligament tissue regeneration and replacement are complex since scaffolds need to guarantee an adequate hierarchical structured morphology, and non-linear mechanical properties. Moreover, to guide the cells\u2019 proliferation and tissue re-growth, scaffolds must provide a fibrous texture mimicking the typical of the arrangement of the collagen in the extracellular matrix of these tissues. Among the different techniques to produce scaffolds, electrospinning is one of the most promising, thanks to its ability to produce fibers of nanometric size. This manuscript aims to provide an overview to researchers approaching the field of repair and regeneration of tendons and ligaments. To clarify the general requirements of electrospun scaffolds, the first part of this manuscript presents a general overview concerning tendons\u2019 and ligaments\u2019 structure and mechanical properties. The different types of polymers, blends and particles most frequently used for tendon and ligament tissue engineering are summarized. Furthermore, the focus of the review is on describing the different possible electrospinning setups and processes to obtain different nanofibrous structures, such as mats, bundles, yarns and more complex hierarchical assemblies. Finally, an overview concerning how these technologies are exploited to produce electrospun scaffolds for tendon and ligament tissue applications is reported together with the main findings and outcomes

Development of biofunctionalized tubular scaffolds for vascular tissue engineering applications

Dissertação de mestrado integrado em Engenharia Biomédica (área de especialização em Biomateriais, Reabilitação e Biomecânica)One of the major problems related to small-diameter blood vessels replacement is the lack of vascular grafts with suitable mechanical and biological properties. Although there are synthetic vascular grafts in clinical use, these substitutes present thrombogenic behaviour and are too stiff compared to native vessels. Rapid endothelialization and matched mechanical properties are important functional requirements that vascular grafts should accomplish. Herein, an electrospun tubular fibrous (eTF) scaffold was fabricated and functionalized to immobilize tropoelastin at the luminal surface, providing a biomimetic environment to enhance endothelialization. The morphology was assessed by scanning electron microscopy, the effectiveness of surface functionalization by NH2 groups quantification and surface charge measurements, and the mechanical properties by uniaxial tensile tests. Tropoelastin was immobilized at 20 μg/mL by its -NH2 functional groups on activated scaffolds, as well as by its -COOH functional groups on aminolysed scaffolds, in an attempt to expose different conformations of tropoelastin for cell binding. The amount of immobilized tropoelastin on both substrates was quantified by microBCA assay. These constructs were cultured with a cell line of human umbilical vein endothelial cells (HUVECs) for 7 days, to study the endothelialization of eTF scaffolds by evaluating their metabolic activity, proliferation, total protein synthesis, VEGF secretion, as well as cell morphology and phenotype maintenance. Our experimental characterization demonstrated that the eTF scaffolds have a thickness of 240.85 ± 46.91 μm and their luminal surface was 33.55 % porous mix of micro to submicro fibers diameters, pore sizes less than 23 μm and pore areas up to 70 μm2. The eTF scaffolds were successfully functionalized by the insertion of 0.5 ± 0.04 nmol/mg of NH2 groups at their surface and confirmed by the differences observed in surface charge. Untreated, activated and aminolysed scaffolds supported higher stresses and strains in axial direction rather than in radial direction. These values are compatible to those of native blood vessels. The exposure of tropoelastin -COOH groups promoted endothelial cells metabolic activity and growth, whereas when exposed its -NH2 groups a significant influence on protein synthesis was observed. Additionally, eTF scaffolds promoted phenotype maintenance and endothelial cell coverage just after 7 days of culture. Altogether, the results confirm that biofunctional eTF scaffolds are suitable for vascular application since they presented adequate mechanical properties and a rapid endothelialization.Um dos maiores problemas associados à substituição de vasos sanguíneos de pequeno diâmetro é a insuficiência de enxertos vasculares com propriedades mecânicas e biológicas adequadas. Embora existam enxertos vasculares sintéticos na prática clínica, estes substitutos apresentam trombogenicidade e são demasiado rígidos comparativamente aos vasos sanguíneos nativos. Uma rápida endotelização e propriedades mecânicas semelhantes aos vasos sanguíneos humanos são requisitos essenciais que um excerto vascular deve possuir. Neste trabalho, estruturas tubulares fibrosas foram produzidas por electrospinning (eTF scaffolds) e funcionalizadas para imobilizar tropoelastina na superfície interna, proporcionando um ambiente biomimético para promover a endotelização. A morfologia foi analisada por microscopia eletrónica de varrimento (SEM), a eficiência da funcionalização da superfície pela quantificação dos grupos amina (-NH2) e pela carga de superfície, e as propriedades mecânicas foram analisadas por testes uniaxiais à tração. A tropoelastina foi imobilizada a uma concentração de 20 μg/mL através dos seus grupos -NH2 nos eTF scaffolds activados, bem como pelos seus grupos carboxílicos (-COOH) nos scaffolds aminolisados, de forma a expor diferentes conformações para a ligação com as células. A quantidade de tropoelastina imobilizada em ambos os substratos foi quantificada através do método microBCA. Por último, os eTF scaffolds foram semeados com uma linha celular de células endoteliais da veia umbilical humana durante 7 dias para estudar a endotelização. Desta forma, a atividade metabólica, a proliferação celular, a síntese proteica e de VEGF, bem como a morfologia celular e a manutenção do fenótipo dos eTF scaffolds foram investigadas. Os resultados experimentais demonstraram que os eTF scaffolds possuem uma espessura de 240.85 ± 46.91 μm e uma superfície interna 33.55% porosa com diâmetros de fibras na ordem do micro ao submicro, tamanhos de poros inferiores a 23 μm e áreas de poros até 70 μm2. Os eTF scaffolds foram efetivamente funcionalizados através da inserção de 0.5 ± 0.04 nmol de grupos NH2 na superfície e pelas diferenças observadas na carga de superfície. Os eTF scaffolds não tratados, activados e aminolisados suportaram tensões e elongamentos mais elevados na direção axial do que na radial. Estes resultados obtidos são compatíveis com os valores reportados para os vasos sanguíneos nativos. A exposição dos grupos -COOH da tropoelastina induziu um aumento da atividade metabólica e crescimento das células endoteliais. Quando expostos os grupos -NH2, uma influência significativa na síntese proteica foi observada. Além disso, os eTF scaffolds promoveram a manutenção do fenótipo e a formação de uma monocamada de células endoteliais na superfície após 7 dias de cultura. De um modo geral, estes resultados confirmam que estes eTF scaffolds biofuncionais são adequados para aplicação vascular, uma vez que apresentam propriedades mecânicas adequadas e uma rápida endotelização

Polymers and Their Application in 3D Printing

Dear Colleagues, Fused filament fabrication, also known as 3D printing, is extensively used to produce prototypes for applications in, e.g., the aerospace, medical, and automotive industries. In this process, a thermoplastic polymer is fed into a liquefier that extrudes a filament while moving in successive X–Y planes along the Z direction to fabricate a 3D part in a layer-by-layer process. Due to the progressive advances of this process in industry, the application of polymeric (or even composite) materials have received much attention. Researchers and industries now engage in 3D printing by implementing numerous polymeric materials in their domain. In this Special Issue, we will present a collection of recent and novel works regarding the application of polymers in 3D printing

Study on the Mechanical Properties of Carbon Nanotube Coated‒Fiber Multi-Scale (CCFM) Hybrid Composites

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

Mechanical characterization of wood plastic composite sandwich panels with foam core

Tableau d'honneur de la Faculté des études supérieures et postdorales, 2015-2016Le but de ce travail est de produire et de caractériser des structures sandwich à trois couches asymétriques avec ou sans cœur moussé. Pour ce faire, le travail est divisé en deux sections. Dans la première partie, l'effet de la variation des quantités d'agent de couplage et de fibres sont étudiés. La microscopie et la caractérisation mécanique sont utilisées pour évaluer l'effet du polyéthylène greffé d’anhydride maléique (MAPE) sur l'amélioration de la compatibilité entre les fibres de chanvre et le polyéthylène de haute densité (HDPE). Les résultats montrent que les propriétés mécaniques optimales (tension, flexion, torsion et impact) sont obtenues à 9% en poids de MAPE. Dans la deuxième partie, des structures sandwich asymétriques à trois couches, avec ou sans cœur moussé, sont produites par extrusion suivi par un moulage en compression. Les effets de paramètres tels que la densité du cœur, la concentration en chanvre dans les peaux, les épaisseurs des couches et la séquence d'empilage sur leurs comportements en flexion et en impact sont étudiés. Les effets combinés de tous les paramètres mènent à contrôler les propriétés mécaniques (traction, torsion, flexion et impact) des structures sandwich asymétriques.The aim of this work is to produce and characterize asymmetric three-layer sandwich structures with and without foam core. In order to do so, the work is divided in two sections. In the first part, the effect of coupling agent and fiber content is investigated. Micrographs and mechanical characterizations are used to show that the addition of maleic anhydride polyethylene (MAPE) improved the compatibility between hemp and high density polyethylene (HDPE). It is found that the optimum mechanical properties (tension, flexion, torsion and impact) are obtained with 9% wt. of MAPE in the composite. In the second part, asymmetric three-layer sandwich structures with and without foam core were produced using extrusion followed by compression molding. The effect of different parameters such as core density, skin hemp content, layer thickness, and stacking sequence on their flexural and impact behaviors are studied. The combined effect of all the parameters was found to control the mechanical properties (tension, torsion, flexion and impact) of asymmetric sandwich structures

Theoretical, numerical, and experimental methodologies for structural analysis of polymeric aeronautical elements produced via additive manufacturing

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

A new mixed model based on the enhanced-Refined Zigzag Theory for the analysis of thick multilayered composite plates

The Refined Zigzag Theory (RZT) has been widely used in the numerical analysis of multilayered and sandwich plates in the last decay. It has been demonstrated its high accuracy in predicting global quantities, such as maximum displacement, frequencies and buckling loads, and local quantities such as through-the-thickness distribution of displacements and in-plane stresses [1,2]. Moreover, the C0 continuity conditions make this theory appealing to finite element formulations [3]. The standard RZT, due to the derivation of the zigzag functions, cannot be used to investigate the structural behaviour of angle-ply laminated plates. This drawback has been recently solved by introducing a new set of generalized zigzag functions that allow the coupling effect between the local contribution of the zigzag displacements [4]. The newly developed theory has been named enhanced Refined Zigzag Theory (en- RZT) and has been demonstrated to be very accurate in the prediction of displacements, frequencies, buckling loads and stresses. The predictive capabilities of standard RZT for transverse shear stress distributions can be improved using the Reissner’s Mixed Variational Theorem (RMVT). In the mixed RZT, named RZT(m) [5], the assumed transverse shear stresses are derived from the integration of local three-dimensional equilibrium equations. Following the variational statement described by Auricchio and Sacco [6], the purpose of this work is to implement a mixed variational formulation for the en-RZT, in order to improve the accuracy of the predicted transverse stress distributions. The assumed kinematic field is cubic for the in-plane displacements and parabolic for the transverse one. Using an appropriate procedure enforcing the transverse shear stresses null on both the top and bottom surface, a new set of enhanced piecewise cubic zigzag functions are obtained. The transverse normal stress is assumed as a smeared cubic function along the laminate thickness. The assumed transverse shear stresses profile is derived from the integration of local three-dimensional equilibrium equations. The variational functional is the sum of three contributions: (1) one related to the membrane-bending deformation with a full displacement formulation, (2) the Hellinger-Reissner functional for the transverse normal and shear terms and (3) a penalty functional adopted to enforce the compatibility between the strains coming from the displacement field and new “strain” independent variables. The entire formulation is developed and the governing equations are derived for cases with existing analytical solutions. Finally, to assess the proposed model’s predictive capabilities, results are compared with an exact three-dimensional solution, when available, or high-fidelity finite elements 3D models. References: [1] Tessler A, Di Sciuva M, Gherlone M. Refined Zigzag Theory for Laminated Composite and Sandwich Plates. NASA/TP- 2009-215561 2009:1–53. [2] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. Assessment of the Refined Zigzag Theory for bending, vibration, and buckling of sandwich plates: a comparative study of different theories. Composite Structures 2013;106:777–92. https://doi.org/10.1016/j.compstruct.2013.07.019. [3] Di Sciuva M, Gherlone M, Iurlaro L, Tessler A. A class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory. Composite Structures 2015;132:784–803. https://doi.org/10.1016/j.compstruct.2015.06.071. [4] Sorrenti M, Di Sciuva M. An enhancement of the warping shear functions of Refined Zigzag Theory. Journal of Applied Mechanics 2021;88:7. https://doi.org/10.1115/1.4050908. [5] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses, Ibiza, Spain: 2013. [6] Auricchio F, Sacco E. Refined First-Order Shear Deformation Theory Models for Composite Laminates. J Appl Mech 2003;70:381–90. https://doi.org/10.1115/1.1572901