Modelling of mechanical properties of CRFC composites under flexure loading

Carbon Fibre Reinforced Carbon (CFRC) Composites are increasing their applications due to their high strength and Young’s Modulus at high temperatures in inert atmosphere. Although much work has been done on processing and structure and properties relationship, few studies have addressed the modelling of mechanical properties. This work is divided in two parts. In the first part, a modelling of mechanical properties was carried out for two bi-directional composites using a model based on the Bernoulli-Euler theory for symmetric laminated beams. In the second part, acoustic emission (AE) was used as an auxiliary technique for monitoring the failure process of the composites. Differences in fracture behaviour are reflected in patterns of AE.

Effect of particle morphology on the mechanical and thermo-mechanical behavior of polymer composites

Fiber reinforced polymer composites have been used in many applications, such as in automobile, aerospace and naval industries, due basically to their high strength-to-weight and modulus-to-weight, among other properties. Even though particles are usually not able to lead to the level of reinforcement of fibers, particle reinforced polymer composites have been proposed for many new applications due to their low cost, easy fabrication and isotropic properties. In this work, polymer composites were prepared by incorporating glass particles of different morphologies on poly(aryl sulfones) matrices. Particles with aspect ratios equal to 1, 2.5 and 10 were used. The prepared composites were characterized using electron microscopy and thermal analysis. Mechanical properties of the composites were evaluated using a four-point bending test. The thermo-mechanical behavior of the obtained composites was also investigated. The results showed that the morphology of the particles alter significantly the mechanical properties of composites. Particles with larger values of aspect ratio led to large elastic modulus but low levels of strain at failure. This result was explained by modeling the thermo-mechanical behavior of the composites using a viscoelastic model. Parameters of the model, obtained from a Cole-Cole type of plot, demonstrated that interactions at the polymer-reinforcing agent interface were higher for composites with large aspect ratio particles. Higher levels of interactions at interfaces can lead to higher degrees of stress transfer and, consequently, to composites with large elastic modulus, as experimentally observed.

Impact of mineral fillers on the properties of extruded wood-polypropylene composites

The main aim of this thesis is to study the effect of mineral fillers on the properties of extruded wood-polypropylene composites (WPC). The studied minerals are Talc, Calcite (CaCO3), two quantities of Wollastonite and Soapstone, and the level of mineral addition is 20 w-%. The study shows that mineral fillers can be used to modify and improve the properties of woodplastic composites. Especially the moisture-related properties of WPCs were found to be improved significantly by mineral addition. As the WPCs of the studied type are commonly used in outdoor applications, this is of importance in terms of usability. In machining, the addition of two minerals retained the surface roughness at same level throughout the test, indicating a favorable effect on machinability. The use of hard minerals shortened the tool life in machining. In general, a modest increase in density was observed. In many of the studied properties, no apparent influence of mineral addition was found, indicating that the properties were not weakened. An overall result was that talc showed the best overall performance, indicating that it can be used as an active filler improving most of the studied properties, especially moisture resistance. Calcite was found to have nearly similar performance. According to the findings, mineral addition to wood-plastic composites appears to be beneficial; especially moisture resistance can be enhanced without diminishing the other properties or usability in general.

Avaliação da deposição da calda de pulverização em função da densidade populacional de Brachiaria plantaginea, do volume e do ângulo de aplicação: effects of density, volume and spraying angle

O presente trabalho teve por objetivo avaliar a quantidade de calda de pulverização depositada nas folhas de Brachiaria plantaginea, em aplicações de pós-emergência precoce, em que se variou o volume de calda de pulverização, a densidade de plantas m-2 e o ângulo de posicionamento da ponta de pulverização na barra de aplicação. Para isso, foram conduzidos três experimentos em condições de laboratório. Nestes estudos, o volume de calda de pulverização foi obtido por meio da variação da velocidade de deslocamento de um veículo composto por plataforma e quatro rolamentos tracionados por um motor elétrico. Foi utilizada a ponta de pulverização XR Teejet 8001 EVS, na pressão de 241,4 kPa. O delineamento experimental utilizado foi o inteiramente casualizado, com cinco repetições. No primeiro experimento, os volumes utilizados foram de 1147,57; 860,68; 573,78; 459,02; 344,27; 229,51; 114,75; e 57,37 L ha-1 de calda de pulverização, com densidade de 600 plantas m-2. No segundo experimento foram estudadas as densidades de 300, 600, 900 e 1.200 plantas m-2; neste caso, utilizou-se o volume de 229,51 L ha-1 de calda de pulverização. No terceiro experimento avaliou-se o posicionamento do ângulo da ponta de pulverização na barra de aplicação e utilizou-se a densidade de 600 plantas m-2. Estudaram-se os ângulos de -30º, -15º, 90º, +15º e +30º e os volumes de calda de pulverização de 198,76; 221,69; 229,51; 221,69; e 198,76 L ha-1, respectivamente. Foram adotados sinais negativos para o sentido de deslocamento do veículo e sinais positivos para o sentido contrário ao deslocamento. As avaliações do depósito de calda de pulverização, na planta e no solo, foram feitas utilizando-se condutividade elétrica. A porcentagem de depósito de calda de pulverização nas plantas de B. plantaginea foi incrementada com a redução do volume de calda pulverizada por hectare. O depósito de calda por planta foi maior nas densidades maiores de plantas. O ângulo de posicionamento da ponta de pulverização na barra de aplicação incrementou o depósito de calda nas plantas de B. plantaginea, quando comparado com o ângulo de 90º.

Improving the usability of extruded wood-plastic composites by using modification technology

Using cellulosic reinforcement to produce plastic composites is a globally growing trend. One of such materials are wood-plastic composites, which are an extensively studied group of materials for which the global industry is looking for new applications. Issues such as bondability, durability and fire resistance still require development to improve the usability of the wood-plastic composite material. Improvement of the usability of wood-plastic composites is studied in this thesis through the effects of using selected modification technology in wood and plastic industry. The applied modification methods are surface by mechanical abrasion and plasma, chemical impregnation of wood flour, and structural modification by the co-extrusion process. The study shows that the properties of WPC can be influenced by the selected modification methods. The selected methods are also found to be able to result as improvement in the properties of the material. The may also affect other than just the targeted properties of the end-product, either in a positive or a negative manner. Therefore modification as performance improvement should be considered as a caseby- case study. Introducing WPC materials for new applications can be done by using modification technology. Structuralmodification can possibly be used to reduce material costs of the modified WPC material.

Ultraviolet light protection and weathering properties of wood-polypropylene composites

The main aim of this thesis is to study the effect of pigments on the weathering properties of wood-polypropylene composites (WPC). The studied properties are color change, water absorption, thickness swelling and Charpy impact strength. The impact of weathering and UV exposure on WPCs was studied by using pigments and minerals as protective agents. The study shows that the pigments and/or mineral fillers can be used to improve the weathering properties of WPCs. The effect of pigments was found to vary with the type of pigment and the method of weathering. The black pigment, an inorganic carbon black master-batch, was found to be the most effective one in reduction of the discoloration of WPCs. By preventing discoloration, and further reducing the degradation of the surface of the WPC, the pigments were found to reduce the decrease in the impact strength after weathering. As well as UV protection, the moisture resistance is a significant factor affecting the durability of WPCs. The addition of mineral fillers was found to improve the moisture-related properties, such as water absorption and thickness swelling, of WPC significantly. According to the findings, addition of pigments and mineral fillers to wood-polypropylene composites appears to be beneficial: color stability and moisture resistance can be enhanced especially in outdoor weathering. The combined effect of black pigment (carbon black master-batch) and wollastonite as a mineral filler was found to bring about the most effective properties against weathering.

Improving the fire retardancy of extruded/coextruded wood-plastic composites

The main objective of this thesis is to study the impact of different mineral fillers and fire retardants on the reaction-to-fire properties of extruded/coextruded wood-plastic composites (WPCs). The impact of additives on the flammability properties of WPCs is studied by cone calorimetry. The studied properties are ignition time, peak heat release rate, total heat release, total smoke production, and mass loss rate. The effects of mineral fillers and fire retardants were found to vary with the type of additive, the type of additive combinations, the amount of additives, as well as the production method of the WPCs. The study shows that talc can be used to improve the properties of extruded WPCs. Especially ignition time, peak heat release rate and mass loss rate were found to be improved significantly by talc. The most significant improvement in the fire retardancy of coextruded WPCs was achieved in combinations of natural graphite and melamine. Ignition time, peak heat release rate and total smoke production were improved essentially. High increase in smoke production was found in samples where the amount of ammonium polyphosphate was 10% or higher. Coextrusion as a structural modification was found as a promising way to improve the flammability properties of composite materials in a cost-effective way.

Effect of image resolution manipulation in rearfoot angle measurements obtained with photogrammetry

The aim of this study was to investigate the influence of image resolution manipulation on the photogrammetric measurement of the rearfoot static angle. The study design was that of a reliability study. We evaluated 19 healthy young adults (11 females and 8 males). The photographs were taken at 1536 pixels in the greatest dimension, resized into four different resolutions (1200, 768, 600, 384 pixels) and analyzed by three equally trained examiners on a 96-pixels per inch (ppi) screen. An experienced physiotherapist marked the anatomic landmarks of rearfoot static angles on two occasions within a 1-week interval. Three different examiners had marked angles on digital pictures. The systematic error and the smallest detectable difference were calculated from the angle values between the image resolutions and times of evaluation. Different resolutions were compared by analysis of variance. Inter- and intra-examiner reliability was calculated by intra-class correlation coefficients (ICC). The rearfoot static angles obtained by the examiners in each resolution were not different (P > 0.05); however, the higher the image resolution the better the inter-examiner reliability. The intra-examiner reliability (within a 1-week interval) was considered to be unacceptable for all image resolutions (ICC range: 0.08-0.52). The whole body image of an adult with a minimum size of 768 pixels analyzed on a 96-ppi screen can provide very good inter-examiner reliability for photogrammetric measurements of rearfoot static angles (ICC range: 0.85-0.92), although the intra-examiner reliability within each resolution was not acceptable. Therefore, this method is not a proper tool for follow-up evaluations of patients within a therapeutic protocol.

Utilization of recycled mineral wool as filler in wood plastic composites

The impact of a recycled mineral wool filler on the various properties of wood plastic composites was studied and the critical factors affecting the formation of the properties were determined. An estimation of the volume of mineral wool fiber waste generated in the European Union between the years 2010-2020 was presented. Furthermore, the effect of fiber pre-treatment on the properties of the wood plastic composites were studied, and the environmental performance of a wood plastic composite containing recycled mineral fibers was assessed. The results showed that the volumes of construction and demolition waste and new mineral wool produced in the European Union are growing annually, and therefore also the volumes of recycled mineral wool waste generated are increasing. The study showed that the addition of recycled mineral wool into composites can enhance some of the mechanical properties and increase the moisture resistance properties of the composites notably. Recycled mineral wool as a filler in wood plastic composites can also improve the fire resistance properties of composites, but it does not protect the polymer matrix from pyrolysis. Fiber pre-treatment with silane solution improved some of the mechanical properties, but generally the use of maleated polypropylene as the coupling agent led to better mechanical and moisture resistance properties. The environmental performance of recycled mineral wool as the filler in wood plastic composites was superior compared to glass fibers. According to the findings, recycled mineral wool fibers can provide a technically and environmentally viable alternative to the traditional inorganic filler materials used in wood plastic composites.

Research progress in wood-plastic composites: A review

The interest towards wood-plastic composites (WPCs) is growing due to growing interest in materials with novel properties, which can replace more traditional materials, such as wood and plastic. The use of recycled materials in manufacture is also a bonus. However, the application ofWPCs has been limited because of their often poor mechanical and barrier properties, which can be improved by incorporation of the reinforcing fillers. Nanosized fillers, having a large surface area, can significantly increase interfacial interactions in the composite on molecular level, leading to materials with new properties. The review summarizes the development trends in the use on nanofillers for WPC design, which were reported in accessible literature during the last decade. The effect of the nanofillers on the mechanical properties, thermal stability, flammability and wettability ofWPC is discussed.

Viologen based electroactive polymers and composites for durable electrochromic systems

Electrochromism, the phenomenon of reversible color change induced by a small electric charge, forms the basis for operation of several devices including mirrors, displays and smart windows. Although, the history of electrochromism dates back to the 19th century, only the last quarter of the 20th century has its considerable scientific and technological impact. The commercial applications of electrochromics (ECs) are rather limited, besides top selling EC anti-glare mirrors by Gentex Corporation and airplane windows by Boeing, which made a huge commercial success and exposed the potential of EC materials for future glass industry. It is evident from their patents that viologens (salts of 4,4ʹ-bipyridilium) were the major active EC component for most of these marketed devices, signifying the motivation of this thesis focusing on EC viologens. Among the family of electrochromes, viologens have been utilized in electrochromic devices (ECDs) for a while, due to its intensely colored radical cation formation induced by applying a small cathodic potential. Viologens can be synthesized as oligomer or in the polymeric form or as functionality to conjugated polymers. In this thesis, polyviologens (PVs) were synthesized starting from cyanopyridinium (CNP) based monomer precursors. Reductive coupling of cross-connected cyano groups yields viologen and polyviologen under successive electropolymerization using for example the cyclic voltammetry (CV) technique. For further development, a polyviologen-graphene composite system was fabricated, focusing at the stability of the PV electrochrome without sacrificing its excellent EC properties. High electrical conductivity, high surface area offered by graphene sheets together with its non-covalent interactions and synergism with PV significantly improved the electrochrome durability in the composite matrix. The work thereby continued in developing a CNP functionalized thiophene derivative and its copolymer for possible utilization of viologen in the copolymer blend. Furthermore, the viologen functionalized thiophene derivative was synthesized and electropolymerized in order to explore enhancement in the EC contrast and overall EC performance. The findings suggest that such electroactive viologen/polyviologen systems and their nanostructured composite films as well as viologen functionalized conjugated polymers, can be potentially applied as an active EC material in future ECDs aiming at durable device performances.

[1er mai 1920 à Paris, agent cycliste et cavaliers du service d'ordre à l'angle du boulevard Magenta et de la rue La Fayette] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 59109

1er mai 1920 à Paris, [des policiers molestent des manifestants devant le café Aux sources, à l'angle du boulevard de Magenta et de la rue Beaurepaire] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 59135

1er mai 1920 à Paris, [des policiers molestent des manifestants devant la taverne du Château d'Eau, à l'angle du boulevard de Magenta et de la rue Boulanger] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 59136