Impact load behaviour of Resin Transfer Moulding (RTM) hemp fibre composite laminates

13 pages, 23 figures.Aim of this work is to determine experimentally some important mechanical characteristics of RTM hemp plain weave fabric/epoxy laminates. Equipment and test methods are described and critically discussed. Main subjects of this work are: RTM process improvement, preliminary tensile and flexural tests and impact performance. The latter is analyzed with particular attention, also comparing data with other experimental results. Attention is devoted both to the process, which strongly influences the mechanical performance of natural long fibres reinforced composites and to the low-velocity impact behaviour. This is a very important requirement for future aeronautical applications, in that composite structures should retain sufficient residual compression properties (CAI: Compression After Impact) after a Barely Visible Impact Damage (B.V.I.D).Publicad

Hybrid Single Shot Manufacturing of Multi-Materials Structure for Automotive Applications

Multi-material design is one of the most attractive methods for automakers to reduce production cost while achieving lightweighting to meet stringent regulations and fuel efficiency concerns. Lightweighting, parts consolidation, reduction in assembly time and cost, and diverse functionalities are some advantages to the use of multi-material design in the automotive industry. However, the current technology of multi-material manufacturing faces some drawbacks, such as high cycle time, the necessity of various tooling and machinery systems, tight tolerance requirements, and extended planning effort on the production line. In this study, a technique named the Hybrid Single Shot (HSS), which is similar to Polymer Injection Forming (PIF), is used to manufacture CF/Epoxy-Thermoplastic components in a single operation. Unlike the PIF method, a carbon fiber /epoxy prepreg sheet is used as an insert material instead of sheet metal. In this technique, an injected polymer melt behaves like a forming medium to form the inserted thermoset sheet, in a single operation. Molten polymer not only forms but also bonds with the thermoset sheet using the high temperature of the polymer, in one process. CF/Epoxy sheet with injected thermoplastic is a hybrid structure that combines high mechanical properties of thermoset composite with the toughness and complex geometries of injected thermoplastic into a single component. A feasibility study was conducted for developing an integrated technology for the manufacturing of thermoset CF/Epoxy prepreg sheet with an injection of polypropylene to overcome the high cycle time and production cost associated with the manufacturing of such hybrids. Several sample parts were manufactured to demonstrate the effect of the process parameters on the process performance and the appearance of the final hybrid component. Although the results were promising, it showed some practical challenges such as excessive penetration, inadequate deformation, and warpage. Various process and design parameters are applied to the hybrid single shot process to circumvent these challenges. For example, a lower injection speed rate and the injection temperature are applied to increase the viscosity to prevent the penetration of polymeric melt through the thermoset sheet. Also, to evaluate the impact of polymer injection on the degree of cure of the prepreg sheet, Differential Scanning Calorimetry (DSC) analysis is conducted at a different pre-heat time before and after injection. The results showed that an increase in pre-heating time and injection temperature significantly enhanced the curing of the prepreg sheet after injection. Further, the mechanical properties of the hybrid part will be examined to identify the effect of individual properties of CF/ Epoxy and PP on the final component. Another contribution of this study is that it avoids many difficulties that conventional TS/TP joining techniques face. Specifically, these traditional joining methods, namely mechanical fastening, adhesive bonding, and welding, are time-consuming and labor-intensive. Also, mechanical fastening causes delamination and possible galvanic corrosion while adhesive bonding requires extensive surface preparation. Despite the time and weight advantages, welding techniques tend to create local delamination due to high local temperature. The hybrid single shot method is a promising alternative to overcome all the challenges that conventional methods face. A lap shear test is conducted to address the bonding conditions between polypropylene and CF/Epoxy prepreg. The experimental results presented in the previous chapters have revealed that the final geometry of the hybrid part is highly dependent on the preheating conditions and pressure field applied on the prepreg sheet during the injection phase. The pressure distribution is then a function of selected polymer, process settings, and most importantly of the geometry of the flow channel. To model the forming of the prepreg sheet due to this non-uniform pressure field, it is essential to couple all the physical events occurring inside the cavity. Therefore, the last contribution of this study is to have a better understanding on the effect of interaction injection, forming and curing on the final geometry of prepreg sheet, a quick yet accurate simulation of the HSS process. This simulation includes the consideration of the non-uniform pressure distribution of the melt flow and the prepreg sheet deformation behavior based on a new experimentally calibrated numerical approach

Methods for high-precision subsurface imaging using spatially dense seismic data

Current state-of-the-art depth migration techniques are regularly applied in marine seismic exploration, where they deliver accurate and reliable pictures of Earth’s interior. The question is how these algorithms will perform in different environments, not related to oil and gas exploration. For example, how to utilise those techniques in an elusive environment of hard rocks? The main challenge there is to image highly complex, subvertical piece-wise geology, represented by often low reflectivity, in a noisy environment

Development of the in situ forming of a liquid infused preform (ISFLIP) process : a new manufacturing technique for high performance fibre reinforced polymer (FRP) components

A problem is not a problem anymore if no solution exists; therefore, in the present dissertation, a novel manufacturing technique, the In Situ Forming of a Liquid Infused Preform (ISFLIP), is proposed as a solution to some typical problems that manufacturing of Fibre Reinforced Polymer (FRP) parts through Vacuum Infusion (VI) involves, such as not taking advantage of the full potential of FRPs, long processing times and lack of reproducibility. ISFLIP is a hybrid process between VI and diaphragm forming in which a flat preform of a stack of reinforcement fabrics is firstly impregnated with a low viscosity matrix and, then, formed over a mould while the matrix is still in the low viscosity state. Being focused on high performance FRPs and shell components, from simple to complex double curvature shapes, a number of trade-offs between VI and diaphragm forming were overcome to lay the foundations from which ISFLIP ability to manufacture FRP components has been proven. In order to adopt a VI manufacturing methodology that fitted ISFLIP targets, important contributions to more general VI have also been made in terms of part quality optimization, addressing the major concern that void content is in VI, with competitive manufacturing times. An effective vacuum degassing procedure in which bubble formation is enhanced through high speed stirring, and a non-conventional filling and post-filling strategy are proposed for this purpose. Eventually, void content was virtually eliminated and post-filling time minimized without affecting fibre content. In ISFLIP, textile preforms are formed together with a series of auxiliary materials (plastic films and sheets, textile fabrics and knitted meshes), most of them showing different in-plane deformation mechanisms. Forming performance of preforms, as well as final part quality, are severely affected by interactions between all these materials different in nature. Uncertainties on this respect and an initial evaluation of attainable shapes were also addressed to define a more focused research plan to the final goal, still distant, of implementing ISFLIP in a real production environment. Results obtained throughout the research project give cause for reasonable optimism in ISFLIP potential and future prospects.Un problema deja de ser un problema si no existe solución; por lo tanto, en esta disertación, una novedosa técnica de fabricación, el Conformado In Situ de una Preforma Infusionada con resina Líquida (ISFLIP, por sus siglas en inglés), se propone como solución a algunos problemas típicos relacionados con la fabricación de piezas de Polímero Reforzado con Fibra (FRP) a través de la Infusión por Vacío (VI), problemas tales como el desaprovechamiento de todo el potencial de los FRPs, largos tiempos de procesado y falta de reproducibilidad. ISFLIP es un proceso híbrido entre la VI y el conformado por membrana elástica en el que una preforma plana formada a partir de un apilado de tejidos de refuerzo es en primera instancia impregnada con una resina de baja viscosidad y, entonces, conformada sobre un molde mientras que la matriz permanece todavía en el estado de baja viscosidad. Estando centrado en los FRPs de altas prestaciones y en componentes con formas tipo concha, desde curvaturas simples hasta formas con doble curvatura complejas, un número importante de compensaciones entre la VI y el conformado por membrana se han ido superando para asentar las bases a partir de las cuales se ha probado la capacidad de ISFLIP para fabricas componentes de FRP. Con la vista puesta en implementar una metodología de fabricación por VI que cumpliese los objetivos definidos para ISFLIP, también se han realizado importantes contribuciones de carácter más general relacionadas con la VI en términos de optimización de parámetros de calidad de las piezas, abordando la gran preocupación que la porosidad final supone en la VI, y consiguiendo unos tiempos de fabricación competitivos. Con este propósito se han propuesto un proceso de desgasificación por vacío muy efectivo en el que se favorece la nucleación de burbujas mediante la agitación a alta velocidad, y una prometedora y no convencional estrategia de llenado y post-llenado de la preforma. Finalmente, se consiguió virtualmente eliminar la porosidad atrapada en las piezas, minimizando el tiempo de post-llenado sin afectar la fracción de fibra contenida. En ISFLIP las preformas textiles se conforman junto con una serie de materiales auxiliares (films y hojas plásticas, mallas y tejidos textiles), que muestran diferentes mecanismos de deformación en plano. El conformado de las preformas y el acabado final de las piezas se ve severamente afectado por todas las interacciones entre todos estos materiales diferentes en naturaleza. También se han abordado las incertidumbres que surgen al respecto y una evaluación inicial de las geometrías abarcables para definir un plan de investigación más concreto con el que poder afrontar la meta final, todavía distante, de implementar ISFLIP en un entorno productivo real. Los resultados obtenidos a lo largo de este proyecto de investigación permiten ser razonablemente optimistas en cuanto al potencial de ISFLIP y sus expectativas

Effect of Processing Parameters and Matrix Shrinkage on Porosity Formation During Synthesis of Metal Matrix Composites with Dual-scale Fiber Reinforcements Using Pressure Infiltration Process

This is first such study on porosity formation phenomena observed in dual-scale fiber preforms during the synthesis of metal matrix composites (MMCs) using the gas-based pressure infiltration process (gas PIP). In this thesis, different mechanisms of porosity formation during pressure infiltration of Al-Si alloys into Nextel\u27s 3D woven ceramic-fabric reinforcements (a dual-porosity or dual-scale porous medium) are studied. The effect of processing conditions in terms of the infiltration temperature and pressure on porosity content of the ceramic fabric infiltrated by the alloys through the gas PIP is investigated. Relative density (RD), defined as the ratio of the actual MMC density and the density obtained at ideal 100% saturation of the preform, was used to quantify overall porosity. Increasing the infiltration temperature led to an increase in RD (and reduction in porosity) due to reduced viscosity and enhanced wettability leading to improved feedability of the liquid metal. Similarly, increasing the infiltration pressure led to enhanced penetration of fiber tows and led to higher RD and reduced porosity. For the first time, the modified Capillary number (Ca*), which is found to predict formation of porosity in polymer matrix composites quite well, is employed to study porosity in MMCs made using PIP. It is observed that in the high Ca* regime used in the present study (and common in PIP), the overall porosity shows a strong downward trend with increasing Ca* due to a decrease in the size of trapped air pockets inside fiber tows due to increased infiltration pressures. This contradicts the well-known result of increasing porosity with Ca* observed by Patel et al. in [1]. In addition, the effect of matrix shrinkage on porosity content of the samples is studied through using a zero-shrinkage Al-Si alloy as the matrix: usage of this alloy as the matrix led to a reduction in porosity content

Evolution FP7 funded project: body structure design strategies using new composite and aluminium materials and enabled technologies

Based on Pininfarina Nido EV concept, EVolution aims to reduce the vehicle weight through new materials and process technologies, focused on five demonstrators: underbody, front crossbeam, mechanical subframe, shotgun system and door. This paper refers to body structure design strategies using new composite, Al materials and enabled technologies, focusing in particular on demonstrators design and manufacturing. The new front crossbeam geometry of the front shell is adapted starting from the Nanotough design, while the rear shell is specific for EVolution. The subframe demonstrator is redesigned to fulfil mechanical requirements of the part and manufacturing feasibility either. The EVolution door concept consists of two semistructural composite skins including a structural Al frame. The underbody is conceived through an integrated approach, optimising each element for its function. The shotgun component is designed to link parts obtained with different manufacturing technologies and several aluminium alloys in one single component: the structural node demonstrator.The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 314744

Influence of the natural additive on natural fiber reinforced thermoplastic composite

Composite materials have a wide range of application in various domains. The fact behind using composite materials is that they give the same almost strength as metal parts in presenting lesser weight. However, the plastic parts are non-biodegradable, and they lead to the polluted environment during the disposal after end-of-life of a particular part. Nowadays natural and easily recyclable composites were preferred due to environmental concerns. The major disadvantage of using natural fibre composites is that they have low strength compared to conventional glass or carbon reinforced composite. To enhance the strength of Natural-Fiber-Reinforced Plastics (NFRP) various techniques have been followed (Chemical treatment of the fibre, post-curing of the composites, sandwiching the composite, adding additives/fillers to the matrix) based on the feasibility and application of the composites. Among those techniques, adding additives to the matrix is one of the simple and effective ways to enhance the properties of the composite. A natural additive is developed in concern to the environmental impact of the composite. Two different types of the composite laminate were manufactured. One is with additive and one is without the additive. It is necessary to validate the strength of the composite with and without the additives by mechanical testing. Thus, tensile, flexural and moisture absorption tests were performed to verify the mechanical property enhancement achieved due to the use of additives. These tests help in characterizing the material to specific applications. The composite with the natural additive showed better mechanical properties. However, the moisture absorption tendency of the composite is increased as well, mainly due to the presence of additives on the surface of the composite along with the matrix.info:eu-repo/semantics/publishedVersio