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Theses and dissertations (Engineering and Built Environment)

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End date: 2019Subject: search.filters.subject.Fibrous composites

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    High speed, high precision processing of dry pre-pregs for composite structures
    (2019-08-15) Ramsaroop, Avinash; Kanny, Krishnan
    In this study, a computational code was developed that was used to optimise the fibre orientation angles, layer thicknesses, number of fibre layers and the weight in fibre reinforced composites. In addition, an interface was created between the computational code and the robotic apparatus that performed the fibre placement. Fibre reinforced composites are extremely versatile materials and may be tailor designed to suit various applications. However, the design techniques commonly associated with composite structures make them inadequate for industries with high production rates. Conventional design techniques have the disadvantage of numerous tedious and laborious matrix calculations. Also, there is uncertainty with assigning values to the input parameters for the equations used in the design process. In addition, conventional design techniques result in constant stiffness structures, that is, structures with the same fibre layup throughout. These disadvantages result in increased manufacturing costs as more material and labour, than necessary, are used. This study presents a solution in the form of computational codes developed in Matlab. The codes are used to perform all the necessary matrix calculations easily and swiftly. Further, the uncertainty experienced with the input parameters, in conventional design techniques, is removed. The code is used to optimise the fibre orientation angles and layer thicknesses in a composite structure, as well as the number of fibre layers and the weight. In addition, it is able to create variable stiffness structures, that is, structures where the fibre layup varies throughout. The use of the code in the design process would decrease the design costs, as the design time is reduced, and decrease the material costs, as only the required amount of material is used. The developed codes were validated using examples from texts, finite element modelling and experimental methods. The development of the computational codes created a problem with regards to the fibre layup process. Any process that employed manual placement of the fibres became inadequate as they proved to be extremely labour intensive and would result in increased labour costs. Further, with manual placement of fibres, precise fibre orientation cannot be guaranteed. Therefore it was decided to use an automated system, such as Robotic Fibre Placement (RFP), to perform the fibre layup. Such a system was designed and built in-house in a previous study. In the current study, a Matlab code was developed as an interface between the developed computational code and the fibre placement system. Other codes as well as graphical interfaces were developed in order to improve the interaction between the user and the codes.
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    Methodologies for the optimal design of fibre-reinforced composite structures
    (2003) Smith, Ryan Elliot; Walker, Mark
    Composites have become important engineering materials, especially in the fields of automotive, aerospace and marine engineering. This is due to the high specific strength and stiffness properties they offer. At present, fibre-reinforced plastic (FRP) laminates are some of the most common types of composite used. They are produced in various forms with different structural properties. As with all engineering materials, there is the existence of both advantages and disadvantages. One of the main disadvantages is the expense involved in producing both the material and the finished product. The design time is also costly as the material has to be designed concurrently with the structure.
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    Material characterisation for the modelling of the vacuum infusion process
    (2015) Gilpin, Mark; Jonson, Jon David
    Vacuum Infusion (VI) and Resin Transfer Moulding (RTM) are liquid composite moulding processes used in the manufacture of components from composite materials. The composite material in this case consists of a resin matrix combined with fibre reinforcement. In both moulding processes, a dry reinforcement preform is placed in the mould cavity and a liquid resin is introduced, driven by a pressure differential. Two rigid surfaces are used in RTM to create a fixed mould cavity. In contrast VI implements only one rigid surface and a flexible membrane or vacuum bag to form a non rigid cavity. The flexible cavity in VI influences and differentiates resin flow behaviour from that of RTM. Modelling resin flow enables the velocity, pressure and flow direction to be predicted. Resin flow in the RTM process is understood and modelled using Darcy’s law. However, flow in the VI process is not accurately modelled due to the added complexity introduced as a result of the flexible cavity. In the present work a novel approach was developed to investigate fluid flow in both processes. A unique experimental setup and testing procedure allowed for the direct comparison of fluid flow in RTM and VI. Identical flow parameters, conditions and preform construction were used in the assessment. The comparison isolated the effect of preform thickness variation as a differentiating factor influencing flow. From the experimentation, material behaviour was characterised and used to evaluate flow models for RTM and in particular VI. The model solutions were compared back to corresponding experiments. The pressure distribution behind the flow front, fill time and thickness behaviours were assessed. The pressure distribution / profiles behind the flow front of both VI and RTM were noted to be scalable with flow front progression. The profiles were curved in the VI experiments and linear in the RTM case. All VI models evaluated including the non accumulation based model accurately predicted the pressure distribution and consequently thickness variations in the VI tests. Fill times of the VI experiments were longer than that of the equivalent RTM tests. This behaviour is in contrast to previously interpreted fill time behaviour for the VI process based on VI models. It was also noted that the VI fill times were not only proportional to the square of the fill length, as in the RTM case, but also proportional to the square of the mass present. In addition, no significant accumulation was noted in the VI experiments.
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    Methodologies for the optimization of fibre-reinforced composite structures with manufacturing uncertainties
    (2006) Hamilton, Ryan Jason
    Fibre Reinforced Plastics (FRPs) have been used in many practical structural applications due to their excellent strength and weight characteristics as well as the ability for their properties to be tailored to the requirements of a given application. Thus, designing with FRPs can be extremely challenging, particularly when the number of design variables contained in the design space is large. For example, to determine the ply orientations and the material properties optimally is typically difficult without a considered approach. Optimization of composite structures with respect to the ply angles is necessary to realize the full potential of fibre-reinforced materials. Evaluating the fitness of each candidate in the design space, and selecting the most efficient can be very time consuming and costly. Structures composed of composite materials often contain components which may be modelled as rectangular plates or cylindrical shells, for example. Modelling of components such as plates can be useful as it is a means of simplifying elements of structures, and this can save time and thus cost. Variations in manufacturing processes and user environment may affect the quality and performance of a product. It is usually beneficial to account for such variances or tolerances in the design process, and in fact, sometimes it may be crucial, particularly when the effect is of consequence. The work conducted within this project focused on methodologies for optimally designing fibre-reinforced laminated composite structures with the effects of manufacturing tolerances included. For this study it is assumed that the probability of any tolerance value occurring within the tolerance band, compared with any other, is equal, and thus the techniques are aimed at designing for the worst-case scenario. This thesis thus discusses four new procedures for the optimization of composite structures with the effects of manufacturing uncertainties included.
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    Increasing the use of fibre-reinforced composites in the Sasol group of companies : a case study
    (2007) Mouton, Jacques
    A composite material comprises two or more materials with properties that are superior to those of the individual constituents. Composites have become important engineering materials, especially in the fields of chemical plant, automotive, aerospace and marine engineering. The development of more advanced materials and manufacturing techniques in composites has grown from humble beginnings in the 1930s to a recognized and well-respected engineering discipline, providing solutions to conventional and challenging applications. At present, fibre-reinforced composites (FRCs) are amongst the most common types of composites used. They are produced in various forms with different structural properties, and designers, specifiers and end-users can choose from an almost endless list of these materials, providing design flexibility as well as low manufacturing and maintenance cost. Many suggest that composites have revolutionised the chemical and petro-chemical industries. Examples of applications include tanks and chemical reactor vessels that contains many hundreds of litres of hazardous chemicals, reinforced pipes measuring up to several meters in diameter conveying dangerous gases and so on. The South Africa Coal, Oil and Gas Corporation Limited (SASOL) was established in September 1950. From a small start-up, the company has grown to be a world leader in the commercial production of liquid fuels and chemicals from coal and crude oil. Sasol manufactures more than 200 fuel and chemical products at its main plants in Sasolburg and Secunda in South Africa as well as at several other plants abroad. Its products are exported to more than 90 countries around the world. The use of composites in general, and fibre reinforced composites in particular has received little support in Sasol through the years. Some sporadic use of these materials in the construction of process equipment, e.g. tanks, vessels and piping has taken place with varying degrees of success. While the use of equipment fabricated with fibre-reinforced composites has proven extremely successful in the chlorine producing facility in Sasolburg, catastrophic failures have taken place in Secunda in critical fire water systems made of these materials. The history of correct use and application of fibre-reinforced equipment has shown that the cost of ownership of such equipment is significantly lower than similar metallic equipment, therefore reducing costs and safety risks. However, even though this technology brings a company like Sasol closer to the realisation of the vast number of advantages and solutions offered by these materials, the reality is that most engineering personnel are still applying traditional (viz. steel and wood) technology as used by our predecessors. The work presented here attempts to indicate the relevance of fibre-reinforced composites for Sasol, and to detail efforts aimed at the raising of awareness amongst appropriate personnel at Sasol to increase the use of these materials in major capital projects and day-to-day maintenance contracts, therefore taking advantage of the superior performance of fibre-reinforced composites in demanding applications. In support of this drive, part of the work presented indicates the status as well as progress of the composites industry in the last few years. This project was therefore aimed at identifying the level of utilization of fibre-reinforced composites at Sasol, and the possible improvement in benefits of using these technologies. A methodology was developed, using engineering as well as marketing principles, to reach the engineering personnel in various divisions and seniority levels of Sasol to increase the awareness of the capabilities of composites materials, specifically regarding fibre-reinforced composites. Questionnaires were used to gauge the level of awareness while various methods, e.g. one-on-one meetings, seminars, conferences, electronic media, etc were used to upgrade the target groups’ knowledge. The results of the initial survey to determine the status of various dimensions in the company are indicated as well as the outcomes at the end of the research period. In support of the process in Sasol, the development, interaction and cross-pollination of international and national role-players in the fibre-reinforcement industry with respect to chemical containment and Sasol are indicated. The importance of this two-legged process is demonstrated: it ensures a professional national support framework for companies like Sasol. Results are indicated, compared and discussed to give future direction in this ongoing process. As important to this process was the development of appropriate technical resources (like design standards and codes) to enable their use within the group. It was recognised early on that raising the level of awareness of the target groups was not enough and that these resources had to be in-place down the line so that those who chose to could start to implement these material technologies with the aid of the resources. The development of the necessary resources is also discussed. Finally, it will be shown that significant growth has taken place regarding the awareness within the group over the course of implementation of this project. Specifically, about 20% of the target groups have moved from a stage of no knowledge to higher levels of confidence. In terms of use of these materials, significant growth has also taken place judging by the number of plant requests, activity on major capital projects and so on. In fact, from almost nothing in 1999, over the last 5 years in excess of R137 Million has been spent on capital equipment manufactured from composite materials, with the majority in the last 2 years.