Theses and dissertations (Engineering and Built Environment)

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An investigation into a magnetic compaction technique for composite manufacturing
(2023-09) Salot, Yazid; Gilpin, Mark
Fiber reinforced polymer composites are an aerospace and defense material. These materials are widely used in the production of components and parts which require high weight to strength ratios or corrosion resistance. The automotive, aero, marine as well as sporting industries are increasingly requiring components with such characteristics. This has led to an increase in demand in the composite industry. A composite is a material made from a combination of fiber reinforcement and resin. The reinforcement is generally made of Glass, Carbon or Aramid fiber which is woven in a fabric. While resins are typically thermoplastic such as polyester, vinyl ester, phenolic and epoxy. The fiber and resin are combined and compacted together in order to manufacture an item. There are various manufacturing techniques which are utilized to produce fiber reinforced composite components. Many items are manufactured using closed moulding techniques. The process involves the combining of fabric preform with a liquid resin within the mould cavity. After a certain period the component is removed from the mould. The strength, stiffness (mechanical properties) and strength to weight ratio of a composite material are affected by voids (air pockets) and the component’s thickness. Both the air voids and thickness are influenced by compaction during the manufacturing process. Increasing compaction during moulding improves the material properties and ultimately the final product, component or part. This research is aimed at investigating the possibility of utilizing magnetic compaction in fiber reinforced composite manufacturing. The desired technique will be intended to offer improved compaction without requiring any tooling modifications. The proposed technique would fall into the category of the light closed mould compression techniques which utilizes Glass Reinforced Plastic (GRP) tooling. This technique will also attempt to address certain issues experienced in light closed mould techniques. The magnetic compaction technique would be investigated in an effort to offer a scalable technique which has an improved fiber volume fraction and mechanical properties. Currently no closed mould techniques implement magnetic compaction. The research will review the combination of light closed moulding techniques and the working principles of magnetism.
Hybrid syntactic foam core cased natural-glass fibre sandwich composite
(2023-05) Afolabi, Olusegun Adigun; Kanny, Krishnan; Mohan, Turup Pandurangan
Composite materials comprised of two separates with different properties to form a single material that reflect the properties of the combined materials. Syntactic foam composites (SFC) are made from the combination of hollow glass microspheres and epoxy resin. They are lightweight and used as a core in the hybrid sandwich composite. Hollow glass microspheres (HGM) are high strength microballoons that provide closed cell porosity and help to reduce material weight. SFCs made of HGM, and resin matrix are used as the core in sandwich composite material and reinforced with natural or synthetic fiber materials. The sandwich syntactic foam composite (SSFC) has a wide range of applications in the marine, aerospace, structural, and automobile industry. Therefore, it is important to investigate their physical, mechanical, thermal, and morphological properties to achieve high strength and low density. Most of the previous work in literature employed the use of different fillers and core materials in sandwich composite but are limited in strength because of their high density. In this study, a single HGM filler was employed as heterogeneous and homogenous by varying into four different particle sizes to investigate the effect of these particle sizes on the mechanical and physio-mechanical properties of the SFC used as the core in the SSFC. The effect of wall thickness and radius ratio of the HGM on the microstructural properties of SFC was also determined. The heterogeneous and homogeneous SFC was fabricated by degassing method mixing the epoxy matrix with HGM filler, the filler was varied into five-volume fractions of 5, 10, 15, 20, and 25%. The functional group of the HGM filler and the neat epoxy was determined and compared with that of the SFCs fabricated using Fourier Transform Infrared Spectroscopy (FTIR). The results showed that the filler contain various functional groups such as hydroxyl group, phenol-OH, aldehyde C-H group, aromatic proton, epoxy group, which enhanced the bonding process. It was determined that the intensity of the SFCs for all the volume fractions increased more than the neat epoxy due to the shifts in the peaks representing the filler and the matrix groups. The physical (density, water absorption, buoyancy) properties and the mechanical (hardness, tensile, flexural, and impact) properties of the SFCs improved significantly compared with the neat epoxy. The Scanning Electron Microscopy (SEM), Dynamic Mechanical Analysis (DMA), and Thermo-gravimetric Analysis (TGA) were also used to determine the morphological structure, the viscoelastic properties, and degradation temperature of the HGM and the neat epoxy and compared with the fabricated SFCs. The surface of the HGM showed the microballoons in their different sizes before separation. The surface of the SFCs showed the epoxy matrix, matrix porosity, microballoons porosity, and microballoons structure in their mixed state. It was an indication of good interaction between the epoxy matrix and the HGM filler using degassing processing method. The DMA showed improved storage and loss modulus values by 9% and above 100% respectively compared to the neat epoxy and the TGA showed better glass transition Tg values of 4.5% and 2.7% at 20% and 55% weight loss respectively compared to the neat epoxy. This indicated that good interaction and interfacial bonding existed between HGM and the epoxy matrix and because of lower density and void content. The SFC was used as the core to fabricate a lightweight sandwich syntactic foam composite (SSFC). The SSFC was made into four different orientations (kenaf-SFC-kenaf, as KK; glass –SFCglass, as GG; glass/kenaf – SFC – kenaf/glass, as GK; and kenaf/glass –SFC- glass/kenaf, as KG) using kenaf and glass fibers as reinforcement. The physical properties (density, water absorption capacity, and buoyancy), mechanical properties (hardness, tensile, compression, and flexural), morphological properties (SEM), and acoustic properties were determined. The porosity of KK increased by 21.6% because the kenaf fiber is less dense and more porous in terms of water absorption which makes it require higher buoyancy force to stay afloat. The mechanical properties results showed that GK and KG have the highest hardness, flexural and compressive strength of 70.2%, 74.4%, and 42.7% respectively, while GG has improved tensile strength of 210.96% increase than KK. The acoustic properties results showed that GG improved in sound level (P) dB by 24.1% compared to KK, while the sound pressure (Lp) dB does not show a significant difference in the SSFC. In conclusion, the degassing processing method of SFCs improved its physical and mechanical properties by reducing the density using particle distribution analysis (PSA) and particle variation analysis (PVA) with the aid of a gas pycnometer, and porosity values thereby making it a suitable core material for the sandwich composite. A novel sandwich syntactic foam composite (SSFC) material was fabricated by hybridizing the face-sheets in different layering pattens. The SSFC physical and mechanical properties improved significantly with the use of hybrid fibers. Hence, this study has demonstrated that for structural and marine purposes, hybrid fibers can perform better as reinforcement in the sandwich composite than using a single fiber.
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.
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.
Acousto-ultrasonics for defect assessment of composite materials
(2002) Dugmore, Kevin M.; Jonson, Jon David; Walker, Mark
The experiments and their results contained herein will form the basis for the development of a portable non-destructive testing device for composite structures. This device is to be capable of detecting any of a variety of defects and assessing their severity within a short time
An improved finite element model for vibration and control simulation of smart composite structures with embedded piezoelectric sensor and actuator
(2001) Kekana, Marino; Tabakov, Pavel Y.
This thesis details a study conducted to investigate the dynamic stability of an existing active control model (ACFl) of a composite structure embedded with a piezoelectric sensor and actuator for the purpose of vibration measurement and control. Criteria for stability are established based on the second method of Lyapunov which considers the energy of the system. Results show that ACFl is asymptotically stable although piezoelectric control effects persist when the feedback gain is set to zero. Meanwhile, it is required that there should be no control effects occurring through the piezoelectric actuator when the gain is set to zero. In this study, a new active control model (ACF2) is developed to satisfy the stability criteria, which satisfies the requirement of no piezoelectric control effects when the gain is set to zero. In ACF2 - as well as ACFl - the displacement and potential fields are discretised using the finite element method. In light of the locking phenomena associated with discrete displacements - which is expected to be pronounced in the case of discrete potentials due to their element geometry, ACF2-mixed is developed. ACF2 and ACF2-mixed control methodologies are similar except that in ACF2 both the displacement and potential field are discretised whereas in ACF2-mixed, only the displacement field is discretised and the potential field is continuous. Consequent to ACF2 and ACF2-mixed, stability analysis of the resulting time integration scheme is investigated as well. The results show that the damping forces due to the piezoelectric effect do not add energy to the structure. Hence, asymptotic stability is achieved. The time integration scheme yielded a small error, consistent with the literature. Numerical results revealed that ACFl exhibits a high degree of locking which is relaxed in ACF2 whereas ACF2-mixed exhibits envisaged results when compared with the other two models. Therefore, the ACF2 and ACF2-mixed will provide engineers with an alternative simulation model to solve actively controlled vibration problems hitherto.
Development of prototype UCAV airframe components using advanced composite materials
(2004) Jordan, Kenneth Gary; Jonson, Jon David
The study presented here addresses the design of the composite wing and canard structures for an -un-inh-ab-it-ed-combat air vehicle. The desian philosophy is based on a ~- combination of finite element analysis and mathematical programming. The wings and canards were manufactured using advanced composite materials. the manufacturing methodology was based on a rapid protoryping approach using 3D computer models and eNe machining. The theory of composite materials is covered in detail, attention IS given to the properties of the separate constituents, composite material properties and manufacturing methods that are relevant to the project. The finite element method and sequential linear programming are discussed in the context of structural analysis and optimisation. An overview of the methodology and how it is implemented is presented. Numerical optimisation techniques are discussed with particular emphasis being placed on sequential linear programming. The optimisation problem formulation is presented in detail with attention paid to elements and their formulation as well as design variables, constraints and sensitivity analysis. Two design concepts were considered for the wing and canard structures, the first being a conventional configuration and the second being a novel radial design. The development and evaluation of these structural concepts are presented in detail. The optimisation study done on the canard is also presented as well as the manufacture thereof. Details regarding the manufacturing methodology used in the construction of the canard for the uninhabited combat air vehicle are presented in detail with particular
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.
The development of an advanced composite structure using evolutionary design methods
(2008) Van Wyk, David; Jonson, Jon David
The development of an evolutionary optimisation method and its application to the design of an advanced composite structure is discussed in this study. Composite materials are increasingly being used in various fields, and so optimisation of such structures would be advantageous. From among the various methods available, one particular method, known as Evolutionary Structural Optimisation (ESO), is shown here. ESO is an empirical method, based on the concept of removing and adding material from a structure, in order to create an optimum shape. The objective of the research is to create an ESO method, utilising MSC.Patran/Nastran, to optimise composite structures. The creation of the ESO algorithm is shown, and the results of the development of the ESO algorithm are presented. A tailfin of an aircraft was used as an application example. The aim was to reduce weight and create an optimised design for manufacture. The criterion for the analyses undertaken was stress based. Two models of the tailfin are used to demonstrate the effectiveness of the developed ESO algorithm. The results of this research are presented in the study.
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.

Theses and dissertations (Engineering and Built Environment)

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