Theses and dissertations (Engineering and Built Environment)
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Item High speed, high precision processing of dry pre-pregs for composite structures(2019-08-15) Ramsaroop, Avinash; Kanny, KrishnanIn 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.Item Fracture properties of fibre and nano reinforced composite structures(2007) Ramsaroop, AvinashInterlaminar cracking or delamination is an inherent disadvantage of composite materials. In this study the fracture properties of nano and fibre-reinforced polypropylene and epoxy composite structures are examined. These structures were subjected to various tests including Single Edge Notched Bend (SENB) and Mixed Mode Bending (MMB) tests. Polypropylene nanocomposites infused with 0.5, 1, 2, 3 and 5 weight % nanoclays showed correspondingly increasing fracture properties. The 5 weight % specimen exhibited 161 % improvement in critical stress intensity factor (KIC) over virgin polypropylene. XRD and TEM studies show an increase in the intercalated morphology and the presence of agglomerated clay sites with an increase in clay loading. The improvement in KIC values may be attributed to the change in structure. Tests on the fibre-reinforced polypropylene composites reveal that the woven fibre structure carries 100 % greater load and exhibits 275 % lower crack propagation rate than the chopped fibre specimen. Under MMB conditions, the woven fibre structure exhibited a delamination propagation rate of 1.5 mm/min which suggests delamination growth propagates slower under Mode I dominant conditions. The woven fibre / epoxy structure shows 147 % greater tensile modulus, 63 % greater critical stress intensity factor (KIC), and 184 % lower crack propagation rate than the chopped fibre-reinforced epoxy composite. MMB tests reveal that the load carrying capability of the specimens increased as the mode-mix ratio decreased, corresponding to an increase in the Mode II component. Delamination was through fibre–matrix interface with no penetration of fibre layers. A failure envelope was developed and tested and may be used to determine the critical applied load for any mode-mix ratio. The 5 weight % nanocomposite specimen exhibited a greater load carrying capability and attained a critical stress intensity factor that was 10 % less than that of the fibre-reinforced polypropylene structure, which had three times the reinforcement weight. Further, the nanocomposite exhibited superior strain energy release rates to a material with ten times the reinforcement weight. The hybrid structure exhibited 27 % increase in tensile modulus over the conventional fibre-reinforced structure. Under MMB conditions, no significant increase in load carrying capability or strain energy release rate over the conventional composite was observed. However, the hybrid structure was able to resist delamination initiation for a longer period, and it also exhibited lower delamination propagation rates.