Innovative new flooring systems utilising lightweight fibre reinforced polymer composite materials may have the significant potential to offer both economic and performance benefits for infrastructure asset owners compared to conventional concrete and steel systems. Over recent years, a range of prototype floor systems using fibre reinforced polymer composites have been developed by researchers at the University of Southern Queensland. However before such structural systems can be widely adopted by industries, fundamental understanding of their behaviour must be improved. Such work will allow for the development of new design and analysis procedures which will enable engineers to efficiently and accurately design and analyse such structures. This dissertation presents an investigation into a new two-way fibre reinforced composite floor slab system. The proposed new two-way slab system is, in essence, a sandwich structure with an innovative hollow core made from a castable particulate filled resin system. The key focus of this dissertation is the development of a new analysis tool to analyse the two-way fibre reinforced composite slab and facilitate subsequent parametric studies into slab configurations for concept refinement. The detailed 3D finite element analyses and experimental investigations are performed to verify the new analysis tool, and provide more detailed insight into the structural behaviour of this new two-way fibre reinforced composite slab. Comparisons with detailed 3D FEA and experiments illustrate that the simplified analysis tool is capable of providing sufficient accuracy for the preliminary analysis of a slab structure. Moreover, the 3D finite element analyses agree well with the experiments, and it is concluded that the behavioural responses of the proposed new slab structure can be reliably predicted. The experimental results show that this new slab concept exhibits quite a robust static behaviour and is likely to have a robust fatigue performance.

Abstract Electromagnetic shielding of nylon-66 composites applied to laser modules was studied experimentally and theoretically. The effects of conductive carbon fiber length and weight percentage upon the shielding effectiveness (SE) of nylon composites were investigated. The result showed that the SE of long carbon fiber filled nylon-66 composites was found to be higher SE than short carbon fiber filled nylon-66 composites under the same weight percentage of carbon fibers. In addition, higher electromagnetic shielding was obtained for the composite with higher contents of carbon fibers at the same length. The SE of conductive carbon fiber filled nylon-66 composites was measured to be 41 dB at low frequency of 30 MHz and 59 dB at high frequency of 1.5 GHz. The results of SE predicted by the proposed theoretical model and the results measured by experiments were in good agreement with each other for carbon fibers filled nylon-66 composites of different lengths. The effects of fiber orientation on SE of nylon and LCP composites were also investigated. The result showed that the SE of LCP composites was found to be higher than nylon composites under the same weight percentage of carbon fiber. This is due to that the fiber orientation in LCP composites attempts to keep the same direction.

The purpose of this work is to solve governing differential equations of laminated anisotropic plates and shells by using the Chebyshev collocation method. This method yields these results those can not be accomplished easily by both Navier¡¦s and Levy¡¦s methods in the case of any kind of stacking sequence in composite laminates with the variety of boundary conditions subjected to any type of loading. The Chebyshev polynomials have the characteristics of orthogonality and fast convergence. They and Gauss-Lobatto collocation points can be utilized to approximate the solution of these problems in this paper. Meanwhile, these results obtained by the method are presented as some mathematical functions that they are more applicable than some sets of data obtained by other methods. On the other hand, by simply mathematical transformation, it is easy to modify the range of Chebyshev polynomials from the interval [-1,1] into any intervals. In general, the research on laminated anisotropic plates is almost focused on the case of rectangular plate. It is difficult to handle the laminated anisotropic plate problems with the non-rectangular borders by traditional methods. However, through the merits of Chebyshev polynomials, such problems can be overcome as stated in this paper. Finally, some cases in the chapter of examples are illustrated to highlight the displacements, stress resultants and moment resultants of our proposed work. The preciseness is also found in comparison with numerical results by using finite element method incorporated with the software of NASTRAN.

Σκοπός της παρούσας εργασίας ειδίκευσης ήταν η παρασκευή νανοσύνθετων υλικών οργανικής μήτρας, καθώς και η θεωρητική πρόβλεψη της θερμικής τους αγωγιμότητας. Στα πλαίσια της εργασίας πραγματοποιήθηκε η παρασκευή σύνθετων πολυμερικών υλικών εποξειδικής μήτρας, ενισχυμένων με δύο είδη νανοσωματιδίων ίδιας φύσης και διαφορετικής δομής (πολυφλοιϊκοί νανοσωλήνες άνθρακα - MWCNTs και πολυστρωματικά γραφένια - GNPs) καθώς και ένα τρίτο είδος νανοσωματιδίων διαφορετικής φύσης (νανοκαρβίδιο του πυριτίου - NanoSiC). Επίσης, πραγματοποιήθηκε η παρασκευή ινωδών σύνθετων υλικών (CFRP μονής διεύθυνσης και διάταξης [0]16) ενισχυμένων με δύο είδη νανοσωματιδίων (GNPs και MWCNTs). Για την παρασκευή των δοκιµίων εφαρμόστηκε η μέθοδος του «masterbatch», σύμφωνα με την οποία παρασκευάζεται ένα μίγμα εποξειδικής ρητίνης και νανοσωματιδίων, υψηλής κατά βάρος περιεκτικότητας, που αναδεύεται σε αναµίκτη υψηλών στροφών, υπό συνθήκες κενού, ελεγχόμενης θερµοκρασίας και ταχύτητας ανάµιξης. Από το «masterbatch», προσθέτοντας κάθε φορά, την επιθυμητή ποσότητα ρητίνης προέκυψαν μίγματα διαφόρων κατά βάρος περιεκτικοτήτων (1, 3, 5, 10 και 15% κ.β. σε GNPs - 1 και 3% κ.β. σε MWCNTs - 1, 3, 5 και 10% κ.β. σε NanoSiC). Το τελικό µίγµα εγχύθηκε σε καλούπια σιλικόνης και εισήχθη σε φούρνο, όπου ακολούθησε η διαδικασία πολυµερισµού για 2h σε θερμοκρασία 120°C. Τέλος, παρασκευάστηκαν πολύστρωτες πλάκες [0]16 πολυστρωματικών γραφενίων και πολυφλοιϊκών νανοσωλήνων άνθρακα αντιστοίχων περιεκτικοτήτων. Τα δοκίµια που προέκυψαν από την παραπάνω διαδικασία, χρησιμοποιήθηκαν για το χαρακτηρισμό της θερμικής αγωγιμότητας, με τη βοήθεια του Mathis Tci Analyzer. Από τη μελέτη των πειραματικών αποτελεσμάτων προέκυψε ότι η θερμική αγωγιμότητα των συνθέτων αυξάνεται, αυξανομένης της συγκέντρωσης των νανοεγκλεισμάτων. Επίσης, τα πολυστρωματικά γραφένια αποτελούν τη βέλτιστη ενίσχυση, σε σχέση με τα υπόλοιπα είδη νανοσωματιδίων που χρησιμοποιήθηκαν, για την βελτίωση της θερμικής αγωγιμότητας τόσο των νανοενισχυμένων πολυμερών όσο και των ινωδών συνθέτων, γεγονός το οποίο οφείλεται κυρίως στη δομή και τη γεωμετρία του. Επίσης, πραγματοποιήθηκε εφαρμογή επιλεγμένων θεωρητικών μοντέλων πρόβλεψης της εγκάρσιας θερμικής αγωγιμότητας, προκειμένου να διαπιστωθεί τυχόν σύγκλιση των θεωρητικών τιμών με τις πειραματικές τιμές. Από την μελέτη των θεωρητικών αποτελεσμάτων προέκυψε ότι το μοντέλο Lewis – Nielsen προβλέπει με τον βέλτιστο δυνατό τρόπο τη θερμική αγωγιμότητα των νανοενισχυμένων πολυμερών, ενώ το μοντέλο που ανέπτυξε ο Hashin τη θερμική συμπεριφορά των ινωδών σύνθετων υλικών. / The purpose of the present master thesis was the experimental and modeling study on the through-thickness thermal conductivity of epoxy nanocomposites. The first step was the dispersion of three different nanoparticles (Graphite-Nanoplatelets - GNPs, Multi Walled Carbon Nanotubes – MWCNTs, Nano-Silicon Carbide - NanoSiC) in a high volume fraction mixture, which is called «masterbatch». The manufacturing technique that was applied was mechanical high speed shearing. Then, «masterbatch» was used for the preparation of epoxy polymers of various volume fractions, reinforced with GNPs, MWCNTs and NanoSiC. Silicon molds were used for the fabrication of the polymer specimens. The polymerization profile was consisted of two hours in temperature 120°C. Moreover, two different types of carbon fiber-reinforced nanocomposites (Unidirectional – UD [0]16) were prepared, which were reinforced with GNPs and MWCNTs in corresponding volume fractions to polymers. The through-thickness thermal conductivity characterization was materialized through Mathis Tci Analyzer. Next, multiple theoretical models were evaluated to predict through-thickness thermal conductivity of both composite systems, and then compared to the experimental results. The results showed that high filler volume fractions heighten thermal conductivity. Moreover, Graphite – Nanoplatelet nanoparticles showed greater thermal conductivity than Carbon Nanotubes and Nano-Silicon Carbide, thanks to its structure and morphology. Lewis –Nielsen model was the appropriate one for the prediction of epoxy polymers, reinforced both GNPs and MWCNTs. Hashin model predicted the through thickness thermal conductivity of carbon fiber reinforced nanocomposites, reinforced both GNPs and MWCNTs.

Steel Fibre Reinforced Concrete (SFRC) is defined as concrete containing randomly oriented discrete steel fibres. The main incentive of adding steel fibres to concrete is to control crack propagation and crack widening after the concrete matrix has cracked. Control of cracking automatically improves the mechanical properties of the composite material (SFRC). The most significant property of SFRC is its post-cracking strength that can impart the ability to absorb large amounts of energy before collapse. Ground slabs are structural applications that could benefit from these advantageous features of the SFRC. Many tests on SFRC ground slabs show that the material can offer distinct advantages compared to plain concrete. In concrete road pavements, SFRC is particularly suitable for increasing load-carrying capacity and fatigue resistance. Not surprisingly, recent years have witnessed acceleration in full-scale tests of SFRC and eventually acceptance of its use in concrete pavements. The use of SFRC in pavements has been slowed down by the absence of a reliable theoretical model to analyse and design these pavements. The analysis of ground slabs has traditionally been based on an elastic analysis assuming un-cracked concrete. Using such a method for SFRC would ignore the post-cracking contribution the SFRC can make to the flexural behaviour of the slab. Despite the growing trend of using methods of analysis based on yield-line theory, which can consider the post-cracking strength of SFRC, these methods were also found to underestimate the load-carrying capacity of SFRC ground slabs. To effectively account for the post-cracking strength of SFRC in the analysis of such slabs requires a method such as the finite element method. In the present work, non-linear methods are used to model the behaviour of SFRC ground slabs subjected to mechanical load. An analytical method is used to determine a tensile stress-strain response for SFRC. In this method, the post-cracking strength of SFRC is taken into account and hence the material model is sensitive to the element size used. The calculated stress-strain response is utilised in finite element analysis of SFRC beams and ground slabs. A smeared crack approach is used to simulate the behaviour of concrete cracking. The analytical method used to determine the tensile stress-strain response, as well as the finite element model, are evaluated using results from experiments on SFRC beams and ground slabs. The analytical results are found to compare well with the observations. The non-linear methods are further used to study the effect of the material model parameters as well as the support stiffness on load-displacement behaviour of SFRC ground slabs. The developed finite element model is shown to be more efficient compared to methods based on the yield-line theory. This is because it produces the load-displacement behaviour of the SFRC ground slab up to a reasonable limit and it provides the tensile stresses as well as the extent of cracking of the slab at every point on the load-displacement response. Using the developed finite element model will allow for considerable material saving since smaller slab thickness can be calculated compared to analytical models currently in use. / Thesis (PhD(Transportation Engineering))--University of Pretoria, 2008. / Civil Engineering / PhD / unrestricted

This diploma thesis deals with short-fibre reinforced composites for dental applications. Particulate barium filler, short polyacrylonitryle fibres or short glass fibres were added to the dimethacrylate matrix to study their effect on the composite material properties. Methods used for this study were thermogravimetric analysis (TGA), differential compensation photocalorimetry (DPC), dynamic mechanical analysis (DMA), three point bending, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The matrix curing was defined by heat of polymerisation, degree of conversion and polymerisation rate. Composite materials were characterized by the glass transition temperature, storage moduli at 35 °C and 100 °C, elastic modulus, strength, the critical value of stress intensity factor and the critical value of energy release rate. Fracture surface investigation is also included in this thesis.

Bioactive glasses exhibit unique characteristics as a material for bone tissue engineering. Unfortunately, their extensive application for the repair of load-bearing bone defects is still limited by low mechanical strength and fracture toughness. The main aim of this work was two-fold: the reinforcement of brittle Bioglass®-based porous scaffolds and the production of bulk Bioglass® samples exhibiting enhanced mechanical properties. For the first task, scaffolds were coated by composite coating constituted by polyvinyl alcohol (PVA) and microfibrillated cellulose (MFC). The addition of PVA/MFC coating led to a 10 fold increase of compressive strength and a 20 fold increase of tensile strength in comparison with non-coated scaffolds. SEM observations of broken struts surfaces proved the reinforcing and toughening mechanism of the composite coating which was ascribed to crack bridging and fracture of cellulose fibrils. The mechanical properties of the coating material were investigated by tensile testing of PVA/MFC stand–alone specimens. The stirring time of the PVA/MFC solution came out as a crucial parameter in order to achieve a more homogeneous dispersion of the fibres and consequently enhanced strength and stiffness. Numerical simulation of a PVA coated Bioglass® strut revealed the infiltration depth of the coating until the crack tip as the most effective criterion for the struts strengthening. Contact angle and linear viscosity measurements of PVA/MFC solutions showed that MFC causes a reduction in contact angle and a drastic increase in viscosity, indicating that a balance between these opposing effects must be achieved. Concerning the production of bulk samples, conventional furnace and spark plasma sintering technique was used. Spark plasma sintering performed without the assistance of mechanical pressure and at heating rates ranging from 100 to 300°C /min led to a material having density close to theoretical one and fracture toughness nearly 4 times higher in comparison with conventional sintering. Fractographic analysis revealed the crack deflection as the main toughening mechanisms acting in the bulk Bioglass®. Time–dependent crack healing process was also observed. The further investigation on the non-equilibrium phases crystallized is required. All obtained results are discussed in detail and general recommendations for scaffolds with enhanced mechanical resistance are served.

Composite laminated structures have many application fields such as aerospace, civil, marine, bio medical, transportation, and mechanical engineering because of their convenience in handling, and very good mechanical properties. Buckling behavior of laminated composite plates subjected to plane loads is indeed an important consideration in the primary design of aircraft and launch vehicle components. In addition, these elements may expose to high-temperature fields (while launching or reentry) which may result in failure due to thermal buckling. Composite laminated plates with holes and other openings are used as structural members in aerospace industry. The buckling behavior of such plates has always received much attention.In this study buckling analysis has been carried out of a laminar composite plate with an elliptical cut to shape. In the analysis, finite element method (FEM) was applied to perform parametric studies on various plates based on the shape and position and orientation of the hole.ANSYS software has been used as a platform for buckling analysis.

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