The objective of this research was the development of a novel synthetic method for preparation of silver/polymer nanocomposites containing finely dispersed silver nanoparticles. The surface of nanosilver was functionalized by amino groups, which then reacted with end acidic groups of polylactide (PLA) and its co-polymer with polyglycolide (PLGA). The condensation reaction was conducted in the presence of diisopropylcarbodiimide. Nanosilver coating with the polymers was confirmed by FT-IR and UV-vis spectroscopy. It was found that not only acid-terminated but also ester-terminated polymers can react with functionalized nanosilver. However, high dispersibility of the nanoparticles was achieved with acid-terminated polymers only. Obtained materials demonstrated X-ray contrast and bactericidal properties that makes possible their prospective application in biology and medicine.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfiment of the requirements for the degree of Master or Science in Engineering. Johannesburg, 1993. / The stress concentration factors around rectangular holes in carbon-fibre reinforced epoxy plates, subject uniaxial loads, were investigated experimentally and theoretically. To obtain theoretical solutions, two approaches were adopted; the finite element method and the theory of elasticity using the method of complex variable functions. Reflective photoelasticity was used as the experimental method. The determination of the stress concentration factor around a rectangular hole in a glass-fibrereinforced plate was attempted using transmissive photoelasticity, but no meaningful results were obtained. [Abbreviated Abstract. Open document to view full version} / MT2017

Bonding composite structures using adhesives offers several advantages over mechanical fastening such as better flow stress, weight saving, improved fatigue resistance and the ability to join dissimilar structures. The hesitation to adopt adhesively bonded composite joints stems from the lack of knowledge regarding damage initiation and propagation mechanisms within the joint. A means of overcoming this hesitation is to continuously monitor damage in the joint. This study proposes a methodology to conduct structural health monitoring (SHM) of an adhesively bonded composite lap joint using acoustic, guided Lamb waves by detecting, locating and predicting the size of damage. Finite element modeling of a joint in both 2D and 3D is used to test the feasibility of the proposed damage triangulation technique. Experimental validation of the methodology is conducted by detecting the presence, location and size of inflicted damage with the use of tuned guided Lamb waves.

No description available.

Carbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization. These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The formulation of a new fitting procedure using the pseudo-Voigt function is presented and shown to minimize the uncertainty of characteristics within the Raman G and D doublet. Methods for optimization of manufacturing processes using the Raman characterization are presented for selected applications in a polymer multiwalled nanotube (MWNT) composite and laser-sintered ceramic-MWNT composite. In the first application, the evolution of the MWNT microstructure throughout a functionalization and processing of the polymerMWNT composite was monitored using the G peak position and D/G intensity ratio. Processing parameters for laser sintering of the ceramic-MWNT composites were optimized by obtaining maximum downshift in stress sensitive G-band peak position, while keeping disorder sensitive D/G integrated intensity ratio to a minimum. Advanced Raman techniques, utilizing multiple wavelengths, were used to show that higher excitation energies are less sensitive to double resonance Raman effects. This reduces their influence and allows the microstructural strain in CNT composites to be probed more accurately. iii The use of these techniques could be applied to optimize any processing parameters in the manufacturing of CNT composites to achieve enhanced properties.

Composite materials are extensively used as an advanced engineering material, particularly in aerospace, automotive, and buildings industries due to its superior properties such as high strength to weight ratios and resistance to corrosion. As composite materials are rapidly replacing traditional materials in aircraft manufacturing, improved methods of identifying damage and critical failure is in development. One of the most commonly used procedures utilizes a health monitoring system that relies on transducers to monitor transmitted waves generated by ultrasonics. By replacing this method with a nanotechnology-based one, it is possible to efficiently detect damage without the time-extensive process of scanning the structure. This research investigated the development of a nanomaterial-based sensor for health monitoring of composite structures. To develop the sensor, carbon nanotube/epoxy mixture (2%wt CNT) was coated on a strand of E-glass fibre to be adhered onto a fiberglass composite specimen. The selection of E-glass fibre and fibreglass plate was largely due to its electrical insulating properties to demonstrate that the carbon nanotube is driving the sensing capabilities through its highly conductive nature. In addition, by adhering the coated E-glass fiber to a fibreglass coupon, the homogeneity and material properties were approximately maintained. Tensile testing of the specimen conducted through a Lloyd LD50 tensile testing machine provided data on the actual strain which was correlated with the experimental differential resistances measured by a multimeter, both at the same specified tensile loading conditions. With two sets of data, the experimental resistance data was calibrated with the actual strain data collected. Ultimately, the experimental sensors created a sample of gauge factors which represents 91.24% probability of replicating the observed range of gauge factors by using the same manufacturing procedures, providing a valid alternative and consistent method to detecting composite damage.

A computationally efficient analysis approach is developed to predict buckling load of geodesically stiffened composite panels under in-plane loads. The analysis procedure accounts for the contribution of the in-plane extensional and out-of-plane bending stiffnesses of the stiffeners through the use of Lagrange multipliers in an energy method solution. The analysis is used to isolate the effect of various stiffener deformation modes on the buckling load and skin deformation patterns of geodesically stiffened panels under various load combinations. The analysis routines are then coupled with the numerical optimizer ADS to create a package for the design of minimum-mass stiffened panels, subject to constraints on buckling of the panel assembly and material strength failure. Material failure in the skin and stiffeners are estimated using a maximum strain criterion. The design variables that can be used for optimization include thickness of the skin laminate, stiffener thickness and height, and positions of straight stiffeners. Applied loads are uniaxial compression, pure shear, and combined compression-shear. / Master of Science

This thesis provides a general theory of the diffraction of ultrasonic waves. The theory is then used to find the apparent attenuation which would result if certain damage states (transverse cracks and delaminations) are introduced into a graphite/epoxy laminate through which the ultrasonic wave passes. and [0, ±45, 90]s) is presented which shows changes in the apparent attenuation of, about 1 dB. These changes generally occur at loads which correspond to the range predicted for the formation of the above mentioned damage. Though no exact correlation between theoretical and experimental results is given, the predicted changes in the attenuation for several simple and common damage states are well within the range of experimental values. It is hoped that the technique described herein can be further developed and used to detect the formation and growth of damage in composite specimens in regions not readily visible by conventional techniques. / Master of Science

No / Advances in micromoulding technology are leading to complex,net-shape products having sub-milligramme masses with micro-scale surface features in a range of polymer and nano-composite materials.For such small components subjected to the extreme stress,strain-rate and temperature gradients encountered in the micromoulding process,detailed process monitoring is desirable to highlight variations in moulding conditions and assist in creating a viable manufacturing process with acceptable quality products.This paper covers the implementation of a suite of sensors on a commercial micromoulding machine and detailed computer monitoring during processing of a polyacetal component over a range of processing conditions.The results determined that cavity pressure curve integral data provides the most sensitive factor for characterisation of a moulding process of a 0.34 mm~3(0.49 mg)product.The repeatability of the process is directly compared with that of a 15.6mm~3(22.2 mg)product and shown to beinferior.DSC measurements of the whole products indicated little variation in average crystallinity of the products manufactured over a mould temperature range of 30 to 130deg C.

The primary objective of this research is to investigate the morphological and mechanical properties of composite materials and porous materials prepared by thermally induced phase separation. High melting crystallizable diluents were mixed with polymers so that the phase separation would be induced by the solidification of the diluents upon cooling. Theoretical phase diagrams were calculated using Flory-Huggins solution thermodynamics which show good agreement with the experimental results. Porous materials were prepared by the extraction of the crystallized diluents after cooling the mixtures (hexamethylbenzene/polyethylene and pyrene/polyethylene). Anisotropic structures show strong dependence on the identity of the diluents and the composition of the mixtures. Anisotropic crystal growth of the diluents was studied in terms of thermodynamics and kinetics using DSC, optical microscopy and SEM. Microstructures of the porous materials were explained in terms of supercooling and dendritic solidification. Dual functionality of the crystallizable diluents for composite materials was evaluated using isotactic polypropylene (iPP) and compatible diluents that crystallize upon cooling. The selected diluents form homogeneous mixtures with iPP at high temperature and lower the viscosity (improved processability), which undergo phase separation upon cooling to form solid particles that function as a toughening agent at room temperature. Tensile properties and morphology of the composites showed that organic crystalline particles have the similar effect as rigid particles to increase toughness; de-wetting between the particle and iPP matrix occurs at the early stage of deformation, followed by unhindered plastic flow that consumes significant amount of fracture energy. The effect of the diluents, however, strongly depends on the identity of the diluents that interact with the iPP during solidification step, which was demonstrated by comparing tetrabromobisphenol-A and phthalic anhydride. A simple method to prepare composite surfaces that can change the wettability in response to the temperature change was proposed and evaluated. Composite surfaces prepared by nanoporous alumina templates filled with polymers showed surface morphology and wettability that depend on temperature. This effect is attributed to the significant difference in thermal conductivity and the thermal expansion coefficient between the alumina and the polymers. The reversibility in thermal response depends on the properties of the polymers.