Strategies to improve stem yield and juice quality in sweet sorghum were investigated in this study. Seed quality of sixty five accessions (landraces) from Botswana was investigated. Standard germination tests revealed that only 66% of the accessions had germination percentages in excess of 85%. The Accelerated Ageing test showed that only 50%of the 26 accessions had germination percentages above 80%. The results indicated that Botswana sweet sorghum seed quality is generally poor. Seed development and maturity observations demonstrated that maximum seed quality occurred 14 to 17 days after mass maturity (physiological maturity) and this coincided with maximum seed germination. These results suggest that harvesting sweet sorghum seed prior to mass maturity can lower seed quality. Farmers should, therefore be advised to select plants intended for seed harvesting and allow them to mature properly before the seeds are harvested. Differences in seed colour, shape and compactness of the inflorescences were observed amongst the 65 landraces collected from farmers in Botswana. Ten landraces were characterised and from the results it was evident that there was a range of genetic diversity which can be utilized in the improvement of the crop. Large panicles were characteristic of most sweet sorghum landraces, the effect of tiller, panicle and floret removal on juice quality was consequently studied. Removal of panicles and florets significantly improved juice quality whilst removal of tillers did not. Selection and breeding of genotypes with small panicles and male sterile varieties may improve juice quality and should be investigated. Effect of planting date, spacing and nitrogen were investigated. Early planting (October) resulted in increased stem yields but reduced juice quality. A 30 cm intra-row spacing resulted in high stem yields per plant and good juice quality. Nitrogen fertilisation increased stem yield and improved juice quality. On the bases of the results obtained from this study, early planting (October), application of 60 kg N ha-¹, and 30 cm intra-row spacing could be recommended for sweet sorghum production in pure stands. In pure stands yields of more than 37 000 stems (per hectare) of good quality can be attained. These could be sold at an estimated price of P2.00 (R2.25) per stem indicating the potential of sweet sorghum as a cash crop. However, its economic viability depends on the price elasticity in the supply - demand function. / Dissertation (PHD)--University of Pretoria, 2003. / Plant Production and Soil Science / unrestricted

AR-Glas wird in Form von Multifilamentgarn zur Verstärkung in textilbewehrtem Beton eingesetzt. Während des Herstellungsprozesses wird auf die AR-Glasfilamente die Schlichte aufgebracht, deren chemische Zusammensetzung maßgeblich die Qualität der Filament-Matrix-Grenzschicht bestimmt, sowie die chemische Beständigkeit im alkalischen Milieu gewährleistet. Zur Beurteilung der chemischen Beständigkeit in alkalischer Umgebung werden beschleunigte Alterungsversuche in wässrigen, alkalischen Lösungen durchgeführt. Die Reaktion von Hydroxid-Ionen mit dem Si-O-Si-Gruppen des Glasnetzwerkes führt zur Ausbildung hydratisierter Oberflächen und gelösten Silikaten. Das Ausmaß der Glaskorrosion ist von der chemischen Zusammensetzung der Glasfaser, der Schlichte bzw. Beschichtung und der alkalischen Lösung sowie von Zeit und Temperatur abhängig. Die beschleunigte Alterung von verschiedenen AR-Glasfasern in NaOH-Lösung sowie Zementlösung zeigt, dass sich der Korrosionsmechanismus aufgrund der vorhandenen Calcium-Ionen unterscheidet. Die Filamentbruchspannung wird anhand der Weibull-Verteilungsfunktion analysiert. Das mechanische Verhalten hängt deutlich von der chemischen Zusammensetzung der Alterungslösung ab, was zu unterschiedlichen Parametern der Weibull-Verteilungsfunktion sowie vermengten Verteilungen führen kann. Die Alterung in NaOH-Lösung führt zur Ausbildung einer korrodierten Schicht an der Filamentoberfläche. In Ca-haltigen Zementlösungen kommt es dagegen zu einer lokal begrenzten Korrosion. Für die Beurteilung verschiedener Polymerbeschichtungen werden Betonverbunde bei unterschiedlichen Temperaturen und Umgebungsfeuchten gelagert, wodurch geeignete Alterungsbedingungen evaluiert werden und den Vergleich der chemischen Beständigkeit unterschiedlicher Beschichtungen ermöglichen. / Rovings made of AR-glass are used in textile reinforced concrete. During the manufacturing process the sizing is applied on the AR-glass filaments. The chemical constitution of the sizing determines the quality of the filament-matrix-interface but also the chemical durability of the glass filaments in alkaline environment. The durability is evaluated by accelerated ageing tests in aqueous, alkaline solutions. In alkaline solutions, the reaction of hydroxyl ions with Si-O-Si-groups of the glass network leads to the formation of hydrated surfaces and dissolved silicate. The rate of this corrosion depends on the chemical constitution of the fibre and the alkaline solution as well as on time and temperature. The investigation of the ageing of glass fibres with different chemical constitutions in NaOH and cement solutions shows that the corrosion mechanism changes due to the inhibiting effect of calcium ions. The strength distributions have been evaluated using a Weibull distribution function. The mechanical behaviour strongly depends on the chemistry of the solution and determines the parameters of the Weibull distribution function in terms of either single or mixed distributions. The corrosion in NaOH solution leads to a strong dissolution of the outer layer of the glass fibres, whereas during aging in cement solution at the same pH-value a limited, local attack was revealed. The evaluation of polymer coatings is realised by the ageing of concrete composites at different temperatures and humidities to deduce adequate ageing conditions for the comparison of different coatings.

In alkalischen Lösungen führt die Reaktion von Hydroxylionen mit den Si-O-Si-Bindungen des Glasnetzwerks zur Bildung hydratisierter Oberflächen und gelöstem Silikat. Der Grad der Korrosion bzw. der Alterung der Glasfaser ist abhängig von der chemischen Zusammensetzung des Glases und Korrosionslösung sowie von Zeit und Temperatur. Die Untersuchung von Glasfasern verschiedener chemischer Zusammensetzung in NaOH- sowie Zementlösungen zeigte, dass die inhibierende Wirkung von Ca-Ionen zu einem veränderten Korrosionsmechanismus führt. Dies konnte anhand der mechanischen Eigenschaften der Glasfasern sowie rasterelektronenmikroskopischen Untersuchungen gezeigt werden. Während die Korrosion in NaOH-Lösung zu einer ausgeprägten Umwandlung der gesamten äußeren Glasfaserschicht in Reaktionsprodukte führte, zeigten Glasfasern in Zementlösung bei gleichem pH-Wert einen stark lokal begrenzten, punktförmigen Angriff. Daraus resultieren unterschiedliche mechanische Eigenschaften der Glasfasern in Abhängigkeit von der gewählten Korrosionslösung.

The physical complications of Type 1 diabetes mellitus (T1DM) have been understood as an accelerated ageing process (Morley, 2008). Do people with T1DM also experience accelerated cognitive and brain ageing? Using findings from research of the normal cognitive and brain ageing process and conceptualized in theories of the functional brain changes in cognitive ageing, a combination of cognitive testing and functional magnetic resonance imaging (fMRI) techniques were used to evaluate evidence of accelerated cognitive and brain ageing in middle-aged adults with T1DM. The first part of this thesis comprises a cognitive study of 94 adults (≥ 45 years of age) with long duration (≥ 10 years) of T1DM. Participants completed cognitive assessment and questionnaires on general mood and feelings about living with diabetes. Findings highlighted the importance of microvascular disease (specifically retinopathy) as an independent predictor of cognitive function. The incidence and predictors of mild cognitive impairment (MCI) were then explored. Results indicate a higher percentage of the group met criteria for MCI than expected based on incidence rates in the general population, providing initial evidence of accelerated cognitive ageing. Psychological factors were explored next. The relationship between the measures of well-being, diabetes health, and cognitive function highlighted the need for attention to patient's psychological well-being in diabetes care. Finally, a subgroup of 30 participants between the ages of 45 and 65 who differed on severity of retinopathy were selected to take part in an fMRI study. Blood oxygen level dependent (BOLD) activity was evaluated while participants were engaged in cognitive tasks and during rest. The findings provided evidence that the pattern of BOLD activation and functional connectivity for those with high severity of retinopathy are similar to patterns found in adults over the age of 65. In line with the theories of cognitive ageing, functional brain changes appear to maintain a level of cognitive function. Evidence of accelerated brain ageing in this primarily middle-aged group, emphasizes the importance of treatments and regimens to prevent or minimize microvascular complications.

Le domaine aéronautique connait de nos jours un engouement sans précédent autour de l’avion plus électrique. L’importance du nombre d’équipements électriques est à un tel point que l’amélioration de leur fiabilité devient incontournable. Actuellement, les composants passifs occupent 75 % des éléments électroniques utilisés en avionique dont la moitié correspond à des condensateurs. Ces derniers doivent donc répondre aux exigences environnementales avioniques assez contraignantes. C’est dans ce contexte que nous nous sommes intéressés particulièrement à l’étude des condensateurs à technologie film utilisant le polypropylène ou le polyester comme diélectrique. Afin de mieux comprendre le comportement fréquentiel de cette technologie, deux modèles fins de condensateurs films ont été développés, permettant ainsi de suivre les évolutions de leurs grandeurs électriques dans des conditions cohérentes avec l’application. Dans un deuxième temps, l’effet des contraintes en tension et en température constantes a été étudié sous la forme de facteurs d’accélération du vieillissement. Cela a été établi par l’intermédiaire de plusieurs essais, permettant d’établir les lois d’évolutions temporelles des paramètres électriques des condensateurs. Comme ces contraintes constantes ne sont pas toujours représentatives des conditions réelles d’utilisation, les cinétiques de dégradation ont été comparées à celles où les condensateurs sont sollicités par de fortes ondulations de courant, seules ou associées à une tension continue. Enfin, la dernière partie de notre travail expose l’utilisation des données expérimentales issues des essais de vieillissement dans un objectif de diagnostic en ligne. Les techniques utilisées assurent l'analyse de la dégradation de ces composants, étape essentielle dans la prédiction de l’état de santé des condensateurs en ligne / Nowadays, aeronautic research field is moving towards a more electric aircraft. Although this evolutionary path offers many advantages from a financial and ecological point of view, the increased power source usage sets additional constraints on the different electrical systems used onboard. Currently, passive components occupy 75% of the overall electronic equipments used in avionics, whose 50% corresponds to capacitors. Consequently, these latter must be able to withstand the harsh avionic operating conditions. In this thesis we were particularly interested in the study of metallized film capacitors technology using polyester or polypropylene as dielectric. A first approach consisted on the modeling of these components as function of frequency in order to study the evolution of their electrical parameters under consistent avionic stresses. These models were also developed on the purpose of tracking the degradation of the capacitors parameters over time. This operation was done by the means of accelerated floating ageing tests, where capacitors were subjected to different constant voltages and temperatures. Original capacitance ageing laws were thus proposed based on the identification of voltage and temperature degradation kinetics. However, since traditional floating ageing tests, do not reflects the normal ageing of the component, degradation kinetics of metallized films capacitors under high ripple currents, alone or combined with a DC voltage across the devices terminals where also studied, and the associated failure mechanisms were identified. A final step consisted on the health monitoring of metallized film capacitors online based on the experimental ageing data

In recent years, due to growing environmental awareness, considerable attention has been given to the development and production of natural fibre reinforced polymer (both thermoset and thermoplastic) composites. The main objective of this study was to reinforce epoxy and polylactic acid (PLA) with hemp fibre to produce improved composites by optimising the fibre treatment methods, composite processing methods, and fibre/matrix interfacial bonding. An investigation was conducted to obtain a suitable fibre alkali treatment method to: (i) remove non-cellulosic fibre components such as lignin (sensitive to ultra violet (UV) radiation) and hemicelluloses (sensitive to moisture) to improve long term composites stability (ii) roughen fibre surface to obtain mechanical interlocking with matrices (iii)expose cellulose hydroxyl groups to obtain hydrogen and covalent bonding with matrices (iv) separate the fibres from their fibre bundles to make the fibre surface available for bonding with matrices (v) retain tensile strength by keeping fibre damage to a minimum level and (vi) increase crystalline cellulose by better packing of cellulose chains to enhance the thermal stability of the fibres. An empirical model was developed for fibre tensile strength (TS) obtained with different treatment conditions (different sodium hydroxide (NaOH) and sodium sulphite (Na2SO3) concentrations, treatment temperatures, and digestion times) by a partial factorial design. Upon analysis of the alkali fibre treatments by single fibre tensile testing (SFTT), scanning electron microscopy (SEM), zeta potential measurements, differential thermal analysis/thermogravimetric analysis (DTA/TGA), wide angle X-ray diffraction (WAXRD), lignin analysis and Fourier transform infrared (FTIR) spectroscopy, a treatment consisting of 5 wt% NaOH and 2 wt% Na2SO3 concentrations, with a treatment temperature of 120oC and a digestion time of 60 minutes, was found to give the best combination of the required properties. This alkali treatment produced fibres with an average TS and Young's modulus (YM) of 463 MPa and 33 GPa respectively. The fibres obtained with the optimised alkali treatment were further treated with acetic anhydride and phenyltrimethoxy silane. However, acetylated and silane treated fibres were not found to give overall performance improvement. Cure kinetics of the neat epoxy (NE) and 40 wt% untreated fibre/epoxy (UTFE) composites were studied and it was found that the addition of fibres into epoxy resin increased the reaction rate and decreased the curing time. An increase in the nucleophilic activity of the amine groups in the presence of fibres is believed to have increased the reaction rate of the fibre/epoxy resin system and hence reduced the activation energies compared to NE. The highest interfacial shear strength (IFSS) value for alkali treated fibre/epoxy (ATFE) samples was 5.2 MPa which was larger than the highest value of 2.7 MPa for UTFE samples supporting that there was a stronger interface between alkali treated fibre and epoxy resin. The best fibre/epoxy bonding was found for an epoxy to curing agent ratio of 1:1 (E1C1) followed by epoxy to curing agent ratios of 1:1.2 (E1C1.2), 1: 0.8 (E1C0.8), and finally for 1:0.6 (E1C0.6). Long and short fibre reinforced epoxy composites were produced with various processing conditions using vacuum bag and compression moulding. A 65 wt% untreated long fibre/epoxy (UTLFE) composite produced by compression moulding at 70oC with a TS of 165 MPa, YM of 17 GPa, flexural strength of 180 MPa, flexural modulus of 10.1 GPa, impact energy (IE) of 14.5 kJ/m2, and fracture toughness (KIc) of 5 MPa.m1/2 was found to be the best in contrast to the trend of increased IFSS for ATFE samples. This is considered to be due to stress concentration as a result of increased fibre/fibre contact with the increased fibre content in the ATFE composites compared to the UTFE composites. Hygrothermal ageing of 65 wt% untreated and alkali treated long and short fibre/epoxy composites (produced by curing at 70oC) showed that long fibre/epoxy composites were more resistant than short fibre/epoxy composites and ATFE composites were more resistant than UTFE composites towards hygrothermal ageing environments as revealed from diffusion coefficients and tensile, flexural, impact, fracture toughness, SEM, TGA, and WAXRD test results. Accelerated ageing of 65 wt% UTLFE and alkali treated long fibre/epoxy (ATLFE) composites (produced by curing at 70oC) showed that ATLFE composites were more resistant than UTLFE composites towards hygrothermal ageing environments as revealed from tensile, flexural, impact, KIc, SEM, TGA, WAXRD, FTIR test results. IFSS obtained with untreated fibre/PLA (UFPLA) and alkali treated fibre/PLA (ATPLA) samples showed that ATPLA samples had greater IFSS than that of UFPLA samples. The increase in the formation of hydrogen bonding and mechanical interlocking of the alkali treated fibres with PLA could be responsible for the increased IFSS for ATPLA system compared to UFPLA system. Long and short fibre reinforced PLA composites were also produced with various processing conditions using compression moulding. A 32 wt% alkali treated long fibre PLA composite produced by film stacking with a TS of 83 MPa, YM of 11 GPa, flexural strength of 143 MPa, flexural modulus of 6.5 GPa, IE of 9 kJ/m2, and KIc of 3 MPa.m1/2 was found to be the best. This could be due to the better bonding of the alkali treated fibres with PLA. The mechanical properties of this composite have been found to be the best compared to the available literature. Hygrothermal and accelerated ageing of 32 wt% untreated and alkali treated long fibre/PLA composites ATPLA composites were more resistant than UFPLA composites towards hygrothermal and accelerated ageing environments as revealed from diffusion coefficients and tensile, flexural, impact, KIc, SEM, differential scanning calorimetry (DSC), WAXRD, and FTIR results. Increased potential hydrogen bond formation and mechanical interlocking of the alkali treated fibres with PLA could be responsible for the increased resistance of the ATPLA composites. Based on the present study, it can be said that the performance of natural fibre composites largely depend on fibre properties (e.g. length and orientation), matrix properties (e.g. cure kinetics and crystallinity), fibre treatment and processing methods, and composite processing methods.

Chromatography and extraction techniques, and also chemiluminescence have been utilized to develop new rapid and informative tools in the evaluation of long-term properties and environmental effects of polymeric materials. Methods were developed for classification of materials and for early and rapid degradation detection. Degradable polyethylene films were classified on the basis of their incorporated prooxidant systems using chromatographic fingerprinting of carboxylic acids, the dominating type of degradation product. The fingerprints were also shown to be useful for prediction of the degradation states and evaluation of the degradation mechanisms. Classification and prediction models were obtained by Multivariate Data Analysis, where the diacids were grouped according to both their type of prooxidant system and their state of degradation. The use of total luminescence intensity (TLI) measurements was also investigated as a means of classifying films and for the early detection of degradation. Comparisons were carried out with common techniques, e.g. FTIR and DSC, after both thermal and UV oxidation. TLI gave an earlier detection of degradation and was more sensitive than carbonyl index and crystallinity measurements to relative differences in degradation between the materials. It furthermore offered complementary information regarding changes in activation energies during the course of the degradation. The results were compared with the chromatographic fingerprints. A new way to evaluate the low temperature long-term stabilisation efficiency of antioxidants was investigated. A prooxidant was used to obtain catalytic oxidation, instead of using thermal acceleration, to evaluate the stabilisation efficiency of antioxidants at low temperatures but still during reasonably short aging times. Comparisons were made between polypropylene films stabilised with primary antioxidants (Irganox 1076, Irganox 1010 and α-tocopherol) with and without the prooxidant manganese stearate at different temperatures. The relative efficiencies of the antioxidants obtained under prooxidant acceleration test correlated better than thermal acceleration test with the results of a long-term low temperature test. Additives in plastic packaging materials may affect the environment after migration from the packaging to e.g. their contents, especially if they consist of organic aqueous solutions or oils. The use of Solid-Phase Microextraction (SPME) for the specific task of extraction from an organic aqueous solution such as a simulated food or pharmaceutical solution consisting of 10 vol-% ethanol in water was investigated. Methods were developed and evaluated for extraction both with direct sampling and with headspace sampling. If the extraction method and temperature were selected to suit the concentration levels of the analytes, it was possible to quantify several degradation products simultaneously. Comparisons made with Solid Phase Extraction showed the advantage of SPME for this purpose. / QC 20100929

Dans le cas des installations photovoltaïques, l’onduleur est le premier élément défaillant dont il est difficile d’anticiper la panne, et peu d’études ont été faites sur la fiabilité de ce type de convertisseur. L'objectif de cette thèse est de proposer des outils et méthodes en vue d'étudier le vieillissement des modules de puissance dans ce type d'application en se focalisant sur les phénomènes de dégradation liés à des aspects thermomécaniques. En règle générale, le vieillissement accéléré des modules de puissance est effectué dans des conditions aggravées de courant (Cyclage Actif) ou de température (Cyclage Passif) pour accélérer les processus de vieillissement. Malheureusement, en appliquant ce type de vieillissement accéléré, des mécanismes de défaillances qui ne se produisent pas dans la vraie application peuvent être observés et, inversement, d'autres mécanismes qui se produisent habituellement peuvent ne pas apparaître. La première partie de la thèse se focalise donc sur la mise en place d'une méthode de vieillissement accéléré des composants semi-conducteurs des onduleurs photovoltaïques. Cela est fait en s’appuyant sur l’analyse des profils de mission du courant efficace de sortie des onduleurs et de la température ambiante, extraits des centrales photovoltaïques situées au sud de la France sur plusieurs années. Ces profils sont utilisés pour étudier les dynamiques du courant photovoltaïque, et sont introduites dans des modèles numériques pour estimer les pertes et les variations de la température de jonction des semi-conducteurs utilisés dans les onduleurs, en utilisant l’algorithme de comptage de cycles "Rainflow". Cette méthode est ensuite mise en œuvre dans deux bancs expérimentaux. Dans le premier, les composants sous test sont des modules IGBT. Les composants sont mis en œuvre dans un banc de cyclage utilisant la méthode d'opposition et mettant en œuvre le profil de vieillissement défini précédemment. Un dispositif in-situ de suivi d'indicateurs de vieillissement (impédance thermique et résistance dynamique) est également proposé et évalué. Le deuxième banc est consacré à l'étude de modules de puissance à base de MOSFET SiC. Le vieillissement est effectué dans les mêmes conditions que pour les modules IGBT et de nombreux indicateurs électriques sont monitorés mais, cette fois ci, en extrayant les composants de l'onduleur de cyclage. Les résultats obtenus ont permis de déterminer des indicateurs de vieillissement d’IGBT et de MOSFET SiC utilisés dans un onduleur photovoltaïque / In the case of photovoltaic installations, the DC/AC inverter has the highest failure rate, and the anticipation of its breakdowns is still difficult, while few studies have been done on the reliability of this type of inverter. The aim of this PhD is to propose tools and methods to study the ageing of power modules in this type of application, by focusing on ageing phenomena related to thermo-mechanical aspects. As a general rule, the accelerated ageing of power modules is carried out under aggravated conditions of current (Active Cycling) or temperature (Passive Cycling) in order to accelerate the ageing process. Unfortunately, when applying this type of accelerated ageing tests, some failure mechanisms that do not occur in the real application could be observed, while inversely, other mechanisms that usually occur could not be recreated. The first part of the PhD focuses on the implementation of an accelerated ageing method of the semiconductor devices inside photovoltaic inverters. This is accomplished by analyzing the mission profiles of the inverter’s output current and ambient temperature, extracted over several years from photovoltaic power plants located in the south of France. These profiles are used to study photovoltaic current dynamics, and are introduced into numerical models to estimate losses and junction temperature variations of semiconductors used in inverters, using the cycle counting algorithm “Rainflow”. This method is then performed in two experimental test benches. In the first one, the devices under test are IGBT modules, where the accelerated ageing profile designed is implemented using the opposition method. Moreover, an in-situ setup for monitoring ageing indicators (thermal impedance and dynamic resistance) is also proposed and evaluated. The second bench is devoted to study the ageing of SiC MOSFET power modules. The accelerated ageing test is carried out under the same conditions as for the IGBT modules with more monitored electrical indicators, but this time by disconnecting the semiconductor devices from the inverter. The results obtained allowed to determine several potential ageing indicators of IGBTs and SiC MOSFETs used in a photovoltaic inverter

Ces travaux s’intègrent dans le projet de recherche SUPERSWITCH dans lequel des solutions alternatives à l’IGBT, utilisées dans les convertisseurs de puissance dans la gamme des tenues en tension 600-1200 V, sont envisagées. Les nouvelles structures du transistor MOS basées sur le principe de Super-Jonction tel que le transistor DT-SJMOSFET et sa terminaison originale, la « Deep Trench Termination » se propose comme alternative aux IGBT. Dans ce contexte, cette thèse se focalise sur la caractérisation de la robustesse de la terminaison DT2 adapté à une diode plane. Après avoir effectué un état de l’art sur les composants de puissances à semi-conducteur unidirectionnels en tension, les terminaisons des composants de puissance et la fiabilité des modules de puissance, un véhicule de test a été conçu en vue de réaliser les différents essais de vieillissement accéléré et suivi électrique. La fiabilité de la terminaison DT2 a été évaluée par des essais expérimentaux et des simulations numériques, dont une méthodologie innovante a été proposée. Au final de nouvelles structures ont été proposées pour limiter les problèmes de délaminage et de charges aux interfaces mis en avant dans notre étude. / This work is a part of the research project SUPERSWITCH in which alternatives solutions to the IGBT, are investigated. This solution was used IGBT in power converters in the 600-1200 V breakdown voltage range. The new MOSFET structures based on the super-junction, such as the DT-SJMOSFET and its "Deep Trench Termination", is proposed as an alternative to IGBT. In this context, this thesis focuses on the robustness characterization of the DT2 termination adapted to a planar diode. After a state of the art on unidirectional voltage power components, the power components termination, and power modules reliability, a test vehicle has been designed in order to carry out different accelerated ageing tests and electrical monitoring. The reliability of DT2 termination was evaluated by experimental tests and numerical simulations. An innovative modeling methodology has been proposed. Finally, new structures have been proposed to limit the delamination failure mechanisms and interface charges problems highlighted in this thesis.