This study was undertaken to develop an analytical model that is capable of predicting the torque requirements of a rotavator fitted with commercially available L-shaped blades. An analytical approach based on the limit equilibrium analysis was used to develop the proposed model. The proposed model was verified by comparing the model and measured torque requirements at predetermined rotavator blade angular positions from the horizontal for a down-cut rotavator. The study findings indicated that there was an optimum set tillage depth for each rotavator configuration and operational conditions at which the resultant horizontal thrust generated was greatest. This unique depth was influenced by the bite length. The validation of the proposed model showed that the predicted and measured torque requirements, at different angular blade positions from the horizontal, correlated reasonably well for all the set tillage depths. As the depth of tillage increased, however, the curve for the measured torque requirements exhibited a cyclic behaviour after the peak torque requirements value had been recorded. The cyclic behaviour was probably due to the re-tilling and the instability of the tool-frame carrier, which increased with the set tillage depth. The knowledge contributed by this research will afford the designers of active tillage tools a better understanding of the operations of the rotavator, particularly in deep tillage. The modelling approach, and instrumentation technique used in this research, can be extended to analyze the performance of rotavators fitted with other types of commercial blades. / Thesis (PhD)--University of Pretoria, 2010. / Civil Engineering / unrestricted

Geosynthetics are used in conjunction with soil/particulate materials to serve various functions like reinforcement, drainage, filtration and containment. The shear behavior of soil-geosynthetic interfaces hugely depends upon on the morphological properties of particulate materials and surface characteristics of geosynthetics. However, many researchers have ignored the effects of morphology, owing to the difficulty in finding the morphological characteristics of sand particles. Few of them used visual, manual and imaged based quantifications, which are not very effective. Also, the effects of particle size and morphology are often combined and the individual effect of these parameters cannot be easily separated. In addition to this, there are very few studies which have given importance to quantitative understanding of surface features/roughness of geosynthetics and almost all of them are limited to 2D surface measurements. The objective of this thesis is to understand the interface shear mechanisms of sand-geosynthetic systems through modified large interface direct shear tests coupled with morphological characterization of sands using advanced image based and optical techniques and surface topographical analysis of geosynthetics using 3D interferometry. The individual effects of particle size and morphology on interface shear mechanism are investigated by carefully selecting the sands having specific size fractions and different morphological characteristics. A new computational method based on image analysis is proposed in this study to quantify the morphology of sands (roundness, sphericity and roughness) more accurately by writing several algorithms and implementing them in MATLAB. The roundness and sphericity of sand particles in this method are quantified as per Wadell (1932) and Krumbein and Sloss (1963) respectively and the root mean square roughness is used as a measure of surface roughness. Out of total four sands, namely coarse sand (CS), medium sand (MS), fine sand (FS) and angular coarse sand (ACS) used in this study, CS, MS and FS have similar morphology and different particle sizes, whereas CS and ACS have same size and dissimilar morphology. The effects of size and morphology of sand particles on the interface shear behavior are examined through direct shear tests on dilative and non-dilative interfaces. After examining the boundary effects on deformation patterns analyzed using shear bands in conventional, fixed box and symmetric interface direct shear tests, symmetric interface direct shear test is observed to show uniformity in stresses and deformations across the shear box and hence the same is adopted in this thesis. Test results revealed that the peak interface friction and dilation angles in case of dilative interfaces are hugely dependent upon the interlocking between the sand particles and the asperities of geosynthetic material, which in turn depend on the relative size of sand particles and asperities. Highest interface shear strength is observed when the asperity size of the geosynthetic material matches with the mean particle size of sand, which is also manifested in terms of highest shear band thickness. Direct shear tests on non-dilative interfaces (sand-smooth geomembrane) revealed that interface friction angle depends on the number of effective contacts rather than the particle size. Morphology of sands is found to have major influence on the interface shear strength among all the parameters investigated. Results from interface shear tests are examined in the light of topographical analysis of sand particles and shear induced surface changes in geomembrane. Possible shearing mechanisms at the interface and the influence of particle size, morphology and normal stress on sliding or plowing are brought out from 3D surface roughness measurements using 3D optical profilometer. The stress-shear displacement response of sand-geomembrane interfaces are correlated to the surface changes on sheared geomembranes through visual observations and roughness quantifications. Medium sand used in this study could make more number of effective contacts with deeper grooves, resulting in highest interface friction. The number of grooves are less in case of coarse sand and the depth of grooves is less in case of fine sand, resulting in lesser interface friction for these two sands compared to medium sand, supporting the results of interface shear tests.

In the light of extreme events of natural disasters (earthquakes or hurricanes) and accidents (fire or explosion), repairing and strengthening of existing concrete structures has become more common during the last decade due to the increasing knowledge and confidence in the use of composite advanced repairing materials. The past experience from real fires shows that it is exceptional for a concrete building to collapse as a result of fire and most fire-damaged concrete structures can be repaired economically rather than completely replacing or demolishing them. In this connection an experimental study was conducted to investigate the effectiveness of fibre reinforced polymer jackets for axial compressive and seismic shear performance of post-heated columns. This study also investigates the effectiveness of ferrocement laminate for the repairing of post-heated reinforced concrete columns.A total of thirty-five reinforced concrete columns were constructed and then tested after categorising them into three main groups: un-heated, post-heated and post-heated repaired. The post-heated columns were initially damaged by heating (to a uniform temperature of 500°C). The concrete cubes were also heated to various temperatures to develop the relation between compressive strength and ultrasonic pulse velocity. The residual compressive strength of the concrete cubes and reinforced concrete columns were determined by ultrasonic testing. The post-heated columns were subsequently repaired with unidirectional glass or carbon fibre reinforced polymer and ferrocement jackets. The experimental programme was divided into two parts. The columns of experimental part-1 were tested under axial compressive loading. The columns of experimental part-2 with a shear span to depth ratio of 2.5 were tested under constant axial and reversed lateral cyclic loading. The results indicated that the trend of reduction in ultrasonic pulse velocity values and in residual compressive strength of concrete was similar with increasing temperature. The reduction in residual stiffness of both post-heated square and circular columns was greater than the reduction in ultimate load. The circular sections benefited more compared to the square cross-sections with fibre reinforced polymers for improving the performance of post-heated columns in terms of compressive strength and ductility tested under axial compression. GFRP and CFRP jackets performed in an excellent way for increasing the shear capacity, lateral strength, ductility, energy dissipation and slowed the rate of strength and stiffness degradation of fire damaged reinforced concrete square and circular columns tested under combined constant axial and reversed lateral cycle loading. However, the effect of a single layer of glass or carbon fibre reinforced polymer on the axial stiffness of post-heated square and circular columns was negligible. The use of a ferrocement jacket for the repairing of post-heated square and circular columns enhanced the axial stiffness and ultimate load carrying capacity of columns significantly.

Orientador: Luis Roberto Marcondes Martins / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-07T21:42:27Z (GMT). No. of bitstreams: 1 PedrosaFilho_CelsodeFreitas_D.pdf: 1514708 bytes, checksum: 68479f75bac6f0d3bdbb5ec943719f31 (MD5) Previous issue date: 2006 / Resumo: Neste estudo avaliou-se a resistência ao cisalhamento por extrusão de pinos de fibra de vidro, reembasados ou não com compósito, cimentados com cimento resinoso em dentina intra-radicular, avaliando os segmentos cervical, médio e apical. Selecionaram-se 20 incisivos bovinos com dimensões semelhantes, removendo a porção coronária, padronizando o comprimento das raízes em 16 mm. Após, incluiu-se as raízes em resina acrílica, realizando tratamento endodôntico e, então o preparo dos espaços para os pinos, dividindoas, em seguida, aleatoriamente em dois grupos com dez amostras cada. Os elementos do grupo 1 receberam pinos de fibra de vidro somente cimentados, e do grupo 2 pinos de fibra de vidro reembasados com compósito e posteriormente cimentados. Ao término dos procedimentos de cimentação, realizou-se a secção dos segmentos radiculares, submetendo, então, os corpos-de-prova ao teste push-out em máquina de ensaios universal, através de ponta ativa cilíndrica com 1 mm de diâmetro, à velocidade de 0,5 mm/min, até extrusão do retentor. Obteve-se os seguintes valores médios de resistência de união, em MPa: grupo 1, terços cervical = 6,24 ± 2,68(b), médio = 4,27 ± 2,00(b) e apical = 4,46 ± 2,82(b); grupo 2, terços cervical = 11,83 ± 1,69(a), médio = 11,81 ± 3,86(a) e apical = 10,39 ± 2,44(a). Submeteram-se os valores à análise de variância e ao teste de Tukey com nível de significância de 5%, indicadas acima através de letras diferentes. Os pinos de fibra de vidro reembasados com compósito apresentaram valores estatisticamente superiores de união em todos os segmentos radiculares quando comparados com pinos somente cimentados. Observou-se também a ausência de diferença significativa entre os terços radiculares avaliados para cada grupo distintamente. Os resultados demonstraram que a técnica de reembasamento mostrou-se efetiva em melhorar a retenção do pino de fibra de vidro estudado / Abstract: This study evaluated the bond strength of fiber posts, relined or not with composite resin, luted with resinous cement to radicular dentin, evaluating cervical, median and apical root segments. Twenty bovine incisors, with similar dimensions, were selected and cut 16 mm from the apical limit. The roots were embedded in acrylic resin and the radicular canals were root treated and post space prepared with a depth of 9 mm. Samples were randomly assigned to two groups of ten roots each. Group 1 received glass fiber posts (Fibrekor) luted with dual-cure resin cement (RelyX ARC) in association with a bonding system (Adper Single Bond). In Group 2 the same type of posts were relined with composite (P-60) for further cementation with the same materials used in Group 1. After cementation procedures roots were sectioned transversally and three sections, from cervical, medium and apical thirds were obtained. Push-out test was performed in a universal testing machine with a 1 mm diameter steel rod at cross-head speed of 0,5 mm/min until post extrusion. Collected data was statistically analyzed by twoway ANOVA and Tukey HSD test (p<0,05). The measured retention strengths for cervical, medium and apical thirds were: Group 1, 6.24 ± 2.68(b), 4.27 ± 2.00(b) and 4.46 ± 2.82(b) ; Group 2, 11.83 ± 1.69(a), 11.81 ± 3.86(a) and 10.39 ± 2.44(a). Glass fiber composite relined posts presented statistically higher retention values in cervical, medium and apical thirds when compared to non-relined posts. Within each group, no differences were found among radicular thirds. The results indicate that the tested technique showed effective improvement of glass fiber post retention strength / Doutorado / Dentística / Doutor em Clínica Odontológica

Objetivo: Comparar in vitro la resistencia adhesiva a dentina de tres sistemas adhesivos universales con y sin aplicación de una sustancia neutralizadora de la capa inhibida de oxígeno. Materiales y métodos: La muestra estuvo conformada por 90 dientes bovinos, distribuidos aleatoriamente en 6 grupos (n=15): G1-Ambar™ Universal, G2-Tetric® N-bond, G3-Scotchbond™ Universal sin aplicación de sustancia inhibidora: alcohol Isopropílico y G4-Ambar™ Universal, G5-Tetric® N-bond, G6-Scotchbond™ Universal con aplicación de sustancia inhibidora. Los procedimientos adhesivos se realizaron según las indicaciones de cada fabricante y los procedimientos restauradores con cilindros (matrices tipo Tygon 4 x 2 mm) de resina compuesta Filtek™ Z350XT-A2. Las muestras fueron almacenadas en una estufa a 37°C (+/- 5°C) por 24 horas. Se evaluó la resistencia al cizallamiento a dentina en una máquina de ensayos universal Instrom (velocidad 0.5 mm/min/500N). Los resultados fueron analizados mediante estadística descriptiva (Media y desviación estándar) e inferencial (U Mann Whitney, Kruskal Wallis). Resultados: La media y desviación estándar registrada para los grupos con y sin aplicación de alcohol Isopropílico fue; Ambar™ Universal (13.7±5.7) (14.0±5.2), Tetric® N-Bond Universal (16.5±7.2) (14.2±3.9) y Scotchbond™ Universal (13.6±4.5) (18.3±7.5) respectivamente. No se encontraron diferencias estadísticamente significativas en la resistencia adhesiva a dentina de los adhesivos universales con (p=0.528) y sin (p=0.193) aplicación de la sustancia neutralizadora. Conclusión: Los valores de resistencia adhesiva a dentina de los sistemas adhesivos universales con y sin aplicación de alcohol Isopropílico como sustancia neutralizadora de la capa inhibida de oxígeno no presentaron diferencias estadísticamente significativas. / Objective: Compare in vitro bond strength to dentin of three universal adhesive systems with and without application of an oxygen-inhibited layer neutralizing substance. Materials and methods: The sample was composed by 90 bovine teeth, randomly distributed in 6 groups (n=15): G1-Ambar™ Universal, G2-Tetric® N-bond, G3-Scotchbond™ Universal without application of inhibiting substance: Isopropyl alcohol and G4-Ambar™ Universal, G5-Tetric® N-bond, G6-Scotchbond™ Universal with application of inhibiting substance. Then, the adhesive phase was made according to each group and restorative procedures with composite resin Filtek™ Z350XT-A2, according to the manufacturer´s instructions. It was made of tygon composite resin (4 x 2 mm). The samples were stored in an incubator at 37°C (+/- 5°C) for 24 hours. Subsequently, dentin shear strength was evaluated on an Instrom universal testing machine (speed 0.5 mm/min/500N load). The results were analyzed using descriptive (mean and standard deviation) and inferential (U Mann Whitney, Kruskal Wallis) statistics. Results: Mean and standard deviation registered for the groups with and without application of Isopropyl alcohol was; Ambar™ Universal (13.7±5.7) (14.0±5.2), Tetric® N-Bond Universal (16.5±7.2) (14.2±3.9) and Scotchbond™ Universal (13.6±4.5) (18.3±7.5) respectively. No found statistical significant differences between bond strength in dentin of the universal adhesives with (p=0.528) and without (p=0.193) application of the neutralizing substance. Conclusion: The values of bond strength in dentin of the universal adhesive systems with and without application of Isopropyl alcohol as neutralizing substance of the oxygen inhibited layer did not show statistically significant differences. / Tesis

Cieľom diplomovej práce je príprava polymerných kompozitov vyztužených sklenenými vláknami s riadenou medzifázou za použitia metódy plazmochemickej depozície z plynnej fáze a monomeru tetravinylsilanu. Teoretická časť je zameraná na literárnu rešerš o plazme, plazmovej polymerácií, tenkých vrstvách a kompozitoch. Experimentálna časť popisuje použité materiály a aparaturu použitú na povrchovú modifikáciu sklenených vlákien a prípravu vláknom vyztužených kompozitov. Povrchová úprava sklenených vlákien prebiehala za rôznych depozičných podmienok. Chemické a mechanické analýzy vytvorenej medzivrstvy prebiehali za použitia FTIR spektrometrie a vrypového testu. Vliv povrchovej úpravy bol zistený pomocou získanej interlaminárnej šmykovej sily použítím testu krátkych trámečkov.

An investigation of the variability of engineering properties of municipal solid waste as a function of placement conditions was conducted. Limited data have been reported for the engineering properties of municipal solid waste (MSW) as a function of placement conditions. Wastes have high variability of engineering properties due to heterogeneity in composition and component size; influence from time based effects; and presence of compressible solids. Control of moisture content of MSW at the time of waste placement provides opportunity for increased capacity at a given landfill site due to higher compacted unit weight as well as for control of other geotechnical properties. A laboratory experimental test program was conducted on manufactured municipal solid waste (MMSW) that was representative of waste stream in the United States. Large scale test equipment was used to minimize the effects of scaling on results. The experimental program included compaction, compressibility, hydraulic conductivity, and shear strength testing over moisture contents ranging from 11% to 110%. Baseline compaction curves were developed for different compactive efforts. Similar to soils, the MMSW had bell shaped compaction curves that peaked at a maximum dry unit weight and associated optimum moisture content. The compaction curve generated at modified compactive effort had a maximum dry unit weight of 5.1 kN/m3 and optimum moisture content of 66%. Four times modified compactive effort testing resulted in a maximum dry unit weight of 5.9 kN/m3 and corresponding optimum moisture content of 56%. The compaction curve generated for four times modified compactive effort was used as a baseline for subsequent testing. Compression index was calculated from the strain-log stress curves for total stress conditions and is referred to as apparent compression index. Apparent compression index decreased from 1.1 to 0.34 with increasing moisture content. Secant modulus of elasticity was calculated between 1% and 25% strain and ranged from approximately 200 kPa to 4,800 kPa over the range of tested moisture contents. Tangent modulus ranged from 400 kPa to 6,200 kPa between 1% and 25% strain. Both the secant and tangent modulus peaked between 30% and 56% moisture content. Wet of optimum, the moduli of elasticity decreased with increasing moisture content. The hydraulic conductivity was measured under constant head at a hydraulic gradient of 1 and decreased asymptotically from approximately 1.3x10-2 cm/s to 8x10-5 cm/s as the moisture content was increased to optimum. The hydraulic conductivity of the MMSW increased slightly wet of optimum. The internal angle of friction of the MMSW was measured at 15% shear strain and decreased from approximately 40° to 30° with increasing moisture content. Test results demonstrated that both the molding moisture content and dry unit weight have significant impact on the MMSW geotechnical properties, although it appears that molding moisture content ultimately controls the behavior. Based on the results of the tests it was speculated that, similar to clay soils, increases in moisture content allowed for breakdown of the fabric and physical rearrangement of waste components which in turn controlled geotechnical behavior. Overall trends were comparable for MMSW and soil and included: increased dry density and increased stiffness to optimum moisture content; decreased hydraulic conductivity with increased compaction moisture content; and decreased shear strength with increased compaction moisture content. The results of the test program have environmental and economic implications for design and operation of landfills as well as post closure use.

The work deals with issues of evaluation of the shear properties of timber structural materials, particularly CLT elements. The work contains an overview of extensive research so far presented scientific studies dealing with the characteristic shear properties of wood. In the practical part was carried out the experiment dealing with the failure mode of transverse lamellae of CLT elements that were exposed to shear stress. There were observed individual effects that this may affect the material properties. In the first part of the experiment were performed numerical models using FEM. In the second part, the test specimens were tested in three point bending. Here, attention was paid to the influence of macroscopic properties of wood on the distribution of stress cracks and shear strength, the tests were recorded using DIC system.

The doctoral thesis is aimed at preparation of glass fiber reinforced polymer composites with controlled interphase formed by plasma-polymerized tetravinylsilane and tetravinylsilane/oxygen thin films. The thin polymer films of specific physico-chemical properties and thickness were deposited to improve interfacial adhesion of glass fiber/polyester composites. The fiber surface modification was performed by using plasma enhanced chemical vapor deposition in low-temperature RF plasma operating in an various effective power range and different treatment time. Test results were examined in relation to the interlayer thickness and different treatment conditions. The prepared interlayers were analyzed to evaluate physico-chemical composition and properties (XPS, RBS, ERDA, FTIR and spectroscopic elipsometry). Selected mechanical properties were evaluated by AFM. Mechanical response of plasma interlayers was evaluated by short beam shear test and direct method of testing the interfacial shear strength using microindentation. The interphase shear failure was controlled by the shear strength at the interlayer/fiber interface as follows from experimental and model data.

La nature complexe de l'argile a amené les chercheurs à s’intéresser à ses comportements mécaniques et microstructure. L'objectif de cette recherche est d'étudier l'influence des chemins de contrainte triaxiaux sur le comportement mécanique et sur les mécanismes qui se produisent au niveau microstructural. L’étude est réalisée en considérant à un niveau de contrainte donné, le phénomène de dilatance est approché suivant des chemins de contraintes différents. Dans un deuxième temps, l’étude se porte sur l’influence de la succion sur le comportement. Pour les argiles remaniées saturées, le comportement dilatant à un niveau de contrainte donné, atteint par deux chemins de contrainte différents a été finement analysé. L’influence du niveau de contrainte a été également abordée dans le cadre de cette étude. L’analyse microstructurale a été analysée à différentes échelles au moyen de différentes méthodes. Au niveau macroscopique, les résultats ont montré que, pour un niveau de contrainte donné, le comportement volumétrique est fonction du chemin de contrainte. La dilatance est activée dans le cas d’argiles surconsolidées principalement lorsque le chargement est purement déviatorique. Au niveau microscopique, les résultats mettent en évidence cinq modes d’orientation des particules qui pourraient être activés sous chargement triaxial. Les résultats révèlent que l’apparition de la dilatance dans les argiles remaniées fortement surconsolidées peut être attribuée à l'arrangement tortueux des particules d'argile, l'ouverture des micropores ainsi que la formation et l’ouverture de fissures mésoscopiques. Pour les argiles remaniées non saturées, les études sont réalisés par les essais macroscopiques et mésoscopiques sur l'argile Kaolin K13 et un mélange kaolinite-montmorillonite. L’évolution des succions a été mesurée au moyen d’hygromètres placés dans les extrémités supérieure et inférieure d’échantillon. Les résultats démontrent que la contrainte déviatorique d’argile non saturée, lorsque la succion est forte, commence par augmenter jusqu'à un sommet puis diminue pour rejoindre une valeur résiduelle. La résistance au cisaillement d’argile non saturée augmente généralement avec la contrainte moyenne et la succion. Cependant, dans nos essais à succion très élevée le développement d’une fissuration lors du séchage a conduit à perdre l’homogénéité du matériau et à réduire la résistance au cisaillement de l’éprouvette / The complex nature of clay has aroused great interest of researchers in its mechanical behaviour and microstructure. The objective of this research is to examine the influence of triaxial stress paths on the mechanical behaviour of remoulded clay and the mechanisms that occur at the microstructural level. The dilatancy phenomenon is particularly investigated considering a given stress level reached by following different stress paths. In the second part, this research focuses on the influence of suctions on the mechanical behaviour. For the saturated remoulded clay, the dilative behaviour at a given stress level, reached by following two different stress paths was analysed in detail. The influence of stress levels was also examined in this research. The microstructural analysis was conducted at different scales by means of different methods. The macroscopic results of saturated clay show that, at a given stress level, the volumetric behaviour greatly depends on the stress path. In the case of overconsolidated clay, the dilatancy is activated especially when triaxial shearing is performed following the purely deviatoric stress path. At the microscopic level, the results highlight five modes of particle orientation that could be activated under triaxial loading. The results also reveal that the appearance of dilatancy phenomenon in highly overconsolidated remoulded clay may be attributed to the tortuous arrangement of clay particles, the opening of micropores, and the formation and opening of mesocracks. For the unsaturated remoulded clay, the studies were performed through many macroscopic and mesoscopic tests on Kaolin K13 clay and a kaolinite-montmorillonite mixture. The evolution of suctions was measured using hygrometers placed near the upper and lower ends of clay specimens. The results show that, at a high suction level, the deviatoric stress of unsaturated clay increases to a peak and then decreases down to a residual value. The shear strength of unsaturated clay generally increases with increasing mean stress and suction. However, in the high suction tests, the development of cracks during drying led to the inhomogeneity of the specimens and thus resulted in relatively small shear strengths