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High levels of vibration are essential for the proper operation of vibrating screens. However, this motion imparts high dynamic loads on their support structures leading to premature failure or costly construction. Various methods exist for the attenuation of these forces, but they require undesirable addition of weight to the screen assembly, which can be as much as 130% of the screen mass. More appropriate methods are pendulum, hydraulic and liquid inertia vibration absorbers. These devices can provide similar isolation at only a fraction of the weight increase of current screen isolation methods. The liquid inertia vibration absorber's unique properties make it ideal for the attenuation of screen forces, as this study will show. A mathematical model describing the motion for the vibration absorber was derived. This led to an equation describing the force transmissibility, which was used to show which parameters influence the absorber's performance. The model was extended to take into account the effect of conical port inlets/outlets, which were used to reduce the viscous damping. The effect of viscous damping was quantified using computational fluid dynamics. The mathematical model was used to show how an optimal set of parameters could be found. Two design procedures were developed for the vibration absorber and were then used to design an experimental absorber. The experimental absorber was used to validate the mathematical model. Several practical considerations for the design were discussed and solutions suggested. The stiffness of the absorber was estimated using finite element modelling. Two elastomeric springs of different hardnesses were fitted to the absorber. The softer spring achieved a transmissibility of 16% by 42 Hz. The main stumbling block in reducing the transmissibility even further is the reduction of the damping. The experience gained from the experimental absorber was used to suggest how an absorber could be applied to a screen. An absorber isolating at 12.5 Hz was designed for this purpose. A theoretical design study investigated two possible configurations of absorber fitment. When the absorber was fitted directly to the screen the force transmitted was reduced 7.2 times. Fitting the absorber to the sub-frame gave similar transmissibility results to that of a screen fitted with a sub-frame only, but the mass ratio was only 15%. The outcome of this study is a thorough understanding of liquid inertia vibration absorbers as well as a procedure for their optimal design. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

This dissertation involves the experimental investigation of commercially pure titanium (CP Ti) which was subjected to laser forming and mechanical forming processes. Commercially pure titanium grade 2 was formed to a radius of curvature of approximately 120 mm using three forming procedures, i.e. i) laser forming; ii) mechanical forming (stretched forming) and iii) a combined forming process (laser-mechanical forming). Fatigue testing revealed, for all the forming processes, that samples produced by laser forming performed the best at high load settings. However, mechanically formed specimens performed the best at low load settings, whereas the laser-mechanical process resulted in midway performance between laser and mechanical processing. Considering microstructure vs fatigue; impact vs fatigue; and residual stress vs fatigue; at high load settings it is evident that the microstructure is the dominant contributor to crack initiation and growth. Crack morphology of fatigue samples revealed that secondary cracks (parallel to main crack front) followed the grain boundaries of the Widmanstätten microstructure, whereas irregular secondary cracks grew parallel and through the twinning planes and along the grain boundaries of the equiaxed microstructure. Laser forming resulted in microstructural changes from equiaxed grains to a Widmanstätten structure due to fast cooling rates. Excessive twinning is developed within the equiaxed microstructure after the mechanical forming procedure. This is due to cold working / strain hardening. The combined process shows a combination of equiaxed grains and Widmanstätten microstructure. Residual stress relieved for all forming processes revealed an increase in the magnitude of the residual stress compared to the parent plate and that the maximum values were obtained at the inner radius of curvature (i.e. 118.4 mm). Laser forming revealed the highest values in residual stress whereas the other two processes i.e. mechanical and laser-mechanical forming exhibited an increase midway between the parent plate and laser forming. The second most influential factor with regards to fatigue was the magnitude of the residual stress, especially at medium to low load settings. When considering theoretical models to predict fatigue life it was found that the Goodman model showed the closest relation to the actual fatigue data when considering the entire theoretical curve. Vickers microhardness profiling was applied to the thickness of the samples for the parent plate and all forming processes. No significant hardening occurred due to the forming processes and differences in hardness were considered negligible. Charpy impact testing revealed that the laser formed specimens exhibited the most brittle behaviour when compared to the parent plate results. Mechanical formed specimens showed a slight increase in brittleness compared to parent plate whereas the combined process yielded results midway between the laser and mechanically formed specimens. Mathematical equations are formulated and presented for predicting the fatigue life of CP Ti grade 2 for the parent plate and the three forming processes. This study proved that the laser forming process can be successfully used as a production stage in the forming of CP Ti grade 2.

In recent years a great deal of research has focussed on understanding and exploiting self assembling peptides as they form fibrillar hydrogels for use in a variety of different applications, such as tissue engineering and drug delivery. A particular class of such peptide systems are ionic-complementary peptides, composed of alternating hydrophobic and hydrophilic amino acids. Their simple structure is generally seen to assemble into β sheet rich fibrils, and easy modification of the primary structure is possible to allow the inclusion of recognition motifs tailored for a specific use. This can be done simply via physical mixing. To maximise the potential of such systems it is important to understand the interactions that govern the self-assembly behaviour. Here a variety of different peptides have been studied to elucidate control of peptide conformation and fibril morphology. The ability to easily tune the mechanical strength of the hydrogel has been explored by mixing peptide systems. The peptide FEFEFKFK (FEKII) was seen to assemble into β sheet rich fibrils of ~3 nm in diameter. Control of pH and hence the charge state of the E and K side chains altered sample properties. Gelation at pH 2.8 occurred at a concentration between 20 30 mg ml 1. At pH 4, 5 and 10 where the peptide has a lower net charge gelation was lowered to ~10 mg ml 1. Mechanical properties varied with G' values of 20-1200 Pa as pH was altered. Stronger gels were formed with lower net peptide charge. Hierarchical fibre assembly was observed for positively charged peptides, with fibres forming from lateral association of fibrils. Negatively charged peptides at pH 10 showed no such hierarchical assembly, and lower fibril persistence length. This was related to the change in charge along the fibril structure. At pH 7, where the peptide has no net charge, precipitation occurred. This showed a net charge was required on the peptide to disperse fibrils and prevent aggregation. The work showed the importance of ionic-interactions in determining both network morphology and bulk properties, and also elucidated control of such behaviour. AEAEAKAK (AEKII) was shown to assemble into α helix fibres. Alanine (A) is less hydrophobic than F, and is a known helix former. The role of F and A in assembly was assessed by the design of peptides FEAEFKAK (FAIEKII) and FEFEAKAK (FAIIEKII). Mixing A with F disrupted the peptides' ability to form a β sheet network by lowering the driving force for assembly given by the F residues. Trace amounts of β sheet were observed at low concentration, but at a critical concentration β sheet content increased and gelation occurred. This was found to be pH dependent. FAIEKII formed β-sheet fibrils at a lower concentration than FAIIEKII. While FAIEKII was able to assemble into different fibril structures, FAIIEKII showed no specific aggregation. This not only highlighted the importance of Hydrophobicity as a key driving force to assembly but also how the grouping of these amino acids in the primary sequence can determine the overall assembly characteristics of the peptide. The peptides FEFEFKFKGGFEFEFKFK (FEKII18-1) and FEFEFKFKGGFKFKFEFE (FEKII18-2) were designed to co-assemble with FEKII. Individually both peptides were seen to assemble into β sheet fibrils. FEKII18-1 formed fibrils of 2.3 3.1 nm in size, a result of folding along the chain caused by intra molecular attractive ionic interactions. FEKII18-2 formed larger fibrils of 4.4 5.2 nm from a straightened peptide chain given by the change in charge distribution. When co assembled with FEKII mechanical properties were enhanced, with G' increasing from 40 Pa at 20 mg ml 1 to 2400 Pa, depending on the concentration of FEKII18-1/FEKII18-2 added to the system. This was a result of these peptides providing fibril connections acting as cross links. This work has detailed control over the assembly process via peptide conformation and fibril interactions and the effect this has on overall macroscopic sample properties. This is vital in determining the viability of such systems in various biomedical applications.

In this work, structure/property relationships in polypropylene (PP) nanocomposites have been investigated for different nanofillers. Nanofillers of modified clay based on montmorillonite (MMT) and multi-wall carbon nanotubes (MWNTs) have been selected and incorporated to the PP matrix as either single nanofillers or hybrid nanofillers. Melt mixing via a twin screw extruder and further moulding by injection moulding have been used to prepare PP nanocomposites. Moreover, the dilution of MWNT masterbatch has been used to prepare PP/MWNT and PP/clay/MWNT nanocomposites. Three types of the PP nanocomposites have been obtained: PP/clay, PP/MWNT and PP/clay/MWNT nanocomposites. In all three types of the PP nanocomposites, α- and -PP crystals were observed in the wide angle X-ray diffraction (WAXD) patterns. Furthermore, the addition of nanofillers to the PP did not appear to affect the PP orientation. Slight PP orientation in the PP nanocomposites was shown in the two-dimensional X-ray diffraction (2D-XRD) patterns. Mixed clay layers were combined in the PP/clay and PP/clay/MWNT nanocomposites and investigated by WAXD as well as transmission electron microscopy (TEM). In addition, the aggregated and individual MWNTs were present in both the PP/MWNT and PP/clay/MWNT nanocomposites TEM images. A rough fracture surface with cracks was revealed from the scanning electron microscopy (SEM) images of the three types of PP nanocomposites. Polarized optical microscopy (POM) micrographs were taken at different temperatures during cooling in a hot stage and revealed the limitation of PP spherulite growth upon adding the nanofillers to the PP. The incorporation of nanofillers was found not to affect the glass transition temperature (Tg) of PP which investigated by dynamic mechanical analysis (DMA). However, the increase of both the peak melting temperature (Tm) and the peak crystallization temperature (Tc) of PP with adding the nanofillers was shown by differential scanning calorimetry (DSC) thermograms. In addition, the nanofillers also have been shown to act as nucleating agents. The thermal stability of PP in a nitrogen atmosphere was enhanced by the nanofillers when examined by thermogravimatric analysis (TGA). DMA and tensile testing were performed and showed that the nanofillers act as reinforcement for the PP. The distribution, orientation and deformation of MWNTs in the PP/MWNT and PP/clay/MWNT nanocomposites have been followed by Raman spectroscopy. Significant shifts of the Raman G'-band from the MWNTs was obtained during deformation of the MWNT nanocomposites and the hybrid clay/MWNT nanocomposites as the stress transfer from the PP matrix to the MWNTs has occurred. A correlation between calculated modulus from deformation and measured modulus from DMA and tensile testing has been found for PP/MWNT and PP/clay/MWNT nanocomposites. Finally, the PP nanocomposites have been considered for use in packaging applications.

LFC is cementatious material integrated with mechanically entrained foam in the mortar slurry which can produce a variety of densities ranging from 400 to 1600 kg/m3. The application of LFC has been primarily as a filler material in civil engineering works. This research explores the potential of using LFC in building construction, as non-load-bearing partitions of lightweight load-bearing structural members. Experimental and analytical studies will be undertaken to develop quantification models to obtain thermal and mechanical properties of LFC at ambient and elevated temperatures. In order to develop thermal property model, LFC is treated as a porous material and the effects of radiant heat transfer within the pores are included. The thermal conductivity model results are in very good agreement with the experimental results obtained from the guarded hot plate tests and with inverse analysis of LFC slabs heated from one side. Extensive compression and bending tests at elevated temperatures were performed for LFC densities of 650 and 1000 kg/m3 to obtain the mechanical properties of unstressed LFC. The test results indicate that the porosity of LFC is mainly a function of density and changes little at different temperatures. The reduction in strength and stiffness of LFC at high temperatures can be predicted using the mechanical property models for normal weight concrete provided that the LFC is based on ordinary Portland cement. Although LFC mechanical properties are low in comparison to normal weight concrete, LFC may be used as partition or light load-bearing walls in a low rise residential construction. To confirm this, structural tests were performed on a composite walling system consisting of two outer skins of profiled thin-walled steel sheeting with LFC core under axial compression, for steel sheeting thicknesses of 0.4mm and 0.8mm correspondingly. Using these test results, analytical models are developed to calculate the maximum load-bearing capacity of the composite walling, taking into consideration the local buckling effect of the steel sheeting and profiled shape of the LFC core. The results of a preliminary feasibility study indicate that LFC can achieve very good thermal insulation performance for fire resistance. A single layer of 650 kg/m3 density LFC panel of about 21 mm would be able to attain 30 minutes of standard fire resistance rating, which is comparable to gypsum plasterboard. The results of a feasibility study on structural performance of a composite walling system indicates that the proposed panel system, using 100mm LFC core and 0.4mm steel sheeting, has sufficient load carrying capacity to be used in low-rise residential construction up to four-storeys.

M.Sc. (Chemistry) / The fabrication of multiwalled carbon nanotube/polyvinyl chloride (PVC) composites and a study of their thermal, fire retardancy and mechanical properties are reported. Triphenylphosphine linked - multiwalled carbon nanotube (TPP-MWCNT) and pristine MWCNT were used. The MWCNT were embedded in the polymer matrix through melt blending and solvent casting. The phosphorylation of the MWCNT and their dispersion in the PVC matrix was characterized by scanning electron microscopy and Raman spectroscopy. Thermal analysis of the nanocomposites by thermal gravimetric analysis (TGA) in both solvent casting and melt bending processes, showed different results when compared with the neat PVC. The modulus of the MWCNTs / PVC nanocomposites synthesized via melt blending increased, whilst there was a reduction in their tensile strength, indicating a decrease in polymer toughness. The tensile modulus and strength of MWCNTs / PVC nanocomposite synthesized via Solvent casting decreased whilst there was an increase in Tpp-MWCNT/PVC nanocomposite when compared with its counterpart MWCNTs / PVC nanocomposite, indicating an increase in stiffness and strength. The limited oxygen index (LOI) fire retardant tests of all the neat PVC and its nanocomposites showed no value difference.

Orientador: Maria Isabel Felisberti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-07T19:58:46Z (GMT). No. of bitstreams: 1 Turchet_Renato_D.pdf: 5552615 bytes, checksum: 362eca7d5bc2f3df61a1e1672d181201 (MD5) Previous issue date: 2006 / Resumo: O objetivo deste trabalho foi preparar e avaliar o comportamento de blendas ternárias PPO/AES/PS com relação aos aspectos de miscibilidade, compatibilidade, propriedades mecânicas e estabilidade fotoquímica, bem como comparar estas propriedades com as das blendas PPO/HIPS. Neste trabalho as blendas ternárias PPO/AES/PS foram elaboradas a partir da mistura mecânica no estado fundido de PS, poliestireno, PPO, poli(2,6-dimetil-1,4-óxido de fenileno) e AES, um elastômero termoplástico obtido pela enxertia de SAN, poli(estireno-co-acrilonitrila) no EPDM, poli(etileno-co-propileno-co-5-etilideno-2-norboneno). Foram preparadas três séries de blendas ternárias, contendo respectivamente 40, 50 e 60 % de PPO. Em cada série variou-se a fração mássica do AES de 10, 15, 20 e 30 %. Para fins de estudos comparativos, também foram preparadas as blendas binárias PPO/AES, PPO/PS e AES/PS na composição 50/50 e as blendas binárias de PPO e poliestireno de alto impacto, HIPS, contendo o mesmo teor de PPO que as blendas ternárias. A análise dinâmico-mecânica das blendas ternárias revelou um comportamento de fases complexo, sendo possível verificar a existência de uma fase elastomérica de EPDM dispersa em uma matriz constituída por várias fases, sendo uma delas a mistura miscível PPO/PS. Tal comportamento deve-se ao fato do PPO e PS serem totalmente miscíveis, já o PS é miscível com SAN quando este contém menos que 5% em massa de acrilonitrila, e o PPO é miscível com SAN quando este contém menos que 10% em massa de acrilonitrila. As blendas ternárias apresentam propriedades mecânicas dependentes do teor de AES. O aumento do teor de AES promoveu um significativo aumento na resistência ao impacto com ligeira queda no módulo e na resistência à tração. Entretanto, somente algumas composições apresentaram desempenho mecânico superior às blendas PPO/HIPS. Ensaios de envelhecimento acelerado mostraram que as blendas ternárias são mais estáveis que as blendas PPO/HIPS que possuem uma fase elastomérica insaturada / Abstract: The aim of this work was to prepare and to evaluate the PPO/AES/PS ternary blends behavior with respect to miscibility, compatibility, mechanical properties and photochemical stability aspects, as well as to compare these properties to the PPO/HIPS blends. In this work, the PPO/AES/PS ternary blends were obtained from the melt mixture PS, polystyrene, PPO, poly(2,6-dimethyl-1,4-phenylene oxide), AES, a thermoplastic elastomer constituted by a grafting of SAN, poly(styrene-co-acrylonitrile), on EPDM, a poly(ethylene-co-propylene-co-diene) elastomer.Three series of the ternary blends containing 40, 50 and 60 % of PPO were prepared. In each ternary blends series the AES¿s mass fraction variation was 10, 15, 20 and 30 %. To perform a comparative study, the binary blends PPO/AES, PPO/PS and AES/PS, with composition 50/50%, and the PPO/HIPS binary blend with the same PPO¿s contents that the ternary blends, were also prepared. The dynamical mechanical analysis of the ternary blends showed a complex phases behavior, with the EDPM elastomeric phase dispersed in a matrix constituted by several phases, one of them the miscible blend PPO/PS. Such behavior is due to the fact that PPO and PS blends are miscible blends, while PS is only miscible with SAN when it contains less than 10 % wt of acrylonitrile and PPO/SAN blends are also miscible if the acrylonitrile composition is less than 5 wt %. The ternary blends presents mechanical properties dependent on the blend AES content. The increase in the AES content in the blends resulted in a significative increase in the impact resistance and a slight drop in the modulus and tensile resistence. However, only some compositions showed better mechanical performance than PPO/HIPS blends. Accelerated aging showed that the ternary blends are more stable than the PPO/HIPS blends that present an unsaturated elastomeric phase / Doutorado / Físico-Química / Doutor em Quimica

O aquecimento terapêutico e o treinamento com saltos verticais são modalidades de escolha para tratamentos nas várias áreas da medicina e da fisioterapia. Na literatura poucos estudos avaliaram a resistência do tendão calcâneo pós-aquecimento, principalmente em tecidos aquecidos a temperaturas elevadas (42 e 45°C). Este estudo teve o objetivo de comparar certas propriedades mecânicas do tendão calcâneo de ratos como: força no limite de resistência máxima (N), rigidez (N/m) e energia absorvida até o ponto de ruptura (mJ), após o aquecimento induzido in vivo por convecção associado ao exercício físico (saltos verticais) e posteriormente investigar quantitativamente e qualitativamente as alterações estruturais na proteína colágeno presente no tendão, por meio de análises histológicas (hematoxilina e eosina, picro-sirius), força atômica (AFM) e birrefringência. No presente estudo foram utilizados 35 Ratos Albinus da Raça Wistar, todos machos divididos em 7 grupos (grupo controle GC, I, II, III, IV, V e VI). O GC foi utilizado exclusivamente para análises histológicas, os grupos I (sem alteração térmica), III (42°C) e V (45°C) não passaram por exercícios físicos, os grupos II (sem alteração térmica), IV(42°C) e VI (45°C) passaram por exercícios físicos (saltos verticais) e todos os grupos passaram por ensaio mecânico de tração. De uma maneira generalizada os resultados para as análises mostraram uma diferença do grupo controle GC, I, II em relação aos grupos III, IV, V e VI, o que fez perceber que em temperaturas elevadas há danos no tecido tendíneo e em temperaturas iguais e ou acima de 42°C e 45°C associado ao exercício físico de saltos verticais o dano acentua-se. Há um início de danos ao tecido tendíneo, acentuando-se na temperatura de 45°C e os eventos constatados nas análises histológicas foram comprovados nos resultados dos ensaios mecânicos de tração. / Therapeutic heating and vertical jumps are training modalities of choice for treatment in various areas of medicine and physiotherapy. In the literature, few studies have evaluated the resistance of the Achilles tendon post-heating, especially in tissues heated to high temperatures (42 to 45°C). This study aims to compare certain mechanical properties of the Achilles tendon of rats as: strength in the limit of maximum resistance (N), stiffness (N/m) and energy absorbed to the point of rupture (mJ) after heat induction in vivo by convection associated with exercise (vertical jumps)and subsequently investigate qualitatively and quantitatively the structural changes in collagen protein present in the tendon by histological analysis (hematoxylin and eosin, picro-sirius red), atomic force (AFM) and birefringence. The present study used 35 Wistar rats, all males divided into 7 groups (control group GC, I, II, III, IV, V e VI). GC was used exclusively for histological analysis, the group I (no thermal alteration), III (42°C) and V (45°C) did not undergo physical exercises, groups II (without thermal alteration), IV (42°C) and VI (45°C) underwent exercise (vertical jumps) and all groups underwent mechanical tests. The results for the analyzes showed a difference between the GC, I, II groups in relation to III, IV, V and VI, showing that at elevated temperatures occurred a damage in tendon tissue and for temperatures equal or above 42°C and 45°C associated with the exercise of vertical jumps the damage is accentuated. There is an early tissue damage, with a peak temperature of 45°C and the events recorded in the histologic analyses were confirmed in the results of tensile test.

A ingestão de dietas com níveis elevados de flúor interfere na mineralização óssea e, conseqüentemente, poderá influenciar nas propriedades mecânicas dos ossos. Este trabalho teve como objetivo estudar e avaliar algumas propriedades mecânicas de fêmures de coelhos submetidos a dietas com diferentes concentrações de flúor, mediante ensaios mecânicos de flexão em três pontos. Foram utilizados os fêmures de 40 coelhos machos, albinos, da raça Nova Zelândia com 1 mês de idade. Durante 40 dias os animais, divididos em 5 grupos, receberam dietas contendo diferentes concentrações de flúor. As propriedades mecânicas da deformação proporcional e resiliência, apresentaram diferença estatisticamente significante. Houve redução nos valores para rigidez, tensão máxima, carga máxima, mas sem diferença estatisticamente significante, para os grupos com maior concentração de flúor. Diante destas considerações e dos achados neste trabalho, fica evidente a necessidade de mais investigações para caracterizar a relação entre o flúor e as propriedades mecânicas. / High levels of fluoride ingestion may interfere with bone mineralization and, therefore, cause modification in the bone mechanical properties. In this investigation we studied the relationship between some mechanical properties of the rabbit femur and different concentration of fluoride in the diets. It was performed the three bending test in forty femurs obtained from New Zealand white rabbits that had been fed with diet with different fluoride concentration during 40 days since they were one month old. The animals were divided into 5 different groups according to the fluoride concentration in diets. The resilience and proportional deformation were higher for the group with the highest fluoride ingestion and there was no difference among the other groups. Rigidity, ultimate load and tension were lower as fluoride concentration increased but with no statistical difference. It was concluded that more investigation is necessary to establish the relationship of the mechanical properties with fluoride intake.