Made available in DSpace on 2016-12-06T17:07:13Z (GMT). No. of bitstreams: 1 RESUMO.pdf: 26325 bytes, checksum: b3675c6043e597d4b7943a6b80a68275 (MD5) Previous issue date: 2001-12-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A variety of reconstructive surgical procedures rely on the strength improvement of tendon-to-tendon linkage. Thus, methods to improve tendon ruptures may allow earlier rehabilitation and fast return to the daily living. The purpose of this study was to evaluate the mechanical strength of aquilles tendon 2-mm defect in male rabbits. The created gap was filled with bovine collagen (biomaterial) in nine specimens and a suture with no filling in other nine specimens. The other aquilles tendons were the control group as pattern of normality. In all eighteen tendons (eighteen animals) the strength were tested in a material testing machine for a pull-out strength. Ultimate strength and dislocation were analyzed in all groups. One-way analysis of variance (ANOVA) at a p£ 0.05 was used to compare the biomechanical data in the sixth week period of time. There were no obvious slipping at the interface between the clamp and the muscle-tendon fixation. There was no significantly difference among the groups. For the strength variable p=0.0467 and for the displacement p=0.1950. The coefficient of variation of 30% for the control group, 25% for the biomaterial group and 18% for the suture group when analyzing the tendon strength. In the displacement data, the control group presented a coefficient of variation of 37%, biomaterial group of 25% and the 42% for the control group. The presented data have not shown any improvement using biomaterial. However, the collagen group has shown similar curves compared to the control group. / O presente estudo teve como objetivo avaliar o comportamento biomecânico do tendão calcaneano de coelhos, quando utilizado um componente biológico para o preenchimento de uma falha. Os biomateriais são substâncias biologicamente ativas, que apresentam efeito osteogênico e formador de partes moles, isto é, ativam a formação de osso e colágeno novos nos organismos vivos. Neste estudo o biomaterial foi o colágeno bovino. A amostra foi caracterizada por dezoito coelhos da raça Nova Zelândia, adultos, machos em que foi criada uma falha cirúrgica de 2 mm no tendão calcaneano de todos os animais. Em nove animais foi realizada simples sutura sem biomaterial, nos restantes nove animais foi realizada a implantação dos biomateriais nas falhas criadas. No período de seis semanas estes animais foram sacrificados e os tendões submetidos ao teste de tração. A comparação foi utilizada pelo tendão não operado, como forma de obter-se o padrão de normalidade da resistência dos tendões. Foram utilizadas as garras para o ensaio de tração, próprias da máquina de ensaios biomecânicos. Os resultados da carga máxima aplicada para a ruptura destes espécimes e o deslocamento, a partir da curva carga-deslocamento foram registrados e avaliados o comportamento biomecânico destes espécimes. Utilizando-se a análise da variância (ANOVA) com um p£ 0,05 não foram observados diferenças estatisticamente significantes entre os grupos de estudo e o grupo controle. O coeficiente de variação (CV%) em relação à variável carga máxima à falência no grupo controle foi de 30%, no grupo biomaterial 25% e no grupo sutura 18%. Na análise do grau de deslocamento, o grupo controle apresentou um CV de 37%, o biomaterial de 25% e 42% para o grupo controle. Em análise do coeficiente de variação acumulado, houve uma tendência para estabilização da curva nos grupos apresentados. Os dados acima apresentados não demonstraram um efeito benéfico na adição do colágeno bovino nestes grupos estudados. Ainda assim, em observação qualitativa, as curvas do grupo biomaterial apresentaram um traçado semelhante aos da normalidade.

O uso de novos materiais na construção civil combinado com a alta tecnologia dos processos construtivos pode conduzir à redução de custo e melhoria no comportamento da estrutura. Recentemente, em função da corrosão das barras de aço dentre outros fatores, muitos pesquisadores têm sugerido a utilização de barras não-metálicas como substituição das barras aço nas estruturas em concreto. Além das barras não-metálicas permitirem cobrimentos menores e possibilitarem menor custo de manutenção, outras vantagens no seu uso podem ser citadas, tais como: pequeno peso específico, alta resistência à tração, não condutibilidade elétrica, térmica e magnética, entre outras. Este trabalho analisa o comportamento da aderência entre barras de GFRP (barras de fibra de vidro impregnada por polímero) e o concreto, por meio de uma revisão bibliográfica e ensaios de arrancamento padronizados, segundo o RILEM-FIP-CEB (1973). Foram consideradas as influências dos parâmetros como a resistência à compressão do concreto e o diâmetro da barra de GFRP. Com base nos resultados experimentais, buscou-se comparar o comportamento de aderência barra de GFRP-concreto e barra de aço-concreto, além da verificação das formulações para previsão da resistência de aderência segundo códigos normativos e a literatura técnica, para estruturas armadas com barras de aço e barras de FRP. Posteriormente, realizou-se a análise numérica da aderência, por meio do método dos elementos finitos. Nos modelos experimentais de arrancamento pode-se perceber a influência das propriedades mecânicas e da conformação superficial das barras de GFRP no comportamento da aderência, apresentando menores resistências de aderência quando comparadas às barras de aço de diâmetro similar. O valor da resistência de aderência determinado experimentalmente foi maior que o valor proposto pelos códigos normativos. Os modelos numéricos não representaram satisfatoriamente o comportamento experimental, visto que se trata de uma simulação numérica linear e o comportamento experimental força x deslocamento é não-linear. / The use of new materials in civil construction combined with high technology processes leads to improvements in many aspects, like cost reductions and better structural behavior. Recently, due to corrosion of the steel bars, among other factors, many researchers have been suggesting the use of non-metallic bars as a substitution of the steel reinforcement in concrete structures. Besides, the non-metallic bars allow smaller clear cover and make possible lower maintenance cost, other advantages can be mentioned, such as: low specific weight, high tensile strength, electrical, thermal and magnetic non-conductivities, and others. This work analyzes the bond behavior between GFRP bars (Glass Fiber Reinforced Polymer bars) and concrete, through state-of-art and standard pull-out tests, according to RILEM-FIP-CEB (1973). The influence of some parameters, as compressive concrete strength and GFRP bar diameter, was considered. Based on the experimental results, it was aimed at comparing the bond behavior of the GFRP-concrete bar with the steel-concrete bar, in addition to the verification of bond strength formulations established by the standards codes and the bibliography for structures reinforced with steel bars and FRP bars. Further, the bond numerical analysis was carried out through finite elements. In the pull-out tests, the influence of mechanical properties and superficial conformation on the GFRP bars was observed in the bond behavior, presenting smaller bond strength than the steel bars of similar diameter. The value of the experimental bond strength was larger than the value proposed by standards codes. The numerical models did not represent well the experimental behavior given that a linear numerical simulation was considered, but, actually, the experimental load x slip behavior is non-linear.

Com o objetivo de avaliar a influência do processo de cicatrização óssea sobre o desempenho biomecânico de mini-parafusos utilizados como ancoragem em ortodontia, foram inseridos 60 mini-parafusos (1,6 x 6mm) auto-rosqueantes (Tomas® Dentaurum / Germany) na maxila e na mandíbula de 5 cães adultos da Raça Beagle. Os pré-molares (P1, P2, P3, P4) superiores e inferiores foram extraídos três meses antes da inserção vertical dos mini-parafusos. Os cães foram sacrificados nos dias 0, 2, 7, 15 e 30 após a instalação dos mini-parafusos. Os maxilares foram dissecados e os corpos de provas contendo os mini-parafusos foram preparados para avaliação da resistência à tração na Máquina de Ensaios Universal EMIC® 2000, utilizando uma garra desenvolvida especificamente para este estudo. Os valores e gráficos correspondentes ao desempenho mecânico foram imediatamente gerados e registrados pelo programa de aquisição Tesc 3.01®. As possíveis diferenças entre os períodos de cicatrização foram avaliadas pela análise de variância (ANOVA) e pelo teste de comparações múltiplas de Bonferroni. Os resultados demonstraram um índice de sucesso de 100% dos mini-parafusos inseridos. Após a dissecação dos segmentos ósseos, verificou-se que em alguns casos a superfície da rosca ficou parcialmente exposta, razão pela qual o cálculo da resistência à tração (média na maxila de: 141,76 ± 92,82 Ncm a 237,02 ± 78,34 Ncm e média na mandíbula de: 156,86 ± 75,55 Ncm a 328,76 ± 82,17 Ncm) foi feito em relação à área real de inserção (maxila: 24,01 ± 6,09mm2 e mandíbula: 22,88 ± 5,31mm2), observando-se um valor médio por mm2 significativamente maior na mandíbula (11,60 ± 5,22 Ncm) quando comparado à maxila (8,22 ± 5,04 Ncm). A relação entre a intensidade da força de tração (Ncm), superfície inserida (mm2) e períodos de cicatrização não apresentaram diferenças significantes (p= 0,126). Com base nestes resultados podemos concluir que os mini-parafusos avaliados demonstraram excelente desempenho biomecânico nos diferentes períodos de cicatrização analisados, apresentando maior resistência à tração no osso mandibular. / With the purpose of evaluating the influence of bone healing process on the biomechanical performance of mini-screws used as anchorage in orthodontics, 60 self-tapping (Tomas® - Dentaurum / Germany) mini-screws were inserted (1.6 x 6 mm) in the maxilla and in the mandible of 5 adult Beagle dogs. Upper and lower premolars (P1, P2, P3, P4) were extracted three months before the vertical insertion of mini-screws. The dogs were sacrified on days 0, 2, 7, 15 and 30 after the insertion of mini-screws. The jaws were dissected and the bone blocks, containing the miniscrews, were prepared to the axial pull-out strength in the Universal Testing Machine EMIC ® 2000, using a device developed specifically for this study. The values and graphics for the mechanical performance were immediately generated and recorded by the acquisition program. The clinical success rate of mini-screws was 100%. The possible differences between the healing periods were analyzed by Bonferroni´s multiple test comparisons and variance analysis (ANOVA). After the dissection of the bone segments, it was found that in some cases, the mini-screw thread was not fully inserted into the bone, reason why the pull-out strength (average of the maxilla: 141.76 ± 92.82 Ncm to 237.02 ± 78.34 Ncm and average in the mandible of 156.86 ± 75.55 Ncm to 328.76 ± 82.17 Ncm) was evaluated in relation to the real area of insertion (maxilla: 24.01 ± 6.09 mm2 and mandible: 22.88 ± 5.31 mm2). Mean value/mm2 were significantly higher in the mandible (11.60 ± 5.22 Ncm/mm2) than the maxilla (8.22 ± 5.04 Ncm/mm2). There was no statistically significant difference (p = 0126) between pull-out strength (Ncm), surface inserted (mm2) and the observed healing periods. Based on these results it can be concluded that mini-screws evaluated in this study demonstrated an excellent biomechanical behavior in all different periods of healing, showing more resistance to traction in the mandibular bone.

The classical test to confirm the performance of a given fibre design for use in reinforced concrete is the pull-out test. While attempts have been made to simulate the performance of such pull-out tests, in practice it has been found that there is a significant disparity between prediction and real-life performance. The high strength of steel reinforcing fibres is a consequence of the cold wire drawing process and subsequent fabrication. Residual stresses exist in cold drawn wire as a consequence of the elastic response to a non-uniform distribution of plastic strain. This also introduces a yield strength profile where yield strength varies radially through the wire. The question arises as to whether fibre design should use a starting material model that considers these properties. This thesis examines whether the tensile test, simple bend test and pull-out test provide enough information to define a starting material model that may be used for further design and simulation of such fibres. Since the details of the wire drawing process and material specification are proprietary and therefore unknown, a sensitivity study was conducted to determine which aspects of the wire drawing process have the greatest effect on the pull-out curve and the following were established as being significant: • Plastic strain due to wire drawing was shown to be the most important factor. • The bilinear curve was shown to be a suitable approximation for the stress-strain curve. • Replacing the plastic strain profile with a single value of average equivalent plastic strain is practical. The following were established as having negligible effect: • The consequences of the hooked-end forming process. • The residual stress profiles due to wire drawing provided that the above was also excluded. • The hardening law While inverse analysis demonstrated that all tests provide sufficient information to determine the required properties for this bilinear material model, the pull-out test was shown to provide more accurate approximations of the maximum pull-out force at the first and second peaks and the bend test was shown to produce more accurate approximations of the energy associated with pull-out. Good correlation with the baseline pull-out curve was found for both the isotropic and the kinematic hardening laws and it is concluded that behaviour during pull-out is insensitive to the hardening law. Sensitivity analysis and characterisation of the material model using an experimental pull-out curve demonstrated the importance of the coefficient of friction. Full characterisation using the pull-out curve therefore requires the solution to a three-variable problem: yield strength, tangent modulus and coefficient of friction. This was a suggested topic for further study. / Dissertation (MEng)--University of Pretoria, 2019. / Mechanical and Aeronautical Engineering / MEng (Mech) / Unrestricted

This experimental study focuses on the links that exist between the mechanical pull-out behaviour of multi-filament yarns embedded in concrete and the impregnation of the yarn by the concrete. To this aim, 5 glass yarns have been embedded in concrete (AR and E glass yarns from assembled or direct roving). A pre-treatment was applied to the yarn before the casting, and was chosen in the following three: wetting, drying or pre-impregnation with a cement slurry. By this way, 15 yarn / pre-treatment combinations were obtained that generate 15 conditions of impregnation of the yarn by the cementitious matrix. In each case, the mechanical properties were determined from a classical pull-out test and the yarns impregnation properties were characterized by two dedicated tests: yarns porosity measurements and along yarn water flow measurements. By studying the relationship between the mechanical behaviour and the physical properties of the impregnated yarns, it is shown that the pre- and post-peak behaviour are mainly connected to the flow rate measured during the water flow measurements, which suggest a specific influence of the connected pores parallel to the filaments and of the penetration depth of the matrix into the yarn. The postpeak and the residual behaviour are moreover linked to the yarn pore volume associated to the disorder induced in the filaments assembly by the penetration of the matrix. The overall result of this work is a contribution to the understanding of the relationship between the impregnation of the yarns and the pull-out behaviour.

Bewehrungen mit einer hochmoduligen Polymertränkung erreichen im Betonbauteil Textilspannungen von über 1200 N/mm². Ab diesem Niveau wurden in Dehnkörperversuchen Längsrisse und Betonabplatzungen beobachtet. Für die Eingrenzung und Identifikation der elementaren, verantwortlichen Mechanismen weisen großformatige Dehnkörper störende Einflüsse von Randeffekten und Imperfektionen auf. Daher wurde ein neuer Versuchsaufbau entwickelt, bestehend aus einem in einen Betonquader eingebetteten Einzelroving. Die simple Herstellung und die Verlässlichkeit dieser Kategorie von Experimenten in Bezug auf die Reproduzierbarkeit und der geringen Streuung der Resultate machen sie zu einer robusten Grundlage für experimentelle Untersuchungen des Verhaltens von TRC. Die experimentell ermittelten Bruchlasten werden zunächst bezüglich ihrer Leistung diskutiert und dann die beobachteten Bruchvorgänge kategorisiert hinsichtlich kompatibler mechanischer Hypothesen für die Initiierung von Längsrissen und des Spaltversagen. / Reinforcements with a high-modulus, polymeric impregnation achieve textile tensions of 1200 N/mm² and more in concrete parts. Starting at this level longitudinal cracks and splitting were observed in tests. In order to isolate and identify the fundamental, responsible mechanisms large-scale specimen show an interfering impact of boundary effects and imperfections. Therefore a new test set-up was developed, consisting of a single roving embedded in a single concrete cuboid. The simplicity of production and reliability of this class of experiments in terms of repeatability and low scatter of results makes them a robust basis for experimental investigation of TRC behavior. The experimentally obtained strengths are discussed in terms of the performance, followed by the categorization of observed failure patterns with respect to the available mechanical hypotheses of the longitudinal crack initiation and splitting failure.

El interés por las estructuras mixtas de hormigón y madera está plenamente justificado por su aplicación técnica en rehabilitación de forjados antiguos de madera, en nuevos forjados o en cualquier otra tipología estructural al amparo, entre otros, de criterios ambientales y de sostenibilidad, al ser la madera un material de menor coste energético que los clásicos hormigón o acero. En éste tipo de estructuras la conexión entre materiales es la que hace posible el trabajo conjunto de todos ellos. En la presente tesis se ha realizado una revisión pormenorizada de las características mecánicas de los conectores utilizados para este tipo de estructuras, en términos de resistencia a esfuerzo rasante, rigidez y modo de rotura, encontrando que estas propiedades mecánicas son manifiestamente mejorables. A partir de una idea preconcebida, se realizan ensayos con el material necesario y se desarrolla el diseño de un nuevo conector que, colocado inclinado respecto del plano de contacto entre materiales, trabaja a flexotracción y supera los inconvenientes de los precedentes. Se analiza con detalle cuáles han de ser sus características geométricas y cuáles son las propiedades mecánicas de la conexión resultante. Se comparan estas propiedades con las de algunas de las conexiones precedentes encontrando que su resistencia por unidad de área es superior a la de cualquier conexión anterior. Además con dicha disposición se moviliza un rozamiento en el plano de contacto que es en parte responsable de esas altas propiedades mecánicas conjuntas Mediante otra serie de ensayos se evalúa experimentalmente la magnitud del coeficiente de rozamiento para distintos acabados superficiales y sucesivos ciclos de carga. Se obtiene que la resistencia a rasante aportada por el rozamiento potencial puede llegar a ser del mismo orden que la propia resistencia del elemento en la dirección del deslizamiento. Se han fabricado dos prototipos de forjado mixto a escala real unidos con las conexiones diseñadas y se ensayan a flexión simple analizando su comportamiento, registrando en ambos casos las flechas resultantes en centro de vano. A partir de la teoría clásica de estructuras mixtas, se ha desarrollado un modelo matemático para el comportamiento a flexión del forjado con conexiones cuyo comportamiento rasante-deslizamiento se encuentra en rango elástico lineal, elastoplástico o plástico. Se ha aplicado a la conexión diseñada y, a pesar de las hipótesis realizadas para su desarrollo, el modelo predice con suficiente aproximación las flechas observadas y es, por tanto, una buena herramienta de diseño de los forjados de hormigón-madera.

A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles. Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced. Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. / QC 20100506

This study investigates the tensile behavior of anchor pull-out tests from super early age concrete(less than 12h) by finite element(FE) software ANSYS Workbench. In previous experiment, several series of pull-out tests were finished and analyzed. In each per hour, different speeds(1mm/s, 0.2mm/s, 0.1mm/s and 0.833mm/s) were evaluated, getting the results about correlation of pull-out force and displacement(F-D curve). It is difficult to evaluate the specific development of tensile strength in super young concrete, due to the super plasticity that makes itself soft and unstable. The first step of this study is to collect relevant empirical formula, theoretical varying material properties with time and pull-out force of experimental applied anchors. Comparison of simulation analysis results and empirical formulas determines whether the establishment of the finite element model and adapted constitutive model of known natural hardened concrete(NHC) are valid or not. The second procedure is that the material properties of NHC are replaced by different age values and modified until getting the same simulation results as experiment outcome. The propose of this paper is to investigate a more accurate modified formula to describe the development of tensile behavior in super early age concrete:1. Introduction 2. Background 2.1 Modes of failure 2.2 A new failure mode 2.3 Finite Element Numerical Simulation 3. Research Questions 4. Aims/Objectives of the Research 5. Proposed Research Method 5.1 Previous Empirical theory 5.1.1 Cubic Compressive strength of Early Age Concrete 5.1.2 Tensile Strength of Early Age Concrete 5.1.3 Modulus of Elasticity in Early Age Concrete 5.1.4 Prediction of pull-out maximum force to headed studs from concrete 5.2 Pervious Experiment 5.3 Numerical Simulation 6. Significance/Contribution to the Discipline 7. Experiment Program 7.1 Experiment Setup 7.2 Experiment Result 8. Numerical simulation and analysis 8.1 Material Properties 8.2 Modelling Setup 8.3 The first pull-out test 8.4 Comparison Results at different stages 9. Discussion and Results 10. Summary and Conclusion 11. Recommendation for future studies 12. References 13. Appendix

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