The goal of this research was to investigate the tensile fatigue behavior of a carbon fiber / epoxy composite material. Specifically, the stress levels at which cracks initiated in static and fatigue loading in the 90 degree plies of a "quasi-cross ply layup" [0/905]S was investigated. For layups which contain them, cracks in composite laminates initiate and propagate from 90 degree plies (including the ubiquitous "quasi-isotropic layup" 0/±45/90). Thus, this work provides valuable insight into the fatigue behavior of the plies which originate fatigue damage. Unidirectional off-axis 90 degree and 10 degree specimens were also tested, but the bulk of testing was done on the cross-ply laminates. The project sponsors, Boeing, were in the process of extending a failure model to the case of fatigue. The body of work presented here provided empirical data for that effort. Several different inspection techniques were used to investigate for cracking in the 90 degree plies, including: x-ray images, edge replicates, dye penetrants, and optical microscopy. Plots of the stress level at which crack initiation occurred will be presented, as well as images illustrating damage development in these layups. Comparisons are made to the experimental results of other investigations of this type of layup. Explorations of the effect of R-ratio (including R = 0.1 and 0.5), loading frequency (including 3, 10, and 30 Hz), and surface roughness (hand polished specimen edges to 1500 grit smoothness) on fatigue crack initiation were also performed. For the most damaging case (10 Hz, R = 0.1, no polishing), the crack initiation strain (0.00276) was one half of the strain at which cracks initiated in static monotonic loading (0.0054), and was 16% of the cross-ply specimen's (0 degree fiber dominated) ultimate strain value of (0.018).

Composite materials are being widely used in light weight structural applications due to their high specific stiffness and strength properties. However, predicting their mechanical behaviour accurately is a difficult task because of the complicated nature of these heterogeneous materials. This behaviour is not easily modeled with most of existing macro mechanics based models. Designers compensate for the model unknowns in failure predictions by generating overly conservative designs with relatively simple ply stacking sequences, thereby mitigating many of the benefits promised by composites. The research presented in this dissertation was undertaken with the primary goal of providing efficient methodologies for use in the design of composite structures considering inherent material variability and model shortcomings. A micromechanics based methodology is proposed to simulate stiffness, strength, and fatigue behaviour of composites. The computational micromechanics framework is based on the properties of the constituents of composite materials: the fiber, matrix and fiber/matrix interface. This model helps the designer to understand in-depth the failure modes in these materials and design efficient structures utilizing arbitrary layups with a reduced requirement for supporting experimental testing. The only limiting factor in using a micromechanics model is the challenge in obtaining the constituent properties. The overall novelty of this dissertation is to calibrate these constituent properties by integrating the micromechanics approach with a Bayesian statistical model. The early research explored the probabilistic aspects of the constituent properties to calculate the stiffness characteristics of a unidirectional lamina. Then these stochastic stiffness properties were considered as an input to analyze the wing box of a wind turbine blade. Results of this study gave a gateway to map constituent uncertainties to the top-level structure. Next, a stochastic first ply failure load method was developed based on micromechanics and Bayesian inference. Finally, probabilistic SN curves of composite materials were calculated after fatigue model parameter calibration using Bayesian inference. Throughout this research, extensive experimental data sets from literature have been used to calibrate and evaluate the proposed models. The micromechanics based probabilistic framework formulated here is quite general, and applied on the specific application of a wind turbine blade. The procedure may be easily generalized to deal with other structural applications such as storage tanks, pressure vessels, civil structural cladding, unmanned air vehicles, automotive bodies, etc. which can be explored in future work. / Graduate / 0548 / enginer315@gmail.com

The objective of this work was to determine the influence of recovered fibres on the mechanical properties of board. Industrial board was provided by Fiskeby Board AB and laboratory board was made by using an isotropic sheet former. Board properties such as tensile strength, tensile stiffness, z-strength and bending stiffness were evaluated. Variation in the grammages of the middle and bottom layers of laboratory board was done and influence on the mechanical properties was studied. Each layer of multiply board was also tested separately at industrial board grammage and standard grammage. Results showed an increase in the tensile properties with the increase in the grammage of bottom layer, an increase in the z-strength of the board was also observed. Bending stiffness calculated by laminate theory also indicated an increase with the increase in the grammage of bottom layer. While testing of the separate layers showed an increase in the tensile properties of the layers with increasing the grammage while a decrease in z-strength was observed. Cracks occurred in the bottom layer of the multiply boards but an increase in the mechanical properties of board was observed. / Returfibrer är miljövänliga och ger ett försprång framför nyfiber på grund av låg kostnad. Det är dock allmänt känt att returfibrer inte uppvisar samma egenskaper som nyfibrer, i själva verket försämras fiberegenskaperna efter varje återvinningsprocess. Mekaniska egenskaper är mycket viktiga för kartongproducenter och därmed läggs en hel del energi på förbättringar utan kostsamma investeringar.   I detta examensarbete utvärderades mekaniska egenskaper för 4-skikts kartong såsom dragstyrka, dragstyvhet, böjstyvhet och z-styrka. Den industriella kartongen som användes kom från Fiskeby Board AB och laboratoriekartong tillverkades med en isotrop arkformer. Separata skikt formades och guskades därefter samman. Ytvikten av det mellersta och undre skiktet ändrades och effekten på kartongens egenskaper utvärderades. Varje lager testades också separat vid ytvikter representativt för den industriella kartongen samt vid standardiserade ytvikter. Styrkan i tjockleksriktningen utvärderades med z-styrka och Scott Bond. Böjstyvheten beräknades med hjälp av laminatteorin.   Skillnaderna i dragstyrka mellan kartong framställd i industrin och laboratorie var små, men dragstyvheten var lägre för laboratoriearken på grund av torktekniken. Skillnaderna i z-styrka var inte signifikanta, men baserat på trenden uppvisade laboratoriearken en lägre styrka på grund av ett lägre presstryck. Delamineringen i de testade proverna skedde i det undre skiktet och inga sprickor uppstod mellan skikten.   Genom ökning av ytvikten av de separata skikten ökade styrkeegenskaper såsom dragstyrka och Scott Bond medan z-styrkan minskade. Genom att minska ytvikten av det mellersta lagret och öka ytvikten av det nedre kunde en ökning av styrkeegenskaperna observeras. Ökningen av z-styrkan var inte signifikant men baserat på trenden kan en ökning förväntas. En betydande ökning av Scott Bond kunde dock ses. Böjstyvheten beräknad genom laminatteorin visade också på en ökning. Även om sprickor fortfarande förekommer i det undre skiktet efter ökning av ytvikten, kan förbättrade kartongegenskaper uppnås.

For the next generation of aircraft, the use of fibre-reinforced polymer composites and the design of

The objective of the present work is to investigate the behavior of laminated fiber -reinforced polymer matrix composite shell structures under bending load with the help of a modified finite element computer code which was previously developed for the analysis of pseudo-layered single material shells. The laminates are assumed to be orthotropic and the formulation is adapted to first order shear deformation theory. The aim is to determine the large deformation characteristics numerically, and to predict the modes of failure by the illustration of the critical elements of the model. Therefore, several failure theories are also integrated to the code to detect first ply failure. Triangular shell elements are used and all the related data are generated from the mid-plane. Laminates under transverse loading are analyzed through several boundary conditions and ply orientations. To verify the numerical results obtained, a commercial finite element program is used to compare the outputs of the study, and the comparison is found to have shown good agreement. The onset of damage is investigated by using different failure criteria consisting of maximum stress, Tsai-Wu, and Tsai- Hill theories and close results are obtained.

Resumo: O trator agrícola é uma das principais fontes de energia e de trabalho no meio rural. A utilização correta de pneus, tanto em relação ao seu tipo quanto a calibração de sua pressão interna, são fatores que influem significativamente no seu desempenho. Outros fatores de regulagem do trator; tais como, a lastragem e a velocidade de deslocamento ideal para cada condição de superfície de solo, são fatores que modificam sua eficiência trativa. Esse trabalho foi realizado com o objetivo de comparar o desempenho operacional e energético de um trator equipado com pneus radiais e com pneus diagonais, em três condições de lastragem líquida (0%, 37,5% e 75% de água), três condições superficiais de um Nitossolo Vermelho Distrófico (superfície firme, superfície mobilizada e superfície firme com cobertura de restos da cultura do milho) e três condições de deslocamento, distinguidas pela mudança de marchas do trator que correspondem as seguintes velocidades teóricas: 4 km.h-1, 5km.h-1 e 7 km.h-1, informadas no painel do trator. Foi utilizado o delineamento experimental simples em faixas, correspondendo às condições superficiais do solo e um arranjo fatorial de 2x3x3 (pneus, lastros, e velocidades) em cada faixa, distribuídos em blocos ao acaso, com três repetições, totalizando 162 unidades experimentais. Esses fatores foram arranjados para permitir a avaliação dos efeitos das variáveis individualmente ou em grupos, sendo todos os dados submetidos à análise de variância, aplicando o teste de Tukey a 5% de probabilidade, para a comparação das médias...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The agricultural tractor is one of principal source of energy and power in rural land. The correct utilization of tires, related to the construction type and internal inflation pressure, both are factors that interfere significantly on its performance. Other factors of tractor adjustment, such as ballasting and ideal forward speed for each condition of soil surface are factors that modify its tractive efficiency. This research was carried out with the aim to compare the operational and energetic performance of a tractor equipped with radial tires and with bias ply tires, in three conditions of liquid ballast (0%, 37,5% and 75% of water), three conditions of surface in a Nitossolo Vermelho Distrófico (rigid surface, mobilized surface and rigid surface covered with remaining leaves of corn after its harvest) and three distinct conditions of forward speed, performed by changing the tractor gears (B1, B2 and C1), that are correlated to the following theoretical forward speed: 4 km.h-1, 5km.h-1 and 7 km.h-1, informed on tractor panel. The experiment design was in simple strips related to soil surface conditions and a factorial settlement 2x3x3 (tires, ballasts, surfaces, and forward speeds) in each strip, divided in random blocks replicated three times, totalizing 162 experimental units. These factors were arranged in order to permit an evaluation of the effects of variables individually or in groups. All data were analyzed statistically using Tukey test at 5% of probability to compare the means. To realize...(Complete abstract, click electronic access below) / Orientador: Kléber Pereira Lanças / Coorientador: Antonio Gabriel Filho / Banca: Saulo Philipe Sebastião Guerra / Banca: Paulo Roberto Arbex Silva / Mestre

Mechanical performance of composite structures is influenced by the accumulation of damage from the manufacturing process and throughout the whole service life. For instance, an aircraft is subjected to a combination of mechanical loading and the thermo-oxidative environment from the take-off to the landing. Therefore, this degree project consists of studying the damage initiation and evolution in carbon fibre reinforced polyimide composites and assesses the thickness effect of the laminated composites. After manufacturing, the level of residual thermal stresses occurring at room temperature lead to the occurrence of microcracks in bundles of the quasi-isotropic composites. Further cooling to cryogenic temperature creates new cracks were appearing. This reinforces the conclusion that cracks are created due to thermal stresses. Comparison between a baseline composite made of carbon fibre T650 8-harness satin weave with thermosetting polyimide resin (ply thickness= 190µm) and thin-ply textile laminate made of Textreme carbon fibre IMS65 (ply thickness=83µm) with the same resin shows that the ply thickness has a significant effect on suppressing or delaying the occurrence and the propagation of microcracks after mechanical loading. It is assumed that there are some edge effects leading to different damage state in 90° and ±45° layers.

Made available in DSpace on 2014-06-11T19:24:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-15Bitstream added on 2014-06-13T19:31:27Z : No. of bitstreams: 1 monteiro_la_me_botfca.pdf: 514192 bytes, checksum: 1bee58c13636c9333836a8b89b794984 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O trator agrícola é uma das principais fontes de energia e de trabalho no meio rural. A utilização correta de pneus, tanto em relação ao seu tipo quanto a calibração de sua pressão interna, são fatores que influem significativamente no seu desempenho. Outros fatores de regulagem do trator; tais como, a lastragem e a velocidade de deslocamento ideal para cada condição de superfície de solo, são fatores que modificam sua eficiência trativa. Esse trabalho foi realizado com o objetivo de comparar o desempenho operacional e energético de um trator equipado com pneus radiais e com pneus diagonais, em três condições de lastragem líquida (0%, 37,5% e 75% de água), três condições superficiais de um Nitossolo Vermelho Distrófico (superfície firme, superfície mobilizada e superfície firme com cobertura de restos da cultura do milho) e três condições de deslocamento, distinguidas pela mudança de marchas do trator que correspondem as seguintes velocidades teóricas: 4 km.h-1, 5km.h-1 e 7 km.h-1, informadas no painel do trator. Foi utilizado o delineamento experimental simples em faixas, correspondendo às condições superficiais do solo e um arranjo fatorial de 2x3x3 (pneus, lastros, e velocidades) em cada faixa, distribuídos em blocos ao acaso, com três repetições, totalizando 162 unidades experimentais. Esses fatores foram arranjados para permitir a avaliação dos efeitos das variáveis individualmente ou em grupos, sendo todos os dados submetidos à análise de variância, aplicando o teste de Tukey a 5% de probabilidade, para a comparação das médias... / The agricultural tractor is one of principal source of energy and power in rural land. The correct utilization of tires, related to the construction type and internal inflation pressure, both are factors that interfere significantly on its performance. Other factors of tractor adjustment, such as ballasting and ideal forward speed for each condition of soil surface are factors that modify its tractive efficiency. This research was carried out with the aim to compare the operational and energetic performance of a tractor equipped with radial tires and with bias ply tires, in three conditions of liquid ballast (0%, 37,5% and 75% of water), three conditions of surface in a Nitossolo Vermelho Distrófico (rigid surface, mobilized surface and rigid surface covered with remaining leaves of corn after its harvest) and three distinct conditions of forward speed, performed by changing the tractor gears (B1, B2 and C1), that are correlated to the following theoretical forward speed: 4 km.h-1, 5km.h-1 and 7 km.h-1, informed on tractor panel. The experiment design was in simple strips related to soil surface conditions and a factorial settlement 2x3x3 (tires, ballasts, surfaces, and forward speeds) in each strip, divided in random blocks replicated three times, totalizing 162 experimental units. These factors were arranged in order to permit an evaluation of the effects of variables individually or in groups. All data were analyzed statistically using Tukey test at 5% of probability to compare the means. To realize...(Complete abstract, click electronic access below)

This thesis presents a grey-box model of the temperature and moisture content for each layer of the multi-ply paperboard inside the drying section of a paper mill. The distribution of the moisture inside the board is an important variable for the board quality, but is unfortunately not measured on-line. The main goal of this work is a model that predicts the moisture evolution during the drying, to be used by operators and process engineers as an estimation of the unmeasurable variables inside the drying section. Drying of carton board is a complex and nonlinear process. The physical phenomena are not entirely understood and the drying depends on a number of unknown parameters and unmodelled or unmeasurable features. The grey-box modelling approach, which consists in using the available measurements to estimate the unknown disturbances, is therefore a suitable approach for modelling the drying section. A major problem encountered with the modelling of the drying section is the lack of measurements to validate the model. Consequently, the correctness and uniqueness of the estimated variables and parameters are not guaranteed. We therefore carry out observability and identifiability analyses and the results suggest that the selected model structure is observable and identifiable under the assumption that specific measurements are available. Based on this analysis, static measurements in the drying section are carried out to identify the parameters of the model. The parameters are identified using one data set and the results are validated with other data sets. We finally simulate the model dynamics to investigate if predicting the final board properties on-line is feasible. Since only the final board temperature and moisture content are measured on-line, the variables and parameters are neither observable nor identifiable. We therefore regard the predictions as an approximation of the estimated variables. The semiphysical model is complemented with a nonlinear Kalman filter to estimate the unmeasured inputs and the unmodelled disturbances. Data simulations show a good prediction of the final board temperature and moisture content at the end of the drying section. The model could therefore possibly be used by operators and process engineers as an indicator of the board temperature and moisture inside the drying section. / QC 20101112

Composite layups have been continuously used over many years in various applications. It is necessary to optimize its composition by studying various parameters influencing the mechanical properties and studying the failure behavior. In this master thesis, the objective was to test five different plies manufactured using thick and thin plies and various combinations of thick and thin laminates called hybrid laminates. Bearing tests are performed for five layups with each layer has its thickness varying from 40μm to 130μm, and a combination called hybrid laminate, and the results from the tests are investigated. The resulting system has a good performance with onset damage above 700 MPa and an ultimate failure above 1130 MPa, using fibers' full potential. Also, the different failure modes like fiber kinking, matrix crack, delamination, and their effect on the layup's strength are investigated using fractography. This paper also investigates the influences of the thickness of the laminate on the strength of hybrid composites jointed using different mechanisms, and its failure modes are checked. Results from this experiment are used to validate in the form of FEM model, which is a part of an internal project at RISE SICOMP AB. This thesis is suitable for an engineering student in mechanical engineering, material science interested in composite materials and fractography.