Composite panel structure optimization is commonly decomposed into panel optimization subproblems, with specified local loads, resulting in manufacturing incompatibilities between adjacent panel designs. Using genetic algorithms to optimize local panel stacking sequences allows panel populations of stacking sequences to evolve in parallel and send migrants to adjacent panels, so as to blend the local panel designs globally. The blending process is accomplished using the edit distance between individuals of a population and the set of migrants from adjacent panels. The objective function evaluating the fitness of designs is modified according to the severity of mismatches detected between neighboring populations. This lays the ground work for natural evolution to a blended global solution without leaving the paradigm of genetic algorithms. An additional method applied here for constructing globally blended panel designs uses a parallel decomposition antithetical to that of earlier work. Rather than performing concurrent panel genetic optimizations, a single genetic optimization is conducted for the entire structure with the parallelism solely within the fitness evaluations. A guide based genetic algorithm approach is introduced to exclusively generate and evaluate valid globally blended designs, utilizing a simple master-slave parallel implementation, implicitly reducing the size of the problem design space and increasing the quality of discovered local optima. / Ph. D.

Composite panel structure optimization is commonly decomposed into panel optimization subproblems, with specified local loads, resulting in manufacturing incompatibilities between adjacent panel designs. Using genetic algorithms to optimize local panel stacking sequences allows panel populations of stacking sequences to evolve in parallel and send migrants to adjacent panels, so as to blend the local panel designs globally. The blending process is accomplished using the edit distance between individuals of a population and the set of migrants from adjacent panels. The objective function evaluating the fitness of designs is modified according to the severity of mismatches detected between neighboring populations. This lays the ground work for natural evolution to a blended global solution without leaving the paradigm of genetic algorithms. An additional method proposed here for constructing globally blended panel designs uses a parallel decomposition antithetical to that of earlier work. Rather than performing concurrent panel genetic optimizations, a single genetic optimization is conducted for the entire structure with the parallelism solely within the fitness evaluations. A guide based genetic algorithm approach is introduced to exclusively generate and evaluate valid globally blended designs, utilizing a simple master-slave parallel implementation, implicitly reducing the size of the problem design space and increasing the quality of discovered local optima. / Master of Science

Laminados compósitos com matrizes poliméricas, respectivamente termorrígida e termoplástica, reforçadas com fibras contínuas de carbono foram submetidos a impacto único transversal com diferentes níveis de energia. Os danos imprimidos aos materiais estruturais foram avaliados por termografia ativa infravermelha na modalidade transmissão. Em geral, os termogramas do laminado termoplástico apresentaram indicações mais claras e bem definidas dos danos causados por impacto, se comparados aos do compósito termorrígido. O aquecimento convectivo das amostras por fluxo controlado de ar se mostrou mais eficaz que o realizado por irradiação, empregando-se lâmpadas incadecentes. Observou-se também que tempos mais longos de aquecimento favoreceram a visualização dos danos. O posicionamento da face impactada do espécime, relativamente à câmera infravermelha e à fonte de calor, não afetou a qualidade dos termogramas no caso do laminado termorrígido, enquanto que influenciou significativamente os termogramas do compósito termoplástico. Os resultados permitiram concluir que a termografia infravermelha é um método de ensaio não-destrutivo simples, robusto e confiável para a detecção de danos por impacto inferior à 5 Joules em laminados compósitos poliméricos reforçados com fibras de carbono. / Continuous carbon fiber-reinforced thermosetting and thermoplastic composite laminates were exposed to single transversal impact with different energy levels. The damages marked to the structural materials were evaluated by active infrared thermography in transmission mode. In general, the thermoplastic laminate thermograms showed more clear and delineated damage indications when compared to the ones from thermosetting composite. The convective heating of the samples by controlled hot air flow was more efficient than via irradiation using lamp. It was also observed that longer heating times improved the damage visualization. The positioning of the specimen´s impacted face regarding the infrared camera and the heating source did not affect the thermo-imaging of thermosetting specimens, whereas it substantially influenced the thermograms of thermoplastic laminates. The results allow concluding that infrared thermography is a simple, robust and trustworthy methodology for detecting impact damages as light as 5 Joules in carbon fiber composite laminates.

The PhD thesis evaluates the mechanical properties and damage tolerance of aerospace carbon/epoxy laminates containing long, narrow interlaminar galleries. The term 'galleries' refers to thin and long holes in a laminate used for the installation of small measuring devices, such as structural health monitoring (SHM) sensors. The galleries considered in this study are similar to those used in a novel SHM system known as 'Comparative Vacuum Monitoring (CVM)'. CVM was developed by the Australian company - Structural Monitoring Systems (SMS) - for damage detection in aircraft structures. CVM is a SHM system that utilises pressure differentials between a parallel series of galleries at atmospheric or low pressure to detect damage initiation and propagation. Thus far, CVM has been used for the monitoring of surface cracks in metallic structures using surface mounted sensors. Recent research has also demonstrated that it may be possible to monitor damage along the bond- line of both metallic and composite joints using CVM. The ability of CVM sensors to detect delamination damage inside composite structures is less well understood. It is envisaged that CVM can be used for the through-life health monitoring of composite aircraft structures prone to delamination damage. However, a major concern with applying CVM to composite laminates is the open-hole design of the galleries that may initiate damage growth under external loading. Material property data, structural tests, and models for predicting the properties of laminates containing galleries is needed before CVM technology can be certified for use in aircraft composite structures. The primary objectives of this PhD thesis are the development of an optimum process method for introducing multiple interlaminar CVM galleries in composite laminates; the development of a validated model for calculating changes to the mechanical properties of laminates containing CVM galleries; and the determination of optimum CVM gallery shape, size and orientation combinations for minimising the effect of the galleries on the mechanical properties of laminates. The effects of the shape, size and orientation of CVM galleries on the mechanical properties of carbon/epoxy laminates are evaluated by an extensive experimental research program, and the results are presented in the thesis. The properties investigated include the in-plane tensile and compressive properties, tensile and compressive fatigue life, through-thickness tensile strength, interlaminar shear strength, mode I and mode II interlaminar fracture toughness, and impact damage resistance. The results from tensile tests on lap-joints and T-joints containing CVM galleries are also presented.

This work begins by establishing the necessary and sufficient conditions for hygrothermal stability of composite laminates. An investigation is performed into the range of coupling achievable from within all hygrothermally stable families. The minimum number of plies required to create an asymmetric hygrothermally stable stacking sequence is found to be five. Next, a rigorous and general approach for determining designs corresponding to optimal levels of coupling is established through the use of a constrained optimization procedure. Couplings investigated include extension-twist, bend-twist, extension-bend, shear-twist, and anticlastic. For extension-twist and bend-twist coupling, specimens from five- through ten-ply laminates are manufactured and tested to demonstrate hygrothermal stability and achievable levels of coupling. Nonlinear models and finite element analysis are developed, and predictions are verified through comparison with test results. Sensitivity analyses are performed to demonstrate the robustness of the hygrothermal stability and couplings to deviations in ply angle, typical of manufacturing tolerances. Comparisons are made with current state-of-the-art suboptimal layups, and significant increases in coupling over previously known levels are demonstrated.

Man-made materials such as fiber-reinforced composites (FRCs) can be tailored for optimum performance in product design applications in terms of strength and weight. The current work is aimed at studying the behaviors of composite laminates based on E-glass CSM (Chopped Strand Mat) or WRM (Woven Roving Mat) plies with a polyester resin for impact protection applications. Detailed mechanical characterization of CSM and WRM laminates till failure is carried out for tensile, compressive and shear loads by varying manufacturing process, number of plies, and laminate thickness. The effect of fiber volume fraction on mechanical properties is shown. The efficacy of CSM and WRM laminates as energy- absorbing countermeasures is studied by performing quasi-static and axial impact tests on cylindrical tubes made of the stated FRCs. In addition to load-displacement and specific energy absorption attributes, failure modes are of interest in such studies. The potential of FRC laminates for protection against projectile impact is investigated by performing low velocity impact perforation tests with a falling tup fitted with an indentor, and medium to high velocity projectile impact tests in a gas gun-based device. The valuable results generated are used for the validation of nonlinear finite element-based CAE (Computer-Aided Engineering) procedures including application of a multi-modal failure criterion for explicit dynamic analysis. The present study not only throws light on complex mechanical behavior of an important class of lightweight materials under static and dynamic loads, but also simulation tools for the design of impact safety countermeasures such as bullet-proof laminates and energy–absorbing components for automotive body structures.

L’étude réalisée dans le cadre de cette thèse représente une recherche sur la durabilité de la réparation par collage de patchs externes de structures composites endommagées. Le comportement des réparations sollicitées en traction a été étudié. Les approches expérimentale et numérique ont été réalisées. La qualité et la répétitivité des réparations dépendent fortement du savoir-faire employé durant leur mise en œuvre. A ce titre, un protocole de fabrication précis a été établi et validé. Ce protocole a ensuite été appliqué strictement dans l’ensemble de l’étude. L’effet de la géométrie des patchs sur la performance des réparations en traction a été discuté. De plus, deux séries de patchs présentant des rigidités de membranes et des séquences d’empilement différentes ont été testées. Pratiquement, plusieurs méthodes de contrôle ont été appliquées pour localiser l’initiation de l’endommagement et suivre son évolution jusqu’à la rupture final. L’observation des scénarios d’évolution de l’endommagement a conduit à proposer trois modèles phénoménologiques permettant l’élaboration et la validation d’un modèle numérique.Le modèle numérique proposé a été validé grâce à la corrélation avec les résultats expérimentaux. Ensuite, ce modèle a été appliqué pour réaliser une étude paramétrique. Les résultats obtenus ont permis de proposer un modèle d’aide à la conception et à l’optimisation des structures composites réparées. Ce modèle fournit des informations intéressantes sur la meilleure combinaison des paramètres de réparation à utiliser. / The study in this thesis represents research on the durability of the repair of damaged composite structures by bonding external patches. The behaviour of the remedies sought in tension was investigated. The experimental and numerical approaches have been made.The quality and repeatability of repairs depends heavily on skills used during their installation works. As such, a specific manufacturing protocol was established and validated. This protocol was then applied strictly throughout the study. The effect of patch geometry on the performance of repair in tension has been discussed. In addition, two sets of patches with the different membrane stiffness and stacking sequences were tested. Practically, several control methods were applied to locate damage initiation and follow its evolution until the final rupture. Observing damage evolution scenarios has led to propose three phenomenological models for the development and validation of a numerical model.The proposed numerical model has been validated through correlation with experimental results. Then, this model was applied to perform a parametric study. The results obtained allowed to propose a model to help design and optimization of repaired composite structures. This model provides interesting information on the best combination of repair settings.

No description available.

Laminados compósitos com matrizes poliméricas, respectivamente termorrígida e termoplástica, reforçadas com fibras contínuas de carbono foram submetidos a impacto único transversal com diferentes níveis de energia. Os danos imprimidos aos materiais estruturais foram avaliados por termografia ativa infravermelha na modalidade transmissão. Em geral, os termogramas do laminado termoplástico apresentaram indicações mais claras e bem definidas dos danos causados por impacto, se comparados aos do compósito termorrígido. O aquecimento convectivo das amostras por fluxo controlado de ar se mostrou mais eficaz que o realizado por irradiação, empregando-se lâmpadas incadecentes. Observou-se também que tempos mais longos de aquecimento favoreceram a visualização dos danos. O posicionamento da face impactada do espécime, relativamente à câmera infravermelha e à fonte de calor, não afetou a qualidade dos termogramas no caso do laminado termorrígido, enquanto que influenciou significativamente os termogramas do compósito termoplástico. Os resultados permitiram concluir que a termografia infravermelha é um método de ensaio não-destrutivo simples, robusto e confiável para a detecção de danos por impacto inferior à 5 Joules em laminados compósitos poliméricos reforçados com fibras de carbono. / Continuous carbon fiber-reinforced thermosetting and thermoplastic composite laminates were exposed to single transversal impact with different energy levels. The damages marked to the structural materials were evaluated by active infrared thermography in transmission mode. In general, the thermoplastic laminate thermograms showed more clear and delineated damage indications when compared to the ones from thermosetting composite. The convective heating of the samples by controlled hot air flow was more efficient than via irradiation using lamp. It was also observed that longer heating times improved the damage visualization. The positioning of the specimen´s impacted face regarding the infrared camera and the heating source did not affect the thermo-imaging of thermosetting specimens, whereas it substantially influenced the thermograms of thermoplastic laminates. The results allow concluding that infrared thermography is a simple, robust and trustworthy methodology for detecting impact damages as light as 5 Joules in carbon fiber composite laminates.

No description available.