Purpose: While there are diagnostic criteria for functional gastrointestinal disorders (FGIDs), their evaluation is challenging. This is because criteria are based on symptoms, and the underlying pathophysiology is not clear; as such, there are no gold standard tests. Diagnosis is further challenged by considerable clinical overlap between different FGIDs as well as other organic diseases, while many people with FGIDs have more anxiety and depression than healthy individuals. I hypothesised that assessment of separate components of FGIDs that also indicate their effect on the patient could improve diagnosis. My aim was to investigate the evolution of opinions from experts involved in the development of FGID diagnostic criteria on the proposal for the development of multiaxial assessment criteria (MAC) for FGIDs. Methods: I conducted a web-based Delphi study using a group of purposively sampled experts identified from committees of the Rome Foundation and the International Foundation for Gastrointestinal Disorders. From a systematic search of relevant articles, I generated132 items that were sent to experts as a first round survey. The items assessed risk and contributing factors, the therapeutic relationship, areas of evaluation and the advantages and disadvantages of multiaxial assessment. Consensus on an item was reached when 75% of experts indicated that they agreed or strongly agreed with the statement. Key results: 36 of 68 eligible participants (52%) responded to the first round. Consensus was reached on 96 items. Using participant feedback, thematic analysis was used to generate 33 additional items for round two. Thirty-one of 36 participants (86%) replied to rounds two and three. In round two, 19 items gained consensus, and in round three, nine items gained consensus. Participants agreed that multiaxial assessment was needed, using a systematic approach to establish the physiological and psychosocial components of FGIDs. Participants were unable to agree on the importance of physical risk factors such as previous surgery and genetic association. Overall, 124 of the 167 items achieved consensus. Conclusion and inferences: The key finding from my study shows that experts agree that multiaxial assessment of FGIDs is needed. I also identified expert agreement on the consideration of psychological risk factors and the importance of the impact of FGID symptoms on daily life. Findings also show that experts disagreed on the impact of physical risk factors, socioeconomic status and spirituality on people with FGIDs. While experts could not agree on genetic and gender-based risk factors, they considered that these areas are important and require further research.

Dans le cadre d’une Cifre avec Airbus Helicopters, le projet a pour but le développement d’un modèle pour le pré-dimensionnement de pièces lamifiées élastomère-métal dont le rôle est critique en termes de conception et de sécurité pour les architectures de rotors d’hélicoptères. Pour cela, un premier volet de la thèse a consisté à caractériser le comportement élasto-dissipatif du matériau d’étude (un butadiène chargé de noir de carbone) via une campagne d’essais statiques et dynamiques, sous différents modes de sollicitations (uniaxiales et biaxiales) et sur un spectre assez large de fréquences, d’amplitudes et de températures. A partir de ces observations, un modèle phénoménologique de comportement hyper-viscoélastique est proposé. Sur la base d’un modèle de Maxwell généralisé, il permet de traduire les phénomènes observés sur la gamme de sollicitations visées. Un accent particulier a été porté sur la prise en compte de l’effet Payne en adoptant une approche originale. Les paramètres du modèle sont identifiés par une méthode robuste et rapide. Le modèle est ensuite développé à la fois dans un code commercial de calcul par éléments finis et dans un outil de calcul basé sur une méthode de réduction de modèles. Enfin, une étude du comportement en fatigue est réalisée à travers une campagne d’essais originaux servant de point de départ à la proposition d’une loi d’endommagement continu. / In association with Airbus Helicopters, the aim of the project is to develop a model to pre-size elastomer-metal laminated devices whose role is critical in terms of design and safety for helicopters rotor architectures. To do so, the first part of this thesis consisted in characterizing the elasto-dissipatice behavior of the studied material (a carbon black filled butadiene rubber) thanks to static and dynamic tests, with several kind of loading (uni-axial and bi-axial) and over a wide range of frequences, amplitudes and temperatures. From these observations, a phenomenological hyper-viscoelastic model is proposed. Based on a generalized Maxwell model, it is able to describe the phenomena over the loading range of concern. A particular focus is made to take in account the Payne effect thanks to an original approach. The model parameters are identified with a fast and robust method. The model is then implemented in a commercial finite element code and in a tool based on a model reduction method. Last, a study of the behaviour in fatigue is performed with an original characterization campaign from which a continuous damage law is proposed.

Mental illness is common, and usually starts early in life. However, the majority of those affected never seek mental health care. The overall aim of this thesis was to increase knowledge about help-seeking young adults with mental illness in order to improve diagnostic procedures in clinical psychiatry. A group of young adult psychiatric out-patients (n=217) were consecutively invited to participate in the study between October 2002 and September 2003. Altogether 200 (92%) agreed to participate. Among them, there were 161 (80%) women and 39 (20%) men. Participants’ mean age was 22.4±1.9 years. All participants were carefully and comprehensively assessed with respect to axes I, II, IV and V in the DSM-IV. Psychiatric disorders and personality disorders were assessed using the Structured Clinical Interview for DSM-IV for axis I disorders and the Structured Clinical Interview for DSM-IV for axis II disorders. Psychosocial and environmental problems (axis IV) were evaluated through structured interviewing by a social worker and by self-assessment with a questionnaire. Professional and patient ratings on the Global Assessment of Functioning scale were compared before and after treatment. Patients also reported on the Swedish universities Scales of Personality, the Child and Adolescent Psychiatric Screening Inventory-Retrospect and the Coddington’s life event scale. Taken together, the young adult, psychiatric outpatients were characterized by an early onset of their mental disorders, by co-morbidity, by being female and by having mood or anxiety disorders. There were no significant differences between self-referred and those referred by medical professionals according to either number of current or lifetime diagnoses. Childhood onset of depression was associated with more severe symptoms, more psychosocial risk factors, and more childhood developmental delays. Axis IV psychosocial stress categories were related to the presence of axis I disorders, personality disorders, co-morbidity, and impaired functioning. Agreement between patients’ and professionals’ ratings on the GAF scale was good before treatment and excellent after treatment. In summary, the findings suggest that direct self-referral to specialized psychiatric care does not seem to be associated with overutilization of such care. Childhood onset of depression is associated with a more complex illness. The revised axis IV according to DSM-IV seems to have concurrent validity, but is still hampered by limited reliability. And finally, the results support the usefulness of the self-report GAF instrument for measuring outcome in psychiatric care.

Les composites SiC/SiC sont envisagés comme matériaux pour des composants de cœur de réacteurs nucléaires du futur. Le dimensionnement de ces structures par la simulation numérique repose sur une modélisation du comportement mécanique de ces matériaux. Ces travaux visent à améliorer la compréhension de leurs mécanismes de déformation afin de construire une loi de comportement à même de prédire la réponse du matériau sous chargements complexes. Une caractérisation approfondie du comportement macroscopique de tubes SiC/SiC multicouches - similaires aux concepts de gaines de combustibles - a été entreprise, par des essais de traction-pression interne, traction-torsion et flexion multi-instrumentés, et a permis de constituer une importante base expérimentale pour la compréhension des mécanismes d'endommagement et l'identification de modèles. Des observations in-situ et après rupture ont permis de quantifier l'orientation des fissures matricielles observées en surface en fonction du type de chargement appliqué. Des mesures de champs de déplacement par Corrélation d'Images Numériques à l'échelle d'un motif du textile ont permis d'apporter des informations fines sur la cinématique de la surface du composite, telles que l'ouverture des fissures ou la déformation des fragments matriciels. Ces mesures ont également permis de mettre en évidence l'importance de la réorientation des torons dans la direction de chargement, mécanisme pouvant expliquer certaines spécificités du comportement macroscopique du fait de son couplage avec la fissuration matricielle. Enfin, ces différentes données expérimentales ont permis de construire un modèle phénoménologique, identifiable sur quatre essais uniaxiaux, permettant de prédire de manière satisfaisante le comportement macroscopique sous divers chargements bi-axés. L'accord de certaines quantités locales, telles que les caractéristiques de la fissuration en traction, ont également été vérifiées. / SiC/SiC composites are candidate materials for in-core components of future nuclear reactors. The analysis of these structures using numerical simulations requires material constitutive laws. The present work focuses on understanding the deformation mechanisms of these materials in order to build a constitutive model able to predict their stress-strain response under complex loadings. An extensive characterization of the mechanical behaviour of SiC/SiC multi-layered tubes – similar to fuel cladding concepts - was carried out, using tension-internal pressure, tension-torsion and bending tests, that allowed to build an important experimental basis for the understanding of the mechanisms and the identification of constitutive laws. In-situ and post-failure observations have allowed quantifying the orientation of surface matrix cracks as a function of the loading type. Full-field measurements using Digital Image Correlation at the tow scale brought precise information on the composite surface kinematics, such as the crack opening or the deformation of the matrix fragments. These measurements also evidence the importance of the tow reorientation, that could explain specific features of the macroscopic behaviour because of its coupling with matrix cracking. Finally, these experimental data allowed to build a constitutive model, identified on only four uniaxial tests, able to predict satisfactorily the macroscopic behaviour under several biaxial loadings. The correct prediction of local quantities, such as the characteristics of the matrix cracking in tension, has also been verified.

Magnesium is the lightest metal that can be used for structural applications. For the reasons of weight saving, there has been an increasing demand for magnesium from the automotive industry. However, poor formability at room temperature, due to a limited number of slip systems available owing to its hexagonal close packed crystal structure, imposes severe limitations on the application of Mg and its alloys in the wrought form. One possibility for improving formability is to form the components superplastically. For this, it is necessary to refine the grain structure. A fine-grained material is also stronger than its coarse grain counterpart because of grain size strengthening. Moreover, fine-grained magnesium alloys have better ductility as well as a low ductile to brittle transition temperature, thus their formability at room temperature could be improved. In addition to grain refinement, the issues pertaining to poor formability or limited ductility of Mg alloys can be addressed by controlling the crystallographic texture. Recently, it has been shown that warm equal channel angular extrusion (ECAE) of magnesium led to reduction in average grain size and shear texture formation, by virtue of which subsequent room temperature rolling was possible. Based on the literature, it was also certain that, in order to make magnesium alloys amenable for processing, grain refinement needs to be carried out and the role of shear texture needs to be explored. Since processing at higher temperature would lead to relatively coarser grain size, large strain deformation at lower temperatures is desirable. The present thesis is an attempt to address these issues. The thesis has been divided in to eight chapters. The chapters 1 and 2 are dedicated to introduction and literature review on the subject that provides the foundation and motivation to the present work. Subsequent chapters deal with the research methodology, experimental and simulation results, discussion, summary and conclusion. In the present investigation, two single phase alloys were chosen, the commercially pure magnesium and the magnesium alloy AM30. These materials were subjected to suitable processing techniques, detailed posteriori. A systematic analysis of microstructure and texture for each of the as-processed materials was performed by electron backscattered diffraction (EBSD) using a field emission gun scanning electron microscope (FEG-SEM). Bulk texture measurement by X-ray diffraction, neutron diffraction and local texture measurement by synchrotron X-rays were also carried out. In addition, dislocation density was measured using X-Ray diffraction line profile analysis (XRDLPA). The experimental textures were validated by using Visco-Plastic Self Consistent (VPSC) simulation. The details of experimental as well simulation techniques used in the present investigation is described in chapter 3. To understand the philosophy of large strain deformation by shear in magnesium and its alloy, free end torsion tests could provide a guide line. Based on the understanding developed from these tests, further processing strategy could be planned. Therefore, a rigorous study of deformation behaviour under torsion was carried out. In chapter 4, the results of free end torsion tests carried out at different temperatures, 250⁰C, 200⁰C and 150⁰C and strain rates, 0.01 rad.s-1, 0.1 rad.s-1, 1 rad.s-1 are presented for both the alloys. In addition to the analysis of stress-strain behaviour, a thorough microstructural characterization including texture analyses pertaining to deformation and dynamic recrystallization was performed. Both pure Mg and the AM30 alloy exhibit similar ductility under the same deformation condition, while the strength of AM30 was more. The strain hardening rate decreased with temperature and increased with strain rate for both the materials. However, the strain hardening rate was always higher in case of the alloy AM30. Large amount of dynamic recrystallization (DRX) was observed for both the alloys. The initial texture had an influence on the deformation behaviour under torsion and the resulting final texture. The initial non-axisymmetric texture of pure Mg samples led to nonaxisymmetric deformation producing ear and faces along the axial direction, and the final texture was also non-axisymmetric. An examination of the texture heterogeneity was carried out in one of the pure Mg torsion tested samples by subjecting it to EBSD examination at different locations of the surface along the axial direction. The strain induced on the ear portion was maximum, and in the face was lower. This has been attributed to the orientation of basal planes in the two regions. The axisymmetric initial texture in case of the alloy AM30 led to the formation of axisymmetric texture with no change in the shape of the material. Owing to this simplicity, the occurrence of dynamic recrystallization (DRX) was studied in more detail for this alloy. The mechanism of texture development due to deformation as well as dynamic recrystallization could be tracked at every stage of deformation. A typical shear texture was observed with respect to the strain in each case. Very low fraction of twins was observed for all the cases indicating slip dominated deformation, which was validated by VPSC simulation. It was found that with the increase in strain during torsion, the fraction of dynamically recrystallized grains increased. The recrystallization mechanism was classified as “continuous dynamic recovery and recrystallization” (CDRR) and is characterized by a rotation of the deformed grains by ~30⁰ along c-axis. After developing an understanding of large strain deformation behaviour of pure Mg and the alloy AM30 through torsion tests, the possibility of low temperature severe plastic deformation for both the materials by equal channel angular extrusion (ECAE) was explored. The outcome of this investigation has been presented in chapter 5. At first, ECAE of pure magnesium was conducted at 250⁰C up to 4 passes and then the temperature was reduced by 50⁰C in each subsequent pass. In this way, ECAE could be carried out successfully up to 8th pass with the last pass at room temperature. A grain size ~250 nm and characteristic ECAE texture with the fibres B and C2 were achieved. The AM30 alloy subjected to similar processing schedule as pure Mg, however, could be deformed only up to 6th pass (TECAE=150⁰C) without fracture. An average grain size ~ 420 nm and a texture similar to ECAE processed pure Mg was observed for this alloy. The difference in the deformation behaviour of the two alloys has been explained on the basis of the anisotropy in the stacking fault energy (SFE) in the case of pure Mg. Neutron diffraction was carried out to confirm and validate the microtexture results obtained from the EBSD data, while the local texture measurement by synchrotron radiation was carried out at different locations of the ECAE samples to give a proper account of the heterogeneity in texture. The effect of grain refinement was examined, deconvoluting the effect of shear in improving the strength and ductility using another severe plastic deformation technique, namely multi axial forging (MAF). In this process, the material was plastically deformed by a combination of uniaxial compression and plane strain compression subsequently along all the three axes. The details of this investigation has been presented in chapter 6. By this method, the alloy AM30 could be deformed without fracture up to a minimum temperature of 150⁰C leading to ultra-fine grain size (~400 nm) with very weak texture. A room temperature ductility ~55% was observed for this material. Finally, a comparison of room temperature mechanical properties of the alloy AM30 was carried out for the ECAE and MAF processed conditions having similar grain size in order to observe the effect of texture formed during both the processes. A similar strength and ductility for both the cases was attributed to the orientation obtained from both the ECAE and MAF, which is away from the ideal end orientation for tensile tests. The final outcomes of the thesis has been summarized in chapter 7.

This dissertation focuses on the development of three classes of brain-inspired machine learning classification models. The models attempt to emulate (a) multi-sensory integration, (b) context-integration, and (c) visual information processing in the brain.The multi-sensory integration models are aimed at enhancing object classification through the integration of semantically congruent unimodal stimuli. Two multimodal classification models are introduced: the feature integrating (FI) model and the decision integrating (DI) model. The FI model, inspired by multisensory integration in the subcortical superior colliculus, combines unimodal features which are subsequently classified by a multimodal classifier. The DI model, inspired by integration in primary cortical areas, classifies unimodal stimuli independently using unimodal classifiers and classifies the combined decisions using a multimodal classifier. The multimodal classifier models are be implemented using multilayer perceptrons and multivariate statistical classifiers. Experiments involving the classification of noisy and attenuated auditory and visual representations of ten digits are designed to demonstrate the properties of the multimodal classifiers and to compare the performances of multimodal and unimodal classifiers. The experimental results show that the multimodal classification systems exhibit an important aspect of the “inverse effectiveness principle” by yielding significantly higher classification accuracies when compared with those of the unimodal classifiers. Furthermore, the flexibility offered by the generalized models enables the simulations and evaluations of various combinations of multimodal stimuli and classifiers under varying uncertainty conditions. The context-integrating model emulates the brain’s ability to use contextual information to uniquely resolve the interpretation of ambiguous stimuli. A deep learning neural network classification model that emulates this ability by integrating weighted bidirectional context into the classification process is introduced. The model, referred to as the CINET, is implemented using a convolution neural network (CNN), which is shown to be ideal for combining target and context stimuli and for extracting coupled target-context features. The CINET parameters can be manipulated to simulate congruent and incongruent context environments and to manipulate target-context stimuli relationships. The formulation of the CINET is quite general; consequently, it is not restricted to stimuli in any particular sensory modality nor to the dimensionality of the stimuli. A broad range of experiments are designed to demonstrate the effectiveness of the CINET in resolving ambiguous visual stimuli and in improving the classification of non-ambiguous visual stimuli in various contextual environments. The fact that the performance improves through the inclusion of context can be exploited to design robust brain-inspired machine learning algorithms. It is interesting to note that the CINET is a classification model that is inspired by a combination of brain’s ability to integrate contextual information and the CNN, which is inspired by the hierarchical processing of visual information in the visual cortex. A convolution neural network (CNN) model, inspired by the hierarchical processing of visual information in the brain, is introduced to fuse information from an ensemble of multi-axial sensors in order to classify strikes such as boxing punches and taekwondo kicks in combat sports. Although CNNs are not an obvious choice for non-array data nor for signals with non-linear variations, it will be shown that CNN models can effectively classify multi-axial multi-sensor signals. Experiments involving the classification of three-axis accelerometer and three-axes gyroscope signals measuring boxing punches and taekwondo kicks showed that the performance of the fusion classifiers were significantly superior to the uni-axial classifiers. Interestingly, the classification accuracies of the CNN fusion classifiers were significantly higher than those of the DTW fusion classifiers. Through training with representative signals and the local feature extraction property, the CNNs tend to be invariant to the latency shifts and non-linear variations. Moreover, by increasing the number of network layers and the training set, the CNN classifiers offer the potential for even better performance as well as the ability to handle a larger number of classes. Finally, due to the generalized formulations, the classifier models can be easily adapted to classify multi-dimensional signals of multiple sensors in various other applications.

Afin de participer à l’émergence de technologies innovantes et contribuer aux objectifs de développement durable, un consortium composé de 13 partenaires (3 laboratoires académiques et 10 entreprises industrielles) a été formé. Le projet Thermofluid-RT consiste à développer un système de refroidissement à boucle de fluide diphasique à pompage mécanique. Le LMT-Cachan contribue à la conception de l'élément essentiel de la pompe, à savoir, le soufflet. Celui-ci est obtenu en soudant des feuilles d’acier inoxydable à durcissement structural très mince (70 µm) et doit fonctionner sans défaillance pendant 20 ans. Un dimensionnement fiabiliste du soufflet basé sur la théorie du maillon le plus faible est réalisé. Une méthode d'optimisation basée sur la technique d’identification intégrée à la corrélation d'images numériques aboutit à une géométrie d’éprouvette qui minimise l'incertitude des paramètres recherchés. Toutes les données brutes sont combinées à leur juste valeur grâce à une formulation Bayésienne basée sur l’hypothèse de bruits blanc gaussiens. La géométrie optimisée est testée sur Mini-Astrée, la nouvelle machine biaxiale du LMT. Plusieurs lois de comportements sont étudiées et testées sur le matériau étudié. De très fines feuilles du même acier, sont de même testées à l’aide d’essais uni-axiaux et multiaxiaux. Une analyse microscopique est conduite au travers d’un micro-essai de traction sur 2 grains et l’identification de paramètres d’une loi de plasticité cristalline. Enfin, le dimensionnement probabiliste du soufflet est validé à partir de plusieurs mesures expérimentales infra-rouges sur un nouveau banc d’essai. Un modèle probabiliste à deux échelles permet la caractérisation des phénomènes observés relatifs au matériau d’étude et au composant lui-même. / In the context of leveraging and accelerating innovative technological solutions that contribute to meeting sustainable goals, a consortium composed of 13 partners (3 academic laboratories and 10 industrial companies) has been formed. The THERMOFLUID-RT project consists in developing a two-phase fluid loop driven by a mechanical pump. LMT-Cachan contributes to the design of the critical component of the pump, i.e., bellows. This component obtained by welding very thin (70 µm) pre-deformed sheets made of precipitation-hardened stainless steel is expected to operate without failure for 20 years. First, a new probabilistic design methodology allows for the fatigue design of the component. Second, an optimization methodology based on full field measurements and Integrated Digital Image Correlation (IDIC) allows the sample geometry to be designed with the least uncertainty of the sought parameters. All data account for the latter thanks to a Bayesian foundation that equitably weights all measurements. Third, the optimized cruciform geometry has been tested in a new compact biaxial machine, mini-Astrée that allows for a fast, yet robust identification. Several elasto-plastic models with increasing complexity are investigated to probe the material behavior. Ultra-thin sheets are also tested in uniaxial and biaxial experiments thanks to an anti-wrinkling setup. Fourth, a microscopic analysis is also performed via quasi-3D IDIC and a uniaxial micro-specimen allow a crystal plasticity law to be characterized. Last, the probabilistic fatigue design of the bellows based on the weakest link theory and a two-scale probabilistic model is validated with infrared measurements in the high cycle fatigue regime.

Kamouflagenät är ett viktigt verktyg inom försvarsindustrin där det används för att maskera eller dölja objekt från att bli visuellt upptäckta. Kamouflagenät är utformade för att efterlikna den omgivande miljön eller terräng som den appliceras vid. Traditionellt tillverkas kamouflagesystemen genom virkningsstekniken bi-axial varptrikå med två system inslagstrådar i 0° respektive 90°. För produktutvecklingens syfte att tillverka ett lätt kamouflagenät med lämpliga hållfasthetsegenskaper, undersöks tekniken multi-axial varptrikå med fyra system inslagstrådar i 0°, 90° och ±45°. Genom semi-strukturerade intervjuer med experter inom bi- och multi-axial varptrikå samlas det in information och fakta om multi-axial teknik. Detta fungerar som en grund för att avgöra om det är en möjlig teknik för den befintliga produkten. En teoretisk modellering utförs sedan för att undersöka, förutsäga samt jämföra beteenden och egenskaper hos de bi- och multi-axiella strukturerna. De semi-strukturerade intervjuerna resulterade i en omfattande och informativ faktainsamling om multi-axial teknik. Det inhämtades underlag gällande hur tillämpbar den multi-axiella tekniken är för kamouflagenät, samt information om maskinens begränsningar och trådorientering. Den teoretiska modelleringen innebär tillämpning av kända matematiska och fysikaliska begrepp, modelleringen lägger således en grund för att förstå mekaniska beteenden hos bi -och multi-axiella strukturer då de utsätts för små deformationer. Den teoretiska modelleringen resulterade i värden som beskriver styvheten hos de båda strukturerna vid deformationer på =0,01 i fyra riktningar. Kunskapen om lämpliga styvhetsegenskaper för kamouflagenät i kombination med resultatet från den teoretiska modelleringen lade en grund för att dra slutsatser om ifall multi-axiella strukturer, som är lika lätta som motsvarande bi-axiella strukturer vilka idag används i kamouflagenät, är lämpliga för att användas i kamouflagenät. Resultaten från modelleringen visar att de multi-axiella strukturerna i nästan samtliga fall har lägre elasticitetsmodul än deras motsvarande bi-axiella strukturer, detta innebär att det inte krävs lika stor kraft för att deformera de multi-axiella strukturerna. Modelleringen visar även att de båda strukturerna besitter olika egenskaper i olika riktningar, där de multi-axiella strukturerna beter sig likadant i alla fyra riktningar, till skillnad från de bi-axiella strukturerna som inte gör det. Enligt resultatet beror styvheten för de båda strukturerna på ett antal olika faktorer; trådtäthet, garnnummer och effektiv bredd, vilka appliceras som variabler i den teoretiska modelleringen. Modelleringen resulterade alltså därmed både till en förståelse för vilka faktorer som bidrar till skillnader i styvheten, och hur styvheten förhåller sig hos de båda strukturerna i olika riktningar. Studien visar att det i praktiken finns goda möjligheter för tillverkning av kamouflagenät i multi-axial varptrikå och att de multi-axiella strukturerna både kan göra kamouflagenäten mindre styva och bidra till isotropiska egenskaper. / Camouflage net is an essential device in the arms industry, where it is utilized to camouflage and hide objects from being visually detected. The camouflage net is designed to imitate the surrounding environment or terrain in which it is being applied. Traditionally, camouflage systems are manufactured using a knitting technique called bi-axial warp knitting with two systems of inlay yarns in 0° and 90° angles relative to the fabrics warp direction. To enhance the current product and produce light camouflage net with suitable strength properties, the multi-axial warp knitting technique with four systems of inlay yarns at 0°, 90° and ±45° angles is investigated. By utilizing semi-structured interviews with experts in the area of bi- and multi-axial warp knitting, can information and facts about multi-axial be collected and be used as a basis for concluding whether multi-axial is a suitable technique for the existing product. A theoretical modeling is then performed to examine, predict and compare the behaviors and properties of the bi- and multi-axial structures. The semi-structured interviews resulted in a comprehensive and informative collection of data about multi-axial technique. It also gathered information about the suitability and application of the technique to camouflage nets, as well as information regarding the machine’s limitations and thread orientation. The theoretical modeling involves the application of known mathematical and physical concepts, thus providing a foundation for understanding the mechanical behavior of bi- and multi-axial structures under small deformations. The theoretical modeling resulted in values that describe the stiffness of both structures at deformations of =0,01 in four directions. The knowledge of appropriate stiffness properties for camouflage nets, combined with the results from the theoretical modeling, laid the groundwork for drawing conclusions about the suitability of using multi-axial structures, which are as lightweight as the corresponding bi-axial structures currently used in camouflage nets. The modeling results show that the multi-axial structures generally have a lower initial modulus than their corresponding bi-axial structures, indicating that less force is required to deform the multi-axial structures. The modeling also reveals that the two structures exhibit different properties in different directions, with the multi-axial structures behaving similarly in all four directions, unlike the bi-axial structures. According to the results, the stiffness of both structures depends on several factors: thread density, yarn count, and effective width, which are applied as variables in the theoretical modeling. Thus, the modeling provides an understanding of the factors contributing to differences in stiffness and how the stiffness varies between the two structures in different directions. The study demonstrates that there are promising opportunities for manufacturing camouflage nets using multi-axial warp knit fabric in practice, and that the multi-axial structures can both reduce the stiffness of camouflage nets and contribute to isotropic properties.

Infolge des Herstellungsprozesses textiler Bewehrungen ergeben sich unterschiedliche Materialeigenschaften in den beiden Hauptrichtungen (Schuss und Kette). Diese Unterschiede entstehen durch verschiedene Einflussfaktoren, z. B. aus dem Verbundverhalten oder der Querschnittsform der Rovings. Um das Tragverhalten des anisotropen Verbundwerkstoffes Textilbeton experimentell untersuchen zu können, müssen mögliche Einflüsse aus dem Versuchsaubau möglichst gering gehalten werden, bzw. – falls unvermeidbar – in ihrer Wirkung qualitativ und quantitativ bestimmt und bei der Auswertung der Versuchsergebnisse berücksichtigt werden. Auf der Grundlage der durchgeführten umfangreichen experimentellen Untersuchungen wird eine qualitative Bewertung des Versuchsstandes sowie der verwendeten berührungslosen Messtechnik, der Nahbereichsphotogrammetrie, vorgenommen.

Carbon-fibre reinforced polymer (CFRP) laminates are widely used in various engineering applications, such as in race cars and aircrafts, because they are light, stiff and strong. They commonly contain stress raisers in the form of holes and notches (for mechanical joining methods, routing of pipes and cables etc.) and are also often subjected to complex combined multi-axial stress conditions during service. Yet their notched multi-axial fracture behaviour remains largely unexplored. This is the main contribution of the thesis. First, a novel loading fixture for applying a wide range of in-plane loading modes is developed based on the popular Arcan’s method. Termed the ‘modified Arcan rig’, it utilises friction gripping to transfer loads into tabbed specimens. This loading fixture is used to test centre-notched multi-directional CFRP laminates under different combinations of tension and shear stresses. Together with penetrant-enhanced X-ray CT and laminate de-ply, the fracture behaviour of quasi-isotropic CFRP specimens is investigated for the following loading modes: pure tension, pure compression, in-plane shear, and combined tension and shear. Two notch geometries (sharp notch and circular hole) are investigated to allow for an assessment of the role of stress concentration upon strength and damage development to be performed. Three distinct fracture modes are observed in a tensile/compressive-shear stress space (termed Mechanism A, Mechanism B and Mechanism C). It is observed that quasi-isotropic specimens with a central sharp notch are consistently stronger than equivalent specimens with a central circular hole (for all stress states investigated). An underlying micromechanical explanation concerning the effects of damage upon strength is proposed. Second, a finite element (FE) model is developed using the commercial FE program, Abaqus FEA to simulate the observed progressive damage and failure in the quasi-isotropic specimens. The FE model employs independent material property data as inputs. Overall, good correlation between the simulations and the experiments is obtained, validating the FE strategy. The capabilities of the model are extended to predict the notched fracture behaviour of the specimens under combined compression and shear loading, for which experimental work has not been done by the author, but for which literature data exists. Finally, the effect of laminate lay-up upon the notched multi-axial fracture behaviour of the CFRP specimens is explored by considering a 0° ply-dominated lay-up, a ±45° ply-dominated lay-up and a cross-ply lay-up, alongside the quasi-isotropic lay-up. Experiments reveal that all lay-ups exhibit Mechanisms A, B and C. However, the extent of damage in each Mechanism as well as the regime in which each Mechanism operates in (in the failure envelopes) strongly depend on the lay-up of the specimen. As expected, the tensile strengths and compressive strengths increase with the proportion of 0° plies. Surprisingly, the shear strengths do not scale with the proportion of ±45° plies; the specimen geometry and material orthotropy are attributed as reasons for this. In contrast to the case of the quasi-isotropic lay-up, the extent of subcritical damage induced by the circular hole is not always lower than that induced by the sharp notch for the other lay-ups. The difference in the extent of damage between both notch geometries is reflected in the notched strengths of the lay-up in question. These experimental observations are adequately predicted by the FE strategy, which further validates it as a reliable predictive tool for composite fracture.