To prevent the renewed rupture of ligaments and tendons prior to the completed healing process, which frequently occurs in treated ruptured tendons, a temporary support structure is envisaged. The limitations of current grafts have motivated the investigation of tissue-engineered ligament replacements based on the braiding technology. This technology offers a wide range of flexibility and adjustable geometrical and structural parameters. The presented work demonstrates the possible range for tailoring the mechanical properties of polyester braids and a variation of the braiding process parameters. A finite element simulation model of the braiding process was developed, which allows the optimization of production parameters without the performance of further experimental trials. In a second modelling and simulation step, mechanical properties of the braided structures were virtually determined and compared with actual tests. The digital element approach was used for the yarns in the numerical model. The results show very good agreement for the process model in terms of braiding angles and good agreement for the structural model in terms of force-strain behaviour. With a few adaptions, the models can, thus, be applied to actual ligament replacements made of resorbable polymers.

Cette thèse vise à étudier le comportement mécanique de l’acier de cuve 16MND5 (ou A508cl3 pour la norme anglaise) à l’échelle de la microstructure en croisant des approches expérimentale et numérique. Plusieurs contributions au développement de l’essai de traction in-situ à l’intérieur de MEB ont été apportées. En premier, les biais de mesure de différentes modalités (BSE, EBSD et SE) d’acquisition d’images sous MEB ont été caractérisés et corrigés. Les images MEB de différentes modalités ont été corrélées de façon précise afin de décrire la topographie de l’éprouvette. Les images d’orientation cristallographique (EBSD) ont été corrélées afin de révéler la rotation cristalline et les champs de déplacement de surface au long de la traction. La déformation élastique de l’éprouvette a été mesurée par corrélation intégrée des images de diffraction électronique à haute-résolution. Les microstructures fines de l’éprouvette à trois dimensions après déformation ont été mesurées par FIB-EBSD. L’essai a également été simulé par calcul de plasticité cristalline sur un maillage 3D, basé sur les microstructures mesurées dans la configuration déformée. Un algorithme a été proposé pour estimer la configuration initiale de l’éprouvette et identifier les paramètres de loi de plasticité en procédant par itérations. Un cas test synthétique 2D a été employé pour valider la faisabilité de l’algorithme. Deux lois de plasticité cristalline ont été testées sur le maillage 3D: dynamique des dislocations des cristaux cubiques centrés, et une version modifiée de la loi Méric-Cailletaud. Pour cette dernière loi, deux jeux de paramètres ont été identifiés pour les ferrites et bainites par recalage des éléments finis. / The PhD project is devoted to the study of the mechanical response of the reactor pressure vessel steel A508cl3 (or 16MND5 in French nomenclature) at the microscopic scale by experimental analyses and numerical simulations. Different aspects of in-situ tests inside an SEM chamber have been considered. First, the characterization and corrections of bias and uncertainties of different SEM imaging modalities (SE, BSE, and EBSD) have been performed. Precise registrations of SEM images in different modalities have been developed in order to give a comprehensive description of the sample surface topographies. Crystallographic orientation maps (from EBSD analyses) are registered to measure the crystal rotation and displacement fields along the tensile test. The elastic deformations of the surface are assessed by integrated correlation of high-resolution electron diffraction images. The 3D microstructure of the analyzed sample is revealed a posteriori by combining FIB milling andEBSD images.The experimental test is also simulated by crystal plasticity calculations on a 3D mesh created according to the 3D microstructure observed in the deformed configuration. An algorithm has been proposed to estimate its initial configuration and to identify the plastic parameters iteratively. A synthetic 2D model has been used to prove its feasibility. Two crystal plasticity laws have been validated on the 3D mesh, namely dislocation dynamics for body-centered cubic crystals and a modified version of Méric-Cailletaud model. In thepresent work finite element model updating was used to provide two sets of parameters (for ferrite and bainite) for the latter law.

No description available.

A comprehensive background is herein presented for lumbar skin strain and its effect on skin adhered wearable (SAW) products. A background of the development of computational models of the interaction of skin and novel SAWs being researched is also presented. These include products involving the use of high deflection strain gauges to measure skin strain during functional movements (FMs) as a method to address the complicated phenotyping of the etiological causes of low back pain (LBP). The background concludes with the mathematical calculation of the principal skin strain magnitudes and orientations using retroreflective marker coordinate data in a motion capture lab setting and the potential role of principal skin strain on the post-operative management of wounds to accelerate healing and minimize infection and scarring. The mechanics response of lumbar skin among 30 participants was measured during various FMs, for which high strain movements (Flexion, Flexion right/left, Sit To Stand) exhibited principal strain magnitudes repeatedly above 50% while others (Rotation right/left, Lateral Bending right/left, Extension, and Extension right/left) exhibited magnitudes repeatedly below 50%. Principal strain orientation was presented in easily visualizable mappings that demonstrated minimal variability both within and between participants for a given FM. Principal strain rates were measured, ranging between 25% and 151% per second among movements. The mechanics response of lumbar skin was again measured for a single participant, albeit this time between bare skin and skin with a SAW; which in this example was kinesiology tape with a high deflection nanocomposite strain gauge. Results indicated very significant skin restriction during Flexion, for which a macroscopic skin strain of 65% was reduced to 22% because of the KT tape and additionally down to 13% because of the addition of the sensor (on top of the KT tape). A FEM was created based off this scenario, for which it was shown that the mechanical properties of skin in vitro are insufficient in representing the mechanical response of skin due to its stiffness. This was hypothesized to be due to the increased hydration (lower stiffness) of in vivo skin, for which high deformation stiffness in the literature is not available. The thesis is concluded with future research directions that would benefit the design of SAWs where high deformation is considered. Future research directions are also discussed regarding post-operative wound healing and the potential role of repeated skin strains, such as concerning scarring and infection.

Every year, 250,000 people worldwide suffer a spinal cord injury (SCI) that leaves them with chronic paraplegia - permanent loss of ability to move their legs. SCI interrupts axons passing along the spinal cord, thereby isolating motor neurons from brain inputs. To date, there are no effective treatments that can reconnect these interrupted axons. In a recent breakthrough, .NeuroRestore developed the STIMO neuroprosthesis that can restore walking after paralyzing SCI using Epidural Electrical Stimulation (EES) of the lumbar spinal cord. Yet, the calibration of EES requires highly trained personnel and a vast amount of time, and the mechanism by which EES restores movement is not fully understood. In this master thesis, we propose to address this issue using modeling combined with Artificial Neural Networks (ANNs). To do so, we introduce the CyberSpine model to predict EES-induced motor response. The implementation of the model relies on the construction of a multipolar basis of solution of the Poisson equation which is then coupled to an ANN trained against actual data of an implanted STIMO user. Furthermore, we show that our CyberSpine model is particularly well adapted to extract biologically relevant information regarding the efficient connectivity of the patient’s spine. Finally, a user-friendly interactive visualization software is built. / Varje år drabbas 250 000 människor i hela världen av en ryggmärgsskada som ger dem kronisk paraplegi - permanent förlust av förmågan att röra benen. Vid en ryggmärgsskada bryts axonerna som passerar längs ryggmärgen, vilket isolerar de motoriska neuronpoolerna från hjärnans ingångar. Hittills finns det inga effektiva behandlingar som kan återansluta dessa avbrutna axoner. NeuroRestore utvecklade nyligen neuroprotesen STIMO som kan återställa gångförmågan efter förlamande ryggmärgsskada med hjälp av epidural elektrisk stimulering (EES) av ländryggmärgen. Kalibreringen av EES-stimuleringar kräver dock högutbildad personal och mycket tid, och den mekanism genom vilken EES återställer rörelse är inte helt klarlagd. I denna masteruppsats föreslår vi att vi tar itu med denna fråga med hjälp av modellering i kombination med artificiell intelligens. För att göra detta introducerar vi CyberSpine-modellen, en modell som kan förutsäga EES-inducerad motorisk respons. Implementeringen av modellen bygger på konstruktionen av en multipolär bas för lösning av Poisson-ekvationen som sedan kopplas till ett artificiellt neuralt nätverk som tränas mot faktiska data från en implanterad STIMO-deltagare. Dessutom visar vi att vår CyberSpine-modell är särskilt väl anpassad för att extrahera biologiskt relevant information om den effektiva anslutningen av patientens ryggrad. Slutligen bygger vi en användarvänlig interaktiv visualiseringsprogramvara.

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No description available.

<p>  </p> <p>Architectured materials offer engineers more options for choosing materials with their desired properties. Segmenting materials to create topological interlocking materials (TIMs) creates materials, which can deform in greater amounts without failure and absorb more strain energy. Previous research on TIMs has shown that the stiffness and reaction force of these materials can be directly controlled by controlling the boundary forces offered by the frame which constrains these materials.</p> <p>The research presented in this paper investigated a TIM made into a 1-Dimension beam like structure called a lintel. This research investigated not only the mechanics of this structure, but also developed a method of directly controlling the reaction force at a given displacement using shape memory alloy (SMA) wires. These wires would actuate the boundary pieces used to constrain the system. These actuation wires coupled with force sensors imbedded into the lintel allowed a feedback control loop to be established, which would control the reaction force. The reaction force was then controlled to create a smart structure which could optimize the strain energy absorption under the constraint of a maximum allowable load, similar to cellular solids used in packaging and padding materials.</p> <p>To develop this smart structure, four separate investigations occurred. The first was finite element analysis (FEA) performed to model the loading response of the lintel. This experiment demonstrated that the Mises Truss Model was effective at modelling the lintel. The second was an experimental validation of the FEA model performed in the first investigation. This experiment validated the Mises Truss Model for the lintel. The third investigation simulated the active lintel using computational software and the model of the lintel established in the first two investigations. This experiment demonstrated computationally the ability of SMA wires to control the reaction force as desired in an idealized case. The fourth and final investigation experimentally validated the ability to create and active lintel and created a functioning prototype. This demonstrated experimentally the ability of the active lintel to control reaction force as desired.</p> <p>This project has demonstrated the viability to create smart structures using segmented materials, which in the future may be used in a variety of applications including robotics and adaptive structures in harsh environments. </p>

This research aims to investigate the behaviour of glass fibre reinforced polymer bars (GFRP) reinforced continuous concrete deep beams. For this purpose, experimental, analytical and numerical studies were conducted. Nine continuous concrete deep beams reinforced with GFRP bars and one specimen reinforced with steel bars were experimentally tested to failure. The investigated parameters included shear span-to-overall depth ratio (𝑎/ℎ), size effect and web reinforcement ratio. Two 𝑎/ℎ ratios of 1.0 and 1.7 and three section heights of 300 mm, 600 mm and 800 mm as well as two web reinforcement ratios of 0% and 0.4% were used. The longitudinal reinforcement, compressive strength and beam width were kept constant at 1.2%, ≈55 MPa and 175 mm, respectively. The web reinforcement ratio achieved the minimum requirements of the CSA S806-12. The experimental results highlighted that the web reinforcement ratio improved the load capacities by about 10% and 18% for specimens having 𝑎/ℎ ratios of 1.0 and 1.7, respectively. For specimens with web reinforcement, the increase of 𝑎/ℎ ratio from 1.0 to 1.7 led to reductions in the load carrying capacity by about 33% and 29% for beams with overall depths of 300 mm and 600 mm, respectively. Additionally, a considerable reduction occurred in the shear strength due to the increase of the section depth from 300 mm to 600 mm. The experimental results confirmed the impacts of web reinforcement and size effect that were not considered by the strut-and-tie method (STM) of the only code provision, the Canadian S806-12, that addressed such elements. In this study, the STM was illustrated and simplified to be adopted for GFRP RC continuous deep beams, and then, the experimental results obtained from this study were employed to assess the performance of the effectiveness factors suggested by the STMs of the American (ACI 318-2014), European (EC2-04) and Canadian (S806-12) codes as well as those factors recommended by the previous studies to predict the load capacities. It was found that these methods were unable to reflect the influences of member size and/or web reinforcement reasonably, the impact of which has been confirmed by the current experimental investigation. Therefore, a new effectiveness factor was recommended to be used with the STM. Additionally, an upper bound analysis was developed to predict the load capacities of the tested specimens considering a reduced bond strength of GFRP bars after assessing the old version recommended for steel RC continuous deep beams. A good agreement between the predicted results and the measured ones was obtained with the mean and coefficient of variation values for experimental/calculated results of 1.02 and 5.9%, respectively, for the STM and 1.03 and 8.6%, respectively, for the upper-bound analysis. A 2D finite element analysis using ABAQUS/Explicit approach was carried out to introduce a model able to estimate the response of GFRP RC continuous deep beams. Based on the experimental results extracted from the pullout tests, the interface between the longitudinal reinforcement and concrete surface was modelled using a cohesive element (COH2D4) tool available in ABAQUS. Furthermore, a perfect bond between the longitudinal reinforcement and surrounding concrete was also modelled to evaluate the validity of this assumption introduced by many previous FE studies. To achieve a reasonable agreement with the test results, a sensitivity analysis was implemented to select the proper mesh size and concrete model variables. The suitability and capability of the developed FE model were demonstrated by comparing its predictions with the test results of beams tested experimentally. Model validation showed a reasonable agreement with the experiments in terms of the failure mode, total failure load and the load-deflection responses. The perfect bond model has overestimated the predicted results in terms of stiffness behaviour and failure load, while the cohesive element model was more suitable to reflect the behaviour of those specimens. The validated FE model was then employed to implement a parametric study for the key parameters that govern the behaviour of beams tested and to achieve an in depth understanding of such elements. The parametric study showed that the higher the 𝑎/ℎ ratio the more pronounced the effect of web and the longitudinal reinforcements and the lower the effect of concrete compressive strength; and vice versa when 𝑎/ℎ ratio reduces.

Today, there is a significant demand for electricity, a demand expected to increase in the coming years. To meet market needs, the number of offshore wind turbines is increasing, along with their dimensions to generate a greater amount of electricity. This leads to anecessity for a new generation of freight ships with bigger dimensions and capacity for transportation and installation of wind turbine components. Finite Element models enable comprehensive analyses of the hull beams' components, bulkheads, and supports, providing relevant information about the hull's stress impact for different load combinations. The advantage of creating a model is to provide a clear overview while allowing the product to be simulated before production, facilitating a better understanding of the product's future function and appearance. A Finite Element model's analysis results largely reflect reality and thus constitute a valuable tool for ship production. In SAP2000, a shell model was created over a pontoon with interconnected beam and shell elements. The model was simulated with loads from self-weight combined with hydrostatic pressure in combination with various sets of hull components. Four simulations were performed with analyses of shell and frame stresses, showing that a stronger construction results in less stress variation in the pontoon's constituent elements. The upper side of the pontoon did not meet the tolerance values of ±50 MPa for either frame or shell elements in the first analysis. When the frame dimensions were increased, the shell elements met the stress level criteria, but the frame elements still significantly exceeded the tolerance values. An increased plate thickness was not beneficial for the structure’s stress load as the self-weight increased without providing additional stiffness.