Aujourd'hui, les méthodes de corrélation d'images sont largement utilisées pour la caractérisation et le suivi temporel des essais mécaniques. Cependant dans le domaine de l'usinage, ces méthodes sont très peu employées pour l'étude en pointe d'outil de la coupe par manque d'accessibilité, de la faible taille de la zone observée et des fortes déformations dans la zone de coupe. Dans cette thèse, nous mettons en application la technique de corrélation d'images pour l'étude et la caractérisation des champs cinématiques induits dans la matière usinée, durant des essais de coupe conduits avec des conditions opératoires représentatives des opérations industrielles. Ces conditions nous ont permis de développer, en premier lieu, des outils expérimentaux et numériques. Puis, les performances du dispositif expérimental ainsi que les incertitudes de corrélation ont été quantifiées. Différentes stratégies d'exploitation des images ainsi que des outils numériques pour la mesure des caractéristiques de la coupe sont proposés. Ensuite, nous avons développé un outil de corrélation d'images intégrée pour la mesure des efforts dynamiques grâce à un modèle analytique. Pour valider l'ensemble des méthodes, des essais de rabotage, d'abord dans un alliage d'aluminium, puis dans un acier 100~CrMo~7 traité thermiquement, ont été conduits. Ils ont permis de quantifier les champs cinématiques ainsi que les caractéristiques de la coupe. Enfin ces outils ont été appliqués pour la prédiction de l'intégrité de surface engendrée par une géométrie 3D d'outil de coupe dans le matériau dur. / Nowadays, digital image correlation (DIC) methods are widely employed to the mechanical testing characterization and their temporal monitoring. However in the machining field, to study the cutting process at the tool edge, these methods are not commonly applied due to the poor accessibility, the size of the observed area and the large strain occurring herein. In this study, the kinematic fields induced in the material by the cutting process are characterized and analyzed at industrial cutting conditions. In order to take and treat the pictures of the cut, experimental and numerical techniques have been first established. Then, the experimental setup performances and the uncertainties of the DIC were quantified. Different images selection strategies for the DIC and numerical post-processing algorithm for measuring the characteristics of the cut were proposed. Furthermore, a DIC integrated approach based on an analytical model was developed to record dynamics cutting forces. Trials in orthogonal configuration were performed and analyzed to validate the developed procedures first in an aluminium alloy, then in a 100~CrMo~7 hardened steel. The kinematics fields and the macroscopic data of the cut were successfully measured thanks to these tools. Finally, they were used for the prediction of the surface integrity induced by a 3D cutting edge in the hard material.

This thesis is about fundamental interaction mechanisms of laser remote fusion cutting, RFC, which is based on the formation of a quasi-stationary laser-induced boiling front that causes drop ejection, preferably downwards. Laser cutting of metals, invented in 1967, has developed from a niche to a well established high quality cutting technique in the manufacturing industry. Usually a gas jet is employed concentric to the laser beam, to eject the molten metal. One technique option, interesting though hardly applied yet because of usually low quality and speed, is remote laser cutting. Two techniques are distinguished, remote ablation cutting, grooving down through a sheet, layer-by-layer, and the here addressed remote fusion cutting, by a single pass through the sheet. For the latter, the ablation pressure from laser-induced boiling at the cutting front continuously accelerates and ejects the melt downwards. Advantages of remote laser cutting, facilitated by high brilliance lasers during the last decade, are the possibility of a larger working distance along with the avoidance of cutting gas and of a gas jet nozzle.   The review paper of the thesis surveys different laser remote cutting techniques, including their modelling, as well as the transition to keyhole welding, owing to similarities particularly from the boiling front and from root spatter ejection. The six Papers I-VI that compose the thesis address fundamental mechanisms of laser remote fusion cutting, theoretically and experimentally. In Paper I a simplified mathematical model of the RFC cutting front enables to estimate the geometrical and energetic conditions of the process. By evidence and post-modelling from high speed imaging, HSI, the simplified smooth cutting front model is developed further to a wavy topology in Paper III, for more sophisticated absorption analysis. As a systematic support, Paper II categorizes and analyses for the first time the different wavy topologies observed at the front, from HSI. The melt dynamics induced by a pulsed laser beam was studied in Paper IV, again from HSI. Apart from other interesting transient melt phenomena it was demonstrated that the ablation pressure can push the melt to a certain pending position during the laser pulse while the melt retreats by surface tension during the pulse break. To engage remote fusion cutting with additive manufacturing, Paper V introduces a novel technique where the drops ejected from RFC are transferred to a substrate, about a centimetre underneath, on which a continuous track forms. This technique can even be applied as an efficient recycling approach. In Paper VI a variant of the technique is presented, to develop a boiling front along the edge of a metal sheet from which the drop transfer takes place, in a different manner. This enables to systematically machine-off the entire sheet, which can be converted to a new shape and product.   Summarizing, the thesis provides a variety of analysis of fundamental mechanisms of a laser-induced boiling front that bear a certain simplicity and in turn controllability, of interest for established as well as for new applications, in manufacturing and in other sectors, including remote fusion cutting.

L’objectif de cette thèse de doctorat était de concevoir et développer un système permettant de caractériser les épandeurs et de prédire la répartition d’engrais au sol. Nous avons proposé deux approches basées respectivement sur l’imagerie 2D et 3D.Le système 2D a permis de déterminer les déplacements dans les images avec une très haute précision où 90% des estimations ont uniquement moins de 0,2 pixels d’erreur. Cependant cette précision n’était applicable que dans le cas d’un épandeur équipé de disques plats pour lequel la plupart des engrais est éjectée dans le plan horizontal parallèle au plan d’image de la camera. Par conséquent nous avons proposé un système d’imagerie 3D qui a permis de déterminer le mouvement 3D des engrais. Ainsi il peut être appliqué sur des épandeurs équipés de disque concave.Ce nouveau système peut : Caractériser les épandeurs dans un hall avec des conditions contrôlées ;Evaluer les effets de différents réglages des épandeurs ;Etudier le comportement des granulés et améliorer le modèle de vol balistique.Un tel système, moyennant quelques modifications, est envisagé à long terme sur un épandeur, permettant une gestion en temps réel de l’épandage et une rétroaction potentielle sur le fonctionnement de l’épandeur. [extrait du résumé] / The characterization of the fertilizer centrifugal spreading has become an important agriculture scientific issue in order to help farmers having a higher fertilization precision hence higher production efficiency. The ejected fertilizer grains are comparable to projectiles; hence, by using a ballistic flight model, predicting the spread pattern on the ground relies on an estimation of the trajectories and velocities of ejected grains. To estimate those parameters two approaches were proposed. First a two-steps zero mean normalized cross-correlation based algorithm for motion estimation was used to determine the displacement of the grains in the 2D images. The efficiency of this algorithm was evaluated by the mean of a grain images’ simulator. The results showed a high accuracy with an error of less than 0.2 pixels for 90% of the estimated velocities. However, the vertical ejection angle cannot be determined. This limits the use of the technique to spreaders equipped with flat disks where the trajectories of the grains will mostly be in a horizontal plane. This restriction was handled by the second approach. It is based on a 3D stereovision imaging system. A region based stereo matching algorithm with uniqueness and ordering constraints was introduced. It was validated using a grains’ stereo images simulator. 90% of the disparities were estimated with errors less than 2 pixels (around 1%). Moreover a 3D motion estimation algorithm was developed. It is based on an improvement of the previous 2D motion estimation algorithm combined with the estimated 3D coordinates. The efficiency of the whole system was approved via a comparison of its results and a real distribution obtained from a developed cylindrical collector.

<div>There is an increasing need to accurately image objects at a high temporal resolution for different applications in order to analyze the underlying physical, chemical, or biological processes. In this thesis, we use advanced models exploiting the image structure and the measurement process in order to achieve an improved temporal resolution. The thesis is divided into three chapters, each corresponding to a different imaging application.</div><div><br></div><div>In the first chapter, we propose a novel method to localize neurons in fluorescence microscopy images. Accurate localization of neurons enables us to scan only the neuron locations instead of the full brain volume and thus improve the temporal resolution of neuron activity monitoring. We formulate the neuron localization problem as an inverse problem where we reconstruct an image that encodes the location of the neuron centers. The sparsity of the neuron centers serves as a prior model, while the forward model comprises of shape models estimated from training data.</div><div><br></div><div>In the second chapter, we introduce multi-slice fusion, a novel framework to incorporate advanced prior models for inverse problems spanning many dimensions such as 4D computed tomography (CT) reconstruction. State of the art 4D reconstruction methods use model based iterative reconstruction (MBIR), but it depends critically on the quality of the prior modeling. Incorporating deep convolutional neural networks (CNNs) in the 4D reconstruction problem is difficult due to computational difficulties and lack of high-dimensional training data. Multi-Slice Fusion integrates the tomographic forward model with multiple low dimensional CNN denoisers along different planes to produce a 4D regularized reconstruction. The improved regularization in multi-slice fusion allows each time-frame to be reconstructed from fewer measurements, resulting in an improved temporal resolution in the reconstruction. Experimental results on sparse-view and limited-angle CT data demonstrate that Multi-Slice Fusion can substantially improve the quality of reconstructions relative to traditional methods, while also being practical to implement and train.</div><div><br></div><div>In the final chapter, we introduce CodEx, a synergistic combination of coded acquisition and a non-convex Bayesian reconstruction for improving acquisition speed in computed tomography (CT). In an ideal ``step-and-shoot'' tomographic acquisition, the object is rotated to each desired angle, and the view is taken. However, step-and-shoot acquisition is slow and can waste photons, so in practice the object typically rotates continuously in time, leading to views that are blurry. This blur can then result in reconstructions with severe motion artifacts. CodEx works by encoding the acquisition with a known binary code that the reconstruction algorithm then inverts. The CodEx reconstruction method uses the alternating direction method of multipliers (ADMM) to split the inverse problem into iterative deblurring and reconstruction sub-problems, making reconstruction practical. CodEx allows for a fast data acquisition leading to a good temporal resolution in the reconstruction.</div>

As an intrinsic requirement for digital image correlation (DIC)to be applicable, the images must exhibit a speckle pattern of sufficient unique features. Researchers have incorporated X-ray phase contrast imaging (PCI) and DIC (XDIC) and conducted studies on materials with natural internal features as speckles. This study is the first attempt to explore the applicability and standards of XDIC to be applied on materials that are transparent under X-ray PCI, mainly polymers, by deliberately embedding particles into the sample. The goal is to generate a high-quality speckle while maintaining the least influence on the material’s properties. Iron oxide (FeO), tungsten carbide (WC), and platinum (Pt) are embedded into Sylgard® epoxy at various weight ratios, and the Sylgard® samples are loaded with a Kolsky compression bar paired with high-speed X-ray PCI. The speckle quality of the PCI images is assessed using a mean intensity gradient based approach, as well as intensity distribution analysis. DIC is applied to the images to measure the displacement field in the loading direction, and the results are analyzed. The engineering stress-strain relationship is generated from the Kolsky bar apparatus, and the results are compared to find the influence of the added particles.<div><br></div><div>The results indicate thatthe addition of particles does not significantly alter the base polymer’s properties, and the theoretical deviation error can be as low as less than 0.01 pixels. Disregarding the limited applicability to embed into polymer samples, platinum produces the best speckle. WC particle is the superior choice of material to embed for its good speckle quality, ease of embedding, and good availability. Lower weight ratios are shown to be preferential. This study also emphasizes the importance of sample design when applying XDIC to materials with embedded particles. It is preferential for best accuracy to design the region of interest to be away from the surfaces of the samples and be located near the back of the sample with respect to the impact surface.<br></div>

The vocal folds are an essential component of human speech production and communication. Advancements in voice research allow for improved voice disorder treatments. Since in vivo analysis of vocal fold function is limited, models have been developed to simulate vocal fold motion. In this research, synthetic and computational vocal fold models were used to investigate various aspects of vocal fold vibratory characteristics. A series of tests were performed to quantify the effect of varying material and geometric parameters on the models' flow-induced responses. First, the influence of asymmetric vocal fold stiffness on voice production was evaluated using life-sized, self-oscillating vocal fold models with idealized vocal fold geometry. Asymmetry significantly influenced glottal jet flow, glottal area, and vibration frequency. Second, flow-induced responses of simplified and MRI-based synthetic models were compared. The MRI-based models showed remarkable improvements, including less vertical motion, alternating convergent-divergent glottal profile patterns, and mucosal wave-like movement. Third, a simplified model was parametrically investigated via computational modeling techniques to determine which geometric features influenced model motion. This parametric study led to identification and ranking of key geometric parameters based on their effects on various measures of vocal fold motion (e.g., mucosal wavelike movement). Incorporation of the results of these studies into the definition of future models could lead to models with more life-like motion.

The voice is the primary mode of communication for humans. Because the voice is so important, voice disorders tend to severely diminish quality of life. A better understanding of the physics of voice production can help to improve treatment of voice disorders. For this thesis research a self-oscillating synthetic vocal fold model was developed, compared with previous synthetic vocal fold models, and used to explore the physical effects of augmentation injections on vibration dynamics. The research was conducted in two stages. First, four vocal fold models were evaluated by quantifying onset pressure, frequency, maximum glottal gap, flow rate, and medial surface motion. The newly developed model, differentiated from the other models by the inclusion of more layers, adjusted geometry, and an extremely soft superficial lamina propria layer, was included in this study. One of the models, created using MRI-derived geometry, had the most defined mucosal wave. The newly-developed model had the lowest onset pressure, flow rate, and smallest maximum glottal width, and the model motion compared very well with published excised human larynx data. Second, the new model was altered to simulate bowing by decreasing the volume of the body layer relative to that of a normal, unbowed model. Two models with varying degrees of bowing were created and tested while paired with normal models. Pre- and post-injection data (onset pressure, vibration frequency, glottal flow rate, open quotient, and high-speed image sequences) were recorded and compared. General pre- to post-injection trends included decreased onset pressure, glottal flow rate, and open quotient, and increased vibration frequency. Additionally, there was a decrease in mucosal wave velocity and an increase in phase angle. The thesis results are anticipated to aid in better understanding the physical effects of augmentation injections, with the ultimate goal of obtaining more consistent surgical outcomes, and also to contribute to the advancement of voice research through the development of the new synthetic model.

<p>  </p> <p>Acoustic streaming is a phenomenon which occurs when acoustic excitations interact with a fluid (stationary or non-stationary). Exploitation of this phenomenon has the potential to open doors to new methods of flow control through the enhancement or diminishment of the present flow instabilities. A particular use of acoustic streaming shown by previous numerical studies is the enhancement of heat transfer in violation of the Reynold’s Analogy within a small range of Mach numbers and frequencies of periodic excitation. The focus of this thesis is to experimentally assess the usage of a Rossiter cavity in generating periodic acoustic excitations and its effects on the shear stress and heat transfer. </p> <p>In the present research, two large models are tested using a blow-down facility. The models are made of aluminum and Teflon and were developed to ensure optical access for infrared thermography. The geometries are tested at Mach number ranging from 0.373 to 0. 866. The target Mach number-frequency pair where significant heat transfer enhancement is a free stream Mach number at the cavity, Mc, of 0.75 and the frequency, fc, of 7.5 kHz. The cavity is tuned using the Rossiter equation with Rossiter constants k = 0.66 and y = 0.25. The heat transfer and skin friction enhancement are measured immediately upstream and downstream of the cavity and compared to the previous numerical studies.</p> <p>When testing the Teflon model with an ambient back pressure and 11 lb/s mass flow, a frequency of 7.8 kHz was generated by the cavity. For the aluminum model tested at a high vacuum and 3 lb/s mass flow, frequencies near 7, 10, and 20 kHz were generated by the cavity with 10 and 20 kHz appearing most often. High speed schlieren imaging was used to confirm the flow structures being generated in the flow. There was good agreement with the Rossiter modes at lower Mach numbers and moderate agreement at transonic Mach numbers. A correlation is presented which defines a band of Mach number-Reynolds number pairs which present with a discontinuous frequency behavior during operation of the wind tunnel. Measurable effects on both skin friction and heat transfer between tests with comparable operating conditions to a reference were observed and are presented.</p>

Bei Einkopplung von Schall in ein Fluid können durch nichtlineare Effekte und Dämpfung Strömungen erzeugt werden. Diese Strömungen, die ihre Energie aus einem Impulsübertrag der Schallwelle auf die Flüssigkeit beziehen, werden akustische Strömungen genannt (engl.: acoustic streaming). Dieser Impulsübertrag hängt u.a von der Dämpfung der Schallwelle im Medium ab: bei stärkerer Dämpfung nimmt der Impulsübertrag zu und entsprechend die Geschwindigkeit der induzierten Strömung. Eine wichtige Rolle in der vorgelegten Arbeit spielt die Dämpfungserhöhung im Fall in der Flüssigkeit vorhandener Blasen. Dies ist insbesondere bei allen Prozessen von großer Bedeutung, in denen durch intensive (Ultra-)Schallfelder die Blasen in der Flüssigkeit selbst erzeugt werden (akustische Kavitation). Hier entstehen durch die mit den Blasen verbundene Dissipation sehr viel größere akustische Strömungsgeschwindigkeiten als im Fall ohne Kavitation. Zudem werden durch die Volumenoszillation und die Translation der Kavitationsblasen weitere Strömungen auf Skala der Blasengröße induziert. Mit einem in der Arbeit neu entwickelten Versuchsaufbau lassen sich Strömungen auf größeren und mittleren Skalen bis zu einzelnen Blasen in akustischen Kavitationsblasenfeldern abbilden und untersuchen. Durch die Farbtrennung eines speziellen Fluoreszenzmikroskopes ist es möglich, die Flüssigkeitsströmungen und die Kavitationsblasen simultan und getrennt aufzunehmen. Die Abhängigkeit der akustischen Strömungen von verschiedenen Einflussparametern wie Schallleistung, Temperatur und Gasgehalt der Flüssigkeit werden am Beispielfall einer bei 17 kHz betriebenen Ultraschall-Sonotrode (Schallhorn) in Wasser untersucht. Insbesondere der Übergang vom nicht kavitierenden zum kavitierenden Fall ist hier von Interesse, was durch die Möglichkeit eines statischen Überdrucks im Experiment gut beeinflusst werden kann. Es zeigt sich wie erwartet mit dem Einsetzen von Kavitation eine starke Zunahme der akustischen Strömungsgeschwindigkeiten, woraus auf den stark erhöhten Dämpfungskoeffizienten für Schallausbreitung geschlossen werden kann. Ebenfalls werden die sehr schnellen Mikroströmungen auf Blasenebene dokumentiert. Eine genauere Analyse ergibt auch das Auftreten von subharmonischem Verhalten bei Blasendynamik und Strömungsfeld. An speziellen Ultraschallwandlern werden zudem die rein akustischen Strömungen (ohne Auftreten von Kavitation) bei extremen, bisher für Dickenschwinger nicht erreichbaren Schallfrequenzen bis zu 2 GHz in Wasser experimentell untersucht. Hierzu wird ebenfalls der Fluoreszenz-Aufbau verwendet, Es zeigen sich relativ hohe Strömungsgeschwindigkeiten in Form eines vom Wandler weggerichteten Jets, der sich auch weit jenseits der Eindringtiefe des Schalls in die Flüssigkeit erstreckt. Dieses Verhalten wird ebenfalls numerisch mit einer Finite-Elemente-Methode modelliert. Hier wird neben ausführlichen, aber sehr zeitaufwändigen Rechnungen auch erfolgreich eine vereinfachte Simulation der akustischen Strömungen in dem betrachteten Fall sehr hoher Frequenz angewandt.

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