Pierre A. Humblet. / Caption title. / Supported by the Army Research Office. DAAL03-86-K-0171

The effect of microstructure on corrosion resistance and anodising behaviour of a 3rd generation lithium-containing aluminium alloy, AA 2099-T8, has been studied. Microstructural characterisation of the alloy has shown elongated grains with high angle grain boundaries and approximately equiaxed subgrains with low angle grain boundaries. Two types of constituent particles of high and reduced contents of copper were found, which are present individually or in the form of multiphase particles. The alloy also contains rod-like Al-Cu-Mn-Li and spherical (Al3Zr) dispersoids, and fine age hardening precipitates of T1 (Al2CuLi), (Al3Li) and (Al2Cu).Immersion testing in a chloride-containing solution revealed two types of localised corrosion sites: one was initiated from intermetallics and quickly became passivated; the other lasted for the course of testing, with extensive boundary attack. The latter has been correlated to grains and subgrains with relatively high stored energy.Alkaline etching removed intermetallics from alloy surface; generated a copper-enriched layer in the alloy matrix immediately beneath the residual alumina film; and gradually developed a surface nanotexture. The surface nanotexture has been correlated to the formation of copper-rich nanoparticles within the copper-enriched layer.Anodising the alloy in tartaric-sulphuric acid disclosed that copper in the alloy matrix could be occluded in the anodic film material as copper-rich nanoparticles or be oxidized and incorporated into the film material as copper ions, depending on the anodising voltage. In the latter case, the process was accompanied by oxygen gas generation within the film material, forming anodic films with lateral porosity. Intermetallics of different compositions behaved differently during anodising, leading to modification of the morphology and composition of anodic films. Concerning the effect of alkaline etching on anodising behaviour of the alloy, the removal of intermetallics increased anodising efficiency; the pre-developed copper-enriched layer advanced the establishment of the steady-state film/alloy interface. Variation of copper-enriched layer structure is revealed by the detection of copper-rich nanoparticles in the copper-enriched layer. The copper-rich nanoparticles have structures consistent with either θ", θ' or θ phases. Machining damage can be detected not only by chromic acid anodising (CAA) but also by tartaric-sulphuric acid anodising (TSAA). Neither CAA nor TSAA can be used for detecting shallow corrosion pits.

No description available.

This study of the graphic field in notes on space, undated (log 3) focuses on how the white emptiness of a page plays a structural role in the articulation of dissociated fragments of notes. According to the criteria of three theorists (Genette, Lapacherie, Baetens), the distinction between non-linear and tabular proves to be non-exclusive in this particular work. Ostensibly, this non-figurative writing instigates interactive contemplation and lends itself to multiple entries, like an object one contemplates from every possible visual perspective without ever constructing a representation or image. The poetic form that du Bouchet explores renders perceptible the latent materiality of all text.

In der Diagnostik und Reparatur von hyalinem Gelenkknorpel sind neue Methoden zur Quantifizierung von Struktur und mechanischer Belastbarkeit gefragt, um die Behandlung von Knorpelschäden an Millionen von Patienten weltweit zu verbessern. Mittels hochfrequentem, fokussierten Ultraschall werden Oberflächenparameter für Reflektivität und Rauheit an Gelenkknorpel bestimmt. Es wird gezeigt wie die Oberflächenneigung kontrolliert werden kann. Die Ergebnisse vermitteln ein besseres Verständnis über die Zusammensetzung der Ultraschallsignale aus reflektierten und gestreuten Komponenten. 3D Ultraschallscans von Knorpelregeneraten erlauben die Defektstellen volumetrisch zu Quantifizieren. Die Proben wurden zusätzlich nach etablierten Bewertungssystemen benotet, welche auf makroskopischer Beurteilungen, MRT-Scans und Histologie basieren. Die ultraschallbasierten Volumendaten zeigten dabei gute Korrelationen mit den Punktwertungen. Die im Labor verwendeten Messaufbauten zur biomechanischen Charakterisierung von Gelenkknorpel können am Patienten nicht angewandt werden. Daher können Ärzte die Festigkeit von Knorpel bisher nur mittels manueller Palpation abschätzen. Diese Arbeit entwickelt eine Methode der Ultraschall-Palpation (USP), die es erlaubt, die während der manuellen Palpation erzeugte Kraft und Deformation, basierend auf Ultraschallechos, aufzunehmen. Es wurde einen Prototyp entwickelt womit gezeigt werden konnte, dass USP eine ausreichende Genauigkeit und Reproduzierbarkeit aufweist. Wiederholte Messungen können zusätzlich zeitabhängige biomechanische Parameter von Knorpel ableiten. Zusammenfassend zeigt diese Arbeit verbesserte und neue Möglichkeiten zur strukturellen und biomechanischen Charakterisierung von hyalinem Gelenkknorpel bzw. den Ergebnissen von Knorpelreparatur basierend auf Ultraschalldaten. Diese Methoden haben das Potenzial die Diagnostik von Gelenkknorpel und die Quantifizierung von Knorpelreparatur zu verbessern. / In the diagnostics and repair of hyaline articular cartilage, new methods to quantify structure and mechanical capacity are required to improve the treatment of cartilage defects for millions of patients worldwide. This thesis uses high frequency focused ultrasound to derive surface parameters for reflectivity and roughness from articular cartilage. It is shown how to control the inclination dependency to gain more reliable results. Furthermore, the results provided a better understanding of the composition of ultrasonic signals from reflected and scattered components. 3D ultrasound scans of cartilage repair tissue were performed to quantify defect sites after cartilage repair volumetrically. The samples were also graded according to established scoring systems based on macroscopic evaluation, MRI scans and histology. The ultrasound-based volumetric parameters showed good correlation with these scores. Complex biomechanical measurement setups used in laboratories cannot be applied to the patient. Therefore, currently physicians have to estimate the stiffness of cartilage by means of manual palpation. In the last part of this thesis, a method denoted as ultrasound palpation is developed, which allows for measuring the applied force and strain during manual palpation in real time, solely based on the evaluation of the time of flight of ultrasound pulses. A prototype was developed and its measurement accuracy and reproducibility were characterized. It could be shown that ultrasound palpation has sufficient accuracy and reproducibility. Additionally, by repeated measurements it was possible to derive time-dependent biomechanical parameters of cartilage. In summary, this work shows improved and new possibilities for structural and biomechanical characterization of hyaline articular cartilage and the outcomes of cartilage repair based on ultrasound data. The methods have the potential to improve the diagnostics of articular cartilage and quantification of its repair.