Efeito da estampagem incremental de ponto simples na microestrutura e propriedades mecânicas do alumínio e do aço

Mestrado em Ciência e Engenharia de MateriaisNeste trabalho foi investigado o efeito da deformação plástica por estampagem incremental de ponto simples (SPIF) na textura cristalográfica, estrutura de deslocações e propriedades mecânicas de chapas de alumínio, aço com baixo teor em carbono e aço de fase dupla. Foram realizados ensaios de tração nos materiais iniciais para caracterizar as suas propriedades mecânicas. Além disso, foram realizadas análises por difração de eletrões retrodispersados (EBSD), observações por microscopia eletrónica de transmissão (TEM) e cálculos utilizando o modelo viscoplástico autoconsistente para caracterizar a influência da textura cristalográfica e da microestrutura no comportamento mecânico dos materiais. Foram também realizadas medidas de deformação e de espessura, bem como ensaios de microdureza nos materiais deformados por SPIF. Em todos os materiais, a textura cristalográfica inicial revelou-se muito estável durante o processo de SPIF e foi observado um acentuado aumento da densidade de deslocações bem como o desenvolvimento de células equiaxiais de deslocações durante a deformação de ambos os aços. No entanto, na chapa de alumínio, não foram observadas alterações significativas da microestrutura inicial de laminagem. Em todos os materiais foi observado um bom acordo entre a espessura das peças obtidas por SPIF e o valor previsto pela lei do seno.In this work, was investigated the effect of the plastic deformation by single point incremental forming (SPIF) on the crystallographic texture, dislocation structure and mechanical properties of aluminum, low carbon steel and dual phase steel sheets. Tensile tests were conducted on the initial materials to characterize their mechanical behavior. Furthermore, electron backscattering diffraction (EBSD), transmission electron microscopy (TEM) observations and calculations using a polycrystalline viscoplastic self-consistent (VPSC) model were carried to characterize the influence of the crystallographic texture and microstructure on the mechanical behavior of the materials. Strain and thickness measurements and microhardness tests were also conducted on the SPIF deformed materials. The initial crystallographic texture was very stable during the SPIF of all materials and a strong increase of dislocation density and the development of equiaxed dislocation cell structure was observed during the deformation of both steels. However, for the aluminum sheet, no major change was observed on the initial rolling microstructure. For all materials, it was observed a good agreement between the thickness of the SPIF pieces and the value predicted by the sin law

Pom1 gradient buffering through intermolecular auto-phosphorylation.

Concentration gradients provide spatial information for tissue patterning and cell organization, and their robustness under natural fluctuations is an evolutionary advantage. In rod-shaped Schizosaccharomyces pombe cells, the DYRK-family kinase Pom1 gradients control cell division timing and placement. Upon dephosphorylation by a Tea4-phosphatase complex, Pom1 associates with the plasma membrane at cell poles, where it diffuses and detaches upon auto-phosphorylation. Here, we demonstrate that Pom1 auto-phosphorylates intermolecularly, both in vitro and in vivo, which confers robustness to the gradient. Quantitative imaging reveals this robustness through two system's properties: The Pom1 gradient amplitude is inversely correlated with its decay length and is buffered against fluctuations in Tea4 levels. A theoretical model of Pom1 gradient formation through intermolecular auto-phosphorylation predicts both properties qualitatively and quantitatively. This provides a telling example where gradient robustness through super-linear decay, a principle hypothesized a decade ago, is achieved through autocatalysis. Concentration-dependent autocatalysis may be a widely used simple feedback to buffer biological activities

Rtt107 Phosphorylation Promotes Localisation to DNA Double-Stranded Breaks (DSBs) and Recombinational Repair between Sister Chromatids

Efficient repair of DNA double-stranded breaks (DSB) requires a coordinated response at the site of lesion. Nucleolytic resection commits repair towards homologous recombination, which preferentially occurs between sister chromatids. DSB resection promotes recruitment of the Mec1 checkpoint kinase to the break. Rtt107 is a target of Mec1 and serves as a scaffold during repair. Rtt107 plays an important role during rescue of damaged replication forks, however whether Rtt107 contributes to the repair of DSBs is unknown. Here we show that Rtt107 is recruited to DSBs induced by the HO endonuclease. Rtt107 phosphorylation by Mec1 and its interaction with the Smc5–Smc6 complex are both required for Rtt107 loading to breaks, while Rtt107 regulators Slx4 and Rtt101 are not. We demonstrate that Rtt107 has an effect on the efficiency of sister chromatid recombination (SCR) and propose that its recruitment to DSBs, together with the Smc5–Smc6 complex is important for repair through the SCR pathway

Functional study of the Smc5/Smc6 complex through analysis of novel interactors

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Interplay between the microstructure and tribological performance in heat-treated high chromium cast iron alloys

In this dissertation, the microstructural evolution of a 26 wt.% Cr high chromium cast iron (HCCI) alloy was systematically investigated when subjected to varying heat treatment (HT) processes. Due to the vast number of possible parameter combinations, computational tools were utilized to optimize the HT parameters and monitor the resulting modifications before the actual experimental HT was performed. Furthermore, to understand how various microstructural constituents affected the tribological behaviour of the as-cast and heat-treated HCCI alloy, an extensive insight into the sequence of carbide precipitation and the transformation of the surrounding matrix was necessary, given the alloy’s complex multi-scale, multi-phase microstructure. A thorough investigation of the microstructure was conducted at various length scales, and a need for a specificity in the HT was established. Even though the microstructural constituents in heat-treated (HTed) samples were identical, their varying amounts and distribution had a significant impact on the final tribological behaviour, underlining the importance of matrix support in improving the tribological performance of the alloy. Finally, the results obtained from this research shed light on the feasibility of modifying the HT parameters to tailor the microstructure according to the application prerequisite.Hauptziel dieser Dissertation ist die systematische Untersuchung der mikrostrukturellen Entwicklung einer hochchromhaltigen Legierung (HCCI) mit 26 Gew.-% Cr, die verschiedene Wärmebehandlungsverfahren (HT) unterzogen wird. In Anbetracht der umfangreichen Parameterkombinationen werden vor der experimentellen HT computergestützte Werkzeuge zur Feinabstimmung der HTParameter und zur Überwachung der auftretenden Veränderungen eingesetzt. Um zu verstehen, wie das tribologische Verhalten der wärmebehandelten HCCILegierung durch die verschiedenen mikrostrukturellen Bestandteile beeinflusst wird, ist ein grundlegendes Verständnis der Karbidausscheidungssequenz und der Umwandlung der umgebenden Matrix im komplexen mehrskaligen und mehrphasigen Gefüge der Legierung von entscheidender Bedeutung. Das Gefüge wurde über mehrere Längenskalen hinweg charakterisiert und es wurde festgestellt, dass eine Spezifität der HT erforderlich ist. Obwohl die mikrostrukturellen Bestandteile in den HT-behandelten Proben identisch waren, hatten ihre unterschiedlichen Mengen und Verteilungen einen signifikanten Einfluss auf das endgültige tribologische Verhalten, was die Bedeutung der Matrixunterstützung für die Verbesserung der tribologischen Leistung der Legierung unterstreicht. Die Ergebnisse dieser Forschung zeigen das Potenzial der HT-Parametermodifikation zur Anpassung der Mikrostruktur je nach Anwendungsvoraussetzung

The DYRK-family kinase Pom1 phosphorylates the F-BAR protein Cdc15 to prevent division at cell poles.

Division site positioning is critical for both symmetric and asymmetric cell divisions. In many organisms, positive and negative signals cooperate to position the contractile actin ring for cytokinesis. In rod-shaped fission yeast Schizosaccharomyces pombe cells, division at midcell is achieved through positive Mid1/anillin-dependent signaling emanating from the central nucleus and negative signals from the dual-specificity tyrosine phosphorylation-regulated kinase family kinase Pom1 at the cell poles. In this study, we show that Pom1 directly phosphorylates the F-BAR protein Cdc15, a central component of the cytokinetic ring. Pom1-dependent phosphorylation blocks Cdc15 binding to paxillin Pxl1 and C2 domain protein Fic1 and enhances Cdc15 dynamics. This promotes ring sliding from cell poles, which prevents septum assembly at the ends of cells with a displaced nucleus or lacking Mid1. Pom1 also slows down ring constriction. These results indicate that a strong negative signal from the Pom1 kinase at cell poles converts Cdc15 to its closed state, destabilizes the actomyosin ring, and thus promotes medial septation