POLYCRYSTALLINE MODELLING OF UDIMET 720 FORGING

International audienceA crystalline modelling of deformation implemented in a finite element code coupled to a recrystallization Cellular Automaton code is proposed and applied to forging processes of superalloys. The coupled modelling is used in order to obtain a better understanding of the microstructural evolution of superalloys during high temperature forging at different strain rates and temperatures. The framework of the modelling is large plastic deformation and large lattice rotation. The used internal variables are dislocations densities on slip systems of the different phases. Modelling is based on viscoplatic constitutive and hardening laws at the scale of the slip systems and describes local strain and stress fields as well as the stored energy and the rotation of the lattice in the grains of the microstructure. At different steps of deformation, formation of subgrains, annihilation of dislocations, nucleation, growth and new orientation of grains are computed. The 3D aggregates representing the superalloy, are built up from Electron Back Scattered Diffraction method (EBSD) by means of a high resolution Scanning Electron Microscope. The phases are identified by means of EBSD, chemical analysis (EDS) and observations with a Scanning Electron Microscope. In this paper the studied aggregate is realised from a semi product of Udimet 720. Such technique is able to give us, a realistic description of the crystalline orientation, morphology and position of grains in the aggregate. The Finite Element meshing is deduced from the EBSD analysis. At high temperature, the Udimet 720 is constituted by a γ matrix with a Face Centred Cubic structure (FCC) and γ' precipitates (Ni3(Ti,Al)) with a Simple Cubic structure (SC). The various material parameters used for the coupled modelling are previously determined from compression tests performed at several strain rate and temperature; The dislocation densities are measured from Transmission Electronic Microscope

Mammalian forelimb evolution is driven by uneven proximal-to-distal morphological diversity

Vertebrate limb morphology often reflects the environment due to variation in locomotor requirements. However, proximal and distal limb segments may evolve differently from one another, reflecting an anatomical gradient of functional specialization that has been suggested to be impacted by the timing of development. Here, we explore whether the temporal sequence of bone condensation predicts variation in the capacity of evolution to generate morphological diversity in proximal and distal forelimb segments across more than 600 species of mammals. Distal elements not only exhibit greater shape diversity, but also show stronger within-element integration and, on average, faster evolutionary responses than intermediate and upper limb segments. Results are consistent with the hypothesis that late developing distal bones display greater morphological variation than more proximal limb elements. However, the higher integration observed within the autopod deviates from such developmental predictions, suggesting that functional specialization plays an important role in driving within-element covariation. Proximal and distal limb segments also show different macroevolutionary patterns, albeit not showing a perfect proximo-distal gradient. The high disparity of the mammalian autopod, reported here, is consistent with the higher potential of development to generate variation in more distal limb structures, as well as functional specialization of the distal elements

Limited ecological opportunity influences the tempo of morphological evolution in birds

Funding Information: J.P.D., J.C., and H.M. received funding from the Hubert Curien Alliance (project 607280675 ). J.R. received funding from the Agence Nationale de la Recherche ( CEBA : ANR-10-LABX-25-01, TULIP : ANR-10-LABX-0041 , JCJC : ANR-23-CE02-0005-01 ). Collection of trait data was supported by Natural Environment Research Council ( NE/I028068/1 , NE/P004512/1 to J.A.T.). We thank Erandi Bonillas-Monge, Dan Nesbit, Christophe Patterson, Trevor Price, Francisco Henao Diaz, and several anonymous reviewers for helpful comments.Peer reviewe

Orion MinAngle: A flexure-based, double-tilting parallel kinematics for ultra-high precision applications requiring high angles of rotation

If you need to design ultra-high precision devices for mechanisms with multiple axes there are not a lot of ways leading around flexure-based joints. Using this type of articulations totally eliminates backlash and friction and is, by this, providing an accurate mechanical foundation for your device. The most important disadvantage of this technology is the low range of motion. The basic joint types, blades and circular hinges, have angular limits which strongly depend on the targeted stiffness, the quantity of motion cycles and the elastic limit of the material. This article will introduce novel parallel kinematics which are totally based on 1 dof flexures and whose angular range of motion is determined by twice the range of the single joint. It is a 3 dof parallel kinematic based on 3 identical kinematic chains which produce movements in θx, θy and z. The model has been designed to constitute the left hand of a machine tool that requires orienting the workpiece in a very precise manner and with high rotation amplitudes. Additionally to this it presents very interesting characteristics of Remote-Center-of-Motion (RCM) mechanisms. This is a vital feature for applications where the linear movements are highly limited and should not be consumed by parasitic movements of other axes. All these features, combined with the advantages of parallel kinematics, make the Orion MinAngle a very interesting concept. The model has been designed with joints achieving ±7.6° leading to an output angle of ±15° on both rotation axes. The study has shown really promising results concerning the mechanical properties, the high rotation angles and the RCM capabilities. The paper presents the kinematics and its optimization method which is used to guarantee a nearly perfect division of the output angle on all pivots of the mechanism. The next chapters talk about the dimensioning of the flexible joints and generally about the design of the robot. The last part of the paper verifies the optimization trough kinematic modeling of the robot and computes the mechanical properties like stiffness, internal strains and mechanical Eigenfrequencies. At the end we propose a realistic application as a 5-axes parallel-kinematic machine tool and we come to a conclusion about the potential of the Orion MinAngle mechanism

The tempo of cetacean cranial evolution

The evolution of cetaceans (whales and dolphins) represents one of the most extreme adaptive transitions known, from terrestrial mammals to a highly specialized aquatic radiation that includes the largest animals alive today. Many anatomical shifts in this transition involve the feeding, respiratory, and sensory structures of the cranium, which we quantified with a high-density, three-dimensional geometric morphometric analysis of 201 living and extinct cetacean species spanning the entirety of their ∼50-million-year evolutionary history. Our analyses demonstrate that cetacean suborders occupy distinct areas of cranial morphospace, with extinct, transitional taxa bridging the gap between archaeocetes (stem whales) and modern mysticetes (baleen whales) and odontocetes (toothed whales). This diversity was obtained through three key periods of rapid evolution: first, the initial evolution of archaeocetes in the early to mid-Eocene produced the highest evolutionary rates seen in cetaceans, concentrated in the maxilla, frontal, premaxilla, and nasal; second, the late Eocene divergence of the mysticetes and odontocetes drives a second peak in rates, with high rates and disparity sustained through the Oligocene; and third, the diversification of odontocetes, particularly sperm whales, in the Miocene (∼18-10 Mya) propels a final peak in the tempo of cetacean morphological evolution. Archaeocetes show the fastest evolutionary rates but the lowest disparity. Odontocetes exhibit the highest disparity, while mysticetes evolve at the slowest pace, particularly in the Neogene. Diet and echolocation have the strongest influence on cranial morphology, with habitat, size, dentition, and feeding method also significant factors impacting shape, disparity, and the pace of cetacean cranial evolution

Differential influences of allometry, phylogeny and environment on the rostral shape diversity of extinct South American notoungulates

Understanding the mechanisms responsible for phenotypic diversification, and the associated underlying constraints and ecological factors represents a central issue in evolutionary biology. Mammals present a wide variety of sizes and shapes, and are characterized by a high number of morphological convergences that are hypothesized to reflect similar environmental pressures. Extinct South American notoungulates evolved in isolation from northern mammalian faunas in highly disparate environments. They present a wide array of skeletal phenotypes and convergences, such as ever-growing dentition. Here, we focused on the origins of the rostral diversity of notoungulates by quantifying the shape of 26 genera using three-dimensional geometric morphometric analysis. We tested the influence of allometry and phylogeny on rostral shape and evaluated rates of evolutionary change in the different clades. We found strong allometric and phylogenetic signals concerning the rostral shape of notoungulates. Despite convergent forms, we observed a diffuse diversification of rostral shape, with no significant evidence of influence by large-scaled environmental variation. This contrasts with the increase in dental crown height that occurred in four late-diverging families in response to similar environmental pressures. These results illustrate the importance of considering both biological components and evolutionary rates to better understand some aspects of phenotypic diversity.Fil: Gomes Rodrigues, Helder. Muséum National d'Histoire Naturelle; Francia. Centre National de la Recherche Scientifique; FranciaFil: Cornette, Raphaël. Centre National de la Recherche Scientifique; Francia. Muséum National d'Histoire Naturelle; FranciaFil: Clavel, Julien. Ecole Normale Supérieure; Francia. Centre National de la Recherche Scientifique; FranciaFil: Cassini, Guillermo Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Universidad Nacional de Luján. Departamento de Ciencias Básicas; ArgentinaFil: Bhullar, Bhart-Anjan S. . University of Yale; Estados UnidosFil: Fernández-Monescillo, Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Moreno, Karen. Universidad Austral de Chile. Instituto de Ciencias de la Tierra; ChileFil: Herrel, Anthony. Centre National de la Recherche Scientifique; Francia. Muséum National d'Histoire Naturelle; FranciaFil: Billet, Guillaume. Muséum National d'Histoire Naturelle; Francia. Centre National de la Recherche Scientifique; Franci

Relationship between QT interval and outcome in low-flow low-gradient aortic stenosis with low left ventricular ejection fraction

Background QT interval has been shown to be associated with cardiovascular events. There is no data regarding the association between QT interval and left ventricular (LV) function and prognosis in patients with low LV ejection fraction (LVEF), low‐flow, low‐gradient aortic stenosis (LF‐LG AS). We aimed to examine the relationship between corrected QT interval (QT c) and LV function and outcome in these patients. Methods and Results Ninety‐three patients (73±10 years; 74% men) with LF‐LG AS (mean gradient 450 ms in men and >470 ms in women. LV global longitudinal strain was measured by speckle tracking and expressed in absolute value |%|. QT c correlated with the following: global longitudinal strain (r=−0.40, P=0.005), LVEF (r=−0.27, P=0.02), stroke volume (r=−0.35, P=0.007), and B‐type natriuretic peptide (r=0.45, P=0.0006). During a median follow‐up of 2.0 years, 49 patients died. Prolonged QT c was associated with a 2‐fold increase in all‐cause mortality (hazard ratio=2.05; P=0.01) and cardiovascular mortality (hazard ratio=1.89; P=0.04). In multivariable analysis adjusted for EuroSCORE, aortic valve replacement, previous myocardial infarction, LVEF, and ß‐blocker medication, prolonged QT c was independently associated with all‐cause mortality (hazard ratio=2.56; P=0.008) and cardiovascular mortality (hazard ratio=2.50; P=0.02). Conclusions In patients with LF‐LG AS and reduced LVEF, longer QT c interval was associated with worse LV function and increased risk of death. Assessment of QT c may provide a simple and inexpensive tool to enhance risk stratification in LF‐LG AS patients

Absorption lines from magnetically driven winds in X-ray binaries II: high resolution observational signatures expected from future X-ray observatories

In our self-similar, analytical, magneto-hydrodynamic (MHD) accretion-ejection solution, the density at the base of the outflow is explicitly dependent on the disk accretion rate - a unique property of this class of solutions. We had earlier found that the ejection index $p >\sim 0.1 (\dot{M}_{acc} \propto r^p )$ is a key MHD parameter that decides if the flow can cause absorption lines in the high resolution X-ray spectra of black hole binaries. Here we choose 3 dense warm solutions with $p = 0.1, 0.3, 0.45$ and carefully develop a methodology to generate spectra which are convolved with the Athena and XRISM response functions to predict what they will observe seeing through such MHD outflows. In this paper two other external parameters were varied - extent of the disk, $\rm{r_o|_{max}} = 10^5, \, 10^6 \,\, \rm{r_G}$, and the angle of the line of sight, $i \sim 10 - 25^{\circ}$. Resultant absorption lines (H and He-like Fe, Ca, Ar) change in strength and their profiles manifest varying degrees of asymmetry. We checked if a) the lines and ii) the line asymmetries are detected, in our suit of synthetic Athena and XRISM spectra. Our analysis shows that Athena should detect the lines and their asymmetries for a standard 100 ksec observation of a 100 mCrab source - lines with equivalent width as low as a few eV should be detected if the 6-8 keV counts are larger than $10^4 - 10^5$ even for the least favourable simulated cases.Comment: 18 pages, 13 figures in the main body and 3 figures in the appendix. Accepted for publication in MNRA

Developmental origin underlies evolutionary rate variation across the placental skull

The placental skull has evolved into myriad forms, from longirostrine whales to globular primates, and with a diverse array of appendages from antlers to tusks. This disparity has recently been studied from the perspective of the whole skull, but the skull is composed of numerous elements that have distinct developmental origins and varied functions. Here, we assess the evolution of the skull's major skeletal elements, decomposed into 17 individual regions. Using a high-dimensional morphometric approach for a dataset of 322 living and extinct eutherians (placental mammals and their stem relatives), we quantify patterns of variation and estimate phylogenetic, allometric and ecological signal across the skull. We further compare rates of evolution across ecological categories and ordinal-level clades and reconstruct rates of evolution along lineages and through time to assess whether developmental origin or function discriminate the evolutionary trajectories of individual cranial elements. Our results demonstrate distinct macroevolutionary patterns across cranial elements that reflect the ecological adaptations of major clades. Elements derived from neural crest show the fastest rates of evolution, but ecological signal is equally pronounced in bones derived from neural crest and paraxial mesoderm, suggesting that developmental origin may influence evolutionary tempo, but not capacity for specialisation. This article is part of the theme issue 'The mammalian skull: development, structure and function'