This article intends to revisit the electro-diffusional theory for the wall shear stress measurement from mass transfer probes of rectangular shape by considering the existence of two components of ...the wall shear rate (i.e., axial and transversal). General analytical formulas for the effective transfer length and the dimensionless mass transport coefficient were derived as a function of only two parameters: a dimensionless angle of the flow direction, relative to the leading edge of the probe, and the aspect ratio between the width and the length of the strip probe. The correctness of the analytical relations for arbitrary flow direction and the aspect ratio was confirmed by numerical solutions of the transport equation in the convective-diffusive regime. It has also been proved that the differences between the Lévêque solution and the general analytical formula exhibit a significant deviation for a specific range of parameters. In the case of the three-dimensional boundary layers, in addition to the magnitude of the wall shear stress, the direction of the fluid flow in the vicinity of the probe's surface is of paramount importance. Accordingly, a measurement methodology is proposed using two strip probes with different aspect ratios. The resulting equations required to quantify the magnitude of the wall shear rate vector and the dimensionless angle are also derived.
Perilunate dislocations are a rare but serious pathology, often undetected in the emergency setting. In this study, a Deep Learning algorithm is proposed to automatically detect perilunate ...dislocations in frontal radiographs. A total of 374 annotated frontal wrist radiographs, comprising 345 normal and 29 pathological ones from adolescents and adults aged 16 and above with skeletal maturity, were utilized to train, validate, and test two YOLOv8 deep neural models. The first model is responsible for detecting the carpal region, and the second for segmenting a region between Gilula’s 2nd and 3rd arcs. The output of the segmentation model, trained multiple times with varying random augmentations, is then given a probability to be normal or pathological through ensemble averaging. On the considered dataset, the proposed algorithm achieves an overall F1-score of 0.880. The F1-score reaches 0.928 on the normal subgroup with a precision of 1.0, and 0.833 on the pathological subgroup with a recall (or sensitivity) of 1.0, demonstrating that the diagnosis of perilunate dislocations can be improved through automatic analysis of frontal radiographs.
The fracture toughness of inorganic glasses Rouxel, Tanguy; Yoshida, Satoshi
Journal of the American Ceramic Society,
October 2017, Letnik:
100, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Measuring the fracture toughness (KIc) of glasses still remains a difficult task, raising experimental and theoretical problems as well. The available methods to estimate KIc are reviewed, with ...emphasis on their respective advantages and drawbacks. In view of our current understanding, this analysis gives precedence to the SEPB method. The ultimate glass strength, the critical flaw size, and the indentation load for the onset of crack initiation are discussed, in the light of the fundamentals of fracture mechanics and classical background regarding the mechanics of brittle materials. Analytical expressions were further proposed to predict the fracture energy and fracture toughness of glasses from different chemical systems from their nominal compositions. The theoretical values were compared with the experimental ones, as obtained by self‐consistent methods when available. The agreement observed in most cases suggests that measured KIc values correspond to the crack propagation regime (as opposed to the crack initiation threshold), and supports previous investigations in glasses and ceramics, which showed that a crack tip is nearly atomically sharp in these materials (but for metallic glasses). Some ideas to design tougher glasses are finally presented.
Rubber-like materials consist of chain-like macromolecules that are more or less closely connected to each other via entanglements or cross-links. As an idealisation, this particular structure can be ...described as a completely random three-dimensional network. To capture the elastic and nearly incompressible mechanical behaviour of this material class, numerous phenomenological and micro-mechanically motivated models have been proposed in the literature. This contribution reviews fourteen selected representatives of these models, derives analytical stress–stretch relations for certain homogeneous deformation modes and summarises the details required for stress tensors and consistent tangent operators. The latter, although prevalently missing in the literature, are indispensable ingredients in utilising any kind of constitutive model for the numerical solution of boundary value problems by iterative approaches like the Newton–Raphson scheme. Furthermore, performance and validity of the models with regard to the classical experimental data on vulcanised rubber published by Treloar (Trans Faraday Soc 40:59–70,
1944
) are evaluated. These data are here considered as a prototype or worst-case scenario of highly nonlinear elastic behaviour, although inelastic characteristics are clearly observable but have been tacitly ignored by many other authors.
The mechanical properties of titanium alloys result from their complex multi-scale microstructural features, including micron scale precipitates and millimeter scale microtextured regions (MTRs). ...While previous investigations have revealed that the presence of mm-scale MTRs can degrade mechanical properties, particularly fatigue, the accompanying strain localization processes that operate at the microscale within the α grains in MTRs are not well understood. The present work is a mechanistic investigation of MTRs using crystal plasticity simulations of mm3-scale experimentally captured and synthetically generated 3D microstructure datasets. The explicit modeling of both the α grains and MTRs in Ti–6Al–4V enables assessment of the effect of microtexture and local structure variations within the MTR on overall deformation behavior and the onset of plastic slip in MTRs. The presence of MTRs with a dominant 0001 orientation results in both stress and plastic strain hotspots during the early stages of straining. Crystal plasticity predictions are compared to previous digital image correlation studies on early strain localization. The influence of MTRs on the local stress and strain fields is discussed with regard to the monotonic tension, fatigue and dwell-fatigue behavior of titanium alloys.
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Mathematical modeling of cardiac function can provide augmented simulation-based diagnosis tools for complementing and extending human understanding of cardiac diseases, which represent the most ...common cause of worldwide death. As the realistic starting-point for developing a unified meshless approach for total heart modeling, in this paper we propose an integrative smoothed particle hydrodynamics (SPH) method for addressing the simulation of the principle aspects of cardiac function, including cardiac electrophysiology, passive mechanical response and electromechanical coupling. To that end, several algorithms, e.g. splitting reaction-by-reaction method combined with a quasi-steady-state (QSS) solver, as well as anisotropic SPH-diffusion discretization and total Lagrangian SPH formulation, are introduced for dealing with the fundamental challenges of developing an integrative SPH method for simulating cardiac function, including, (i) the correct capture of the stiff dynamics of the transmembrane potential and the gating variables, (ii) the stable prediction of the large deformations and the strongly anisotropic behavior of the myocardium, and (iii) a proper coupling between the electrophysiology and tissue mechanics for the electromechanical feedback. A set of numerical examples demonstrate the effectiveness and robustness of the present SPH method, and render it a potential and powerful alternative that can augment the current lines of total cardiac modeling and clinical applications.
•Integrative SPH modeling of the principle aspects of cardiac function.•Splitting method combined with quasi-steady-state solver.•Modeling anisotropic diffusion discretization.•Modeling passive mechanical response and electromechanical coupling.•Accuracy, effectiveness and robustness demonstrated.
In this paper, we develop a method based on local maximum entropy shape functions together with enrichment functions used in partition of unity methods to discretize problems in linear elastic ...fracture mechanics. We obtain improved accuracy relative to the standard extended finite element method at a comparable computational cost. In addition, we keep the advantages of the LME shape functions, such as smoothness and non-negativity. We show numerically that optimal convergence (same as in FEM) for energy norm and stress intensity factors can be obtained through the use of geometric (fixed area) enrichment with no special treatment of the nodes near the crack such as blending or shifting.
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