Mechanical Behavior of Multi-Phase Steels Comprising Retained Austenite

The retained austenite (RA) in advanced high-strength steel (AHSS) grades, such as dual-phase (DP) steels, plays an important role on their formability. Thanks to the transformation-induced plasticity (TRIP) effect that occurs during the mechanically induced transformation of RA into martensite, additional ductility is obtained. Martensite has a higher flow stress than austenite; hence, the transformation results in an apparent hardening, which is beneficial for the stability of deformation. The stability of RA at a given temperature strongly depends on its carbon content, which, in AHSS, is not uniform but distributed. The aim of this study is to build a model that predicts the transformation as well as TRIP in a DP steel grade with RA. A physics-based kinetic model is presented that captures the transformation of retained austenite based on the thermodynamic driving force of the applied stress. A direct analytical estimate of transformation plasticity is provided, which is consistent with the kinetic model. Transformation kinetics is incorporated in a self-consistent, mean-field homogenization-based constitutive model. Finally, an indication of the effect of transformation of retained austenite on formability is given.

HEATING DEPTH OF GAS SUSPENSION FLOW BY COUNTER RADIATION

Выполнена аналитическая оценка отношения глубины прогрева газовзвеси излучением продуктов горения S к длине свободного пробега излучения в газовзвеси L. Использована одномерная модель стационарного распределения температуры в потоке взвешенных в воздухе монодисперсных инертных частиц, движущихся на равномерно нагретую абсолютно черную поверхность, имитирующую фронт пламени. Учитывается отражение и переизлучение тепловой энергии частицами. S / L >> 1 при низкой степени черноты и/или высокой конечной температуре частиц. It is accepted that the depth of heating of the gas suspension by the radiation of combustion products SR is equal to the length LR of the free path of radiation in the gas suspension: SR ≈ LR. Numerical simulation of gas-air mixture combustion with the addition of inert particles, taking into account the re-emission of heat by heated particles of fresh suspension, shows the possibility of realizing the ratio SR >> LR (Ivanov M.F. et al, 2015). In this work, an analytical estimate of the SR/LR ratio is carried out within the framework of one-dimensional modeling of the temperature distribution in the flow of initially cold monodisperse inert particles suspended in air, moving to a uniformly heated absolutely black surface, permeable to air suspension and simulating a flame front. The following assumptions are used. The solution is stationary in the coordinate system associated with the emitting surface; radiation consists of two oppositely directed streams of electromagnetic energy; the interaction of particles and radiation is described in the approximation of geometric optics and takes into account both the processes of absorption and emission of thermal energy, and the process of reflection of radiation; the temperature inside the particle is the same. In contrast to the previously considered (Poletaev N.L., 2021) the simplified problem of the motion of particles in a vacuum or in the presence of a gas phase heated by particles but not experiencing thermal expansion, this work took into account both the presence of a gas phase heated by particles and expansion of the gas phase. The latter causes the acceleration and expansion of the air suspension as it approaches the radiating surface. The difference in the local values of temperatures and phase motion velocities of the air suspension was neglected. It is shown that the quasi-linear (in the above-mentioned coordinate system) temperature distribution function in the air suspension obtained in this work is qualitatively different from the quasi-exponential temperature distribution function obtained earlier by solving a simplified problem. At the same time, the ratio of the heating depth of the air suspension by thermal radiation and the free path of radiation in the layer of air suspension adjacent to the radiating plane turned out to be similar to that obtained for the simplified solution. Namely, SR/LR >> 1 at a low integral degree of emissivity of the particle material and / or at a high final temperature of the particles, comparable to the temperature of the emitting surface.

Theoretical and Experimental Investigation of Warpage Evolution of Flip Chip Package on Packaging during Fabrication

This study attempts to investigate the warpage behavior of a flip chip package-on-package (FCPoP) assembly during fabrication process. A process simulation framework that integrates thermal and mechanical finite element analysis (FEA), effective modeling and ANSYS element death-birth technique is introduced for effectively predicting the process-induced warpage. The mechanical FEA takes into account the viscoelastic behavior and cure shrinkage of the epoxy molding compound. In order to enhance the computational and modeling efficiency and retain the prediction accuracy at the same time, this study proposes a novel effective approach that combines the trace mapping method, rule of mixture and FEA to estimate the effective orthotropic elastic properties of the coreless substrate and core interposer. The study begins with experimental measurement of the temperature-dependent elastic and viscoelastic properties of the components in the assembly, followed by the prediction of the effective elastic properties of the orthotropic interposer and substrate. The predicted effective results are compared against the results of the ROM/analytical estimate and the FEA-based effective approach. Moreover, the warpages obtained from the proposed process simulation framework are validated by the in-line measurement data, and good agreement is presented. Finally, key factors that may influence process-induced warpage are examined via parametric analysis.

SPECTRUM OF OWN FREQUENCIES OF A SPATIAL SURFACING GIRDER

Statement of the problem. The scheme of a statically definable girder of a spatial rectangular surfacing is discussed. The problem is to identify the formula for the dependence of the lower estimate of the first frequency of the natural oscillations of the structure by means of the Donkerley method on the number of panels. The truss has supports on the sides and consists of separate rod cells connected in pyramids. Results. Based on the analysis of the sequence of analytical solutions for the first frequency of girders with a different number of panels by induction, the coefficients in the desired formula are derived. The common members of the sequences of coefficients are found as solutions of homogeneous recurrent equations formed according to the results of the calculations using Maple operators. The resulting dependences are obtained in the form of polynomials by the number of panels. A comparison of the analytical solution with the numerical one is provided.Conclusions. An algorithm for deriving an analytical estimate of the fundamental frequency of oscillations of a spatial structure depending on the number of panels, mass, size, and elastic properties of the material is shown. The spectrum of oscillation frequencies of the structure is analyzed. The resulting dependences can be employed in seismic and structural optimization problems.

Spectrum of Own Frequencies of a Spatial Surfacing Grid

Постановка задачи. Рассматривается схема статически определимой фермы пространственного прямоугольного покрытия. Ставится задача найти формулу зависимости нижней оценки первой частоты собственных колебаний конструкции по методу Донкерлея от числа панелей. Ферма имеет опоры по сторонам и состоит из отдельных стержневых ячеек, соединенных в пирамиды. Результаты. Из анализа последовательности аналитических решений для первой частоты ферм с различным числом панелей методом индукции выводятся коэффициенты в искомой формуле. Общие члены последовательностей коэффициентов находятся как решения однородных рекуррентных уравнений, образованных по результатам расчетов с помощью операторов Maple . Найденные зависимости получены в виде полиномов по числу панелей. Дано сравнение аналитического решения с численным. Выводы. Приведен алгоритм вывода аналитической оценки основной частоты колебаний пространственной конструкции в зависимости от числа панелей, массы, размеров и упругих свойств материала. Проанализирован спектр частот колебаний сооружения. Найденные зависимости могут быть использованы в задачах сейсмостойкости и оптимизации конструкции. Statement of the problem. The scheme of a statically definable truss of a spatial rectangular covering is discussed. The problem is to identify the formula for the dependence of the lower estimate of the first frequency of the natural oscillations of the structure by means of the Donkerley method on the number of panels. The truss has supports on the sides and consists of separate rod cells connected in pyramids. Results. Based on the analysis of the sequence of analytical solutions for the first frequency of trusses with a different number of panels by induction, the coefficients in the desired formula are derived. The common members of the sequences of coefficients are found as solutions of homogeneous recurrent equations formed according to the results of the calculations using Maple operators. The resulting dependences are obtained in the form of polynomials by the number of panels. A comparison of the analytical solution with the numerical one is provided. Conclusions. An algorithm for deriving an analytical estimate of the fundamental frequency of oscillations of a spatial structure depending on the number of panels, mass, size, and elastic properties of the material is shown. The spectrum of oscillation frequencies of the structure is analyzed. The resulting dependences can be employed in seismic and structural optimization problems.

Prevalence of Thromboembolic Complications in COVID-19 Infection: A Systematic Review and Meta-Analysis

Introduction: The coronavirus disease (COVID-19) infection is proved to be involved in the onset of thromboembolism episodes. This study aims to evaluate the prevalence of thromboembolic complications in patients with COVID-19 from March until May 2020. Methods: A literature review was conducted in MEDLINE (via PubMed), Scopus, Embase, Cochrane, and CINHAL without any language and date of publication restriction (Prospero registration number CRD42020186925). The inclusion criteria were as following: 1) patients with diagnosis of COVID-19; 2) occurrence of thromboembolic event, and 3) patients older than 18 years of age. A multi-variable random effects model was computed accounting for correlations among outcomes by considering a heterogeneous compound symmetry covariance matrix. Results: Observational studies included 2,442 participants from 268 to 7,999 participants per study, 1,014 (41.52%) were male and 825 (33.78%) were female. The multi-variable pooled event rate of acute myocardial infarction was rare, estimated to be 0.03 (95% confidence interval [CI]: 0.00–0.07; p=0.23); this is also true for the meta-analytical estimate of disseminated intravascular disease which was 0.04 (95% CI: 0.00–0.08; p=0.03). Conversely, other events were found to be more frequent. Indeed, the pooled proportion of pulmonary embolism was 0.14 (95% CI: 0.08–0.20; p<0.001), while the venous thromboembolic event rate is 0.15 (95% CI: 0.09-0.30; p=0.04). The pooled intrahospital mortality rate was equal to 0.12 (95% CI: 0.08–0.16; p<0.001). Conclusions: Thromboembolic events, particularly venous thromboembolic event rate and pulmonary embolism, are a frequent complication in patients hospitalised with COVID-19. These findings suggest that the threshold for clinical suspicion should be low to trigger prompt diagnostic testing and that evaluation of therapeutic treatment should be considered in patients in intensive care units with COVID-19.

Near-exact explicit asymptotic solution of the SIR model well above the epidemic threshold

A simple and explicit expression of the solution of the SIR epidemiological model of Kermack and McKendrick is constructed in the asymptotic limit of large basic reproduction numbers $\ro$. The proposed formula yields good qualitative agreement already when $\ro\geq3$ and rapidly becomes quantitatively accurate as larger values of $\ro$ are assumed. The derivation is based on the method of matched asymptotic expansions, which exploits the fact that the exponential growing phase and the eventual recession of the outbreak occur on distinct time scales. From the newly derived solution, an analytical estimate of the time separating the first inflexion point of the epidemic curve from the peak of infections is given.

Influence of the bend radius for PANDA PM Specialty optical fibers reliability

The research considers the possibility of applying the forced «aging» method used for single-mode cable optical fibers in accordance with IEC 60793-2-50 to confirm the reliability of the PANDA PM Specialty optical fiber under long-term bending. A comparison of the results of PANDA PM Specialty optical fiber with isotropic optical fibers, which differ in the diameters of the quartz cladding and polymer coating, is carried out. An analytical estimate of the lifetime is carried out.

Erratum to: Analytical Estimate of Rotor Controls Required for a Straight Vortex Disturbance Rejection

Correction to:Journal of the American Helicopter Society, Vol. 62, (1), January 2017, pp. 1-4,http://dx.doi.org/10.4050/JAHS.62.015001

Analytical assessment of the frequency of natural vibrations of a truss with an arbitrary number of panels

The aim of the work is to derive a formula for the dependence of the first frequency of the natural oscillations of a planar statically determinate beam truss with parallel belts on the number of panels, sizes and masses concentrated in the nodes of the lower truss belt. Truss has a triangular lattice with vertical racks. The solution uses Maple computer math system operators. Methods. The basis for the upper estimate of the desired oscillation frequency of a regular truss is the energy method. As a form of deflection of the truss taken deflection from the action of a uniformly distributed load. Only vertical mass movements are assumed. The amplitude values of the deflection of the truss is calculated by the Maxwell - Mohrs formula. The forces in the rods are determined in symbolic form by the method of cutting nodes. The dependence of the solution on the number of panels is obtained by an inductive generalization of a series of solutions for trusses with a successively increasing number of panels. For sequences of coefficients of the desired formula, fourth-order homogeneous linear recurrence equations are compiled and solved. Results. The solution is compared with the numerical one, obtained from the analysis of the entire spectrum of natural frequencies of oscillations of the mass system located at the nodes of the truss. The frequency equation is compiled and solved using Eigenvalue search operators in the Maple system. It is shown that the obtained analytical estimate differs from the numerical solution by a fraction of a percent. Moreover, with an increase in the number of panels, the error of the energy method decreases monotonically. A simpler lower bound for the oscillation frequency according to the Dunkerley method is presented. The accuracy of the lower estimate is much lower than the upper estimate, depending on the size and number of panels.