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EN
Ultrafine-grained structure was produced in the Accumulative Angular Drawing(AAD) process in which the complex strain path was applied. The microalloyed steel wire rods were produced using multi-pass wire drawing process where the high strain accumulation is used as a way to achieve much higher microstructure refinement level compared to the conventional wire drawing (WD) process. The wires after both AAD process and WD process were examined in order to assess mechanical properties and microstructure development. In order to evaluate the effects of complex deformation on microstructure development and mechanical properties of the drawn wires, a numerical model of the torsion tests were conducted using Abaqus software. The cyclic torsion tests were performed to study the effects of the applied hardening rule - described as a function of dislocations density and the accuracy of the prediction of material behaviour subjected to strain path change during AAD. It has been shown that an additional advantage of presented approach is its capability of tracking evolution of dislocation density during the deformation process. The initial dislocation densities used in the performed calculations were taken from the microstructural analysis using high resolution EBSD. During strain reversal, annihilation of the dislocations (Bauschinger effect) is a common phenomenon that leads to the decrease in dislocation density and affects the final strength. Finally, based on the proposed constitutive description, multiscale finite element modelling combined with Digital Material Representation (DMR) was used as a tool for prediction of the deformation and microstructure inhomogeneity in the drawn wires.
2
Content available remote Modelling of blood thrombosis at microscopicand mesoscopic scales
EN
Blood coagulation at the place of the complete severing of a vessel or puncturing of a vessel sidewall is usually a beneficial reaction, as it protects the body from bleeding and maintains hemostasis, while the formation of a blood clot inside the blood vessel is a pathological phenomenon, which is highly dangerous, and sometimes leads to serious complications. In this paper, two scales of modelling blood thrombosis will be introduced using numerical methods and fluid dynamics. The meso-scale model of the flow is described by Navier-Stokes equations and the blood thrombosis model is based on equations of transport and diffusion. The equations describing levels of concentrations of factors responsible for blood coagulation can be implemented into a solver solving Navier-Stokes equations, what will enable simulation of blood flow and estimation of the risk of thrombus formation related to flow conditions. The proposed micro-scale model is using molecular dynamics to simulate interactions between blood cells and vascular walls. An effective combination of both models is possible thanks to the introduction of the multiple-time stepping algorithm, which enables a full visualization of blood flow, coupling molecular interaction with the fluid mechanics equation. The goal of the paper is to present the latest literature review on the possibilities of blood coagulation modelling in two scales and the main achievements in blood thrombosis research: the key role of transport and experimental background.
EN
Purpose: The extracorporeal membrane oxygenation (ECMO) is a temporary, but prolonged circulatory support for cardiopulmonary failure. Clinical evidence suggests that pulsed flow is healthier than non pulsatile perfusion. The aim of this study was to computationally evaluate the effects of total and partial ECMO assistance and pulsed flow on hemodynamics in a patient-specific aorta model. Methods: The pulsatility was obtained by means of the intra-aortic balloon pump (IABP), and two different cases were investigated, considering a cardiac output (CO) of 5 L/min: Case A – total assistance – the whole flow delivered through the ECMO arterial cannula; Case B – partial assistance – flow delivered half through the cannula and half through the aorta. Computational fluid dynamic (CFD) analysis was carried out using the multiscale approach to couple the 3D aorta model with the lumped parameter model (resistance boundary condition). Results: In case A pulsatility followed the balloon radius change, while in case B it was mostly influenced by the cardiac one. Furthermore, during total assistance, a blood stagnation occurred in the ascending aorta; in the case of partial assistance, the flow was orderly when the IABP was on and was chaotic when the balloon was off. Moreover, the mean arterial pressure (MAP) was higher in case B. The wall shear stress was worse in ascending aorta in case A. Conclusions: Partial support is hemodynamically advisable.
4
Content available remote Quantum Dynamics for Ion Channel Transport, Poisson-Schrödinger Modell
EN
This paper deals with the mathematical model of the ion permeation in potassium channels of biomembrane. Based on the Hamiltons, variational principle was led out to the set of compiling equations describing quantum dynamics of the potassium ion transport; Poisson-Schrodinger equation for electric potential ϕ(r, t), and Schrodinger equation for wave function ψ(r, t). Received the set of equations was formulated in the form of two variational identities. A numerical algorithm of the solution, was proposed, based on the meshles Galerkin approximation.
PL
W pracy przedstawiono model matematyczny przepływu jonow sodu, potasu w kanałach biomembrany komórki żywej. Podano kryterium funkcji działania Lagrange’a dla kompatybilnosci kwantowego opisu układu. W oparciu o zasadę najmniejszego działania Hamiltona, wyprowadzono sprzężony układ równan opisujący dynamikę transportu jonów; równanie Poissona dla potencjału elektrycznego ϕ(r, t) oraz równanie Shrodingera dla funkcji falowej ψ(r, t). Otrzymany układ równań sformułowano w postaci dwóch tożsamości wariacyjnych Galerkina. Zaproponowano algorytm numeryczny rozwiązania otrzymanych równań oparty o metodę bez siatkowej aproksymacji Galerkina.
PL
Przedstawiono rozwój zastosowań metod numerycznych do symulacji procesów obróbki plastycznej, przy czym szczególny nacisk położono na metodologię uwzględniania w modelowaniu fizycznych aspektów procesów. W pierwszej części omówiono przykłady wybranych symulacji, przeprowadzonych głównie w skali makro z wykorzystaniem programów opartych na MES oraz przedstawiono pierwsze próby tworzenia modeli wieloskalowych, które bazowały na rozwiązaniu równań różniczkowych opisujących zjawiska w skali mikro. W drugiej części zaprezentowano dynamiczny rozwój metod modelowania wieloskalowego, który nastąpił w ostatnim dziesięcioleciu. Omówiono także klasyfikację metod wieloskalowych oraz zaprezentowano opracowane przez Autorów próby analizy wieloskalowej, umożliwiające skuteczną symulację zjawisk związanych z lokalizacją odkształcenia.
EN
A history of numeric methods applications for simulation of metal plastic working processes. Discussion on selected simulation examples generally carried out in the macro scale using the MES based software. Also presented is dynamic development of the multiple scale modelling methods as observed during the current decade.
EN
Multiscale CAFE (Cellular Automata – Finite Element) model of the material undergoing dynamic recrystallization is presented in the paper. The coupled model consists of dislocation and microstructure development description based on Cellular Automata (CA) and continuum macroscale simulation using Finite Element (FE) method. The model is capable of simulate various characteristics of the material, including multi-peak and single-peak flow stress behaviour. Several improvements to the CA model are proposed in the paper. The connection between flow stress characteristic and grain size is properly described by the model with respect to the structural criterion. Additionally, distribution of grain size can be calculated at arbitrary stage of the process. Analysis of recrystallization cycles observed in the material is discussed. The results show good qualitative agreement with the experimental flow stress curves commonly observed in literature.
PL
W artykule zaprezentowano wieloskalowy model CAFE (Cellular Automata – Finite Element). Model ten złożony jest z symulacji rozwoju mikrostruktury i gęstości dyslokacji, opartej o metodę Automatów Komórkowych (AK, CA) oraz modelu skali makro, opartego o Metodę Elementów Skończonych (MES, FE). Zaproponowano szereg usprawnień do modelu skali mikro. Model ten umożliwia uwzględnienie różnych charakterystyk naprężenia uplastyczniajacego, w tym jednopikowego i wielopikowego. Model poprawnie odwzorowuje kryterium strukturalne, łączące charakter krzywej naprężenia uplastyczniajacego z wielkością ziarna. Zaletą modelu jest dostarczanie zarówno informacji o średniej wielkości ziarna jak i o rozkładzie wielkości. W pracy przeanalizowano krzywe opisujące ułamki cykli rekrystalizacji w materiale. Uzyskane z modelu krzywe naprężenia uplastyczniającego wykazuje dobrą zgodność jakościową z powszechnie znanymi z literatury danymi doświadczalnymi.
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