A very good knowledge of material properties is required in the analysis of severe plastic deformation problems in which the classical material processing methods are accelerated by the application ...of the additional cyclic load. A general fuzzy logic-based approach is proposed for the analysis of experimental and numerical data in this paper. As an application of the fuzzy analysis, the calibration of Chaboche–Lemaitre model hardening parameters of PA6 aluminum is considered here. The experimental data obtained in a symmetrical strain-controlled cyclic tension–compression test were used to estimate the material’s hardening parameters. The numerically generated curves were compared to the experimental ones. For better fitting of numerical and experimental results, the optimization approach using the least-square method was applied. Unfortunately, commonly accepted calibration methods can provide various sets of hardening parameters. In order to choose the most reliable set, the fuzzy analysis was used. Primarily selected values of hardening parameters were assumed to be fuzzy input parameters. The error of the hysteresis loop approximation for each set was used to compute its membership function. The discrete value of this error was obtained in the defuzzification step. The correct selections of hardening parameters were verified in ratcheting and mean stress relaxation tests. The application of the fuzzy analysis has improved the convergence between experimental and numerical stress–strain curves. The fuzzy logic allows analyzing the variation of elastic–plastic material response when some imprecisions or uncertainties of input parameters are taken into consideration.
The SARS-CoV-2 pandemic has hit the European region disproportionately. Many HIV clinics share staff and logistics with infectious disease facilities, which are now on the frontline in tackling ...COVID-19. Therefore, this study investigated the impact of the current pandemic situation on HIV care and continuity of antiretroviral treatment (ART) supplies in CEE countries.
The Euroguidelines in Central and Eastern Europe (ECEE) Network Group was established in February 2016 to review standards of care for HIV in the region. The group consists of professionals actively involved in HIV care. On March 19, 2020 we decided to review the status of HIV care sustainability in the face of the emerging SARS-CoV-2 pandemic in Europe. For this purpose, we constructed an online survey consisting of 23 questions. Respondents were recruited from ECEE members in 22 countries, based on their involvement in HIV care, and contacted via email.
In total, 19 countries responded: Albania, Armenia, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Estonia, Georgia, Greece, Hungary, Lithuania, Macedonia, Poland, Republic of Moldova, Russia, Serbia, Turkey, and Ukraine. Most of the respondents were infectious disease physicians directly involved in HIV care (17/19). No country reported HIV clinic closures. HIV clinics were operating normally in only six countries (31.6%). In 11 countries (57.9%) physicians were sharing HIV and COVID-19 care duties. None of the countries expected shortage of ART in the following 2 weeks; however, five physicians expressed uncertainty about the following 2 months. At the time of providing responses, ten countries (52.6%) had HIV-positive persons under quarantine.
A shortage of resources is evident, with an impact on HIV care inevitable. We need to prepare to operate with minimal medical resources, with the aim of securing constant supplies of ART. Non-governmental organizations should re-evaluate their earlier objectives and support efforts to ensure continuity of ART delivery.
Numerical simulations of the KOBO extrusion process are presented in this paper. The coupled thermomechanical Eulerian-Lagrangian approach was applied for the three-dimensional finite element model. ...The dynamic explicit Euler forward method was used in numerical calculations. The elastic-plastic Chaboche model assuming isotropic and kinematic hardening under variable temperature conditions was applied to describe the behaviour of the material under cyclic loading. In numerical computations Chaboche material model implemented in commercial software, as well as the proprietary one written as FORTRAN procedure were tested. The numerical results present the stress and strain distributions in the extruded material, as well as an increase of temperature due to the plastic work and friction. The shape of plastic strain zones was verified experimentally. The approach presented in the paper is a promising numerical tool to simulate the KOBO process.
Objectives
Pre‐exposure prophylaxis (PrEP) for HIV infection is an important intervention for control of the HIV epidemic. The incidence of HIV infection is increasing in the countries of Central and ...Eastern Europe (CEE). Therefore, we investigated the change in PrEP use in CEE over time.
Methods
The Euroguidelines in Central and Eastern Europe (ECEE) Network Group was initiated in February 2016 to compare standards of care for HIV and viral hepatitis infections in CEE. Data on access to PrEP were collected from 23 countries through online surveys in May–June 2017 (76 respondents) and in November 2018–May 2019 (28 respondents).
Results
About 34.2% of respondents stated that tenofovir/emtricitabine (TDF/FTC) was licensed for use in their country in 2017, and 66.7% that it was licensed for use in 2018 (P = 0.02). PrEP was recommended in national guidelines in 39.5% of responses in 2017 and 40.7% in 2018 (P = 0.378). About 70.7% of respondents were aware of “informal” PrEP use in 2017, while 66.6% were aware of this in 2018 (P = 0.698). In 2018, there were 53 centres offering PreP (the highest numbers in Poland and Romania), whereas six countries had no centres offering PreP. The estimated number of HIV‐negative people on PreP in the region was 4500 in 2018. Generic TDF/FTC costs (in Euros) ranged from €10 (Romania) to €256.92 (Slovakia), while brand TDF/FTC costs ranged from €60 (Albania) to €853 (Finland).
Conclusions
Although the process of licensing TDF/FTC use for PrEP has improved, this is not yet reflected in the guidelines, nor has there been a reduction in the “informal” use of PrEP. PrEP remains a rarely used preventive method in CEE countries.
This paper presents the results of experimental studies and numerical simulations of the ratcheting for the PA6 aluminum. In the initial determination of the material hardening parameters, the ...samples were subjected to the symmetrical strain-controlled cyclic tension-compression test. The experimental stress-strain curve was compared with the numerical one obtained for non-linear Frederick-Armstrong and Voce models. For better fitting of both curves, the optimization procedure based on the least-square method and the fuzzy logic was applied. After establishing the hardening parameters, numerical simulations of the ratcheting were made. The boundary value problem was solved by means of discrete analysis. The data (force and displacement) obtained in numerical computations were used to control the ratchetting experiment. The results of experiments and numerical calculations were compared. Good convergence proves the reliability of the determination of material hardening data.
Fuzzy Logic Application to Strain-Stress Analysis in Selected Elastic-Plastic Material Models The common engineering practice is the selection of certain physical factors such as geometry, loading, ...boundary conditions, and material properties. In reality these data are more or less uncertain. In many engineering problems this uncertainty should be taken into consideration. Fuzzy set theory allows to determine randomness model response to the external loading. Two methods - extension principle and α-level optimization are presented and compared in this paper. Advantages and disadvantages of these approaches are discussed on example of mapping function. Next the extension principle and α-level optimization are applied to the analysis of stresses in the bar made of elastic-plastic material subjected to uniaxial tension. The yield stress and hardening modulus are fuzzy variables. The influence of fuzziness of numerical procedure (large integration step) to the result space is also discussed. The main part of this paper is the investigation of influence of selected fuzzy parameters of Bodner-Partom material model to stress analysis in the stretched bar. BP material model allows to take into consideration elastic and plastic material properties, isotropic and kinematic hardening, visco-plastic effects, as well as creep and relaxation. The proper response of the material to external loading requires the correct selection of fourteen material constants. The experimental determination of these data is problematic, and gives imprecise results. The increase of accuracy of BP material parameters may be achieved by application of optimization procedures or genetic algorithms. In this research for the first time the fuzzy sets theory is applied to accomplish this goal.
Fuzzy logic determination of the material hardening parameters based on the Heyer’s method was applied in this research. As the fuzzy input variables, the length of two measuring bases and the ...maximum force registered in the Heyer’s test were used. Firstly, the numerical experiment (the simulation of the fuzzification of the input data) with the assumed disturbance of input variables was performed. Next, on the basis of experimental investigations (eleven samples made from the same material), the membership functions associated with the input data were created. After that, the fuzzy analysis was examined. Fuzzy material hardening constants obtained by means of the α-level optimization and the extension principle methods were compared. Discrete values of the hardening data are found in the defuzzification process, by application of the mass center method.
The application of the linear micropolar theory to the strength analysis of bioceramic materials for bone reconstruction is described. Micropolar elasticity allows better results to be obtained for ...microstructural and singular domains as compared to the classical theory of elasticity. The fundamental equations of the Cosserat continuum are cited. The description of FEM implementation of micropolar elasticity is given. The results of solving selected 3D test problems are presented. Comparison of classical and micropolar solutions is discussed.
We discuss the finite element modeling of porous materials such as bones using the linear micropolar elasticity. In order to solve static boundary-value problems, we developed new finite elements, ...which capture the micropolar behavior of the material. Developed elements were implemented in the commercial software ABAQUS. The modeling of a femur bone with and without implant under various stages of healing is discussed in details.
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