Papers by Keyword: Modeling

Abstract: The paper presents a mathematical model for calculating cutting forces during the machining of 16MnCr5 steel using the Sandvik CNMG 120408 16P25T tool. The modeling process involved the use of a test rig constructed based on the 16Д25 machine, which enabled the measurement of real values of spindle speed, longitudinal feed, cutting depth, and cutting forces. The results transmitted to a computer through the LTR-EU-8 workstation, equipped with galvanic isolated LTR modules and a synchronization interface. Based on the experimental results, the theoretical model demonstrated a deviation from actual measurements of no more than 4.72%. The study provides evidence that the cutting force calculations commonly presented by leading tool manufacturers are inherently overestimated. he difference in cutting forces can be 9%.

Abstract: The combination of advection and migration of grain boundaries is analyzed on the basis of a simple mesoscale model, where parallelepipedic grains are considered under uniaxial compression straining. Strain hardening and dynamic recovery are described by the classical Yoshie-Laasraoui-Jonas equation. Grain-boundary migration is driven by the difference in dislocation densities between one representative grain and the average over the material. Finally, nucleation is assumed to occur at grain boundaries. Special attention is paid to the aspect ratio, which starts from unity (infinitely small cubic nucleus) and tends to zero when the grain disappears. In spite of the role of migration, the average shape of the grains is determined as a first approximation by their lifetimes.

Abstract: Phase boundaries of the pseudo-binary Fe-C diagram are key inputs for the prediction and understanding of matrix phase transformation in steels. The mechanical properties, of such steels, however, are often not dictated by the individual phase fractions, accessible through CALPHAD calculations, but by the arrangement of the phases, i.e., the steel’s microstructure. The prediction of these microstructural constituents requires the application of additional models, which are reviewed in the present contribution. Additionally, the current use and limitations for industrial application are presented together with an outlook to future challenges and opportunities in this field of research.

Abstract: This work deals with the prediction of time-to-rupture (TTR) diagrams of martensitic 9-12% Cr steels. Martensitic 9-12% Cr steels are state of the art materials for powerplants due to their high creep strength and oxidation resistance. Since the experimental determination of TTR diagrams is costly and time-expensive (minimum 10 years), it is of particular interest to be able to model TTR diagrams and gradually replace experiments. Here, we approach the question to what extent we can generate a TTR diagram of a material out of a fraction of experimental results plus detailed understanding of the underlying microstructural/physical phenomena during creep. Our model is based on dislocation creep and includes multiple interactions between the microstructural constituents. We show the applicability of our approach by reproducing a TTR diagram of the well-known material P92. Input parameters are basic material data from literature, the starting microstructure before creep, chemical composition, some model parameters determined on the similar material P91, and one single creep curve of P92. The precipitate evolution is simulated by the software MatCalc, the other microstructural constituents (dislocation densities, subgrain boundaries etc.) by our creep model. By varying the stress between individual creep simulations whilst keeping all input parameters (starting microstructure, temperature and material parameters) constant, we produce multiple creep curves and thus generate the complete dataset for a TTR diagram. The model is of particular interest when it comes to the development of new materials, as the application range of these materials can be estimated quickly and with good reproducibility.

Abstract: Additive manufacturing (AM) provides numerous advantages compared to conventional manufacturing methods, such as high design freedom and low material waste. Among the available materials, precipitation-hardenable aluminum alloys are highly attractive for AM due to their high specific strength and low density. Precise control of the processing conditions during AM and post heat treatment (HT) is required to tailor the final mechanical properties. Consequently, many variables, such as the chemical composition and process and HT parameters, must be considered to design suitable alloys for AM. Experimental investigations are, however, limited in variation of these variables. Therefore, computational alloy design approaches allowing for a faster evaluation of many possible variations must be developed. This work presents a high-throughput approach to determine the precipitation kinetics and thermodynamic properties based on the CALculation of PHAse Diagrams (CALPHAD) method. The developed approach is successfully validated for an Al-Mg-Si-Ti-Fe alloy and is applied to screen 243 combinations of chemical compositions and HT parameters. The results confirm the microstructural stability of the Al-Mg-Si-Ti-Fe system to small composition variations.

Abstract: The effect of part geometry on premature thin wall part failure in laser powder bed fusion (LPBF) is investigated using FEM simulation. Two FEM models are used to simulate the residual stress and buckling modes. Two experimental parts with different lengths are used for model validations. A LPBF FEM model evaluates the residual stress associated with the two experimental parts. A parametric buckling model is developed to determine the eigenvalues for 100 different part geometries including different part lengths (20-60 mm), widths (0.5-2 mm), and heights (10-50 mm). The results show that thin wall parts are more susceptible to buckling mode 1 when part length is small and to a combination of mode 1 and 3 when part length increases. In both cases the threshold stress for buckling is mostly sensitive to part thickness and height.

Abstract: This article discusses the use of solar dryers as a method for stabilizing and reducing the volume of residual sludge produced by wastewater treatment facilities. The study focused on the convective drying behavior of sewage sludge produced by the wastewater treatment plant of Meknes City under convective solar drying. The study aimed to investigate the drying kinetics of sewage sludge and emphasize the effect of temperature and water content on the evolution of the drying rate. The measured water content values showed a decrease as drying time increased. The results revealed the presence of phase II, which characterizes the decreasing rate drying period, and the absence of phase I, which describes the constant rate drying period.The study developed an empirical model to describe the kinetic behavior of convective solar drying of Moroccan domestic sludge. The model can be used to predict the shape of a drying curve under other aerothermal conditions. Additionally, the study analyzed the thermal diffusivity and activation energy of sewage sludge using an experimental macroscopic method based on Fick's diffusion model and the Arrhenius equation. The measured diffusion coefficient values range from 0,71 10^-9 m².s^-1 to 1,47 10^-9 m².s^-1, and the value of activation energy was evaluated at 17.54 kJ/mol.

Abstract: Molecular dynamics simulations were used to model <100> silicon pillars with diameter and spacing of 2.2nm and in a square lattice. Isopropanol (IPA) was added as a wetting liquid, and evaporation of the IPA was simulated to induce capillary forces that can cause pattern collapse. The cylinders were stable up to an aspect ratio of 8, while pillars higher than that collapsed. Additionally we simulated the thermal vibration of silicon pillars with diameters and spacing of both 2.2nm and 4.3nm without the presence of liquid at 300K. The Young's modulus of these pillars was estimated using the mean square displacement of the vibrating pillar tips, and results showed that the modulus decreases significantly from the bulk value for these structures.

Abstract: A membrane reactor is a multifactional vessel used for H₂ production. Hydrogen's three spectrum colors are dependent on carbon present. Two types of membrane with high permeability to hydrogen (polymeric and metallic) Hydrogen is produced in two systems: conventional reactors and membrane reactors (which separate and purify hydrogen in a single vessel). There are many types of membrane reactors according to design (catalytic membrane reactor (CMR), fixed bed reactor (FBMR), fluidized bed reactor (FBMR), etc. The transport mechanism of H₂ through the membrane by a "sorption-diffusion mechanism" and the government equations that are used for membrane reactor modeling and simulation, such as continuity, momentum, mass, and heat transfer equations of the CMR, and the thickness of the membrane. These equations are solved by MATLAB, COMSOL, and the Finite Element Method to simulate the MR at different parameters: rate of conversion, rate of sweep gas, temperature, pressure, rate of H₂ permeation through a membrane, and activity of the catalyst. We summarized theoretical studies for membrane reactors, including the operation conditions, type of hydrocarbon feed, type of production method, kind of catalyst, and heat effect.

Abstract: Reinforced concrete shear walls, which are vertically oriented plate-like elements, are efficient members in controlling the response behavior of buildings against seismic actions. In this research work, the performance of reinforced concrete buildings with shear walls having different shear wall-to-frame stiffness ratios is investigated. The considered buildings were designed in compliance with the requirements of the Algerian seismic code RPA99v2003 and were supposed to be located in regions of high seismicity. Seven 3D finite element models with different shear wall-to-frame stiffness ratios were developed and assessed using the nonlinear static analysis. Engineering Demand Parameters (EDPs) such as lateral displacement, inter-story drift ratio, shear force, and bending moment along the building height were presented. The results clarified that the induced responses can be classified into two major groups: force-based and displacement-based EDPs. Moreover, as the shear wall-to-frame ratio increases, the observed force-based EDPs increase whereas the displacement-based EDPs decrease. From a force point of view, distributing shear walls so that the packet of stiffness is lumped at the center of the building, model G with a stiffness ratio of 6.0906, amplifies the induced forces. This distribution requires more reinforcements and can lead to a conservative design. From a displacement point of view, distributing shear walls so that the packet of stiffness is lumped at the periphery of the building, model C with a stiffness ratio of 1.7879, minimizes the induced shear force and bending moment and produces the lowest values. This represents the optimum case with maximum performance and minimum strength.