This study presents the rheological properties of sewage sludge after conditioning with the application of biomass ash. The impact of sewage sludge pre-treatment on its viscosity, flow curves and thixotropy was investigated. The increase of shear stress and the decrease of viscosity were observed with the increase of shear rate. Obtained results were compared with raw sewage sludge and the sludge after modification by means of polyelectrolyte in the dosage of 1.5 g (kg d.m.)^-1. The findings proved that samples of raw and conditioned sewage sludge had thixotropic characteristics. The correlation between moisture content and capillary suction time reduction as well as selected rheological parameters were also determined. On the basis of the obtained results it was stated that the Ostwald de Vaele model best fits the experimental data.

The FEM simulations of the ECAP including real conditions of the process – the friction between the metal extruded and the die walls, as well as, the channels rounding, were done here in two scales – macro- and micro-. The macroscopic analyses were done for isotopic material with a non-linear hardening using the UMAT user material procedure. The pure Lagrangian approach was applied here. The stress, strains and their increments, as well as, the deformation gradient tensor were recorded for selected finite elements in each calculation step. The displacements obtained in the macroscopic FEM analysis are then used as the kinematic input for the polycrystalline structure. The dislocation slip was included as the source of the plastic deformation here for the face-centered cubic structure. The results obtained with the use of the crystal plasticity show the heterogeneous distribution of stress and strain within the material associated with the grains anisotropy. The results in both micro- and macro- scales are coincident. The FEM analyses show the potential of the application of the crystal plasticity approach for solving elastic-plastic problems including the material forming processes.

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.

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.