Due to inappropriate agricultural treatments, soils often turn into wastelands. After years, the return to cultivation is very difficult or even impossible. It is a serious problem for agriculture, also in Poland. In order to improve soil quality and to restore its value in use, different fertilizers are commonly used. As an alternative for artificial fertilizers, sewage sludge and biomass ashes might be applied. High cost of sewage sludge conditioning with the use of polyelectrolytes has resulted in the development of research dedicated to finding new and inexpensive conditioners. The article discusses the possibility of sludge conditioning by means of wood biomass ash. In the paper, the findings of sewage sludge dewatering with the use of wood ash on a laboratory and on a technical scale are presented. The analysis of results has shown that the addition of wood biomass ash improved sludge dewatering by 10–23% in a laboratory scale and by 15–27% on a technical scale. The application of wood ash also reduced the total bacteria number by 83–89% in a laboratory scale and by 40–53% on a technical scale. Additionally, the obtained mixture of sewage sludge and wood biomass ash might be applied in agricultural practices, especially in fertilizing perennial plants plantations. Thanks to that it is possible to obtain inexpensive and valuable natural fertilizer while reducing costs of sludge dewatering.

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.

Numerical simulations of the extrusion process assisted by die cyclic oscillations (KOBO extrusion) is presented in this paper. This is highly non-linear coupled thermo-mechanical problem. The elastic-viscoplastic Bodner–Partom-Partom material model, assuming plastic and viscoplastic effects in a wide range of strain rates and temperatures, has been applied. In order to perform simulations, the user material procedure for B–P material has been written and implemented in the commercial FEM software. The coupled Eulerian–Lagrangian method has been used in numerical computations. In CEL method, explicit integration of the constitutive equations is required and remeshing is not necessary even for large displacements and large strains analyses. The results of numerical simulations show the heterogeneous distribution of stress and strain inside container and the non-uniform distribution of strain in the extruded material. The increase of material temperature has been noted. The results obtained (stress, temperature, location of plastic zones) qualitatively confirm the results of experimental investigations. The application of the user material procedure allows accessing all material state variables (current yield stress, hardening parameters, etc.), and therefore it gives detailed information about phenomena occurring in extruded material inside recipient. This information is useful for a proper selection of parameters of the KOBO extrusion process e.g. synchronization of the punch displacement with the die oscillations frequency to avoid the saturation of material isotropic hardening, which blocks the progress of extrusion.