The paper deals with the problem of identification of microstructure evolution model on the basis of two-step compression test. Classical interpretation of this test assumes uniform fields of strains, stresses and temperatures in the deformation zone and calculates the coefficients in the model on the basis of force measurements in the second step. In the present paper the inverse approach was applied. Finite element (FE) simulations of the compression test were performed and local values of microstructural parameters were determined accounting for the inhomogeneity of deformation. Objective function was formulated as the Euclid norm for the error between measured and calculated forces for various interpass times. Coefficients in the microstructure evolution model were determined by searching for the minimum of the objective function. Optimized model was validated in simulations of plane strain compression tests.
D. Szeliga, R. Kuziak, R. Kopp, G. Smyk and M. Pietrzyk
Z. Gronostajski, M. Hawryluk, R. Kuziak, K. Radwański, T. Skubiszewski and M. Zwierzchowski
The aim of the research was to determine the deformation condition of ECAP process of multiphase high strength aluminium bronze BA1032. The studies have indicated that it is possible to deform multiphase aluminium bronze BA1032 in the ECAP process at a temperature of 400°C and die angle Φ =110°. The deformation of the bronzes at lower temperatures encounters some difficulties - cracks appear which make repeated ECAP impossible. The cracks appear on the top surface of the samples where it contacts the surface of the outlet channel. FEM simulations show that the largest plastic strains occur in this area. The proposed ECAP method of large plastic deformations as applied to the investigated aluminium bronzes makes it possible to obtain very strong refinement especially of eutectoid α + γ 2.
A. Milenin, R. Kuziak, V. Pidvysots'kyy, P. Kustra, Sz. Witek and M. Pietrzyk
Residual stresses in hot-rolled strips are of practical importance when the laser cutting of these strip is applied. The factors influencing the residual stresses include the non uniform distribution of elastic-plastic deformations, phase transformation occurring during cooling and stress relaxation during rolling and cooling. The latter factor, despite its significant effect on the residual stress, is scarcely considered in the scientific literature. The goal of the present study was development of a model of residual stresses in hot-rolled strips based on the elastic-plastic material model, taking into account the stress relaxation.
Residual stresses in hot-rolled strips were evaluated using the FEM model for cooling in the laminar cooling line and in the coil. Relaxation of thermal stresses was considered based on the creep theory. Coefficients of elastic-plastic material model and of the creep model for steels S235 and S355 were obtained from the experiments performed on the Gleeble 3800 simulator for the temperatures 35-1100°C. Experiments composed small tensile deformations of the sample (0.01-0.02) and subsequent shutter speed without removing the load. Model of the thermal deformation during cooling was obtained on the basis of the dilatometric tests at cooling rates of 0.057°C/s to 60°C/s.
Physical simulations of the cooling process were performed to validate the model. Samples were fixed in the simulator Gleeble 3800, then heated to the temperature of 1200°C and cooled to the room temperature at a rate of 1-50°C/s. Changes of stresses were recorded. Good agreement between calculated and experimental values of stresses was observed. However, due to neglecting the effect of stress relaxation the stress at high temperatures was overestimated. Due to the change of their stress sign during the unloading process the resulting residual stresses were underestimated.
Simulation of residual stresses in rolling and cooling were performed on the basis of the developed model. It was shown that the effect of stress relaxation and phase transformations on the distribution of residual stresses in strips is essential and neglecting these factors could lead to an underestimation of residual stresses.