Papers by Author: Petr Ponížil

Abstract: Physical properties of polymer foams depend on their macrostructure. In this paper, we study a range of polyuretane foams from the stereological point of view. Images of plane surfaces of studied samples were created by printing them on a sheet of paper and scanning these imprints. Consequent operations included reconstruction of pore section areas in the plane of printing and computation of pore volumes. The distribution of pore section was compared with data from computer tomography (CT) in order compare both methods.

Abstract: Experiments were conducted on extremely coarse-grained pure copper to evaluate the effect of equal-channel angular pressing (ECAP) on microstructure evolution in the as-pressed state and after creep exposure using various stereological methods. The microstructure formed by severe plastic deformation is an unusual structure which can be hardly characterized only by the mean grain size especially after low number of ECAP passes. The purpose of this paper is a detailed examination of (sub)boundaries and grain boundaries in the microstructures of the pressed material. The inhomogeneity of deformed microstructures is also evaluated. The detailed description of ECAP microstructures should contribute to the better understanding of mechanical properties of the pressed materials.

Abstract: The estimation of grain size (volume) by using computer database of tessellations is explained and demonstrated. As model material was selected an anisotropic material formed by compression-moulded pellets of PVC. The pellets were first covered with carbon paste to highlight borders of grains in final specimen and then moulded; their volumes were exactly known. Standard profile and intercept counts were carried out on the planar sections of the specimen and used to estimate the grain size by means of computer database. The obtained estimates were then compared with the known pellet characteristics. The estimation of grain volume and of other suitable characteristics by inspection of section planes is necessary in opaque materials (e.g. metal alloys, crystalline polymers, ceramics), where their values are inaccessible by direct measurements. The aim of this work is show that the standard approaches can be improved with the help of a suitably prepared computer database.

Abstract: In an analogy to the 3D tool of tessellation classification – w−s diagram, a similar graphical device is proposed for 2D tessellations. Any tessellation is represented by a point in the Cartesian coordinate system with the axes Ep (the mean cell perimeter) and CV a (the coefficient of cell area variation). Images of tessellations and p−CV a diagrams for selected tessellations with low and high values of CV a are shown as examples.

Abstract: The estimators proportional to (NA(x,y)NA(x,z)NA(y,z))1/2 and (NL(x)NL(y)NL(z)) obtained by profile and intercept counts are recommended by ASTM Standards E 112 for 3D grain intensity l of anisotropic grain structures (NA(•) are estimated in three mutually perpendicular planes suitably oriented with respect to the prevailing anisotropy direction and NL(•) are intercept intensities along three suitably selected mutually perpendicular directions). However, l is also related to the profile and intercept intensities l', l', namely l= c'(l')3/2= c'(l')3. The induced intensities are estimated by arithmetic means NA = (NA(x,y)+NA(x,z)+NA(y,z))/3, NL = (NL(x)+NL(y)+NL(z))/3. A simple model isdeveloped, in which the role of geometric and arithmetic means of profile and intercept counts in the grain size estimation is elucidated. Its results are compared with computer simulated random tessellations with prevailing rod-like and plate-like cells and applied to anisotropic grain structures of pure Al produced by ECAP and to platinum based composite Pt - 0.5 Y2O3.