4 monographs, 8 university textbooks, 6 university notebooks and more than 200 publications in journals and conference proceedings at Slovakia and abroad. He has been worked on many grant projects, research tasks and projects for industry. KEY WORDS ABSTRACTRolling of metallic materials results to anisotropy of their mechanical properties during plastic deformation. In the paper are described some possibilities of analytical and experimental determination of conditions for plastic deformation of cold rolled steel sheets. The experimental analysis is realized by biaxial tensile test with application of strain gage and optical methods. The results gained by experimental procedures are compared with yield conditions according to individual theories. INTRODUCTIONClassical semifinished products that are used for production of thin-walled supporting systems are steel sheets. In order to increase competitiveness of steel there were recently provided massive innovations in the area of new qualities of steel sheets. Increasing of loading capacity and decreasing of structural weight is possible by using of steel sheets with smaller thickness made of materials with higher strength properties. Because the thin-walled elements are often produced by cold forming, there is an effort here, beside of reaching higher strength properties, to preserve (or increase) their plastic properties [7]. Identification of beginning of plastic deformation for plane stress state of sheets is important for modeling of cold forming processes as well as for assessment of loading capacity of thin-walled supporting structural elements. The conditions under which the material yields (beginning of plastic deformation) are called initial yield conditions. In case of material hardening during its plastic deformation we call these current yield conditions. Because the cold rolling of steel sheets changes random arrangement of crystals Fratišek Šimčák (SK)