EXPERIMENTAL DEFINING OF NORMAL ANISOTROPY COEFFICIENT AS FORMABILITY FACTOR OF THIN CAR BODY SHEETS

Abstract

It is well known that anisotropy have very significant influence on car body sheet metals formability in deep drawing process. At the other hand deep drawing is essential technology of all car body parts. Anisotropy can be observe as planar and orthogonal (normal). For deep drawing more significant is normal anisotropy which is represent by coefficient of normal anisotropy or plastic strain value or so called "r" factor. It is numeric value which is obtaining experimentally by uniaxial tension in field of homogenous plastic strain. There is no precise recommendation about intensity of maximal allowed plastic strain during the tensile experiment. In this paper presented is experimental investigation of smaller plastic strains intensities influence on final "r" value. Used are two thin sheet metals: stainless steel X5CrNi18-10, 0.8 mm nominal thick and Al alloy sheet AlMg4.5Mn0.7 (i.e. ENAW 5083) 1 mm nominal thick where the samples are cut in the rolling direction for both materials. Plastic strain was relate to maximal homogenous plastic strain Ag in the following way: 10, 20, 30, 40, 50, 60, 65, 70 and 75 percent of Ag. After the results evaluation can be concluded that there is relatively small influence of plastic strain intensity on "r" value occurred i.e. determining of "r" value can be successfully obtained with smaller intensity of plastic strain.