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196 Costică Atanasiu et al. elasticităţii şi se fac verificări numerice prin MEF pentru a determina tensiunea de rupere la forfecare, iniţierea fisurii şi forma secţiunii de rupere. Cercetarea dovedeşte avantajele folosirii materialelor cromoplastice în cercetările din domeniul elasto-plastic şi plastic.
BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Publicat de Universitatea Tehnică „Gheorghe Asachi“ din Iaşi, Tomul LVIII (LXII), Fasc. 4, 2012 Secţia CONSTRUCŢII DE MAŞINI DETERMINATION OF SHEETS METAL ROUGHNESS VARIATION DEPENDING ON TENSILE STRAIN BY OVIDIU NIŢĂ ∗ , VASILE BRAHA and ANDREI MIHALACHE Received: October 13, 2012 Accepted for publication: October 15, 2012 „Gheorghe Asachi” Technical University of Iasi, Department of Machine Manufacturing Technology Abstract. The aim of this paper is to determine, using an experimental method, a mathematical relationship of interdependence between thin sheets surface roughness and deformation reached in the uniaxial stretching. By determining this relationship is intended to verify the hypothesis that the roughness can be used as a criterion for the occurrence of deformation limit. Also, the authors wanted to highlight how the rolling direction of the material influences the peak strain. Key words: roughness, uniaxial stretching, deformation limit, rolling direction etc. 1. Introduction The easiest method of estimate the deformability of sheet metal blanks used in stamping processes is the forming limit curve method (FLD). This curve provides an indication of admissible deformation in a certain area of piece during its deformation (Banabic et al., 1992). As a result we can say that the size of admissible deformations is dependent on the piece rejection criteria: necking or fracture. However, if we are talking about the quality of sheet metal parts, obtained by cold forming processes, we must view the whole range of defects that may occur in the process of drawing (Charca et al., 2010). Thus, along necking or material fracture, wrinkling or thinning of material, any major changes in the appearance or roughness of parts surfaces may be leading to ∗ Corresponding author: e-mail: ov_nita@yahoo.com
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