Comparative study on theoretical and experimental evaluation of forming limit diagrams

11th Hungarian Conference on Materials Science

Béres, G.^1 ; Weltsch, Z.^1 ; Tisza, M.^2

John von Neumann University, Faculty of GAMF Engineering and Computer Science, Str Department of Materials Technology, Kecskemét, Hungary^1

University of Miskolc, Faculty of Mechanical Engineering and Informatics, Institute of Materials Sciences and Technology, Miskolc-Egyetemváros, Hungary^2

关键词: Comparative studies;    Deformation history;    Experimental determination;    Experimental evaluation;    Forming limit diagrams;    Measuring equipments;    Semiempirical models;    Time-consuming procedure;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/426/1/012005/pdf
DOI  :  10.1088/1757-899X/426/1/012005

来源: IOP

【 摘 要 】

Forming limit diagrams (FLDs) are generally used to reflect the strain limits of sheet metal materials. These diagrams contain essential information for planning of high series stamping processes, however the experimental definition is still a difficult and time-consuming procedure. Five or more samples are needed to cover the different strain paths sufficiently, from pure shear (1 = -22) up to biaxial stretch forming (1 = 2), moreover the experimental detection of the onset of local necking depends on the capability of the measuring equipment and person. The determination of the measurement results is further complicated by the material and other influencing conditions, like strain path (deformation history), rolling direction, sheet thickness, temperature, measuring grid size, tool surfaces, friction and vibrations. All these things supports the development of clearly theoretical and semi-empirical models for defining FLDs. This paper presents a comparative study of some kind of well-known theoretical models and experimental FLDs of automotive dual phase (DP) thin sheets. The experimental determination was carried out by Nakajima tests on five different sample geometries. We used follow-up strain analysis on the cracked samples. The results highlighted that most of the theoretical and semi-empirical models can be appropriately used in the negative quadrant of the FLD despite of the effect of the friction. However, in the positive quadrant, there are some more visible deviations due to outer conditions like lubricant.