A comparative study of the extended forming limit diagrams considering strain path, through-thickness normal and shear stress. (November 2018)

• Record Type: Journal Article
• Authors: Erfanian, Mozhdeh; Hashemi, Ramin
• Is Part Of: International journal of mechanical sciences. Volume 148(2018)
• Page Start: 316
• Page End: 326
• Publication Date: 2018-11
• Subjects: Extended forming limit diagram -- Prestraining -- Through-thickness normal stress -- Through-thickness shear stress -- M-k model; Mechanical engineering -- Periodicals; Génie mécanique -- Périodiques; Mechanical engineering; Maschinenbau; Mechanik; Zeitschrift; Periodicals; 621.05
• DOI: 10.1016/j.ijmecsci.2018.09.005
• Languages: English
• ISSNs: 0020-7403

Abstract

Highlights: The M-K model and Yld2011 advanced anisotropic yield criteria are employed for obtainning forming limits of AA2008-T4. Effect of bi-linear strain path, through-thickness normal and shear stresses are being investigated on different forms of forming limit presentation. Under non-proportional loading condition, diagrams in stress space (i.e., FLSD and XSFLD) are less sensitive to strain paths than PEPS-FLD. The effect of normal stress is more considerable than shear stress in increasing formability of sheet metal. Extended forming limit diagrams are not independent of out-of-plane stresses and the variation depends on the variables of the coordinate plane. Abstract: The substitute presentations of the conventional forming limit diagram (FLD) are stress-based forming limit diagram (FLSD), extended stress forming limit diagram (XSFLD), and polar effective plastic strain forming limit diagram (PEPS-FLD). These diagrams have already been proposed as alternative criteria to the conventional FLD for predicting forming limits in processes that sheet does not experience proportional or in-plane loading conditions. The present study provides a complete comparison of different forms of forming limit diagrams. For this purpose, FLD and extended FLDs are predicted based on the modified Marciniak and Kuczynski (M-K) model with Yld2011 anisotropic yield function while various factors that cause a change in the FLD of a specific alloy including initial imperfection coefficient ( f 0 ), non-linear strain path, through-thickness normal and shear stresses are considered. The results indicate that all forms of extended diagrams are independent of strain path and the diagrams in stress space (i.e., FLSD and XSFLD) are less sensitive to the strain path than PEPS-FLD. In this regard, the main weakness of XSFLD, especially on the right-hand side, is that the safety margin cannot be visualized easily. By increasing the initial imperfection coefficient, the level of all forms of diagram increases. However, the effect of through thickness stresses on different diagrams is not the same. Increase in normal and shear stresses results in a downward shift in FLSD and an upward shift in other types of forming limit diagrams. Graphicalabstract :