چكيده به لاتين
In forming processes, knowing the maximum allowable amount of deformation which material can bear before necking is really essential. For this purpose forming limit diagram obtained with the assumption of plane stress state and linear loading path by Nakajima tests or theoretical approach, was proposed as a first solution for knowing forming limits of sheet metal. But soon it becomes clear that because of these simplifying assumption, the diagrams are not accurate enough and no longer can predict forming limit in manufacturing processes that impose non-linear and 3D state of stress on sheet metals, precisely.
For overcoming these problems, extended diagrams including stress forming limit diagram (FLSD), extended stress forming limit diagram (XSFLD) and polar effective plastic strain diagram (PEPS-FLD) have been proposed. In present study based on modified Marciniak and Kuczynski (M-K) method with Yld-2011 anisotropic yield function, which is proven that can describe an anisotropic behavior of sheet metal precisely, the effect of different factors, including non-linear strain path, normal and shear through-thickness stresses are investigated. The reason for considering these factors is to bring the predictive conditions closer to the actual conditions of the sheet in industrial forming processes and thus to increase the accuracy of the resulting diagrams. Another purpose of this research is to study the extended diagrams under the conditions mentioned above and to compare them.
Keywords: M-K numerical method; extended forming limit diagrams; pre-strain; normal stress; shear stress.
