buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

206 Ovidiu Niţă and Vasile Braha
necking and another one for breaking (Marciniak, 2002; Banabic, 2008).
However, the moment when the necking of material occurs is considered a
deformation limit and this is almost unanimously accepted to be the criterion
that defines the forming limit curve (FLC) of a specific material (Bressan,
2003).
a b
Fig 1 – Forming limit diagram (FLD)
a – FLD (www.eqsgroup.com); b – forming limit curves (FLC) (Marciniak, 2002).
The main objective in developing the proposed paper was to evaluate
how the deformation limit curves characterize the deformation capacity of a
specific material. While the forming limit diagram is the currently the most
widely used tool for assessing the deformability of sheet metal plates, the
approach was intended to identify and study the main factors that affect, or not,
the quality of information transmitted by FLD.
2. Experimental Testing Conditions
2.1. Methods and Equipment Used
The most common method used to determine, experimentally, the
forming limit diagram of deformation is the “network” method. On the surface
of the blank, which will be subjected to a deformation process, the operator will
print a rectangular, circular or radial-circular network (Fig. 2).
a b
Fig. 2 – Circular network with interleaved patterns:
a – before deformation; b – after deformation.