An Investigation of ductile fracture criteria for sheet metal forming /

Abbasnejad Dizaji, Shahram
Deep drawing is a sheet metal forming process in which a sheet metal stock, commonly referred to as a blank, is drawn into a die by a punch. Forming limit diagram (FLD), a representation of the critical combination of the principal surface strains, is an important concept utilized for the evaluation of the formability of sheet metals. Most of the theoretical methods for determining FLDs are strain-path dependent and cannot exactly clarify the location of necking or fracture. Using stress-based forming limits (FLSD) can resolve this problem, but numerical implementations of the FLSDs are difficult and sometimes not reliable. Another way to determine the limits of formability is to apply a ductile fracture criterion (DFC). The main goal of ductile fracture criteria is to predict the location of the fracture in the sheet metals and overcome the deficiency of strain path dependency of FLDs. The objective of the present thesis work is to develop a robust DFC for sheets. The algorithm of proposed criterion is implemented into a commercial explicit finite element code by using user-defined material subroutines. Recently developed constitutive models are used with appropriate hardening rules in the explicit code. The results of numerical implementations are compared with the results of the other known criteria and the experimental tests to validate the newly developed criterion. It is observed that the newly developed ductile fracture criterion can be used efficiently for different materials and predicts the fracture initiation better than the existing DFCs.
Citation Formats
S. Abbasnejad Dizaji, “An Investigation of ductile fracture criteria for sheet metal forming /,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.