Combined influence of geometric defects and thermal gradients on tensile ductility

Abstract

Finite element modeling of sheet tensile specimens has been performed in order to analyze the combined effect of initial geometric defects and thermal gradients on tensile stress-strain behavior. Isothermal tensile ductilities were predicted to decrease dramatically from 0.555 for a specimen with no taper to 0.116 for a specimen with 50 pct taper. The corresponding reductions in tensile ductility for assumed adiabatic conditions were found to be from 0.46 to 0.099. These results demonstrate that thermal gradients are most detrimental for initially uniform tensile specimens and have a smaller effect on tensile ductility for specimens with large initial geometric defects. As a proportion of total ductility, however, thermal gradients decrease ductility by a nearly constant value of 15.5 pct, independent of the size of the initial taper. Comparison of 2-D FEM results with a complete multi-element 1-D analysis indicates that the developed biaxial stress state in the neck accounts for increased total elongations. The increase in total ductility caused by the biaxial stress state in the neck increases with increasing size of initial geometric defect. These results question the value of 1-D analysis of sheet tensile test behavior.