Assessment of void growth models from porosity measurements in cold-drawn copper bars

This work investigates void growth in cold-drawn copper bars containing a fine dispersion of small inclusions at which voids nucleate. Using the Rice and Tracey (RT), the Gurson-Tvergaard (GT), and the Gurson-Leblond-Perrin (GLP) void growth models, a procedure is proposed for deriving the porosity distribution from density measurements on specimens sectioned from the neck of a tensile bar. This procedure allows identification of the parameters of the models. The effect of strain hardening on porosity evolution is analyzed by comparing the behavior of the material in the cold-drawn state (n≈0.1) and in the recrystallized state (n≈0.4). Inclusion dimensions and distributions were found to be identical in these two states. The parameter α of the RT model is found to depend on n, whereas the parameter q of the Gurson-type models does not vary with n. Numerical modeling of porosity variations in notched, round copper bars shows that both the parameter α and the parameter q in the GT model depend on the stress triaxiality in the recrystallized material, whereas the parameter q remains a constant in the GLP model. Accounting for the ellipsoidal void shapes and for the presence of the inclusion significantly affects the prediction of porosity variations.