Issue 39

O. Daghfas et alii, Frattura ed Integrità Strutturale, 39 (2017) 263-273; DOI: 10.3221/IGF-ESIS.39.24 270 Using the identified anisotropic coefficients, the evolution of Lankford coefficient and the anisotropy based on off-axis angles are presented in Fig. 5(a) and Fig. 5(b) respectively. Fig. 5 (a) displays the evolutions of Lankford coefficient based on off-axis angle ψ . A good agreement has found between experimental and predicted Lankford coefficients with respect to the rolling direction. Thus, the behavior model describes very satisfactory the plastic behavior of this alloy because its yield function and its hardening law are suitable for aluminum alloys. The evolution of anisotropy of 7075-T7 is more pronounced especially in 45°direction from the rolling direction (see Fig. 5(b)), therefore the 7075-T7 is more suitable for forming process for the manufacture of the aerospace parts. It is shown that this material has the best performance for plastic forming for the 45° direction from the rolling direction. (a) (b) Figure 5 : (a) Evolution of Lankford coefficient (b) Evolution of the yield stress anisotropy based an off axis  . Third identification step: validation In order to validate the behavior model, the experimental tensile curve in transverse direction and the identified anisotropic parameters of behavior model are used. Fig. 6 shows a good agreement between the theoretical results of behavior model and the experimental data for transverse direction. Evolution of the yield surface in deviatory plane   x x 2 3 , and the yield stress anisotropy After having identified and validate the behavior model, we will study the evolution of load surfaces for several tests and the stress anisotropy of material.