Issue 48

F. V. Antunes et alii, Frattura ed Integrità Strutturale, 48 (2019) 666-675; DOI: 10.3221/IGF-ESIS.48.63 668 specimen was modeled considering adequate boundary conditions, as indicated in Fig. 1a. A cyclic load was applied remotely from crack tip, as illustrated in Fig. 1a, with F max =400 N; F min =4 N (R=0.01). The material studied was the 7050-T6 aluminum alloy, which is strengthened mainly by the addition of Zn, Mg and Cu. The T6 heat treatment comprises homogenization and aging, producing hardening by precipitation. The AA7050-T6 has excellent properties, namely good fracture toughness, high strength and stress corrosion resistance, making it ideal for applications in aircraft industry  21, 22  . Cyclic stress-strain hysteresis loops, obtained in smooth samples, were used to fit the hardening models. The elastic-plastic model adopted assumes that the plastic behavior follows the von Mises yield criterion, coupled with Voce isotropic hardening law  23  : 0 Sat 0 Y( ) Y (Y Y )[1 exp( C )] p p Y        (1) where Y 0 , Y Sat and C Y are material parameters and p  is the equivalent plastic strain, and Lemaître-Chaboche non-linear kinematic hardening law  24  : p X Sat C X             σ X X X   (2) being C x , and X sat material parameters. Table 1 shows the identified set of material parameters of Voce and Lemaître- Chaboche laws. Fig. 1 compares experimental results with the analytical model proposed here. Several load cycles were applied and the cumulative plastic strain is plotted versus stress. An excellent agreement can be seen, indicating that the analytical model is able to simulate the cyclic plastic deformation. Y 0 [MPa] Y sat [MPa] C Y C x X sat [MPa] 420.50 420.50 3.806 228.91 198.35 Table 1 : Material parameters for the 7050-T6 aluminum alloy. Figure 1 : Accuracy of material’s model: experimental results versus analytical model. -800 -600 -400 -200 0 200 400 600 800 0 25 50 75 100 125 Stress [MPa] Equivalent plastic strain [%] AA7050-T6 Fit Voce law parameters Lemaître-Chaboche law parameters