Issue 39

O. Daghfas et alii, Frattura ed Integrità Strutturale, 39 (2017) 263-273; DOI: 10.3221/IGF-ESIS.39.24 266 Figure 3 : Experimental tensile curves obtained at RD, DD and TD from the RD. The 7075-T7 aluminum alloy has high mechanical properties both in terms of strength and ductility compared to pure aluminum A5 [16]. Maximum yield R e and tensile R m strengths are observed especially in the transverse direction but a significant decrease in percentage elongation A%. This is explained by the structural hardening. The commercialized aluminum alloy in T7 temper is much stronger than pure Aluminum (around 40 MPa against 430 MPa for the yield strength), but it has a failure elongation (maximum plastic deformation of 0.13 against 0.27 for pure aluminum). According to the experimental results we are seeing the influence of the anisotropy on the specimen fracture especially after transverse loading (90°). We present in Tab.1 the experimental Lankford coefficients relating to three loading directions. ψ r(ψ) 00° 0.069 45° 0.138 90° 0.099 Table1 : Experimental Lankford coefficient for different loading directions. The anisotropy coefficient illustrates the deformation mode of the metal sheet. A small Lankford Coefficients indicated by 7075-T7 led to a significant reduction in thickness. The tensile test is the simplest and most widely used because it allows obtaining a lot of information (elastic modulus, yield strength, maximum load, elongation at break ...) and maintaining a homogeneous strain in the useful part. A NISOTROPIC ELASTO - PLASTIC MODEL his work is limited to plastic orthotropic behavior. The materials are treated as incompressible with negligible elastic deformations. Models are formulated for standard generalized materials with an isotropic hardening described by an internal hardening variable, a law of evolution and an equivalent deformation. The material is initially orthotropic and remains orthotropic; isotropic hardening is assumed to be captured by a single scalar internal hardening variable denoted by p  . T