Issue 41

L. Patriarca et alii, Frattura ed Integrità Strutturale, 41 (2017) 277-284; DOI: 10.3221/IGF-ESIS.41.37 279 hardening;  is the shear modulus and  0 is a reference value. The expression for the evolution of  relies on a Voce type law:                                   0 1 , , 1 , n s p s p s v p T T T (4) In Eq. (4)  0 is the initial slope of the work hardening curve (in a   vs.  p plot); s n is the number of possible slip systems   s ;   v is the work hardening saturation strength. The definition of   y and   v rely on an Arrhenius type equation [15]:                                       1 1 0, 0, ˆ ˆ , , 1 ln p i q i i i p i p i i i p kT T S T g b (5) Where i S is a scale factor and  ˆ i is a constant for the saturation strength; k is the Boltzman constant; b is the magnitude of the Burgers vector; 0, i g is the activation energy;   0, i is a reference strain rate; i p and i q are statistical constants. P ARAMETERS IDENTIFICATION ccording the Eqs. (3)-(5), there are 16 unknown parameters which are required to be determined for the specific investigated alloy in order to perform the CP simulations. To identify the constants a tensile test was considered. The fitting of the tensile stress-strain curve, following the trial and error procedure, gave an estimation of the CP parameters (Tab. 1). The model used for this simulation was created starting from an EBSD scan of the specimen area showed in Fig. 1. This polycrystalline model was constructed to reproduce the real condition of the experiment, which was in displacement control. Fig. 1a shows the geometry of the tested specimen with a focus on the extracted area which was modeled with CP material. The entire model counts about 12000 linear hexahedral elements distributed over an area of 0.722 mm by 0.702 mm and a thickness of 0.04 mm. The model includes over 700 grains which were modeled columnar through the thickness. The simulation of the tensile test was carried out imposing a displacement to the upper surface of the volume and modeling a double symmetry on the other two surfaces. E    0 b  ˆ a  ˆ y 0, y g y q 195 GPa 0.33 80 GPa 3.5e-7 mm 0 MPa 120 MPa 2.37 1.8 y p   0, y  ˆ v 0, v g v q v p   0, y  0 0.9 1e10 s -1 65 MPa 1.6 0.34 0.5 1e7 s -1 24000 MPa Table 1 : Mechanical Threshold Stress model’s parameters identified by the tensile test simulation. The results in terms of stress-strain curves are shown in Fig. 1b: it is possible to observe a good agreement between the predicted tensile curve and the experimental one adopting the parameters listed in Tab. 1. A