Abstract. This short paper describes the simulation results obtained with the elasto-hysteresis model implemented in the finite element software Herezh++ and compares them with the experimental data of the Roundrobin SMA Modelling benchmark.
The elastohysteresis modelAs proposed in [1,2], the permanence of the simultaneous existence of reversible processes and hysteresis in the thermomechanical behaviour of shape memory alloys suggests to express the total stress σ as the addition of two partial stresses, the first σ r being hyperelastic while the second one is related to hysteresis of elastoplastic type [3][4][5]. A 1-D illustration of the "elastohysteresis model" is shown in figure 1a. In the present work, the partial hyperelastic stress tensor is calculated from the hyperelastic potential proposed by Orgéas [6,7], which leads in the 1-D case (shear test) to the stress-strain curve shown in figure 1b. In the case of shape memory alloys [2], the potential ω = ω(V, Q ε , ϕ ε ) is expressed as function of 3 invariants of the Almansi strain tensor: the relative variation of volume V, the intensity of the deviatoric deformation Q ε , and ϕ ε a measure of the angle giving the direction of the deformation tensor in the deviatoric plane. The hysteresis is described by an incremental model of hypoelastic type :σ = 2µD + βφ∆ t Rσ and an algorithm to manage discrete memory points σ R introduced by P.Guélin [3] and used in the model.D is the deviatoric strain rate tensor and ∆σ = σ(t) − σ R . More details can be found in [2,[4][5][6]9]. Figures 1b-e show the meaning of the parameters used in this work.
Process to parameter identificationFirstly, eight parameters independent of the temperature are used in this model, including 6 parameters involved in the hyperelastic potential and 2 parameters of the hysteresis scheme. The 6 parameters independent of the temperature of the hyperelastic potential (cf. fig. 1 b ) are: the 3 slopes: µ 1 µ 2 µ 3 , the 2 curvatures for the transitions: α 1 α 2 and the bulk modulus K. The 2 hysteresis parameters indepedent of the temperature (cf. fig. 1 c )are: the initial slope µ and the Prager parameter np which controls the transition to the saturation of the hypoelastic scheme). The bulk modulus K is chosen from the literature. The 7 other parameters independent of the temperature are determined from one isothermal tensile test performed at a temperature above Af.a