Finite Strain Shape Memory Alloys Modeling - Scuola di Dottorato in ...

In Fig. 8.6 the applied force is plotted versus the displacement of the point A alongthe free edge for the small and finite strains models.In the first case, i.e. T > A , the arch is subjected to an increasing value of the forcefuntil a maximum of 180N , maintaining constant the temperature at 285K ; then theload is removed allowing the element to recover the starting conditions. Fig. 8.5shows the undeformed and the deformed configurations of the analyzed structure.Therefore, if the material is loaded at a temperature aboveAfmacroscopic nonlinearlarge deformations occur and they are totally recovered during unloading,since the product phase, i.e. the single-variant martensite, is not stable at this value oftemperature. An hysteretic loop in terms of stress and strain (pseudolelasticity) isdescribed.In the second case, i.e. Ms< T < As, the arch is subjected to an increasing value ofthe force until a maximum of 120N , maintaining constant the temperature at 240K .Finally, in the third case, i.e.T≤ Mf, the maximum value of the axial force is 90Nand the temperature is maintained constant at 223K .For the cases in which T < A = 248Kalso the strain recovery induced by a heatingscycle is indicated. In fact, after the loading-unloading cycle, a residual strainremains. With a thermal cycle in which the temperature reaches the maximum valueof 400K and then reduces to the starting value of temperature, the shape memoryalloy is able to recover the original configuration going back to the point defined byzero stress and strain level.All the results underline the model capability to predict:♦ the superelastic effect;♦ the shape-memory effect.140