The value = 2 Obtained during unloading implies an effective Poisson's ratio of 0.5 for this stade of deformation.It has been shown [12] that the early stage of unloading is a bomoganeous strain recovery involving martensite detwinning and reverse transformation as well as elasticity. Martensite detwinning and reverse transformations are isovolumic events,with v=0.5. This implies the compounded Poisson's ratio should be between 0.33 and 0.5 for this stage of deformation,under the pondition that both measurements (in uniaxialtension and equibiaxial tension) involve the same strain recovery mechanisms