Shape memory effects under combined forces

Thin wall tubes made of CuAlZnMn shape memory alloy were subjected to combined axial and torsional loads in low temperature martensite state. The strain recovery accompanying the reverse martensitic transformation upon heating—shape memory effect—was studied. The stress free recovery proceeded by the simultaneous reversion of all induced strains, i.e. the strain path followed the shortest linear trajectory towards the origin of the strain space. When, however, a bias external stress was applied upon the reverse martensitic transformation, the response of the heated tube became remarkably non-linear. The effect was explained on the basis of the interaction of the bias stress with martensite variant particles induced in various stages of the complex deformation history.