LIMITATIONS OF CONSTITUTIVE RELATIONS FOR TINI SHAPE-MEMORY ALLOYS

Phase transformation tensor Omega in the constitutive equation propose d by Tanaka has been evaluated by employing experimental data of TiNi alloys in a constrained recovery process. It demonstrates that the abs olute value of Omega for the constrained recovery process is typically about 0.6 similar to 0.7 x10(3) MPa, which is much smaller than that for the stress - induced martensitic transformation (typically 2.5 sim ilar to 3.5 x10(3)). Based on the evaluated results for Omega, predict ed recovery stress - temperature relations ty the constitutive equatio n are compared with the experimental data for TiNi rods under differen t strains. Big discrepancy exists for large strain conditions. Several transformation kinetic expressions are examined for the constitutive relation of the constrained recovery process.