An experimental study of stress induced martansite transformation by electrical strain gauges is present. The studies were performance on polycrystalline Cu-Al-Be Shape Memory Alloys. Beams and a bar in cantilever flexion hold to punctual load were instrumented with electrical strain gauges in several points where the state of stress is: a) simple tension, b) simple shear and b) tension-shear. Employing the trasforational load values in each plot was calculated critical principal stresses. Employing the results obtained, 1 2 σ −σ plots were constructed and a comparison with the yield Von-Mises criteria, Patoor model and Buchheit model for the critical stress were do.