DAMPING CHARACTERISTICS OF TINI SHAPE-MEMORY ALLOYS

The damping characteristics of TiNi SMAs have been systematically studied by using techniques of resonant-bar and low-frequency inverted torsion pendulum. Experimental results show that both the martensite phase (M) and R phase (R) have high damping due to the movement of twin boundaries. Because the B2 parent phase (B2) has smaller damping, it is suggested that this may come from the dynamic ordering process of lattice defects. In the transformation regions of B2 <-- --> M, B2 <- --> R, and R <-- --> M, there are maxima of the damping capacity which are attributed to two contributions. One arises from the plastic strain and twin-interface movement during the thermal transformation, which obeys a linear variation of peak heights Q(max)-1 vs T at T greater-than-or-equal-to 1-degrees-C/min. The other originates from the stress-induced transformation formed by the applied external stress which dominates at T < 1-degrees-C/min. The elastic modulus E of martensite and the R phase is lower than that of the B2 phase, and a modulus minimum appears in the transformation region.