DAMPING CHARACTERISTICS OF TINI SHAPE-MEMORY ALLOYS

The damping characteristics of TiNi SMAs have been systematically stud ied by using techniques of resonant-bar and low-frequency inverted tor sion pendulum. Experimental results show that both the martensite phas e (M) and R phase (R) have high damping due to the movement of twin bo undaries. Because the B2 parent phase (B2) has smaller damping, it is suggested that this may come from the dynamic ordering process of latt ice 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 a nd twin-interface movement during the thermal transformation, which ob eys 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-ind uced transformation formed by the applied external stress which domina tes at T < 1-degrees-C/min. The elastic modulus E of martensite and th e R phase is lower than that of the B2 phase, and a modulus minimum ap pears in the transformation region.