PSI - Issue 5

J. Morais et al. / Procedia Structural Integrity 5 (2017) 705–712 Morais J et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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parameters (force levels, displacement amplitudes, shape of the hysteresis cycles) by choosing the arrangement, geometry and number of the SMA wires used in the device.

2. Damper concept description

Austenitic SMA wires have been the subject of several works devoted to the study of their mechanical proprieties, particular characteristics and potential usages [Dolce et al. (2000), Zhang and Zhu (2006), Motahari et al. (2007)]. In this work Nitinol austenite SMA wire from MEMRY was used (Ø1.75 mm). Fig. 2 shows its characteristic stress strain curve from a series of tensile tests performed at LNEC for a previous phase of this study.

Fig. 2. Stress-strain curve of the SMA wire used in this study.

The passive energy dissipation damper developed for this study uses two bundles of these SMA wires in a double counteracting arrangement, with pre-strain applied to both wire bundles. We chose this type of configuration because it focuses on maximizing energy dissipation while maintaining the external load (measurable load exerted by the damper when actuated) on predictable levels [Dolce and Cardone (2001)]. This type of damper configuration has the following features:  Energy dissipation : the double counteracting wire arrangement allows the system to dissipate energy when the damper is under traction and compression, from an external point of view. Intrinsically, only the wires being stretched are dissipating energy, but due to this configuration there is always one bundle dissipating energy.  Predictable external load : due to the Superelastic behavior of the SMA wires, combined with the double counteracting wire configuration, the external measurable load of the damper is always the difference between the load levels of both wire bundles (see Fig. 3). Intrinsically, each wire bundle is describing its corresponding stress strain curve as the seismic movement occurs (one bundle is stretched, while the other is shortened, thus increasing and decreasing tensile stress, respectively). This creates a hysteretic cycle that is the basis of the dissipation mechanism for this type of SMA based dampers [Dolce and Cardone (2001)].