Damping in Civil Engineering Using SMA. Part I: Particular Properties of CuAIBe for Damping of Family Houses

The properties of SMA (or smart materials), are associated with a first order phase transition named martensitic transformation, that occurs between metastable phases from the upper temperature phase (austenite) to the lower temperature phase (martensite). The first order transformation (in stress, deformation and temperature coordinates) has a hysteresis and provides different kinds of applications, i.e., actuators and dampers. Two types of applications can be considered in the damping of structures in civil engineering. The first one is related to the reduction of the damage produced by earthquakes. The second one is the increase of the lifetime of cables in bridges. A completely different behaviour of the SMA is required in each case. Several years or decades without any action (except for the effects of summer-winter room temperature evolution) followed by one or two minutes of sudden oscillations is the characteristic pattern in an earthquake. Large numbers of oscillations per day (a half million or more) with pauses of several hours or days could be the typical dYnamic behaviour of stayed cables in bridges. The earthquake engineering would require an excellent performance during one or two minutes, at near 1 Hz, i.e., nearly 200 working cycles or about 1000 oscillations including several replicas, after several years or decades at rest. This paper analyzes the behaviour of a CuAlBe alloy towards its use as a damper in anti-seismic structures: the SMA creep and its reduction by appropriate heat treatment, the evolution of the alloy by the ageing and the fatigue life of the alloy are the subject of studies.