Ferran Martorell

METASTABLE EFFECTS ON MARTENSITIC TRANSFORMATION IN SMA Part 4. Thermomechanical properties of CuAlBe and NiTi observations for dampers in family houses

AbstractThe behavior of shape memory alloys (SMA) allows their use as a passive smart material. In particular, the existence of a hysteretic cycle in the domain of the elementary coordinates strain-stress-temperature (σ, ε, T) suggests its application for damping in mechanical and/or in civil engineering. We are working in the application of SMA as dampers for earthquakes in small houses as family homes. For dampers installed in the inner porticos of the house, the suggested SMA is the CuAlBe and, eventually, the NiTi. At room temperature the used SMA wires induces forces situated between 2–3kN/wire. The properties related with the damping applications for CuAlBe and NiTi, i.e., the SMA creep and the self-heating will be presented, together with some other minor stress and temperature effects on NiTi modifying the hysteretic behavior.

SMA Fatigue in Civil Engineering Applications

Shape Memory Alloys (SMA) show particular properties associated to their martensitic transformation between metastable phases. Their use in dampers requires a deep knowledge of the SMA behavior and its coherence with the application requirements. In earthquakes engineering standard conditions require that, after several years or decades at rest, an excellent performance is necessary for one or two minutes, i.e., nearly 200 working oscillations. When the target is the damping of stayed cables in bridges under the wind or rain actions, a larger number of oscillations is expected per each working day. This contribution analyzes the fatigue behavior of a CuAlBe alloy (appropriate for earthquakes) and discusses the results of some available experiments on a NiTi alloy for their eventual application to stayed cables..

Correction to: Civil Engineering Applications: Specific Properties of NiTi Thick Wires and Their Damping Capabilities, A Review

We regret that a tribute, which was submitted with the original manuscript by the authors, in honor of Prof. Shuichi Miyazaki was unfortunately omitted during the publication process.

Remarks on the Particular Behavior in Martensitic Phase Transition in Cu-Based and Ni–Ti Shape Memory Alloys

Many macroscopic behaviors of the martensitic transformations are difficult to explain in the frame of the classical first-order phase transformations, without including the role of point and crystallographic defects (dislocations, stacking faults, interfaces, precipitates). A few major examples are outlined in the present study. First, the elementary reason for thermoelasticity and pseudoelasticity in single crystals of Cu–Zn–Al (β-18R transformation) arises from the interaction of a growing martensite plate with the existing dislocations in the material. Secondly, in Cu–Al–Ni, the twinned hexagonal (γ′) martensite produces dislocations inhibiting this transformation and favoring the appearance of 18R in subsequent transformation cycles. Thirdly, single crystals of Cu–Al–Be visualize, via enhanced stress, a transformation primarily to 18R, a structural distortion of the 18R structure, and an additional transformation to another martensitic phase (i.e., 6R) with an increased strain. A dynamic behavior in Ni–Ti is also analyzed, where defects alter the pseudoelastic behavior after cycling.

Civil Engineering Applications: Specific Properties of NiTi Thick Wires and Their Damping Capabilities, A Review

This study describes two investigations: first, the applicability of NiTi wires in the damping of oscillations induced by wind, rain, or traffic in cable-stayed bridges; and second, the characteristic properties of NiTi, i.e., the effects of wire diameter and particularly the effects of summer and winter temperatures and strain-aging actions on the hysteretic behavior. NiTi wires are mainly of interest because of their high number of available working cycles, reliable results, long service lifetime, and ease in obtaining sets of similar wires from the manufacturer.

Damping by SMA in civil engineering structures

The particular properties of Shape Memory Alloys associated to their thermoelastic martensitic transformation with hysteresis permits applications of SMA as a damper via the conversion of the work absorbed in each cycle in heat. The guaranteed behavior requires the appropriateness of SMA for the complete requirements of the application. This work shows two complementary aspects of the SMA application in Civil Engineering, the first of them, the SMA dampers in earthquake damping of a family house. The second aspect relates an elementary approach to the damping of stayed cables in bridges, using some data from the Iroise Bridge. The application in the first case needs long time constancy of properties and then around 200 cycles during an earthquake. In the second case, the fatigue life of SMA imposes that only small strains in the alloy can be accepted. Finally, it is emphasized the importance of working conditions, including temperature and time.