Marcos Sade

Shape memory alloys as an effective tool to damp oscillations

The SMA was studied for their macroscopic application in damping for civil engineering. The study is a synthesis and includes an outline of the models required for the SMA simulation and some case studies using the finite element analysis methods. This work is an overview that focuses in the mitigation of the oscillations in structures induced by earthquakes, and for a reduction of the oscillations amplitude in stayed cables under the action of rain, wind or traffic. The analysis needs the required conditions for each application determining the working conditions. The study includes the number of working cycles, the temperature effects and the cooling actions and, for instance, the action of the cycling frequency. The main target relates the appropriateness of the SMA for each purpose, and the suitability of the SMA device is always experimentally guaranteed. Furthermore, the applicability of the obtained results for SMA and the practical behavior of the SMA dampers were studied in international facilities. The paper includes appropriate suggestions for a correct preparation of the SMA dampers. This work outlines the effects of stress and temperature aging in NiTi, describes the particular structural effects between 18R and 6R, introduces a first attempt in the dynamic properties of the CuAlBe single crystals and summarizes some recent suggestions for damping using SMA.

Pseudoelastic cycling in Cu–14.3Al–4.1Ni (wt.%) single crystals

Abstract Pseudoelastic β1↔β′1 and β1↔β′1+γ′1 cycling in Cu–14.3Al–4.1Ni (wt.%) single crystals were performed. For the β1↔β′1 cycling no evolution of the stress-strain curves was observed up to N=2700 in a specimen oriented close to the [100] direction. For the β1↔β′1+γ′1 cycling, made in a sample with orientation near [110], the martensitic transformation changes with the number of cycles, showing a clear inhibition of the γ′1 martensite as the cycling progresses. The disappearance of the 2H martensite is discussed in terms of the introduction of defects during cycling.

Damping via Cu-Zn-Al shape memory alloys (SMA): the action of diffusive effects on the macroscopic description

The thermoelastic martensitic transformation is the origin of the peculiar properties of Cu-based SMA. One of the potential uses consists on taking advantage of their hysteresis cycle to smooth the oscillations induced by wind or quakes. The experimental study at mesoscale level of the Cu-based alloys and in preliminary level of TiNi allows the development of a one-dimensional model that describes their response to the external thermodynamic forces. The evolution associated to diffusion effects (phase coexistence and temperature-time on parent phase) is also included. The results furnished by the model establish the appropriate guarantee of the alloy properties for series of working cycles separated by long times in austenite phase as the scarce events (as in earthquakes). Using a simple case, the simulation determines the boundaries of the suitable fluctuation zone related to the diffusive effects (summer, winter and coexistence effects). The results establish a way to guarantee the damper behavior for several years.

A short review on the interaction of precipitates and martensitic transitions in CuZnAl shape memory alloys

The main effects of γ non-equilibrium nanoprecipitates in CuZnAl shape memory alloys are briefly reviewed. Aspects related to the nucleation and growth of precipitates are commented on and their effect on stress induced martensitic transitions is analyzed. Results concerning the relationship between the size of precipitates and the hysteresis of the stress induced β-18R transition are studied. The improvement of the two-way shape-memory effect after the introduction of precipitates is shortly commented on. The 18R–6R transition is also analyzed and recent findings on the optimization of the mechanical reversibility associated to the 18R–6R transformation in a matrix with a high density of nano precipitates are reviewed.

Plastic deformation under compression of Cu-Zn-Al martensitic single crystals

Abstract In Cu–Zn–Al single crystals, a bcc to 18R martensitic transition can be induced either termally or under applied stresses. In the latter case, a martensite single crystal is obtained. In this work, the plastic deformation behavior of the 18R martensitic phase for two different compositions ( e / a =1.43 and e / a =1.48, M s ≈263 K) is analyzed in order to find out possible differences in both the mechanical behavior and the microstructure. Optical microscopy and transmission electron microscopy were used to study surface and bulk defects. The observed primary slip system was the same for all the samples, independently of the composition and orientation: (011)[100] β , which corresponds to slip in the basal plane of the martensite. In addition, for compression axes near [100] β , a secondary slip system appeared. The corresponding surface traces were far larger than those corresponding to the primary slip system. The measured resolved shear stresses to activate the primary slip system were on average 15% lower for compositions with e / a =1.43, compared to the samples with e / a =1.48. The results obtained for the yield stress of the martensite lend support to the role of plasticity of this phase on the nucleation and growth of the surface and bulk defects generated after pseudo-elastic cycling.

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 in single crystals of Cu-Zn-Al SMA: predictable effects related to external amplitudes and temperature

Achieving guaranteed behavior after many years in the high temperature phase should consolidate the potential capability of SMA in damping of series of oscillation cycles followed by long periods of inactivity. To use an appropriate model in simulation of the material behavior they have been carried out three types of experimental analysis. The first one focuses on the remnant after quench effects. The second one centers on the parent phase and its time-temperature dependence. The third one shows the changes on transformation temperature and on hysteretic width related to the cycling and on the two-phase coexistence.