Shape memory alloys (SMAs) with double martensitic transitions are potential candidates for highly effective, nonstandard mechanical damping systems. This paper presents a numerical model that can be used to simulate pseudoelasticity in... more
Shape memory alloys (SMAs) with double martensitic transitions are potential candidates for highly effective, nonstandard mechanical damping systems. This paper presents a numerical model that can be used to simulate pseudoelasticity in systems with two successive martensitic transformations, such as adequately oriented CuZnAl, CuAlNi and CuAlBe single crystals. The model is based on stress versus strain data obtained from the tensile test of a CuZnAl single crystal and is able to simulate the mechanical damping of SMAs with two successive martensitic transitions. The numerical model has been implemented as an algorithm and used to assess the mechanical damping capacity of a system based on CuZnAl SMA single crystals, considering the complete β-18R–6R cycle. A numerical model with a single degree of freedom is used and the behavior of the SMA-based damper is analyzed both under free and forced oscillation conditions. The results obtained indicate that the alloy studied is a very effective mechanical damper.
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Abstract Strain and temperature aging for a NiTi shape memory alloy is performed at 373 K, using wires of 2·46 mm and eventually 0·5 mm in diameter. Aging under large strains modifies the hysteresis shape and induces an increase in the... more
Abstract Strain and temperature aging for a NiTi shape memory alloy is performed at 373 K, using wires of 2·46 mm and eventually 0·5 mm in diameter. Aging under large strains modifies the hysteresis shape and induces an increase in the maximal stress in the transformation from 600 to 800–1000 MPa (wires of 2·46 mm). On applying a strain up to 7–8%, the effect according to the initial state is close to 50 MPa per month of strain–temperature aging. The results enable efficient NiTi damper application from 233 to 323 K. A partial study of wires of 0·5 mm shows quantitatively different effects.
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This paper regards some characteristics of the standard hysteresis cycle of SMA when used to supply damping in Civil Engineering applications. The mechanical efficiency (ratio between the dissipated energy again the elestic contribution)... more
This paper regards some characteristics of the standard hysteresis cycle of SMA when used to supply damping in Civil Engineering applications. The mechanical efficiency (ratio between the dissipated energy again the elestic contribution) increases when the starting point is situated in parent parent phase or inside the hysteresis cycle. In general the metastable or diffusion effects in parent phase and in coexistence (in static and also in dynamic conditions) remain not well quantified or completely known in SMA.JRC.G.5-European laboratory for structural assessmen
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The name Incorporation refers to the major purpose of project, which it to early integrate university students into the business processes of a vertically integrated oil company. Developed jointly with partner universities, the project... more
The name Incorporation refers to the major purpose of project, which it to early integrate university students into the business processes of a vertically integrated oil company. Developed jointly with partner universities, the project was created as a response to several challenges of the company related to providing cross-functional cooperation and training of highly qualified personnel for the company as well as soft early adaptation into company. Incorporation involves the integration of Industrial and Civil Engineering students into the phase of field concept design, and the further development of a strategy of a construction project based on the oil company's real case. So far, the Incorporation project has been applied in the perimeter of the Capital Construction and Conceptual Engineering functions of a major oil company, but as an educational tool it can be extended to other functions. As a result of two full annual streams of the project, the students of Master's d...
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The application of a SMA implies an accurate knowledge about the eventual time - behavior of the alloys. The effects of quenching and micro-heatings were studied by calorimetric and resistance measurements and the β-martensite coexistence... more
The application of a SMA implies an accurate knowledge about the eventual time - behavior of the alloys. The effects of quenching and micro-heatings were studied by calorimetric and resistance measurements and the β-martensite coexistence by stress - strain - temperature - time observations. Experimental analysis was performed using copper based single crystals (Cu-Zn-Al, e/a ≈ 1.48 e/a with Ms below room temperature). The phenomenological behavior establishes several time constants for each evolution. A change ΔT of temperature of the parent phase near 300 K induces an asymptotic time evolution on M s near 11 per cent. The parent to martensite coexistence produces an evolution of the equilibrium temperature (near 0.5 K) linked to the existence of an interface.
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ABSTRACT Thermally and stress induced martensitic transformations between β and a mixture of martensitic structures, β′ and γ′, were studied in Cu–14.1Al–4.2Ni (wt%) single crystals. In this way information on the relative stability... more
ABSTRACT Thermally and stress induced martensitic transformations between β and a mixture of martensitic structures, β′ and γ′, were studied in Cu–14.1Al–4.2Ni (wt%) single crystals. In this way information on the relative stability between β′ and γ′ martensites, compared to the β phase, was obtained. The measurement of electrical resistance as a function of temperature was used to follow the evolution of thermally induced transitions. The stress induced transformations were analyzed in the small temperature range at which the pseudoelastic behavior between β and a mixture of both martensites plays the main role. A clear inhibition of the γ′ martensite is detected as the number of cycles increases, no matter which thermodynamic coordinate is varied to induce the phase transition, i.e., temperature or stress. An evaluation of the magnitude of the relative stabilization of the β′ martensite compared with γ′ was obtained by a suitably designed experiment.
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Abstract: Several training procedures have been found suitable to induce the two way shape memory effect (TWSME) in copper based alloys. Complex dislocaiion arrangements can be produced by transformation cyclmg, which are believed to be... more
Abstract: Several training procedures have been found suitable to induce the two way shape memory effect (TWSME) in copper based alloys. Complex dislocaiion arrangements can be produced by transformation cyclmg, which are believed to be the cause of the TWSME. Small martensite plates can be stabilized, serving as origin of subsequent transformations, or deformation around second phase precipitates are used. In this work, the role of the dislocations arrangements is investigated. It is shown that the stress field around the dislocations leads to the formation, m the P phase, above the Ms, of small martensite plates. These martensites do not neces- correspond to the trained variant. Complex defects consisting of dislocations and heavily deformed martensites are thus produced. The role of these complex defects on the TWSME is discussed and possible mechanisms are suggested. 1. ZNTRODUCTION The two way shape memory effect (TWSME) has been a subject of increasing interest during the last...
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The thermoelastic martensitic transformation is the origin of the peculiar properties SMA. One of the potential uses consists on taking advantage of their hysteresis cycle to smooth the oscillations induced by wind or quakes. The... more
The thermoelastic martensitic transformation is the origin of the peculiar properties 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 experimental results establish the appropriate working space where the alloy properties are long term predictable including the diffusive effects. For example in series of working cycles separated by long times in austenite phase as the scarce events (as in earthquakes). The results establish a way to guarantee the damper behavior for several years.
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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... more
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.
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The interaction between dislocations and martensitic transformations in Cu–Al–Ni alloys is shortly reviewed. Results from many researchers are critically analyzed towards a clear interpretation of the relevant role played by dislocations... more
The interaction between dislocations and martensitic transformations in Cu–Al–Ni alloys is shortly reviewed. Results from many researchers are critically analyzed towards a clear interpretation of the relevant role played by dislocations on the properties of shape memory alloys in Cu-based alloys. Both thermally and stress-induced transformations are considered and focus is paid on two types of transitions, the β→β′ and the formation of a mixture of martensites: β→β′ + γ′. After cycling in the range where both martensites are formed, the twinned γ′ phase is inhibited and cycling evolves into the formation of only β′. A model which considers the difference in energy of each γ′ twin variant due to the introduced dislocations quantitatively explains the inhibition of γ′ in both thermally and stress-induced cycling. The type of dislocations which are mainly introduced, mixed with Burgers vector belonging to the basal plane of the β′ martensite, enables also to explain the unmodified mechanical behavior during β→β′ cycling. The reported behavior shows interesting advantages of Cu–Al–Ni single crystals if mechanical properties are comparatively considered with those in other Cu-based alloys.
Thin films of Cu–26.9at.% Al–5.5at.% Ni were grown by dc magnetron sputtering from the alloy target previously melted in an induction furnace. The films were grown either on glass or (100)Si substrates at room temperature. The films, of... more
Thin films of Cu–26.9at.% Al–5.5at.% Ni were grown by dc magnetron sputtering from the alloy target previously melted in an induction furnace. The films were grown either on glass or (100)Si substrates at room temperature. The films, of approximately 3μm thickness, were peeled off from the substrate for further studies. The structures and microstructures of the as grown films were
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Cu-Zn-Al single crystals were pseudoelastically cycled between the bcc austenitic phase (β) and the 18R martensite, in the cryogenic range. The microstructural changes which take place in the bulk were studied by different techniques and... more
Cu-Zn-Al single crystals were pseudoelastically cycled between the bcc austenitic phase (β) and the 18R martensite, in the cryogenic range. The microstructural changes which take place in the bulk were studied by different techniques and a consistent description of the defects which are formed is presented. Dislocations and trapped martensite are retained in two-dimensional arrays parallel to the basal plane of the martensite (basal plane defects), and these defects are responsible for the strong temperature effect on the mechanical behaviour of the alloys. The dislocations form the bulk defects during the first cycling stage, and afterwards internal stresses are high enough to retain martensite which shows a 2H structure. Partial recovery takes place at temperatures close to room temperature, which supports the role that point defects play in the mechanical behaviour of these alloys.
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The main effects of [Formula: see text] 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... more
The main effects of [Formula: see text] 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 [Formula: see text]-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.
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Twinned 2H martensite is observed in copper-based shape memory alloys together with basal and non-basal plane stacking faults. Knowledge of the twin-boundary structure and its interaction with the faults is important to understand the... more
Twinned 2H martensite is observed in copper-based shape memory alloys together with basal and non-basal plane stacking faults. Knowledge of the twin-boundary structure and its interaction with the faults is important to understand the deformation mechanism by twin coalescence. High-resolution electron microscopy coupled with image simulations have been used for these studies. The interface of the type I twinning in 2H martensite shows an atomic configuration with mirror antisymmetry. An atomic plane is shared by the twinned variants in such a way that the distance between the planes, parallel to the interface, is unchanged at the boundary and the mean atomic volume is conserved. The interaction of the boundary with a basal plane fault generates a shift in the interface. A mirror antisymmetrical boundary is maintained by introducing an imperfect interface dislocation.
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Se ha simulado el comportamiento del material SMA en la amortiguación de las vibraciones de un cable atirantado. Se han comparado los resultados con los experimentos realizados con el cable instrumentalizado número 1 del ELSA (JRC,... more
Se ha simulado el comportamiento del material SMA en la amortiguación de las vibraciones de un cable atirantado. Se han comparado los resultados con los experimentos realizados con el cable instrumentalizado número 1 del ELSA (JRC, Ispra). El SMA produce un cambio y desdoblamiento de las resonancias. Se producen menores amplitudes de oscilación y decrecimientos más rápidos. Un análisis detallado de fiabilidad del sistema precisa datos experimentales apropiados. Encontrar una configuración óptima de amortiguación en cada caso requiere un trabajo posterior.
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The thermo-mechanical properties of Shape Memory Alloys (SMA) as smart materials suggest their application as actuators, but also as dampers, because the hysteresis of their thermo-elastic martensitic transformation. Damping in Civil... more
The thermo-mechanical properties of Shape Memory Alloys (SMA) as smart materials suggest their application as actuators, but also as dampers, because the hysteresis of their thermo-elastic martensitic transformation. Damping in Civil Engineering is needed to minimize earthquake effects on buildings, and also to limit the damage produced by wind or traffic induced oscillations in stayed cables in bridges. We had characterized NiTi wires for dampers in Civil Engineering, and tested them in facilities, where they showed good performance. In this work, we explore the consequences of strain aging the material at moderate temperatures. A quasi-static stress and temperature aging of NiTi SMA wires of 2.46 mm diameter was done at 373 K. The experimental measurements establish a monotonic effect related to the strain introduced. Aging under larger strains modifies the hysteretic shape and induces an increase in the maximal stress on the transformation from 600 MPa to 800-1000 MPa. Aging at 3...
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ABSTRACT Entropy changes during β1↔β1′ and β1↔γ1′ transformations in Cu–14.3Al–4.1Ni (wt.%) and Cu–14.1Al–4.2Ni (wt.%) single crystals were obtained, in order to evaluate changes on the relative stability of the metastable phases... more
ABSTRACT Entropy changes during β1↔β1′ and β1↔γ1′ transformations in Cu–14.3Al–4.1Ni (wt.%) and Cu–14.1Al–4.2Ni (wt.%) single crystals were obtained, in order to evaluate changes on the relative stability of the metastable phases involved. These values were determined by DSC measurements and isothermal tensile tests performed at different temperatures.
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... Si l'on d sire des r gles plus quantitatives, il est n cessaire d'effectuer un calcul complet de l' nergie des dislocations dans le cadre de la th orie anisotrope. ... Mag. A , 509 (1983). 2. D. Rios-Jara, M. Morin, C.... more
... Si l'on d sire des r gles plus quantitatives, il est n cessaire d'effectuer un calcul complet de l' nergie des dislocations dans le cadre de la th orie anisotrope. ... Mag. A , 509 (1983). 2. D. Rios-Jara, M. Morin, C. Esnouf and G. Guenin, Scripla metall. 19, 441 (1985). ...
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