External temperature effects on the hysteresis of NiTi wires in dampers for stay-cables

The use of NiTi wires, one of the Shape Memory Alloy (SMA) materials that permits efficient damping in stayed cables for bridges, requires an appropriate behavior when exposed to the external temperature effects. The Clausius-Clapeyron thermodynamic equation establishes a shift of the hysteretic cycle in the stress-temperature representation of about 6 MPa/K for the used wires of diameter 2.46 mm. Hence, an adequate experimental study is necessary to characterize the temperature effects in working conditions. The conducted analysis is twofold. First, the practical evolution of the hysteresis cycle is investigated. The results suggest that the wire permits a completely satisfactory use for temperatures as low as 253 K (i.e., -20 oC). Second, the focus is placed on the effects of extreme winter actions (i.e., as low as 233 K or -40 oC). A preliminary stress aging process at 373K seems adequate to this requirement. Indeed, after the stress aging, the SMA wire increases their working domain by 300 or 400 MPa and the temperature domain is expanded by 30 – 50 K. Measurements visualizing recoverable dynamical actions in the SMA alloys are also outlined.Peer ReviewedPostprint (published version

The SMA: an effective damper in civil engineering that smoothes oscillations

The properties of SMA (Shape Memory Alloys, that are smart materials) are associated to a first order phase transition named martensitic transformation that occurs between metastable phases: austenite and martensite. At upper temperature or at lower stress the austenite is the metastable phase. The martensite appears at lower temperature or higher stresses. The hysteresis of the transformation permits different levels of applications, i.e., in their use as a damper. Two types of applications can be considered in damping of structures in Civil Engineering. The first one is related to diminishing the damage induced by earthquakes. The second one is a reduction of oscillation amplitude associate to an increase of the lifetime for the stayed cables in bridges.Peer Reviewe

Suunnitteluohjeiston kehittäminen

In this work we present the general classifier system Sedàs. We show how this system implements the description of the domain and how it builds similarity matrices and classification trees. The system uses a new semantics, introduced in [Torra96], to define a distance between qualitative values

SMA in mitigation of extreme loads in civil engineering: study of their application in a realistic steel portico

Guaranteeing the use of Shape Memory Alloys (SMA) in mitigation of extreme load effects requires a deep study of the SMA behavior according to the specific requirements of the applications in damping. The damper was defined according the expected requirements (length of SMA and number of SMA wires). It is applied to two types of alloys (CuAlBe and NiTi) in the diagonals of a realistic steel portico (2.47 m x 4.10 m). The measurements establish that the used SMA reduces the oscillation amplitude to a less than a half.Preprin

Comment on “Effects of heat-flux features on the differential scanning calorimetry curve of a thermoelastic martensitic transformation” by Benke et al. [Mater. Sci. Eng. A 481–482 (2008) 522]

The martensitic transformation of a Cu–Zn–Al single crystal was measured in a differential scanning calorimeter at different heating rates. The curves were analyzed in order to detect the initial and final temperatures of the transition. The results were analyzed using both, the method suggested by Benke et al. and the conventional method of extrapolating the temperatures to zero rate. They were also compared with those determined in the same calorimetric sample using the electrical resistance measurement. It is concluded that the transition happens in a range higher than that detected by calorimetry and that the inflexion point is not a useful point for a proper temperature determination

Comment on “Effects of heat-flux features on the differential scanning calorimetry curve of a thermoelastic martensitic transformation” by Benke et al. [Mater. Sci. Eng. A 481–482 (2008) 522]

The martensitic transformation of a Cu–Zn–Al single crystal was measured in a differential scanning calorimeter at different heating rates. The curves were analyzed in order to detect the initial and final temperatures of the transition. The results were analyzed using both, the method suggested by Benke et al. and the conventional method of extrapolating the temperatures to zero rate. They were also compared with those determined in the same calorimetric sample using the electrical resistance measurement. It is concluded that the transition happens in a range higher than that detected by calorimetry and that the inflexion point is not a useful point for a proper temperature determination

Sedàs: a semantic based general classifier system

In this work we present the general classifier system Sedàs. We show how this system implements the description of the domain and how it builds similarity matrices and classification trees. The system uses a new semantics, introduced in [Torra96], to define a distance between qualitative values

Reactions at solid-liquid interfaces

SIGLEAvailable from British Library Document Supply Centre-DSC:D206013 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

External temperature effects on the hysteresis of NiTi wires in dampers for stay-cables

The use of NiTi wires, one of the Shape Memory Alloy (SMA) materials that permits efficient damping in stayed cables for bridges, requires an appropriate behavior when exposed to the external temperature effects. The Clausius-Clapeyron thermodynamic equation establishes a shift of the hysteretic cycle in the stress-temperature representation of about 6 MPa/K for the used wires of diameter 2.46 mm. Hence, an adequate experimental study is necessary to characterize the temperature effects in working conditions. The conducted analysis is twofold. First, the practical evolution of the hysteresis cycle is investigated. The results suggest that the wire permits a completely satisfactory use for temperatures as low as 253 K (i.e., -20 oC). Second, the focus is placed on the effects of extreme winter actions (i.e., as low as 233 K or -40 oC). A preliminary stress aging process at 373K seems adequate to this requirement. Indeed, after the stress aging, the SMA wire increases their working domain by 300 or 400 MPa and the temperature domain is expanded by 30 – 50 K. Measurements visualizing recoverable dynamical actions in the SMA alloys are also outlined.Peer Reviewe

The SMA: an effective damper in civil engineering that smoothes oscillations

The properties of SMA (Shape Memory Alloys, that are smart materials) are associated to a first order phase transition named martensitic transformation that occurs between metastable phases: austenite and martensite. At upper temperature or at lower stress the austenite is the metastable phase. The martensite appears at lower temperature or higher stresses. The hysteresis of the transformation permits different levels of applications, i.e., in their use as a damper. Two types of applications can be considered in damping of structures in Civil Engineering. The first one is related to diminishing the damage induced by earthquakes. The second one is a reduction of oscillation amplitude associate to an increase of the lifetime for the stayed cables in bridges.Peer Reviewe