Search Results

You are looking at 1 - 3 of 3 items for :

  • "Passive systems" x
  • Refine by Access: All Content x
Clear All
Pollack Periodica
Authors: Mohammad Reza Ganjali Bonjar, Kristóf Roland Horváth, Bálint Baranyai, and István Kistelegdi

all relevant geometries, structures, HVAC systems and internal use and equipment. Due to high level of complexity, the climate zones and services systems were simplified. The first part of the passive system optimization work package determined the

Open access

Metastable effects on martensitic transformation in SMA

Part VIII. Temperature effects on cycling

Journal of Thermal Analysis and Calorimetry
Authors: V. Torra, C. Auguet, A. Isalgue, F. Lovey, A. Sepulveda, and H. Soul

Abstract  

The use of Shape Memory Alloys (SMA) in technical applications as damping in civil engineering structures requires the characterization of the alloy for each specific application. This involves the evolution of the mechanical properties and damping capacity with the number of cycles, frequency, maximum deformation, applied stresses, and the evolution of the alloy with aging time and temperature. In particular, the temperature effects associated to self-heating need to be evaluated. In continuous cycling the effects of latent heat, the associated dissipation induced by the hysteresis, the heat flow to surroundings and the cycling frequency induce different states of temperature in the specimen, which in turn produces changes in the transformation-retransformation stresses. In this article, the temperature effects associated to cycling are outlined for different cycling frequencies. The results show that, for relatively faster frequency the temperature arrives at an oscillatory state superimposed to an exponential increase. For lower frequencies, some parts of the sample attain temperatures below room temperature. The experimental results are represented with an elementary model (the 1-body model or the Tian equation used in calorimetric representation) of heat transfer. For the higher fracture where life requirements are associated to damping in stayed cables for bridges, the results show (for the NiTi alloy) a reduction of the hysteresis width as the frequency increases for deformations up to 8%. For reduced deformation, under 2% appears an asymptotic behavior where the frictional area is practically independent of the cycling frequency (up to 20 Hz). In addition, it is shown that more than 4 million of working cycles can be attained if the maximum applied stress is kept below a threshold of about 200 MPa. Although under this condition the deformation must remain lower than 2% a reasonable damping capacity can still be obtained.

Restricted access

Abstract  

Nuclear Track Detectors (NTD's) are used as passive systems to detect the alpha contamination on flat or semirough surfaces. The procedure for the application of these devices is simple because the detector needs only to be placed on the area to be surveyed for a short period of time, collected and chemically processed to develop the alpha tracks. For the quantification of the results, it is necessary to have a calibration procedure. This paper presents the response of CR-39 (allyl diglycol carbonate), from American Acrylics and Pershore Companies, to alpha particles from Pu-239 (5.15 MeV) and Am-241 (5.48 MeV). The methods of etching and counting are outlined, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity levels is also discussed.

Restricted access