E.G. Campari

Microstructure-related anelastic and magnetoelastic behavior of nanocrystalline nickel

Nanocrystalline nickel was prepared by a planetary ball milling apparatus working in a vacuum of 10−4 Pa in the 150–300 K temperature range. The kinetic of the milling process and the microstructure evolution upon annealing were followed by x-ray diffraction and mechanical spectroscopy measurements. It was observed that thermal annealing up to 600 K induces a strong reduction of the internal strains without significant grain growth. Measurements of elastic energy dissipation and dynamic elastic modulus as a function of temperature showed that in the nanocrystalline samples, anelastic relaxation processes occur, with the activation energy of grain boundary diffusion. A systematic study of the magnetic field dependence of the dynamic modulus (ΔE effect) revealed a correlation between the ΔE magnitude and the strain values obtained by x-ray diffraction analysis.

Mechanical behaviour of nanocrystalline iron and nickel in the quasi-static and low frequency anelastic regime

Abstract In this research, we made use of mechanical spectroscopy to study the anelastic behaviour of nanocrystalline Fe and Ni in quasi-static, low-frequency (0.01–10 Hz) regime. The elastic energy dissipation coefficient (Q−1) and the stress relaxation have been measured as a function of frequency and temperature, in a range of temperatures where appreciable grain growth is not expected to occur. The use of such low frequency probes puts into evidence a very strong change in the material response, induced by low temperature annealing (T

Off-stoichiometric superconducting phases, oxygen mobility and anelastic relaxation in YBa2Cu3O7−x

Abstract Elastic energy dissipation measurements were carried out using the vibrating reed and torsional pendulum techniques on polycrystalline YBa 2 Cu 3 O 7- x specimens in different stoichiometric conditions. In the 300–900 K range two relaxational damping peaks, P O1 and P O2 , can be observed. The relaxation strength depends considerably on the oxygen deficiency x . As the value of x increases, the intensity of peak P O1 decreases while that of P O2 increases. The two relaxation processes have activation energies H 1 =(1.54±0.09) eV and H 2 =(1.3±0.1) eV , respectively. Models for the relaxation involving the dynamics of oxygen atoms in the Cu-O basal plane and along the twinned interfaces are examined.

Anelasticity and structural stability of nanostructured metals and compounds

Abstract Internal friction and dynamic elasticity moduli on thin reeds of nanostructured Al, Fe, FeAl and Fe 3 Al intermetallics prepared by ball milling have been measured. A relaxational damping peak in pure metals at 350–500 K and a modulus increase at 450–500 K without appreciable grain growth has been detected. Moreover, magnetoelastic coupling dependent on grain size has been observed in iron. In the nanophase intermetallic aluminides a strong relaxational damping peak was observed in the 700–800 K range. These results are briefly discussed with reference to the anelastic behaviour of similar coarse grained materials.

Cellular automata and roundabout traffic simulation

A new software package, named Archirota, for simulating traffic in roundabouts is introduced. Its simulation module is entirely based on cellular automata and is automatically configured for real-world geocoded data. Archirota can be used both as a support for designing new roundabout and for modeling and simulating existing ones. Tests on actual use cases testified the effectiveness of the implemented approach.

A study on the role of Oxygen in the inelastic behaviour of YBa2Cu3O7 − x

Abstract The inelastic behaviour of YBa 2 Cu 3 O 7 − x has been investigated by the vibrating reed technique in the 300–900 K range. In particular the mobility of oxygen and its contribution to the inelastic spectra, measured both in isochronal and isothermal conditions, was studied by testing samples with different initial oxygen contents. Two inelastic peaks of relaxational type were observed at approximately 560 and 680 K associated to stress induced reorientation of structural defects. The relaxation strenght in both cases strongly depends on the oxygen content. The dynamic modulus shows anomalous behaviour at temperatures higher than 740 K where the orthorombic to tetragonal transformation sets up. Some hypothesis on the inelastic behaviour of YBa 2 Cu 3 O 7−x in terms of oxygen content, thermally activated diffusional jumps and structural transformations are discussed.

Automated resonant mechanical analyzer

An automatic vibrating reed apparatus for internal friction and elastic modulus measurements in solids is described. The apparatus is equipped with a resistive heater for measurements up to 1400 K. A magnetic field (up to 250 kAt/m) is also available in the 300–1000 K range. Measurements as a function of temperature and/or magnetic field can be easily carried out. Data acquisition is controlled by a computer and originally written software allows automatic measurements and real time data analysis offering a user-friendly interface. The acquisition rate is nearly two orders of magnitude faster than that achieved manually. The use of the analyzer is straightforward and does not require a prolonged training of particularly skillful personnel.

Magnetoelasticity and internal strains in nanocrystalline nickel

Abstract The magnetic field dependence of the dynamic elastic modulus (ΔE effect) was studied in ball-milled nanocrystalline Nickel, as a function of the milling times and annealing treatments. The analysis of the crystallite size and internal strains has been performed as well by Fourier analysis of the X-ray spectra. A correlation between ΔE and the lattice strain calculated by X-ray analysis is observed, suggesting that the magnetic anisotropy is mainly determined by the internal strains.

Mechanical behaviour of NiAl and Ni3Al ordered compounds entering the nano-grain size regime

Abstract The elastic energy dissipation and dynamic modulus of several intermetallic compounds with the NiAl (B2) and Ni 2 Al (L1 2 ) composition and different grain sizes were measured. The grain dimensions were deduced by XRD data analysis. These alloys exhibit a temperature increasing background damping which raises faster as the grain size enter the nanometric regime. The elastic modulus of out of stoichiometry single crystals increases up to 20 % with temperature in a reproducible manner.

Orthorhombic to tetragonal phase transition in YBa2Cu3O7−x observed by dynamic Young's modulus measurements

Abstract Dynamic Youngs modulus measurements, have been performed by the vibrating reed technique (10 2 –10 4 Hz) on polycrystalline YBa 2 Cu 3 O 7−x samples in the temperature range 300–900 K. A strong modulus softening, indicative of a phase transition, is measured at about x = 0.45. DTG measurements versus temperatures show in correspondence a maximum in the oxygen desorption rate. Long time modulus isotherms display an exponential trend linked to a thermally activated structural process with activation energy H = 0.9 ± 0.1 eV. On the basis of the experimental results a model for the structural transformation linked to the twinned interfaces mobility and to oxygen diffusion is presented and discussed.