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Local fracture events (or labquakes) during compression of shale rocks have been studied by acoustic emission. They are assumed to simulate quakes induced by hydraulic fracturing (fracking)...

We provide a general thermodynamic framework to study multicaloric effects in multiferroic materials. This is applied to the case of a magnetoelectric multiferroic such as BiFeO, which is described by means of a Landau free energy with a biquadratic coupling between polarization and magnetization. We obtain a phase diagram, the isothermal entropy change and the adiabatic temperature change across different continuous and first-order phase transitions as the applied electric and magnetic fields are varied. The multicaloric effects are suitably decomposed into the corresponding electrocaloric and magnetocaloric contributions.

The failure mechanism of porous materials under uniaxial stress has been investigated experimentally. Microporous SiO2, Vycor, has been subjected to slowly increasing compressive uniaxial stress with stress rates between 0.2 and 12.2 kPa/s. With increasing stress the strain changes stepwise with acoustic emission correlated with each volume collapse. The acoustic emission followed the characteristics of ‘crackling noise’ with a power law distribution over an exceptionally large interval of 6 decades at the slowest stress rate. The power law exponent is −1.39. Possible applications in mining industry and others are discussed.

International audience; We studied the effect of Fe and Co 3d elements selective substitution on the structural and magnetic phase transitions in the prototypical magnetic shape memory alloy Ni-Mn-Ga. We determined the phase diagram for each elemental doping substitution by means of calorimetry and ac susceptibility measurements. An effort was made to substitute each constituent element by same amounts of doping and to study the role of parameters other than electronic concentration in controlling phase stability. Specifically, selective doping with atoms of similar atomic radii but different magnetic properties allowed to investigate the role of magnetic interactions on the relative phase stability of the ternary compound. We determined the entropy change associated with the martensitic transition for each quaternary alloy to obtain further information on the effect of magnetism on the relative stability of the involved phases exhibited by these compounds.

We study the structural and magnetic properties of Heusler based Ni50Mn50−x Sb x in the composition range 5.0 ≤ x ≤ 25.0. The cubic phase is preserved in the range 17.0 ≤ x ≤ 25.0, and the presence of martensitic transformations are found in alloys with x ≤ 15.0. In a critical composition range 12.5 ≤ x ≤ 10.0, the magnetic coupling in both austenitic and martensitic phases is paramagnetic, however, the presence of antiferromagnetic short-range correlations is observed in both phases. We discuss the consequences of these correlations on the behavior of the magnetic moment with respect to electronic properties.

We have determined the shape of the miscibility gap of the Cu–Al–Mn alloy system along the Cu3Al → Mn composition line ((Cu3Al)1 − x Mnx with 0 ⩽ x ⩽ 1) using electrical resistance measurements. Electrical resistance measurements have also been used to study the kinetics of the phase separation that takes place within the miscibility gap. The effect of such a phase separation on the magnetic properties of the system and on the martensitic transition displayed by these alloys has also been analysed. The results obtained show that the phase separation produces an enhancement of the ferromagnetic character of the system as a result of the development of ferromagnetic L21 domains. In addition, the phase separation gives rise to an increase in the transition temperature and to a reduction in the associated entropy change. Both effects are a consequence of the growth of L21 Mn-rich domains that do not transform martensitically.

We have investigated the order-disorder phase transition in Cu-Al-Be alloys close to the eutectic composition. X-ray diffraction measurements have been performed to characterize the ordered structure and to follow the evolution of the degree of long-range order with temperature. Results show that the transition is first order and takes place, on cooling, from the disordered to a D03 structure. Taking into account these results, a mean field model has been developed in order to study the superlattice formation in these alloys. Present X-ray measurements together with previous calorimetric measurements of the martensitic transition undergone by Cu-Al-Be alloys, have enabled a determination of their metastable phase diagram. It is remarkable that although the addition of a small quantity of Be has a strong effect on the martensitic transformation, it does not modify the symmetry properties of the binary Cu3Al.

This paper describes a high-sensitivity calorimeter which is capable of carrying out measurements on samples whilst they are subjected to uniaxial tensile stress. It is shown how this device can be...

Simultaneous measurements of acoustic emission and thermal emission have been made during the martensitic transformation of a Cu-Zn-Al alloy after quenching from temperatures Tq between 300 and HOOK. Just after the quench a strong dependence of the thermal and acoustic data on Tq has been observed. This dependence is almost suppressed when the alloy is aged (ageing time t≈50 ks) at room temperature (ageing temperature Ta≈295 K). The results show that the transformation temperature and enthalpy are sensitive to the state of the β-phase after the quench and that the transformation entropy is independent of Tq The acoustic emission is very sensitive to the excess of quenched-in free vacancies in the system. Permanent effects due to γ-type precipitates have also been detected from the energy dissipated by irreversible processes.

The thermoelastic martensitic transformation in shape-memory alloys is studied thermodynamically. Calorimetric experiments on the Cu─Zn─A1 alloy system reveal that the transformation takes place with a practically negligible entropy production. The usual hysteretic subloop behaviour during partial cycling is obtained for the first time by calorimetry. An analysis of the measurements gives the quantitative behaviour of elastic and dissipative energies with the volume fraction of martensite.

We present a phenomenological model to account for the dependence of the elastic constant C' on the atomic ordering in a binary alloy. In particular, we focus our attention on the ageing process in a shape-memory alloy above its transformation point (M s). Both the equilibrium elastic constant and its relaxation to equilibrium after a quench above M s are affected by the ordering process. The behaviour obtained seems consistent with the available experimental data.

A model recently proposed to account for the influence of the β-phase atomic order on the martensitic transformation of binary alloys is generalized to the ternary case. The functional dependence of the transition temperature obtained in both cases is tested on available data for CuZn and CuZnAl. The results show that the coupling term introduced between strain and atomic order is consistent with experimental data.