The aging behavior of precipitation hardenable 17-4 PH stainless steel is studied by analyzing the changes in microstrain, crystallite size, and dislocation density derived from the modified Williamson–Hall (mWH) method and the Fourier analysis of XRD profiles. Aging treatment of this steel at 380, 430, and 480 °C for 0.5, 1, and 3 h durations leads to changes in the microstrain due to precipitation and substructural changes caused by dislocation annihilation. The microstrain estimated from the mWH method is dominated by the precipitate-induced effects. The influence of precipitates and dislocations on the mean squared strain 〈ε2(L)〉 are separated by fitting the variation of 〈ε2(L)〉 with an expression P0 + P1/L + P2/L2, where the parameter (P0)0.5 and P1 are shown to be related to the precipitate-induced and dislocation density-induced microstrain, respectively. The study shows that the XRD profile analysis can be used to separate the combined effects of precipitation and dislocation annihilation.

Shape memory alloys (SMA) are good candidates especially for being used as passivedampers. In order to develop the use of these alloys in structural vibrations control, thedynamical behavior of a NiTi helical spring is led, and the damping effect investigated.First, compression tests on the spring are carried out. These tests allow us to notice theeffect of the maximal compression displacement, the cyclic behavior and the compressionrate on its mechanical behavior. A finite element model analysis of the compression testsis then proposed. In consequence, the materials parameters have been identified after anumerical convergence test. In order to characterize the dynamical behavior of the spring,the innovative tool called equivalent complex stiffness is developed and used. Finally,the one degree of freedom vibration equation is solved with this equivalent complexstiffness. The solution of this equation clearly shows the non linear dynamical behaviorof the SMA spring and its damping potential.

The visual information that first-order cortical cells receive is contained in the visually evoked spike trains of geniculate relay cells. To address functional issues such as the ON/OFF structure of visual cortical receptive fields with modelling studies, a geniculate cell model is needed where the spatial and temporal characteristics of the visual response are described quantitatively. We propose a model simulating the spike trains produced by cat geniculate nonlagged X-cells, based on a review of the electrophysiological literature. The level of description chosen is phenomenological, fitting the dynamics and amplitude of phasic and tonic responses, center/surround antagonism, surround excitatory responses, and the statistical properties of both spontaneous and visually evoked spike trains. The model, which has been constrained so as to reproduce the responses to centered light spots of expanding size and optimal light and dark annuli, predicts responses to thin and large bars flashed in various positions of the receptive field. The switching gamma renewal process method has been introduced for modelling spontaneous and visually evoked spike trains within the same mathematical framework. The statistical structure of the spike process is assumed to be more regular during phasic than tonic visual responses. On the whole, this model generates more realistic geniculate input to cortex than the currently used retinal models.