Klizni lom u modelu snopa vlakana

We study the creep rupture of fiber composites subjected to uniaxial constant load within the framework of the fiber bundle model. Our numerical studies show that in the primary creep, the deformation rate exhibits a power law relaxation followed by a power law acceleration in the tertiary creep. We also investigate the behavior of the failure time and the avalanche size distribution. A good agreement is found between experiments and the model prediction, particularly for deformation power-laws scaling in the primary-creep regime and in the tertiary-creep neighbourhood of rupture.Proučavamo klizni lom vlaknastog kompozita opterećenog stalnom jednoosnom silom primjenom modela snopa vlakana. Naša numerička istraživanja pokazuju da deformacije u početnom klizanju slijede potencijalni zakon, a u tercijalnom ubrzanje s drugim potencijalnim zakonom. Ispitujemo također vrijeme loma i raspodjelu jakosti lavine. Nalazimo dobro slaganje eksperimentalnih podataka s predviđanjima modela, posebice za sumjerenost potencijalnog zakona u početnim kliznim uvjetima i blizu tercijalnog kliznog loma

ACOUSTOÉLASTICITÉ SOUS INCIDENCE ; ANISOTROPIE INDUITE, TEXTURE ET CONTRAINTES RIÉSIDUELLES

In this work, we discuss the limits of the acoustoelastic isotropic model. We examine experimentally the influence on the acoustoelastic behaviour of the plastic strain and recrystallization heat treatment to appreciate the contribution on this behaviour of the texture, residual and applied stresse

Evidence of microstructure evolution in solid elastic media based on a power law analysis

Complex and consolidated granular media or microcracked composites and metals usually exhibit a high level of nonlinearity in their elastic response already at low amplitudes of excitation. To quantify it, a proper nonlinear indicator y is introduced and its dependence on the excitation amplitude x is studied. The dependence of y on x is found in experiments to be a power law. Here we show that the different power law exponents measured for different materials could be predicted by proper classes of discrete models. An application is presented to link the exponent evolution and the changes of the microstructure due to the progression of damage mechanically induce

Modélisation de la propagation ultrasonore en milieu dispersif ; mesure de vitesse et application à la caractérisation des graphites

The measurement of the velocity of propagation of ultrasonic pulse in dispersive media gives a quantity which physical meaning is ambiguous. In this paper we simulate a dispersive medium using the Kramers-Krönig relationship which expresses the causality of a linear system. We develope an appropriate signal processing such as Hilbert transform and cross-correlation to measure the time of flight of an ultrasonic impulse propagating in such a medium. This allows to deduce from this simulation the physical significance of the two informations given by two methods. Then these two methods are applied to several categories of graphites with dispersif character. Thus the differences between the measured velocities by Hilbert transform and cross-correlation are correlated to several microstructural properties of the material such as grain size, porosity and to thermal elaboration treatement

Influence of noise on the threshold for detection of elastic nonlinearity

Nonlinear effects on the propagation of elastic waves in hysteretic media are of great importance, with applications in imaging and monitoring evolution of damage/phase transitions/biological features. However, excitation amplitudes are an issue in order to improve performances of the techniques. Noise effects in the signals can be stronger than the generated nonlinear effects, thus rendering difficult the nonlinear analysis. Here, we analyze the link between the amplitude threshold for detection of nonlinear effects and different kinds of noises which might be present in experiments. We also discuss the implications in the intrpretation of experiments