Comptes Rendus Mecanique最新文献

We use conformal mapping techniques and analytic continuation to prove that the stress field inside a non-parabolic open inhomogeneity embedded in a matrix subjected to uniform remote anti-plane stresses can nevertheless remain uniform despite the presence of a screw dislocation in its vicinity. Furthermore, the internal uniform stresses inside the inhomogeneity are found to be independent of both the shape of the inhomogeneity and the presence of the screw dislocation. On the other hand, we find that the existence of the nearby screw dislocation exerts a significant influence on the non-parabolic shape of the inhomogeneity.

Piezoelectric bimorph actuators are used in a variety of applications, including micro positioning, vibration control, and micro robotics. The nature of the aforementioned applications calls for the dynamic characteristics identification of actuator at the embodiment design stage. For decades, many linear models have been presented to describe the dynamic behavior of this type of actuators; however, in many situations, such as resonant actuation, the piezoelectric actuators exhibit a softening nonlinear behavior; hence, an accurate dynamic model is demanded to properly predict the nonlinearity. In this study, first, the nonlinear stress–strain relationship of a piezoelectric material at high frequencies is modified. Then, based on the obtained constitutive equations and Euler–Bernoulli beam theory, a continuous nonlinear dynamic model for a piezoelectric bending actuator is presented. Next, the method of multiple scales is used to solve the discretized nonlinear differential equations. Finally, the results are compared with the ones obtained experimentally and nonlinear parameters are identified considering frequency response and phase response simultaneously. Also, in order to evaluate the accuracy of the proposed model, it is tested out of the identification range as well.

This paper presents a study of the vibratory behaviour of a flexible workpiece subject to a milling end operation. Indeed, this vibratory behaviour is critical, especially when the excitation frequency is near to the resonance. For this reason, passive vibration suppression is considered in order to attenuate the dynamic response of the milled workpiece and decrease the dynamic effect on the resulting machined surface roughness and flatness. In order to confirm the efficiency of the passive vibration suppression, the vibratory behaviour and the quality (roughness and flatness) of a machined surface are studied without and with passive absorber (TMD) using a finite-element model.

In this paper, we introduce a new model of the nonisothermal immiscible compressible thermodynamically consistent two-phase flow in a porous domain Ω. This model includes the term describing the skeleton and interphase boundary energies. In the framework of the model, we derive the equation for the entropy function in the whole Ω and then obtain the estimate of the maximal entropy of the system.

The hygroscopic behavior of earthen materials has been extensively studied in the past decades. However, while the air flow within their porous network may significantly affect the kinetics of vapor transfer and thus their hygroscopic performances, few studies have focused on its assessment. For that purpose, a key parameter would be the gas permeability of the material, and its evolution with the relative humidity of the air. Indeed, due to the sorption properties of earthen material, an evolution of the water content, and thus of relative permeability, are foreseeable if the humidity of in-pore air changes. To fill this gap, this paper presents the measurement of relative permeabilities of a compacted earth sample with a new experimental set-up. The air flow through the sample is induced with an air generator at controlled flow rate, temperature, and humidity. The sample geometry was chosen in order to reduce, as much as possible, its heterogeneity in water content, and the tests were realized for several flow rates. The results, which show the evolution of gas permeability with the relative humidity of the injected air and with the water content of the material, either in adsorption or in desorption, were eventually successfully compared to predictions of the well-known Corey's law.