Emile Roux

Shear band initiation, development and mutual interaction are studied in a Zr55Cu30Al10Ni5 metallic glass by means of an innovative experimental technique associating diametral compression test (or Brazilian test), scanning electron microscopy and digital image correlation analysis. The intense strain occurring in shear bands and the deformation map of their overall pattern are both estimated with a high resolution (∼ 5 μm/pixel), offering a better understanding of the phenomenon. Finite element simulations based on a new and original plasticity model, the compartmentalized model, makes it possible to reproduce the shear band development observed experimentally, as well as the interlocking mechanism occurring between the shear bands.

In the field of medical applications, precise localization of medical instruments and bone structures is crucial to ensure computer-assisted surgical interventions. In orthopedic surgery, existing devices typically rely on stereoscopic vision. Their purpose is to aid the surgeon in screw fixation of prostheses or bone removal. This article addresses the challenge of localizing a rigid object consisting of randomly arranged planar markers using a single camera. This approach is especially vital in medical situations where accurate object alignment relative to a camera is necessary at distances ranging from 80 cm to 120 cm. In addition, the size limitation of a few tens of centimeters ensures that the resulting locator does not obstruct the work area. This rigid locator consists of a solid at the surface of which a set of plane markers (ArUco) are glued. These plane markers are randomly distributed over the surface in order to systematically have a minimum of two visible markers whatever the orientation of the locator. The calibration of the locator involves finding the relative positions between the individual planar elements and is based on a bundle adjustment approach. One of the main and known difficulties associated with planar markers is the problem of pose ambiguity. To solve this problem, our method lies in the formulation of an efficient initial solution for the optimization step. After the calibration step, the reached positioning uncertainties of the locator are better than two-tenth of a cubic millimeter and one-tenth of a degree, regardless of the orientation of the locator in space. To assess the proposed method, the locator is rigidly attached to a stylus of about twenty centimeters length. Thanks to this approach, the tip of this stylus seen by a 16.1 megapixel camera at a distance of about 1 m is localized in real time in a cube lower than 1 mm side. A surface registration application is proposed by using the stylus on an artificial scapula.

This paper introduces an optimized orbit jump strategy for nonlinear vibration energy harvesters (VEHs). Nonlinear VEHs are a promising alternative to linear VEHs due to their broadband characteristics. However, they exhibit complex dynamical behaviors, including not only high-power inter-well orbits but also low-power intra-well orbits and chaos. The existence of low-power orbits in their dynamics can restrict their energy harvesting performance. In order to overcome this issue, this study investigates an orbit jump strategy that allows the VEH to transition from low-power intra-well orbits to high-power inter-well orbits. The orbit jump strategy, which is based on varying the buckling level of a bistable VEH, has been previously studied but not yet optimized. In this study, we optimize this orbit jump strategy to ensure practical reproducibility and robustness against variations in parameters or excitation. Through the combination of thorough experimental identification and high-performance computing of the complex transients during orbit jumps, we achieved high numerical accuracy in orbit jump modeling. This was possible by a developed Python CUDA code using GPU parallel computing to handle a large number of numerical resolutions of the nonlinear VEH model. These simulations facilitate the optimization of both the robustness and the energy cost of orbit jumps, based on a novel numerical criterion. Experimental tests were performed on a bistable VEH over a frequency range of 30 Hz, validating the numerical results obtained with the optimized orbit jump strategy. Experimental results show an average success rate of 48%, despite a variation of \\\pm 15\%\∈the starting and ending times of the jump, leading to a robust and optimized orbit jump strategy. The proposed optimization procedure can be applied to other orbit jump strategies, and other types of nonlinear VEHs. The results indicate that the energy consumption required for a successful orbit jump ranges between 0.2 and 1 mJ, and can be restored within 0.2 s in the worst case.