International audienceThis paper develops an experimental and numerical study of dynamic phenomena involving gear impacts with one loose gear (non-engaged gear pair) inside an automotive gearbox. A dedicated test bench was designed for this study. Signal processing tools, based on the Order Tracking Method, were specially developed in order to clarify the underlying phenomena. A particular attention was paid to the relationship between the drive shaft excitation and the energy and nature of impacts. A topological model of contact is being proposed, based on a geometric description of solids in contact. The contact between gear meshes is defined using a Single Degree of Freedom, non-linear, elastic and dissipative model. The chosen parameters of the model are not updated from measurements, but from the knowledge of the gear topology and tolerance class. Simulations, compared with experimental results, confirm the accuracy of the model proposed. Both model and experiments show, for particular excitation conditions, the emergence of repeated impacts on one side of the gear mesh

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This paper presents an experimental study of the effects of prestresses on the vibration behavior of string instruments. These prestresses are created by gluing ribs (crowning) and tensioning string (downbearing). The effects of these prestresses were previously studied numerically for a piano soundboard by Mamou-Mani et al. [J. Acoust. Soc. Am. 123, 2401-2406 (2008)] and analytically for simplified models by Mamou-Mani et al. [Acta Acust. Unit. Acust. 95, 915-926 (2009)]. In the present study, a specified test bench is designed, including a simplified soundboard (a rectangular plate), a bridge, and a single string. The plate is subjected to in-plane and transverse loads. Vibrational eigenmodes are identified using nearfield acoustical holography (NAH) measurement. The evolution of eigenfrequencies with these specific prestresses is studied. The results show the effectiveness of NAH for this purpose and a very good qualitative concordance with previous numerical and analytical calculus.

The Music Museum in Paris recently acquired a harpsichord made by Ioannes Couchet in Antwerp in 1652. This instrument is considered to be a masterpiece and is protected as a "National Treasure." It was restored with the aim to be played again in concert. An experimental and numerical study of the vibraoacoustic behavior of this harpsichord is presented. A numerical modal analysis was performed with a finite element model. For the experimental part, impact nearfield acoustical holography was used. Experimental eigenmodes are compared to literature and to the finite element results. An application of the model for restoration studies is also proposed.