Papers by Author: Taoufik Boukharouba

Abstract: Our contribution in this work is to detect, localize and quantify the noise sources radiated by a spur gear transmission mechanism. The imaging technique is used; it is based on the acoustic inverse frequency response function (IFRF). The IFRF is based on the inversion of the transfer matrix built between the source points represented by their complex source strengths and listening points represented by the complex pressures measured by the hologram. The measurements were performed in a semi-anechoic room where the floor is concrete and the walls are covered with glass wool. The complex acoustic pressures are measured by an antenna with microphones regularly spaced; it is placed above the noisy mechanism. The reconstruction problem is therefore an inverse problem and is said ill-posed; thus, regularizations are needed to stabilize and to find the best solutions. As regularization technique, the Tikhonov method is applied and the regularization parameters are chosen according to the L-curve method. The goal is to reconstruct as accurately as possible the acoustic field radiated by the transmission mechanism on a fictive and tangent plane to the noisy mechanism considered open and sometimes closed. The results obtained showed that the sources were located with good approximation. The IFRF method is able to reconstruct the sound sources responsible for the noise radiated by the mechanism without any a priori information of the sources distribution, and the visualization of spatial acoustic fields facilitate the understanding of the complex phenomena of radiation.

Abstract: The equal channel angular extrusion (ECAE) is an ingenious severe plastic deformation process used to modify texture and microstructure without reducing sample cross-section. The ECAE of polypropylene (PP) was conducted under various extrusion velocities and back-pressure levels using a 90° die. The application of single ECAE pass to PP was meticulously investigated at room temperature. The ECAE-induced deformation behaviour was examined in relation to the load versus ram displacement curves. Depending on extrusion conditions, PP displayed various types of plastic flow. For ram velocities beyond 4.5 mm/min, severe shear bands consisting of successive translucent and opaque bands were observed, accompanied on the top surface by more or less pronounced periodic waves. Although the application of a back-pressure significantly reduced the wave and shear-banding phenomena, slightly inhomogeneous shear deformation was still observed. Shear bands were only suppressed by decreasing extrusion velocity. The strain-induced crystalline microstructure was investigated by X-ray scattering. Shear-banded samples exhibited a strong texturing of the (hk0) planes along the shear direction in the translucent bands whereas perfect crystalline isotropy appeared in the opaque bands. Application of backpressure and/or reducing ram velocity resulted in uniform texturing along the extruded sample. Yet, texturing changed from single shear to twin-like shear orientation about the shear direction. Mechanical properties changes of the extruded specimens due to back-pressure and extrusion velocity effects were analyzed via uniaxial tensile tests. The tensile samples displayed multiple strain localizations in shear-banded materials whereas quite homogeneous deformation appeared for non-banded ones. These effects were connected with the crystalline texturing. The results also revealed significant increase in the strain hardening after ECAE. Full-field strain was measured under tensile loading using an optical strain measuring technique based upon Digital image correlation technique, suitable for large deformation, which confirms these effects.