S. Mezghani

Contribution of human skin topography to the characterization of dynamic skin tension during senescence: morpho-mechanical approach

The structuring of the dermis with a network of collagen and elastic fibres gives a three-dimensional structure to the skin network with directions perpendicular and parallel to the skin surface. This three-dimensional morphology prints on the surface of the stratum corneum a three dimensional network of lines which express the mechanical tension of the skin at rest. To evaluate the changes of skin morphology, we used a three-dimensional confocal microscopy and characterization of skin imaging of volar forearm microrelief. We have accurately characterize the role of skin line network during chronological aging with the identification of depth scales on the network of lines (z ≤ 60μm) and the network of lines covering Langers lines (z > 60 microns). During aging has been highlighted lower rows for elastic fibres, the decrease weakened the tension and results in enlargement of the plates of the microrelief, which gives us a geometric pertinent indicator to quantify the loss of skin tension and assess the stage of aging. The study of 120 Caucasian women shows that ageing in the volar forearm zone results in changes in the morphology of the line network organisation. The decrease in secondary lines (z ≤ 60 μm) is counterbalanced by an increase in the depth of the primary lines (z > 60 μm) and an accentuation of the anisotropy index.

On the optimal choice of wavelet function for multiscale honed surface characterization

Multiscale surface topography characterization is mostly suited than standard approaches because it is more adapted to the multi-stage process generation. Wavelet transform represents a power tool to perform the multiscale decomposition of the surface topography in a wide range of wavelength. However, characterization results depend closely on the topography data acquisition instrument (resolution, height accuracy, sensitivity...) and also on the wavelet analysis method (discrete or continuous transform). In particular, the choice of wavelet function can have significant effect on the analysis results. In this paper, we present experimental work on a number of popular wavelets functions with the aim of finding wavelets that exhibit optimal description of honed surface features when continuous wavelet transform is used. We demonstrate that the regularity property of wavelet function has a significant influence on the characterization performances. This comparative study shows also that the Morlet wavelet is the more adapted wavelet basis function for multiscale characterization of honed surfaces using continuous wavelet transform.

Evaluation of Tooth Surface Micro-Finishing on Gear Noise

For automotive gear manufacturers, reducing gear noise while maintaining the gear load-carrying capacity as well as the wear resistance has become more and more important. Macro- and micro-geometrical defects have long been studied in order to explain the vibratory behavior of gears. However, the contribution of the micro-scale roughness of the flanks, essential in the gear contact mechanics, has not yet been fully understood.This paper addresses this issue where gears were manufactured with two industrial finishing processes (grinding and power-honing) while having the same macro-scale characteristics. Tridimensional topographical features of teeth surface were hence measured using a three-dimensional white light interferometer. As manufactured surface topographies are highly complex, irregular, and multiscale, all the teeth surfaces were characterized in the entire wavelength band using a multiscale method based on wavelets transform. Vibration performances of the gears were then tested on a single-stage low powertrain. Results demonstrate the influence of micro-roughness scales on vibrations amplitude.

Numerical Simulation of Tooth Surface Finish Effects on Gear Noise

Due to the rapid development of electric and hybrid motorisations, gear manufacturers have encountered an increasing need to create high level quality gear flanks. While the main goals are to increase the load-carrying capacity and the wear resistance, reducing gear noise has become more and more important. To answer this, macro- and micro-geometry defects have long been studied as well as their effect in amplifying the vibrations of gears. However, the impact of tooth flanks micro-scale roughness on gear noise has not well been studied and understood, even though the teeth surface contacts are essential in the gear mechanics.This paper aimed to discriminate the influence of the tooth finishing process (grinding, powerhoning) on single stage spur gear noise. A two-dimensional finite-element simulation model of a one-stage gear system was hence developed. The transmission system was composed of two identical loaded gears with one degree of freedom. Topological features of teeth surfaces finished by grinding and powerhoning were measured with a three-dimensional white light interferometer. These real topographic profiles of the tooth surfaces were integrated in the model. The meshing stiffness was determined as an output of this dynamic model. It is a parameter directly linked to the acoustic behaviour of the gear. Results show that gear noise could be reduced by the right choice of the finishing process kinematic.Copyright

Identification of the multiscale diamond turning signature of optical lens surfaces

Functional surfaces of optical lens are commonly achieved by a multi-stage diamond turning. This high precision process acts in a wide range of wavelength and allows producing 3-dimensional free form optical surfaces with excellent surface finish that meets application requirements. However, the relationships between process variables and surface characteristics are not yet predictable. In this paper, the concept of the multiscale process signature (MPS) is applied to track the effect of diamond turning process variables (cutting velocity, feed rate, cutting depth, tool roughness,...) on the surface topography from micro-roughness to waviness. The MPS is developed based on continuous wavelet transform and it depicts the essential changes of the surface state produced on the original surface after diamond turning. Using this concept, the effects of different working variables are isolated and theirs active wavelength bands were identified.