ENI Sfax

LASEM, Tunisia
LASEM, Tunisia
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Alimi A.,ENI Sfax | Alimi A.,University of Sfax | Kchaou M.,ENI Sfax | Kchaou M.,University of Sfax | And 2 more authors.
Transactions of the Indian Institute of Metals | Year: 2014

In high temperature hot forming processes (forging), the tool surfaces are the privileged places for mechanical, thermal and physico-chemical solicitations. More precisely, friction and wear play an important part in tool surface damage. The tool steel grades exhibit damages such as oxidation. Moreover oxide scales formed had a significant effect in failure forging tools on wear mechanisms and have to be considered in the wear model development. The damage caused by oxidation is very different according to the nature and the physical properties of formed oxide layers in the contact surfaces. The objective of the present work is to give an outline of the effects of the nature and the morphology of supplied X40CrMoV5-1 steel (AISI H13) oxides particles before slow sliding onto rubbing brass-steel surfaces on friction transition and wear mechanisms. It is the first to show the effects of thin flats plates having different micrometric size supplied before friction. In order to improve and to have a better insight into the wear phenomena taking place during the first instants of sliding, this work conducted has also demonstrated the role of this third body introduced before friction on the development and establishment of tribological circuit on the rubbing surface. In this paper, the wear investigations are carried out using a pad-on-disc tribometer. The pad-on-disc sliding wear experiments were performed at a load of 500 N and a sliding velocity of 0.065 mm/s in normal atmosphere. The pad is made of brass and the disc is made of cast iron lamellar. Static oxidation test used to evaluate samples oxidation characteristics consisted of one cycle of 70 h at 600 °C. In brief examination of rubbed pad surfaces after friction was conducted using scanning electron microscopy (SEM) to identify the wear mechanisms under oxidation surface. In addition, the samples structure and properties were examined by optical microscopy and SEM, profilometrical measurements and X-ray diffraction. Tribological results, correlated with microscopic observations, are conducted to establish a phenomenological model of wear mechanisms describing the evolution of the third body in contact. The effect of planning flats plates of third body on friction evolution was also discussed. © 2014 Indian Institute of Metals.

Kchaou M.,ENI Sfax | Kchaou M.,University of Lille Nord de France | Kchaou M.,École Centrale Lille | Kchaou M.,Lille Laboratory of Mechanics | And 10 more authors.
Annales de Chimie: Science des Materiaux | Year: 2010

This article deals with the friction-wear behaviour of X40CrMoV5-1 steel under static oxidation, slow sliding velocity and small sliding distance, without overlap to study oxide-induced friction and wear mechanisms. Characterisation of oxide-layer growth is established using Scanning Electron Microscopy (SEM), optical profilometry and X-ray diffraction. Friction tests are carried out on a pin-on-disc configuration. The study shows a transition between a severe-wear regime driven by abrasion and debris detachment to a low-wear regime induced by a tribological circuit where oxides contribute to the formation of a protective third-body layer. © Lavoisier.

Moalla I.,ENI Sfax | Lebourgeois F.,INSA Lyon | Alimi A.,ENI Sfax
Proceedings of the International Conference on Document Analysis and Recognition, ICDAR | Year: 2013

This paper introduces the Generalized Eigen Cooccurrence Matrix (GECM) as a new feature to describe complex structures like images of handwritings for palaeographic expertise. It measures the spatial dependency between two features in the image. It generalizes the popular grey level cooccurrence Dependencies (SGLD) which uses the luminance for the two features. 2nd order statistics generate high dimensional feature space which must be reduced to overcome the curse of dimensionality. Haralick have described several descriptors suited for SGLD matrices that cannot be used in Generalized Cooccurrence. In our case, the cooccurrence matrices are not always symmetric and the contents of each matrice are different from the SGLD. We introduce the GECM which uses the eigen decomposition of the cooccurrence matrices to reduce the number of matrices and decrease the redundancy of spatial information instead to reduce the size of each matrix. We show the effectiveness of the GECM on palaeography application and writing comparison. © 2013 IEEE.

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