Key Engineering Materials Vol. 640

Abstract: The third body concept is a pragmatic tool for analyzing and understanding the friction and wear of sliding materials. This approach is based on the dominating role played by the wear particles under dry sliding conditions. These particles constitute the major part of what is called the third body. The third body concept was introduced by Maurice Godet in the middle of the 70’s and developed by Yves Berthier since the end of the 80’s who added complementary conceptual tools as the tribological triplet, the accommodation mechanisms and the tribological circuit. The aim of this paper is to give a synthetic view of these concepts, which involves mechanical, material and physicochemical subjects. Concrete examples and case studies from various practical applications are given to illustrate the validity and the efficiency of such a phenomenological approach.

Abstract: The wear behaviour of a filled styrene butadiene rubber (SBR) is investigated in this paper. The material contact used is plan /plan with a hard steel XC38. The influence of tribological parameters such as type contact (contact plan/plan under dry friction), relative motion between the contact surfaces (rotational disc/fixed elastomer sample), topography of the surface contact (roughness), loading (normal load or contact pressure), sliding friction and operating time or number of cycles is investigated. The highlighting of these parameters influence and analysis results permits us to formulate a wear model for the filled elastomer SBR. The model is based on the Archard law developed for metallic materials. The modification concerns the introduction of material parameters to take accounts the hyperelastic behaviour of elastomer due to the presence of amorphous phase. Particular interest is given to the influence of the surface state of the indenter given by the counterface arithmetic roughness Ra on the weight loss of the elastomer due to the wear phenomena. For a lower value (little to 6.3μm) of the arithmetic roughness, the weight loss is insignificant for different contact pressure and various sliding speeds. This effect is more noticeable at higher values of roughness and dependent on other tribological parameters. This results comfort other conclusion on the literature that express the influence of roughness by the geometric parameters of the micro-waves in the surface. The effects of the roughness can be explained by the ratio between the amplitude and wavelength of the corrugation. Indeed, we relate the roughness influence at the strain energy restored by material hyperelastic which also is, necessarily, a function of the velocity sliding and pressure contact.

Abstract: This work focuses on the acoustic emission signals related to three different tribological systems: a rotary sliding contact between WC-Co pins against alumina flat counterfaces, a fretting contact between alumina pins against alumina flat counterfaces and a reciprocating sliding flat on flat contact between thermoplastic polyurethanes (TPU) and a steel counterface. This document relates dependences observed between tribological behaviors and variations of acoustic emission signals. Therefore, a third body approach is used to explain these correlations and to highlight the aspect of nature and associated energy of acoustic emission sources.

Abstract: The wear is very difficult to characterize because of its complexity and its measurement phenomenon. Our work is to prepare samples Fan blades, worn, to determine the nature of the wear and damage them. For these reasons, the characterization of these samples was conducted in different microscopic and macroscopic scales. We used non-destructive techniques such as eddy current and penetrant methods. The results obtained allowed us to see the deterioration of fins from one floor to another. These results are directly related to the effects of mechanical, thermal and pressure. It has been, in addition to detecting a different type of damage these fan blades that is the fatigue damage.

Abstract: Buckling of stiffened panels is strongly affected by initial geometric imperfections. The panel assembling technique used can influence both the initial geometric imperfections pattern and material inohomogeneities. It was recognized for the particular case of stir friction welded stiffened panels that the presence of a weld can decrease significantly buckling strength. This is mainly due to the reduction in material strength in the weld zone. In this work, stir friction welded stiffened panels are modeled by using the finite element method. The modelling takes into account distributed and localized initial geometric imperfections as well as material degradation that are generated in the heat affect zone by this process. A parametric study was conducted on the effects of magnitude of geometric distributed imperfections; position, length and depth of a localized depression; as well as material degradation occurring near the weld stripe. Artificial neural network models were built by using the results of various simulations performed according to full factorial design of experiment tables. This has enabled to assess reliability of design of a stiffened panel with regards to the buckling limit state by means of Monte Carlo approach.

Abstract: The Friction Stir Welding FSW is a welding process in the solid state to join metallic alloys that is used in many industrial applications such as aerospace, automotive and shipbuilding. The process parameters such as the geometry of the tool, the speed of rotation and the speed of advance play a major role in determining the weld quality. In this work, an attempt was made to establish a relationship between the properties of the base material and FSW process parameters. Welds were made using AA1050 Aluminum alloy with different combination of parameters. Metallographic analysis was performed to verify the (faulty or fault-free) weld quality. Tests microhardness, tensile and bending were carried out to study the changes in the mechanical properties in the weld zone.