Jean-Yves Paris

General Procedure for Selecting and Testing Materials and Coatings in Response to a Tribological Problem

In general, there is no available tool which can help engineers and researchers to choose optimal materials for friction pairs. This article proposes a dual approach for the choice of materials and coatings. First, in order to select the initial materials, a selection matrix helps to rank a reduced number of solutions to a tribological problem with the aim of building the most credible and viable experimental campaign. Then, this experimental phase is necessary for final selection taking into account tribological properties. The final step involves experimental validation on a prototype and on the real device. This methodology was applied on the complex geometry of an air compressor under severe friction conditions. Technical specifications are defined by a functional analysis of the tribological system. Then, the selection matrix is created on the basis of empirical rules and bibliographic data, including predetermined material/coating properties, process considerations, and tribological features, in accordance with the functional analysis. As an example, four potential solutions were tested: diamondlike carbon (DLC) and polytetrafluoroethylene (PTFE) coatings on 15-5PH stainless steel and two composites, reinforced PTFE and polyetheretherketone (PEEK). Experimental results were then compared to expected values from the specifications. The performance of each solution was highlighted by a graphic radar representation. The selection matrix gave the DLC coatings as one of the best solutions, and experimental tests confirmed this choice while allowing to refine the preselected solutions. This result shows that the selection matrix gives a reliable choice of optimal solutions.

Development of an in-house cutting forces simulation for fir tree broaching process

This article proposes a simulation of cutting forces in broaching of fir tree slots. Every step needed to build an in-house fir tree broaching simulation is presented. This simulation is based on the discretization of each tooth of the broach, computation of elementary cutting forces of each discretized section, and finally the summation of each elementary cutting force into a global axes system. This work also presents orthogonal cutting experiments to implement realistic specific cutting forces into the model. The simulation obtained is compared with the real force signals of a fir tree broach to evaluate the quality of the simulation. At the end, the application to industrial context is developed.

Comprehension of Thermomechanical Phenomena and Material Behavior During High Speed Contact

Civil aircraft engines present a wide range of labyrinth seals to ensure a good airtightness between the different components of the secondary air system. An increase in efficiency requires lower clearances gaps. As a consequence, brief contacts between rotating and stationary parts may occur especially during the engine running-in period. Such events can cause critical situations (seizure…) depending on the working conditions. In this paper, experimental simulations by means of a high-speed contact test device (76 m s−1) was developed to precisely recreate the friction conditions occurring in a turboshaft labyrinth seal and to better understand the material behavior in such tribological cases. This device was instrumented to carry out mechanical (axial and tangential forces and torque) and thermal measurements (IR camera and pyrometer). An experimental campaign was carried to study the contact between a Ti6Al4V rotor and an abradable coating of Al-Si polyester. Presented results show the complex interactions that strongly depend on the way the worn material behaves in the contact area. Local interaction dynamics are analysed with regards to mechanical and thermal measurements with different rotating speeds, incursion depths, and interaction speeds.

Correlation between Acoustic Emission Signals and Friction Behavior under Different Sliding Configurations and Materials Pairs

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.