Multiscale Topography Analysis of Waterjet Pocketing of Silica Glass Surfaces

International audienceGlass workpieces are mainly planar and obtained by diamond cutting however if free-form surfaces are required, manufacturing process is usually based on shaping grinding wheels. Multi-axis waterjet cutting, an other means of obtaining planar workpieces, could also be used to machine complex shapes with appropriate manufacturing strategies. Water jet pocketing could also be achieved but it brings challenging issues since the high pressure jet composed of water and abrasive particles must be contained inside the machined pocket. Water jet glass machining optimization requires understanding of numerous parameters such as interaction between the jet and the brittle material behavior or the identification of the jet himself. We focus our investigation on bottom pocket surfaces to study these parameters. Pocket bottom surfaces are characterized by multi-scale defects: shape defects influenced by the tool path and the manufacturing strategy, macro-craters at waviness scale due to the jet interactions, micro-craters at roughness scale due to particles impacts, sub-surface damages (SSD) at micro- roughness scale. This paper focuses on the study of macro and micro craters. We propose a decomposition of the multi-scale defects using modal filtering. Residual topography will then be analyzed to characterize the surface damages

Multi-scalar analysis of hip implant components using modal decomposition

International audienceThis paper presents a metrological analysis of hip prosthesis components. When changing ceramic prostheses, the surgeon sometimes finds traces of alloy lying in the insert or the femoral head. These traces can be thin and accurate or as a wide band. From the measurements made on the contact areas of hip prosthesis components, we analyse these phenomena by highlighting the defects of form, waviness and roughness of these surfaces using a novel geometric parameterization (namely modal parameterization). The aim of this work is to isolate these defects to characterize the prostheses components. We show that this parameterization allows a multi-scale analysis of surfaces regardless of the type of wear of the prosthesis, and that the results offer some relevant explanations to the analysis of visible damage on the prostheses. In a later study, we are going to analyse the defects influence on the alteration of the performance of hip prostheses

Sub-millimeter measurement of finite strains at cutting tool tip vicinity

The present paper details a simple and effective experimental procedure dedicated to strain measurement during orthogonal cutting operations. It relies on the use of high frame-rate camera and optical microscopy. A numerical post-procedure is also proposed in order to allow particle tracking from Digital Image Correlation (DIC). Therefore strain accumulation within finite strains framework is achieved. The significant magnitude of the calculated strains is partially due to a singular side effect that leads to local material disjunction. The strain localization in the Adiabatic Shear Band (ASB) exhibits different strain paths at various locations along this band and a non-linear evolution of the strain accumulation. A focus is made on the formation mechanisms of serrated chips obtained from Ti6Al4V titanium alloy. The side observation performed during this work allow to proposed three possible scenarios to explain this very phenomenon