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This paper proposes a new method of 3D roughness peaks curvature radius calculation and its application to tribological contact analysis as a characteristic signature of tribological contact. This method is introduced through the classical approach of calculation of radius of asperity in 2D. Actually, the proposed approach provides a generalization of Nowicki's method [], depending on horizontal lines intercepting the studied profile. Here, the basic idea consists in intercepting the rough surface by a horizontal plane and to calculate the cross section area without including “islands into islands”, i.e. the small peaks enclosed in bigger ones. Then, taking into account the maximal value of the height amplitude of the roughness included into this area, an appropriate algorithm is proposed, without requiring the classical hypothesis of derivability, which may be unstable when applied to engineering surfaces. This methodology is validated on simulated surfaces, and applied to engineering surfaces created experimentally, with a laboratory aluminium strip drawing process. The regions of the textured and lubricated specimens surface are analysed, and the results gives interesting prospects to qualitatively identify the local lubrication regimes: regions with high curvature radii correspond to severe contact (boundary/mixed lubrication regime) while regions with low curvature radii correspond to hydrodynamic lubrication regime.

International audience; This paper proposes a new method of roughness peaks curvature radii calculation and its application to tribological contact analysis as characteristic signature of tribological contact. This method is introduced via the classical approach of the calculation of radius of asperity. In fact, the proposed approach provides a generalization to fractal profiles of the Nowicki's method [Nowicki. Wear Vol. 102, p. 161-176, 1985] by introducing a fractal concept of curvature radii of surfaces, depending on the observation scale and also numerically depending on horizontal lines intercepted by the studied profile. It is then established the increasing of the dispersion of the measures of that lines with that of the corresponding radii and the dependence of calculated radii on the fractal dimension of the studied curve. Consequently, the notion of peak is mathematically reformulated. The efficiency of the proposed method was tested via simulations of fractal curves such as those described by Brownian motions. A new fractal function allowing the modelling of a large number of physical phenomena was also introduced, and one of the great applications developed in this paper consists in detecting the scale on which the measurement system introduces a smoothing artifact on the data measurement. New methodology is applied to analysis of tribological contact in metal forming process.

The lubricant entrapment and escape phenomena in metal forming are studied experimentally as well as numerically. Experiments are carried out in strip reduction of aluminium sheet applying a transparent die to study the fluid flow between mesoscopic cavities. The numerical analysis involves two computation steps. The first one is a fully coupled fluid-structure Finite Element computation, where pockets in the surface are plastically deformed leading to the pressurization of the entrapped fluid. The second step computes the fluid exchange between cavities through the plateaus of asperity contacts with the plane tool, one cavity at a time.

Method validation is essential to ensure that an analytical method is fit for its intended purpose. Additionally, it is advisable to estimate measurement uncertainty in order to allow a correct interpretation of the results generated by analytical methods. Measurement uncertainty can be efficiently estimated during method validation as a top–down approach. However, method validation predictions of the quantitative performances of the assay and estimations of measurement uncertainty may be far away from the real performances obtained during the routine application of this assay. In this work, the predictions of the quantitative performances and measurement uncertainty estimations obtained from a method validation are compared to those obtained during routine applications of a bioanalytical method. For that purpose, a new hydrophilic interaction chromatography (HILIC) method was used. This method was developed for the determination of cidofovir, an antiviral drug, in human plasma. Cidofovir (CDV) is a highly polar molecule presenting three ionizable functions. Therefore, it is an interesting candidate for determination by HILIC mode. CDV is an acyclic cytidine monophosphate analog that has a broad antiviral spectrum and is currently undergoing evaluation in clinical trials as a topical agent for treatment of papillomavirus infections. The analytical conditions were optimized by means of design of experiments approach in order to obtain robust analytical conditions. These ones were absolutely necessary to enable the comparisons mentioned above. After a sample clean-up by means of solid phase extraction, the chromatographic analysis was performed on bare silica stationary phase using a mixture of acetonitrile–ammonium hydrogen carbonate (pH 7.0; 20 mM) (72:28, v/v) as mobile phase. This newly developed bioanalytical method was then fully validated according to FDA (Food and Drug Administration) requirements using a total error approach that guaranteed that each future result will fall within acceptance limits of ±30% with a probability of 95% over a concentration range of 92.7–1020 ng/mL. A routine application of the cidofovir determination in two pre-clinical trials demonstrated that the prediction made during the pre-study validation was consistent by retrospective analysis of the quality control (QC) samples. Finally, comparison of the measurement uncertainty estimations calculated from the method validation with those obtained from the routine application of the method was performed, stressing that the estimations obtained during method validation underestimated those obtained from routine applications and that the magnitude of this underestimation was function of the cidofovir concentration. Finally, this new HILIC method is reliable, easily applicable to routine analysis and transposable at low cost in other laboratories.

The mechanisms of liquid lubrication in metal forming are studied at a mesoscopic scale, adopting a 2D sequential fluid‐solid weak coupling approach earlier developed in the first author’s laboratory. This approach involves two computation steps. The first one is a fully coupled fluid‐structure Finite Element computation, where cavities in the surface are plastically deformed leading to the pressurization of the entrapped fluid. The second step computes the fluid exchange between cavities through the plateaus, one cavity at a time. This second step consists in solution of the local Couette’s equation, at the asperity level, in order to quantify the fluid leakage in the cavity/plateau network using the lubricant pressure computed previously.The numerical simulation is validated by experimental tests in plane strain strip reduction of aluminium sheet provided with model cavities in form of pyramidal indentations. The tests are performed with variable reduction and drawing speed under controlled front and ba...

This paper presents a thermodynamic study of Chemical Bath Deposition (CBD) of zinc sulfide based films in aqueous solution. The aim is a better understanding of the effect of temperature and pH on the deposition mechanism and film composition. The formation of solid phases has been predicted by means of the precipitation conditions of ZnO, Zn(OH)2 and ZnS as a function of temperature between 298 and 363 K. Films have been deposited, without ammonia, on the basis of calculated diagrams and first results on solar cells based on electrodeposited CuIn(S,Se)2 layers have been demonstrated.

The photoluminescence properties of a periodically structured organic light-emitting diode are presented. Patterning is achieved using an original single-step autostructuration technique based on photoinduced effects in azo-polymer films. We show that single beam laser irradiation can lead to the induction of regular two-dimensional surface relief gratings. The waveguide properties of these microstructures as well as their effect on the emission properties of a light-emitting material are studied. We demonstrate a new straightforward technique to improve external light emission efficiency by outcoupling part of the light that was initially guided into the different diode layers.

The high pressure structural and elastic behaviour of LGT single crystal has been explored. The phase diagram has been investigated up to 20 GPa by x-ray diffraction and the equation of state deduced. The complete set of second order elastic constants (S.O.E.C.) and their pressure dependence have been determined by bulk acoustic wave measurements up to 8 GPa. The bulk and linear moduli and their pressure variations have been calculated and compared to values obtained by x-ray diffraction. The stability Born criteria have been deduced.

Optical induction of quasi permanent birefringence and dichroism in azo-dye polymers has been the subject of many studies. It is now well established that azobenzene molecules, when excited with a polarized light beam whose wavelength lies in their absorption band, undergo a reversible trans-cis-trans isomerization process leading to a molecular quasi-permanent reorientation in a direction perpendicular to the light polarization direction. More recently, it has been shown that irradiation of an azo-polymer thin film with an interference pattern between polarized laser beams could lead to a direct and reversible topographic modification of the polymer film surface resulting in the induction of surface relief gratings in conjunction with the light interference pattern. [1–3] The position of the maximum heights correspond to the light intensity minima. It has been demonstrated that gratings dynamics and modulation amplitude depend on several parameters among which the polymer film thickness, the grating pitch, the power and time of irradiation, or the writing beams polarization: p-: p-polarizations leading to diffraction efficiencies ten times larger than s-: s- polarizations, modulation amplitudes being larger as the grating pitch is higher. Maximum amplitudes of modulation can be of the order of the initial polymer film thickness. Saturation was shown to depend only on the total energy accumulated although saturation is reached faster as the irradiation power increases.

Several kinds of tests exist to characterize the galling of metals, such as that specified in ASTM Standard G98. While the testing procedure is accurate and robust, the analysis of the specimenʼs surfaces () for the determination of the critical pressure of galling remains subject to operator judgment. Based on the surfaceʼs topography analyses, we propose a methodology to express the probability of galling according to the macroscopic pressure load. After performing galling tests on 304L stainless steel, a two-step segmentation of the S q parameter (root mean square of surface amplitude) computed from local roughness maps () enables us to distinguish two tribological processes. The first step represents the abrasive wear (erosion) and the second one the adhesive wear (galling). The total areas of both regions are highly relevant to quantify galling and erosion processes. Then, a one-parameter phenomenological model is proposed to objectively determine the evolution of non-galled relative area A e versus the pressure load P, with high accuracy () with and with ). From this model, the critical pressure of galling is found to be equal to . The roughness parameter (the five deepest valleys in the galled regionʼs surface) is the most relevant roughness parameter for the quantification of damages in the 'galling region'. The significant valleys' depths increase from 10 μm–250 μm when the pressure increases from 11–350 MPa, according to a power law (, with ).

Based on the importance of uncertainty, another approach to estimate this parameter of performance considering the total error (systematic and random) was applied. The data were obtained from the two main steps of an analytical method lifecycle: validation and routine for levonorgestrel (LNG) assay and routine for oxygen assay. Results obtained allowed drawing suitable conclusion in terms of prediction of routine and establishment of norms.

This paper presents the influence of the solution chemistry of chemical bath deposition (pH and complexing agents) on the performance of CuIn(S,Se)2 cells after an initial CN treatment. It is shown that it is possible to modify the deposition conditions of the CdS by increasing the pH of the solution and by replacing the complexing agent (ammonia) by citrate ions. Both NH3 based and citrate based process give very homogenous and covering thin films. However, in the case of the citrate based process a decrease of open circuit voltage (Voc) and fill factor (FF) and thus of the cell efficiencies is observed. This points out that the main role of the buffer layer is not only related to the specific properties of the CdS itself but also to the near surface modifications of the CuIn(S,Se)2 caused by the presence of the complexing agent in the bath.