The role of temperature and frequency on fretting wear of a like-on-like stainless steel contact

The influences of environmental temperature and fretting frequency on the mechanisms and rates of wear in a like-on-like 304 stainless steel contact were examined, and mainly attributed to changes in the mechanical response of the bulk material and to changes in the behaviour of the oxide debris formed in the fretting process. At low temperatures, wear proceeds by continual oxide formation and egress from the contact, whilst at high temperatures, the rate of wear is much reduced, associated with the development of oxide formed into a protective bed within the contact. The temperature at which the change between these two behaviours took place was dependent upon the fretting frequency, with evidence that, at this transition temperature, changes in behaviour can occur as the fretting test proceeds under a fixed set of conditions. An interaction diagram has been developed which provides a coherent framework by which the complex effects of these two parameters can be rationalised in terms of widely accepted physical principles

Evaluation of Multidrug Efflux Pump Inhibitors by a New Method Using Microfluidic Channels

Fluorescein-di-β-d-galactopyranoside (FDG), a fluorogenic compound, is hydrolyzed by β-galactosidase in the cytoplasm of Escherichia coli to produce a fluorescent dye, fluorescein. We found that both FDG and fluorescein were substrates of efflux pumps, and have developed a new method to evaluate efflux-inhibitory activities in E. coli using FDG and a microfluidic channel device. We used E. coli MG1655 wild-type, ΔacrB (ΔB), ΔtolC (ΔC) and ΔacrBΔtolC (ΔBC) harboring plasmids carrying the mexAB-oprM (pABM) or mexXY-oprM (pXYM) genes of Pseudomonas aeruginosa. Two inhibitors, MexB-specific pyridopyrimidine (D13-9001) and non-specific Phe-Arg-β-naphthylamide (PAβN) were evaluated. The effects of inhibitors on pumps were observed using the microfluidic channel device under a fluorescence microscope. AcrAB-TolC and analogous pumps effectively prevented FDG influx in wild-type cells, resulting in no fluorescence. In contrast, ΔB or ΔC easily imported and hydrolyzed FDG to fluorescein, which was exported by residual pumps in ΔB. Consequently, fluorescent medium in ΔB and fluorescent cells of ΔC and ΔBC were observed in the microfluidic channels. D13-9001 substantially increased fluorescent cell number in ΔBC/pABM but not in ΔBC/pXYM. PAβN increased medium fluorescence in all strains, especially in the pump deletion mutants, and caused fluorescein accumulation to disappear in ΔC. The checkerboard method revealed that D13-9001 acts synergistically with aztreonam, ciprofloxacin, and erythromycin only against the MexAB-OprM producer (ΔBC/pABM), and PAβN acts synergistically, especially with erythromycin, in all strains including the pump deletion mutants. The results obtained from PAβN were similar to the results from membrane permeabilizer, polymyxin B or polymyxin B nonapeptide by concentration. The new method clarified that D13-9001 specifically inhibited MexAB-OprM in contrast to PAβN, which appeared to be a substrate of the pumps and permeabilized the membranes in E. coli

EXPERIMENTAL STUDIES OF SHEAR ZONES DURING CHIP FORMATION IN METAL CUTTING

Les études des micromécanismes de coupe rapide des métaux sont réalisées à l'aide d'une technique fondée sur le mouvement d'un pendule. Un outil tranchant fait une rayure de la forme d'un arc sur la surface de l'échantillon et la structure interne des zones de cisaillement est figée à l'aide d'un système d'arrêt rapide pendant le processus de formation du copeau. Une équation reliant des paramètres de coupe aux mécanismes de déformation dans les zones de cisaillement est proposée.Dynamic studies of the micromechanisms of metal cutting are performed with a pendulum technique. A tool edge cuts an arcuate groove in the specimen surface, and the internal structure of shear zones during chip formation is frozen with the aid of a quick-stop arrangement. An equation relating bulk cutting parameters to the deformation mechanisms in shear zones is suggested

Fretting of titanium nitride and diamond-like carbon coatings at high frequencies and low amplitude

Physically vapour-deposited TiN and chemically vapour-deposited diamond-like carbon (DLC) coatings were tested against corundum under conditions of fretting at frequencies of 750 and 1500 Hz and at a displacement amplitude of 1 mu m. A ballon-flat configuration without external lubrication was used. The energy dissipated in the contact was calculated from the evaluation of experimental tangential force-displacement hysteresis loops. Fretting damage and material modifications in the contact zone were evaluated with light optical microscopy, scanning electron microscopy, laser profilometry and micro-Raman spectroscopy. Information from on-line mechanical analysis and from off-line material behaviour analysis is used to present an explanation of the damage processes. The degradation of the TiN coating is dominated by the development of an oxidation reaction. Under certain conditions the amorphous structure of the DLC will undergo partial graphitization. A comparison with fretting tests at lower testing frequency and higher displacement amplitude shows that the mechanisms of degradation are very different.status: publishe