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International audience; Metal-matrix composites with solid lubricant reinforcements may present a suitable alternative to improve the tribological behavior of sintered components. Besides the performance during the application, the presence of solid lubricants may also modify component manufacture, for example, during machining operations to achieve complex shapes not directly obtained from the sintering process. This work describes a numerical and experimental analysis on the orthogonal cut of metal-matrix composites composed of FeMoS particles embedded in an Astaloy 85 Mo (Höganäes AB) matrix. Specimens were prepared using the Spark-Plasma Sintering (SPS) technique, from mixtures containing powders of Astaloy 85 Mo steel and 2 wt% or 4 wt% of molybdenum disulfide (MoS2). An unreinforced Astaloy 85 Mo specimen (without MoS2) was also included in the analysis. Different microstructures were observed after SPS. The unreinforced specimen presented a ferrite-pearlite structure with a porosity level below 2% and the specimen sintered with 2 wt% of MoS2 presented iron sulfide particles dispersed in the steel matrix. The structure of the specimen sintered with 4 wt % was more complex, with two distinct phases dispersed in the Astaloy 85 Mo matrix. Experimental orthogonal cuts were conducted on the three specimens using a shaper machine tool equipped with a tungsten carbide (WCCo) cutting insert. Tests were recorded using a high-speed camera. The machined surfaces were later analyzed with an optical profilometer and in a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS). The chips were also characterized. The cutting operation was simulated by two-dimensional (2D) finite-element analysis. The meshes were prepared based on the specimen microstructures and considering the properties of the individual phases. Results have indicated significant differences in the cutting process. Observation of the chip surfaces indicates plastic deformation on the unreinforced specimen, in opposition to more uniform scratches on the composite surfaces, especially that of the specimen sintered with 4 wt % of MoS2.

Multiple parallel scratches are often analyzed to understand the material removal mechanisms due to abrasion. However, successive scratches with different orientations may represent better the conditions found in machining processes, such as honing and belt finishing. The objective of this work was to analyze the cutting forces and the phenomena of material removal due to abrasion, arising from angular scratches in low carbon steel. Experimental and numerical techniques were considered. In both, analyses considered the presence of an initial set of parallel scratches, followed by a second set of scratches with different orientations (10, 20 or 30°) with respect to the previous one. The cutting action was performed by a tool representing an abrasive particle, which had a cono-spherical geometry with 235 µm tip radius and 30° apex angle. The cutting settings were: 50 m/min scratch velocity and 100 µm depth of cut. In the experimental part, scratches were conducted using a shaper machine tool equipped with a tungsten carbide (WC-Co) stylus. Tests were conducted on a Kistler platform, which allowed force measurement. Surfaces were later analyzed with an optical profilometer. The numerical simulations considered a ductile damage model with element deletion to provide the material removal during the scratches. Experimental and numerical results showed that the angle affects the cutting forces, especially when one scratch crosses a previously scratched region. The 20° case was the most critical, especially in terms of the cutting forces, due to the accentuated material strain-hardening for this condition. Likewise, this fact was corroborated by numerical results, which indicated a higher energy necessary to plastic deformation, and a reduced material removal at 20°.

International audience

Various Ni–Zn–P alloy coatings were deposited onto aluminum substrates using electroless plating from a sulphate bath containing varying amounts of zinc (II) ions. Different techniques, such as scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, were employed to characterize the morphology, composition and structural properties of the resulting films. The effect of varying Zn content on the corrosion properties of the coatings was tested in 3 wt.% NaCl media, by means of current–potential curves, potential transients and electrochemical impedance spectroscopy measurements. It was found that increasing ZnSO4 concentration from 5 to 25 g l−1 in the plating bath, increases the Zn content in the film from 9.90 wt.% to 12.7 wt.%, reduces the film thickness, modifies the surface morphology and significantly reduces the corrosion rate.

The vibrations undergone by men are a well-known and widely studied risk factor in the industrial world. They are transmitted to the whole body or the upper limbs and they are measured, and limited, according to international standards. Disorders resulting from exposure to vibration are varied in nature: osteoarticular, muscular, vascular, and neurological. In this context, an European Directive 2002/44/EC to the protection of workers exposed to vibration, precises thresholds for vibration exposures and defines the procedure for risk prevention. Nevertheless, the effect of vibration is little studied in sports despite the ubiquity of these. Vibration can induce discomfort, degrading performance or causing musculoskeletal disorders. This paper makes an overview of the studies involving the vibrations during cycling. At first, this paper will summarize the different standards and guidelines relating vibration in humans, which present a guide for the measurement and evaluation of the vibration and exposure limits. Secondly, this paper presents a state of the art vibration effects: (i) the physiological and pathological disorders in athletes, (ii) and the performance. A third part will be devoted to the synthesis of numerical studies that represent the biodynamic response and help to predict the effects of human body vibration. Finally, new research and innovations will be discussed based on studies in other sports.

The aim of this study was to test the validity and the reliability of the G-Cog which is a new BMX powermeter allowing for the measurements of the acceleration on X-Y-Z axis (250 Hz) at the BMX rear wheel. These measurements allow computing lateral, angular, linear acceleration, angular, linear velocity and the distance. Mechanical measurements at submaximal intensities in standardized laboratory conditions and during maximal exercises in the field conditions were performed to analyse the reliability of the G-Cog accelerometers. The performances were evaluated in comparison with an industrial accelerometer and with 2 powermeters, the SRM and PowerTap. Our results in laboratory conditions show that the G-Cog measurements have low value of variation coefficient (CV=2.35%). These results suggest that the G-cog accelerometers measurements are reproducible. The ratio limits of agreement of the rear hub angular velocity differences between the SRM and the G-Cog were 1.010 × ÷ 1.024 (95%CI=0.986-1.034) and between PowerTap and G-Cog were 0.993 × ÷ 1.019 (95%CI=0.974-1.012). In conclusion, our results suggest that the G-Cog angular velocity measurements are valid and reliable compared with SRM and PowerTap and could be used to analyse the kinematics during BMX actual conditions.

Vibrations in cycling produced by road irregularities could cause health problems and affect the cyclist’s comfort and performance. Therefore researchers and manufacturers focus their efforts to reduce the vibrations., Las vibraciones en el ciclismo producidas por las irregularidades de la carretera podrían causar problemas de salud y afectar a la comodidad y el rendimiento del ciclista. Por ello, los investigadores y los fabricantes centran sus esfuerzos en reducir las vibraciones., 1. GRESPI, Moulin de la Housse, Université de Reims Champagne Ardenne, Reims, France 2. IN’BO, ZA Les Bouleaux, Les Voivres, France 3. Escuela Colombiana de Ingeniería Julio Garavito, Bogotá D.C., Colombia 4. Montclair State University, Upper Montclair, New Jersey, USA 5. EPF, 3 bis rue Lakanal, Sceaux, France 6. Arts et Métiers ParisTech, MSMP / EA7350, Châlons-en-Champagne, France

The aim of this study was to describe and validate a new cycling ergometer with original characteristics that allow the measurement of biomechanical variables with position and crank inertial load used by the cyclist in field condition. The braking pedalling force, that permitted the simulation of the resistance to the cyclist in the field, is performed with a brushless electric motor. The validity and the reproducibility of the power output measurements were compared with the widely accepted SRM powermeter. The results indicate that taking into account a systematic error, the measurements are valid compared with the SRM, and the reproducibility of the power output measurements is similar to the SRM. In conclusion, this ergometer is the only one that allows at the same time for (1) valid and reproducible power output measurements at submaximal intensity, (2) utilisation of the personal bicycle of the cyclist, and (3) simulation of the inertial characteristics of the road cycling.

Hot forging tools are exposed to severe thermo-mechanical load which cause their failure. The main failure mechanisms are mechanical fatigue, thermal fatigue, plastic deformation and abrasive wear. The use of hardfacing is an effective solution to increase tool life and consequently reducing the cost of forged part. In this work the use of a cobalt-base hard-facing obtained by Plasma Transferred Arc process is studied. The hardfacing is used for tool failed by thermal cracking. The high rate of temperature variation and high temperature gradient at the tool surface induce material softening and surface plastic deformation. These plastic deformations are accumulated during each cycle and eventually cause cracks in the most exposed zones and then tool failure after a few thousand cycles. Microstructure characterization and mechanical behavior analyses are required to prove the quality of coating. Finite element method is used to calculate stress distribution in tool resulting from external loading in order to optimize the thickness and the choice of coating used. Evaluation of residual stresses by ultrasonic technique is used to validate the finite element results and analyze the stress state by non destructive method.

The aim of this study was to test the validity and reliability of the G-Cog which is a new BMX power meter allowing for the measurements of the power output (250 Hz) at the BMX rear wheel during actual cycling and laboratory conditions. Sprints in road cycling (6-8 s) from static start and incremental tests in the laboratory (100-400 W) have been performed to analyse the validity and reliability of the power output values by comparison with 2 devices: The PowerTap and the SRM which are considered as the gold standard. The most important finding of this study is that the G-Cog power output data were not valid and reliable during sprint and standardised laboratory tests compared with the SRM and the PowerTap devices. During the sprint and the laboratory tests the ratio limits of agreement of the power output differences between the SRM and G-Cog were 1.884×÷1.970 (95% CI = .956-3.711) and 12.126×÷16.281 (95% CI = 0.745-197.430), respectively. In conclusion, the G-Cog must be used with caution regarding the power output measurements. Nevertheless, the G-Cog could be used for the first time to analyse the determinants of the BMX performance from the pedalling profile.

This paper proposes to highlight two aspects of denoising in vibration analysis. The first aspect aims to reveal the singularities, and the second eliminates the noise in order to keep the useful signal. These two aspects are the cause of the surjection of denoising, especially due to the choice of the performance criteria. This paper highlights the use of denoising through these aspects, and then proposes a performance criterion suitable for vibration analysis as part of a noise suppression, to apply a processing method. This paper provides a reflection on the use of discrete wavelet transform through the various parameters which are used during processing.

Nowadays, high quality product becomes more and more required. Particulates reinforced composites have been established as competitive materials for naval, automotive and aerospace manufactory. However, the fatigue behaviour of such materials is so complex and diverse that much more investigations still required for completing knowledge in these fields. Metal matrix composites (MMC) have been increasingly used for critical structural applications in industrial sectors.

In the world of cycling, vibrations generate back (Hill et al. 2009) and hand–arm system injuries (Schwellnus and Derman 2005) resulting from the trauma of bones, causing work disability. At the sa...

Exposure to vibrations can cause discomfort. It can negatively affect performances and is risky for health and for the safety of humans. In particular, the hand–arm system may suffer from vascular ...

BMX racing is an Olympic sport which requires a generation of a high power level (Zabala et al. 2009). This level of power is widely used to evaluate athletes' explosive power which may be poorly e...