Manual asymmetries in reaching movement control. II: Study of left-handers.

Two experiments performed with left-handed subjects investigated how the manual asymmetries and hemispheric specialization involved in visuo-manual coordination are associated with handedness. Pro and retroactive processes involved in rapid movement control were analyzed according to the different movement parameters to be controlled, similar to studies performed with right-handers (Boulinguez, Nougier and Velay, 2001). Manual performances and kinematic properties of reaching movements showed that the left and right hands of left-handers behaved in the same way as the left and right hands of right-handers. Results are discussed in the light of the independence of handedness and other forms of cerebral dominance in sensori-motor information processing involved in hand movements

Manual asymmetries in reaching movement control. I: Study of right-handers.

Two experiments investigated manual asymmetries in the control of rapid reaching movements according to the movement parameters to be controlled. Single- and double-step reaching movements were performed by right-handed subjects with both hands. Pro and retroactive processes involved in rapid movement control were investigated. Manual performances and kinematic properties of hand movements showed that various forms of hemispheric specialization were involved in sensori-motor information processing. It was shown that the effects of hemispheric specialization were specific to the task constraints, that is, to the various operations involved in movement control

Manual asymmetries in reaching movement control. I: Study of right-handers.

Two experiments investigated manual asymmetries in the control of rapid reaching movements according to the movement parameters to be controlled. Single- and double-step reaching movements were performed by right-handed subjects with both hands. Pro and retroactive processes involved in rapid movement control were investigated. Manual performances and kinematic properties of hand movements showed that various forms of hemispheric specialization were involved in sensori-motor information processing. It was shown that the effects of hemispheric specialization were specific to the task constraints, that is, to the various operations involved in movement control

Identification de paramètres de comportement de membranes en polymères durant le procédé de soufflage

Les propriétés bi-axiales des matériaux tels que les élastomères ou les polymères, utilisés dans des applications mécaniques ou thermoplastiques, sont souvent difficiles à identifier. Pourtant, elles s'avèrent nécessaires pour la simulation des procédés de thermoformage, d'injection-soufflage ou de formage par soufflage. La démarche globale de ce travail de recherche est d'identifier à partir d'extraction de contour et de mesure de champs de surface, et par analyse inverse en utilisant des logiciels de simulations numériques type Éléments Finis, le comportement de ce type de matériaux. Le comportement rhéologique et les propriétés mécaniques de tels matériaux peuvent être obtenus en utilisant un rhéomètre permettant le soufflage de bulle. Dans cet article, des résultats expérimentaux obtenus à l'aide d'un rhéomètre élongationnel développé au laboratoire sont présentés. Une description détaillée de la partie expérimentale est faite. Deux méthodes de mesures optiques sont utilisées : (i) une méthode développée à partir d'une mesure de contour avec une seule caméra CCD ; (ii) une méthode de mesure de champs par stéréo-corrélation d'images. La modélisation numérique est réalisée en utilisant le logiciel Éléments Finis ABAQUS$^{\circledR }$. Des résultats préliminaires d'identification (prise en compte des conditions aux limites, fonction coût, paramètres du modèle de comportement) sont présentés, ainsi que la validation de ces résultats en réalisant des essais de traction

Numerical life prediction of mechanical fatigue for hot forging tools

In the forging industry, tools represent an important part in term of production and costs. Enhancing their life cycle is then a challenging issue. Several mechanical and thermal mechanisms are responsible for hot forging tools damage such as wear, thermal and mechanical fatigue. This work will be focused only on the mechanical fatigue life prediction for hot forging tools. Both experimental data analysis and numerical simulation will be discussed in this paper. The aim is to perform qualitative and quantitative indicators of mechanical fatigue. First, experimental data of fatigue tests are used to identify both plastic strain-based Manson Coffin and stress-based Basquin life laws for 2 tool steel grades. These laws are quite classical for fatigue prediction [1-4]. The half-life strain or stress amplitudes are usually used for their identification but these amplitudes are very expensive to obtain from a numerical point of view since it is well known that hot work martensitic steels present a continuous cyclic softening from the first cycle till the rupture. Therefore an important number of cycles have to be simulated to reach these mechanical parameters at half-life. For all theses reasons, an alternative methodology is used [4]. The fatigue life curves are established using the mechanical parameters that are identified from the first hysteresis loops of fatigue experiments. Comparisons are performed with the fatigue laws coming from more classical identification procedure performed at half life cycle. Good agreement is shown between experimental data and the new laws. A lower scattering is even observed in experimental results in comparison to the traditional fatigue laws. Then these new laws are introduced in the commercial software Forge® and are then applied to different industrial cases. A pretty good agreement is observed between predicted tool life and industrial values. © Springer/ESAFORM 2009

Oxygen/nitrogen-assisted embrittlement of titanium alloys exposed at elevated temperature

Due to high solubility of oxygen and nitrogen in titanium alloys, the influence of the diffusion zone on the macroscopic tensile properties of pre-oxidized annealed Ti-6Al-4V tensile specimens was examined at room temperature. Thin microtensile specimens were prepared with different thicknesses ranging from 100 µm to 500 µm and then exposed at 750°C for durations between 5 and 200h. A dedicated gripping technique was developed in the present study to investigate the brittleness of such pre-oxidized and ultrathin specimens at room temperature. Tensile testing was paired with digital image correlation techniques to assess both macroscopic deformation and full-field strain maps. High temperature pre-oxidation treatments significantly decreased the ductility of the specimen and the tensile strength of the materials (yield strength and ultimate tensile strength). Fractographic examinations revealed typical brittle fracture features in the oxygen/nitrogen-affected diffusion zone in the periphery of the cross-section while the fracture remained ductile in the core of the specimen for most of the specimens. Some specimens fully failed in a brittle manner for “(pre-ox. duration)1/2/thickness” configurations with ratio equal or higher than 0.45 h1/2.µm-1

Thermo-mechanical fatigue behaviour of welded tubular parts made of ferritic stainless steel

Car exhaust manifolds are critical components subjected to cyclic thermo-mechanical fatigue (TMF) during function. To reduce design costs, robust numerical design tools are required to assess their behaviour and lifetime. Manifolds are constructed by welding several ferritic stainless steel tubular parts together. TMF behaviour of a 1.4509 steel in welded and unwelded conditions is assessed under various loading conditions. Unified elasto-viscoplastic constitutive laws are developed. The specific thermo-mechanical behaviour of the heat-affected zone (HAZ) is also taken into account for welded steel. The reliability of the proposed models in predicting the mechanical response, in particular in the welded zone, is investigated. The local strains of the welded area are measured using a digital image correlation technique. Hence, several numerical models are implemented in ABAQUS and different areas are analysed to reproduce the mechanical behaviour of the heat-affected zone. Results are discussed and compared with experiments to validate the proposed model of the mechanical response of a welded component. © 2013 Elsevier Ltd. All rights reserved

Oxygen/nitrogen-assisted embrittlement of titanium alloys exposed at elevated temperature

Due to high solubility of oxygen and nitrogen in titanium alloys, the influence of the diffusion zone on the macroscopic tensile properties of pre-oxidized annealed Ti-6Al-4V tensile specimens was examined at room temperature. Thin microtensile specimens were prepared with different thicknesses ranging from 100 µm to 500 µm and then exposed at 750°C for durations between 5 and 200h. A dedicated gripping technique was developed in the present study to investigate the brittleness of such pre-oxidized and ultrathin specimens at room temperature. Tensile testing was paired with digital image correlation techniques to assess both macroscopic deformation and full-field strain maps. High temperature pre-oxidation treatments significantly decreased the ductility of the specimen and the tensile strength of the materials (yield strength and ultimate tensile strength). Fractographic examinations revealed typical brittle fracture features in the oxygen/nitrogen-affected diffusion zone in the periphery of the cross-section while the fracture remained ductile in the core of the specimen for most of the specimens. Some specimens fully failed in a brittle manner for “(pre-ox. duration)1/2/thickness” configurations with ratio equal or higher than 0.45 h1/2.µm-1