This work is devoted to studying the coupled effect of grain size and crystallographic texture on the mechanical behavior at room temperature of Ti-6Al-4V alloy with an equiaxed microstructure. To this end, experimental data was collected on a broad range of mechanical solicitation conditions through monotonic and cyclic tests, followed by macroscopic elasto-viscoplastic modeling. The experimental results show that the mechanical behavior of Ti-6Al-4V is mainly influenced by both the grain size and the crystallographic texture. The microstructure with the finest grain size exhibits the highest flow stress. The weakly textured alloy presents the highest ductility. Moreover, all the Ti-6Al-4V microstructures present cyclic softening behavior. In addition, at room temperature, no microstructure was found to exhibit significant strain rate sensitivity. The results also show that the grain size affects the yield strength of the Ti-6Al-4V alloy, as well as its ductility and its kinematic hardening. The proposed model formulation accurately predicts the effect of the microstructural features of the Ti-6Al-4V alloy. Isotropic and kinematic hardening laws are modified by introducing the grain size effects via the Hall-Petch relationship.

The research article addresses, a novel natural cellulosic fiber namely Doum Palm Leaf Stalk Fibers (DPLSF) were extracted from Doum palm tree ( Chamaerops humilis L.) are rich in cellulose, relatively inexpensive, and readily available in Algeria. The characteristic analysis on morphological, physiochemical, thermal and mechanical proprieties of the extracted raw and treated DPLSF with 20% sodium bicarbonate at various times of treatment were exanimated by optical microscope and scanning electron microscopy (SEM), X-ray diffraction method (XRD), Fourier transform infrared (FTIR) spectroscopy, thermos gravimetric analysis (TGA/DTG), differential scanning calorimetry (DSC). The SEM micrographs of the longitudinal topographic surface of the DPLSF after chemical treatment with sodium bicarbonate at various times treatment indicated that the removed the waxy layer and impurities from surface and formed a roughened surface. XRD analysis further confirmed the treatment’s positive effect on the fibers, with the crystallinity index increasing from 71.43% to 81.03%. However, FTIR analysis showed minimal changes in the peak position and intensity of transmittance. The TGA/DTG results revealed a significant mass loss in treated DPLSF, while thermal stability improved from 290°C to 330°C. Additionally, we analyzed the mechanical tensile properties of the treated fibers and observed that fibers treated at 20% NaHCO 3 for 24 h exhibited the highest Young's modulus 8.63 GPa. To validate the experimental findings, we compared individual DPLSF results to a numerical simulation using ABAQUS code. This study underscores the potential of DPLSF as a sustainable and eco-friendly alternative to synthetic fibers, offering immense promise for diverse applications.

In this work, a study was carried out on the friction and wear behavior of flame thermal sprayed NiCrBSiFeC-WC(Co) composite and NiCrBSiFeC coatings subjected to severe wear conditions. For this purpose, flame remelted samples were tested in reciprocating wear conditions based on a cylinder-on-flat configuration. The wear assessment of the coatings was achieved using scanning electron microscopy (SEM) and 3D optical profilometry. The microstructure and the mechanical properties of the coatings were investigated using SEM, EDS and XRD techniques as along with indentation tests. The tribological behavior of the substrate and the coatings was successfully studied thanks to wear tests conducted on an adapted multi test apparatus. The results show that both NiCrBSiFeC and composite coatings induced a significant increase in the steel substrate hardness and wear resistance due to the formation of precipitates with high hardness well dispersed within an ultra-crystalline structure. Besides, adding WC(Co) to NiCrBSiFeC leads to a composite coating with hardness and wear resistance further improved. In return, it increases the coefficient of friction (COF) and the coatings' roughness. Furthermore, improvements in the surface hardness, the roughness and the coating-substrate adhesion were attained after the remelting process for both NiCrBSiFeC and NiCrBSiFeC-WC(Co) coatings. Wear tracks investigations indicated that reciprocating dry sliding based on cylinder-on-flat test configuration promote several wear mechanisms that may occur simultaneously.

The aim of this paper is to investigate the coupled effects of grain size and crystallographic texture on the mechanical behavior induced by gliding mechanism in Ti-6Al-4V alloy. Thus, four microstructures of Ti-6Al-4V alloy whose grain size and crystallographic texture are different were examined by tensile tests along the rolling direction at room temperature. In this study, the contribution of gliding on basal < a >, prismatic < a > and pyramidal < c + a > plans in the accommodation of plastic strain was estimated by means of a slip trace analysis. The role of the individual grain size and the crystallographic texture was then statistically evaluated. Based on the results of slip trace analysis, numerical optimizations of the Critical Resolved Shear Stress < CRSS > of basal < a >, prismatic < a > and pyramidal < c + a > in the four microstructures were then carried out, using transition scale rules and a local behavior model. The results suggest that the mechanical behavior of Ti-6Al-4V is controlled by the activation of slip systems that depend not only on their CRSS but also the initial orientation and size of each individual grain. The low CRSS of prismatic < a > slip systems can lead to early activation of these systems in favorably oriented coarse grains. Therefore, a local plastic deformation can be shown. At high levels of loading, increasing the grain size can minimize the crystallographic texture effects by deforming the unfavorably oriented coarse grains. Moreover, based on the results of the numerical optimization, it can be also suggested that the CRSS can decrease with the increase in grain size according to the local Hall Petch relationship.

The aim of this work is to optimize the relative and the absolute Critical Resolved Shear Stress (CRSS) of slip mechanism in alpha-phase of Ti-6A1-4V titanium alloy. The influence of grain size is then modeled through a local Hall-Petch relationship. A slip trace analysis technique coupled with statistical reasoning were used to identify the CRSS ratios of basal < a >, prismatic < a > and pyramidal < c + a > slip systems. The multi scale transition rule of Berveiller-Zaoui was then used to determine the absolute CRSS in three different microstructures; Ti-6A1-4V with ultra fine grains (UFG), fine grains (FG) and standard grains (SD). Finally, the local Hall-Petch relationship was optimized. As expected, plastic deformation is mainly accommodated by prismatic and then basal slip systems. Due to their high CRSS, sliding in pyramidal systems is more difficult. Grain size shows a significant role on the activation of slip systems. By increasing the grain size, the CRSS of each slip system type decreases and thus sliding becomes easier in coarse grains.

The present work aims to model the influence of microstructural features of Ti-6Al-4V titanium alloy on its mechanical behavior. A multi-scale approach based on crystal plasticity is considered. The elasto-viscoplastic constitutive equations of Meric-Cailletaud are modified to take into consideration the effect of the grain size by introducing the Hall-Petch relationship at the local scale. This modified model is coupled with finite element calculations under small strain assumption to simulate the monotonic mechanical behavior of Ti-6A-4V at local and global scales. It is shown that the mechanical behavior of Ti-6Al-4V is drastically dependent upon the material features. Strong crystallographic texture can result in the formation of hardened and less hardened areas. Moreover, by increasing the grain size scattering, the heterogeneously deformed areas are multiplied. By decreasing the average grain size, the yield strength increases. It is observed that the effects of grain size, grain size scattering and crystallographic texture are coupled.

Ce travail consiste a etudier l'effet de la taille, la dispersion et la texture cristallographique des grains sur le comportement mecanique d'un alliage de titane Ti-6Al-4V. L'investigation des champs mecaniques (contraintes et deformations) est effectuee aux differentes echelles, sous chargement quasi-statique monotone de traction. Le modele de comportement utilise est developpe dans le cadre de l'approche de plasticite cristalline. Douze volumes elementaires representatifs (VER) permettant la prise en compte des parametres steriologiques (taille, dispersion et texture cristallographique) sont construits, puis la simulation du comportement mecanique du Ti-6Al-4V est effectuee en utilisant le modele de meric-Cailletaud [1] en corporation avec la metode des elements finis. Enfin, l'influence des elements microstructurales du materiau est analysee. Les resultats montrent que le comportement mecanique macroscopique du Ti-6Al-4V est fortement lie a la texture cristallographique des grains, cette derniere donne a la deformation plastique de l'alliage Ti-6Al-4V un caractere heterogene ainsi qu'un comportement mecanique macroscopique anisotrope. La taille moyenne des grains influe egalement sur les proprietes mecaniques du Ti-6Al-4V, en particulier sur la limite d'elasticite; en diminuant la taille moyenne des grains, la limite d'elasticite augmente. Enfin la distribution des tailles des grains influe sur le comportement local du materiau, elle donne aux champs de deformation une heterogeneite suffisante lorsque la dispersion augmente.

The aim of this work is to define the cutting conditions that allow the dry drilling of carbon fiber reinforced epoxy (CFRE) composite materials taking into consideration the quality of the drilled holes (the exit delamination factor and the cylindricity error) and the optimum combination of drilling parameters. A further aim is to use grey relational analysis to improve the quality of the drilled holes. The machining parameters were measured according to 33 full factorial parameter designs (27 experiments with independent process variables). The experiments were carried out under various cutting parameters with different spindle speeds and feed rates. Drilling tests were done using WC carbide, high-speed steel (HSS), and TiN-coated carbide drills. The experiment design was accomplished by application of the statistical analysis of variance (ANOVA). Results show that the thrust force is mainly influenced by the tool materials and the feed rate, which has a strong influence on the exit delamination factor. On the other hand, the spindle speed particularly affects the cylindricity error of the holes. Correlations were established between spindle speed/feed rate and the various machining parameters so as to optimize cutting conditions. These correlations were found by quadratic regression using response surface methodology (RSM). Finally, tests were carried out to check the concordance of experimental results.

The cyclic mechanical behavior, the wear and fatigue resistances and damage developments of working surface of tool steels are dependent on microstructural features. A multi-scale approach combining experimental testing, numerical treatments and simulations is developed to model the surface behavior of X38CrMoV5-1 martensitic tool steels. The multi-scale modeling is coupled with finite element calculations. The elasto-viscoplastic constitutive equations used are based on crystal plasticity model of Méric-Cailletaud and are implemented on the finite element code ABAQUS under a small strain assumption. Trough an appropriate laboratory testing, the microstructure features comparable to the surface of industrial tools or pin/disc in tribology experiments are reproduced by considering plate specimens. Monotonic tensile testing is coupled with in-situ Digital Image Correlation technique (DIC) to determine the surface strain fields. The measured local nonlinear mechanical strain fields are analyzed. The strain localization is related to stereological artifacts. The numerical treatments allow reproducing, qualitatively, the strain localization patterns at the surface observed during tensile testing. The influence of the various stereological parameters such as the morphology of martensitic laths, the crystallographic orientations, the internal hardening state of the surface profiles and their evolutions on the local strain fields are addressed. By such approach, it is possible to get a better insight of some elementary mechanisms acting on tools and/or pin/disc surfaces regarding both tensile and cyclic behavior.

The device presented in this work enables a conventional fatigue machine to be adapted so that it can be used as a tribometer. The DEMAFtrib (Device using Fatigue Machine as Tribometer) adds a second axis to a uniaxial fatigue machine in the form of an add-on accessory. It allows the measurement of wear and friction forces at the contact point of two surfaces in relative motion. The apparatus can also be used as a fretting-wear machine or a fretting-fatigue machine. This device can be used in mechanical-testing laboratories equipped with a fatigue machine and presenting a need to characterize materials under wear and fretting. A sample of study results on the wear and fretting of 7075 aluminium is presented as an application of the use of the DEMAFtrib in tribological and fretting tests.

The mechanical characterisation of the carbon/carbon composite in the transverse direction is essential for the design of braking discs. This paper presents a technique based on spherical indentation to identify the mechanical behaviour of such materials in the transverse direction.After the presentation of the material properties as determined from static and fatigue compression tests, the indentation technique is described in detail. The characterisation technique used takes into consideration the transverse isotropy of these materials. The method used allows to identify the material behaviour in elastic and inelastic fields. Characterisation of elastic parameters is carried out after identification of the Hertz law in the unloading indentation cycles. The hardening parameters and the elastic limit are identified by expressing the law of Hertz in strain/stress form.The identified parameters are used in a simulation of an indentation test by finite element method. A good agreement is found between numerical and experimental results. (C) 2013 Elsevier Ltd. All rights reserved.

In this work, load distribution on ball-screw systems (BSS) is determined by experimental techniques. Two optical techniques are used: photoelasticity for stress-field measurement and the mark-tracking method for displacement-field determination. In parallel to the experimental study, finite element method (FEM) and analytical solutions are used to calculate the loads applied on each ball of the BSS. Experimental results are used to validate the choice of boundary conditions and contact conditions between ball-screw and ball-nut in the FEM solution. The validation criterion is the correspondence between numerical and experimental fringes representing the differences of principal stresses. In addition to the study of load distribution, this paper presents the influence of the angle of contact direction on the stress distribution in BSS.

In this paper, the inverse method is used to identify the mechanical characteristics of a brazed joint. This technique is based upon tensile tests and/or shearing test combined with the results of a calculation using finite elements method. This paper shows that calculation of a brazed assembly under an elastic behavior assumption is flawed. A correct study of a brazed assembly must be done under an elastoplastic assumption. The presented method will be used for calculation of molds manufactured by stratoconception (sheet metal assembling).

The Trimmable Horizontal Stabilizer Actuator (THSA system) equips the whole airbus line. One component of this system is a ball-screw system on which spalling problems appear on the balls. This phenomenon is mostly due to local high pressures and reduces the service life of the system. 3D numerical simulations are usually used to tackle this kind of problems but are subjected to assumptions. As the aim of the project is to build a numerical model able to predict pressure distribution, these assumptions need to be experimentally assessed to be perfectly relevant of the real load distribution in the ball screw system. Due to the 3D geometry of the specimen, a 3D measurement technique, Scattered Light Photoelasticity (SLP), has been chosen to perform experimental measurements,. Because of complexity of the geometry, the study is divided in three steps; the present paper is dealing with the second one where a demonstrator ball-screw system is manufactured in casted epoxy to perform the SLP. This technique gives information on 3D stress fields inside the epoxy specimen from the analysis of photoelastic fringes. They are compared to numerical ones and indicate whether numerical boundary conditions are relevant of the experimental ball-screw system behaviour.

Endocrine tumors could be defined by their ability to produce structural proteins or hormones commons to nervous and endocrine cells. They might induce physiological transforms or outcome adverse events which should be well known in order to prevent or treat them early. The goal of this review was to describe these changes, to describe preoperative assessment, and to discuss intraoperative monitoring and drugs choice based on the literature from the last 30 years. As an example, it should be noticed that: (1) preoperative blood pressure control is essential to prepare phaeochromocytoma for surgery. It should be followed during anaesthesia by intensive fluid load, reversible anaesthetic drugs and rational cardiovascular medications use (as for example remifentanil, sevoflurane, calcium channel blockers and esmolol), and after surgery by narrow clinical and biological monitoring; (2) after medullar thyroid cancer, main adverse events include cervical compressive haematoma and recurrent laryngeal nerve injury as for any thyroid surgery; (3) during pituitary surgery, air embolism might be expected, whereas water dysregulation (diabetes insipidus), corticotroph insuficiency, cerebrospinal fluid (CSF) leak might occur postoperatively. In acromegaly, difficult endotracheal intubation is possible whereas severe Cushing's syndrome may be complicated with hypertensive cardiac failure, infections, thrombosis, delayed cicatrisation; (4) somatostatine analogs are a keystone in carcinoid tumors preoperative and anaesthetic management. (C) 2009 Elsevier Masson SAS. All rights reserved.

Ce travail concerne l'etude de la repartition des contraintes dans une vis a billes. Pour cela, un modele numerique bidimensionnel par elements finis est construit sur ABAQUS T M et valide a partir d'essais experimentaux. La methode de mesure utilisee permettant de mettre en evidence la repartition de charge dans le volume est la photoelasticimetrie. On compare alors les franges experimentales aux franges numeriques calculees a l'aide des resultats du modele elements finis.