Search results for "grain"

The cost of headache disorders in Europe: the Eurolight project

2011

Background and purpose:  Headache disorders are very common, but their monetary costs in Europe are unknown. We performed the first comprehensive estimation of how economic resources are lost to headache in Europe. Methods:  From November 2008 to August 2009, a cross-sectional survey was conducted in eight countries representing 55% of the adult EU population. Participation rates varied between 11% and 59%. In total, 8412 questionnaires contributed to this analysis. Using bottom-up methodology, we estimated direct (medications, outpatient health care, hospitalization and investigations) and indirect (work absenteeism and reduced productivity at work) annual per-person costs. Prevalence data…

Study of the reactive dynamics of nanometric metallic multilayers using Molecular Dynamics: the Al−Ni system

2012

A molecular dynamics study of a layered Ni-Al-Ni system is developed using an embedded atom method potential. The specific geometry is designed to model a Ni-Al nanometric metallic multilayer. The system is initially thermalized at the fixed temperature of 600 K. We first observe the interdiffusion of Ni and Al at the interfaces, which is followed by the spontaneous phase formation of B2-NiAl in the Al layer. The solid-state reaction is associated with a rapid system's heating which further enhances the diffusion processes. NiAl phase is organized in small regions separated by grain boundaries. This study confirms the hypothesis of a layer-by-layer development of the new phase. For longer t…

Micro and macro mechanical characterization of friction stir welded Ti–6Al–4V lap joints through experiments and numerical simulation

2013

Abstract Lap joints of Ti–6Al–4V were produced and the effect of the main process parameters was studied through macro and micro investigations highlighting mechanical resistance, microhardness profiles, grain size and phase distributions. A dedicated numerical model was used to link the input process parameters to temperature and strain distributions and to the final microstructure in the welded joint. It is found that the strain produced in the stir zone by proper combination of process parameters plays a fundamental role in the final microstructure and mechanical properties of the joints.

CDRX modelling in friction stir welding of AA7075-T6 aluminum alloy: analytical approaches

2007

Abstract Friction stir welding (FSW) is an energy efficient and environmentally “friendly” (no fumes, noise, or sparks) welding process, during which the workpiece are welded together in a solid-state joining process at a temperature below the melting point of the workpiece material under a combination of extruding and forging. Significant microstructural evolution takes place during FSW: in particular continuous dynamic recrystallization (CDRX) phenomena result in a highly refined grain structure in the weld nugget and strongly affect the final joint resistance. In the paper two different analytical models aimed to the determination of the average grain size due to continuous dynamic recry…

Metallurgical Phenomena Modelling in Friction Stir Welding of Aluminium Alloys: Analytical vs. Neural Network Based Approaches

2008

In this paper, the metallurgical phenomena occurring in friction stir welding processes of AA6082-T6 and AA7075-T6 aluminum alloys are investigated. In particular, to predict the local values of the average grain size, either a simple analytical expression depending on a few material constants or a properly trained neural network is linked to the finite element model of the process. The utilized tools, which take as inputs the local values of strain, strain rate, and temperature, were developed starting from experimental data and numerical results.

Design of the friction stir welding tool using the continuum based FEM model

2006

In friction stir welding (FSW), the welding tool geometry plays a fundamental role in obtaining desirable microstructures in the weld and the heat-affected zones, and consequently improving strength and fatigue resistance of the joint. In this paper, a FSW process with varying pin geometries (cylindrical and conical) and advancing speeds is numerically modeled, and a thermo-mechanically coupled, rigid-viscoplastic, fully 3D FEM analysis able to predict the process variables as well as the material flow pattern and the grain size in the welded joints is performed. The obtained results allow finding optimal tool geometry and advancing speed for improving nugget integrity of aluminum alloys.

Analysis of the relationship between start of the rainy season and farmer's sowing strategy in the Niamey area and its impacts on the pearl millet yi…

2009

International audience; Relationship between start of the rainy season and farmer's planting date have been analysed at local scale through in situ daily rainfall records and agronomical measurement provided by on-farm survey at plot scale for 10 villages network located on the mesoscale AMMA-CATCH Niger site during the 2004-2007 rainy seasons. Many classical empirical methods of monsoon onset dectection (e.g. Benoit, Kowal, Sivakumar, Ati, Marteau, Balme, Sultan) and numerical methods based on crop model SARRAH have been compared to the observed farmer's sowing date. Results show that SARRAH and Balme mean onset date are close to sowing date. But spatial and temporal variability of the sow…

Effet d'une carence en soufre combinée à un stress hydrique chez le pois protéagineux : Etude des mécanismes moléculaires mis en jeu dans les organes…

2019

Pea (Pisum sativum L.) is a grain legume crop that produces seeds rich in proteins for food and feed and, thanks to its symbiosis with nitrogen-fixing bacteria, enriches the soil with nitrogen. The wider development of pea cultivation is therefore a major agroecological challenge. Water stress combined with sulfur deficiencies in soils (S is a macroelement necessary for plant defense reactions) are two abiotic stresses that interact in the current context of climate change. However, the molecular mechanisms underlying pea adaptation to water stress and their modulation by sulfur nutrition remain to be elucidated. The objectives of this thesis were, first, to describe the impact of an intera…

Cell Parameters of Fine-Grain BaTiO<sub>3</sub> Powders

1993

Destructuration of typical Sicilian calcarenites

2010

The paper discusses some interesting features of Sicilian fine grain calcarenites. Uniaxial, triaxial, oedometer and isotropic compression tests were undertaken on intact specimens of two types of calcarenite in order to investigate their mechanical characteristics. It was found that the strength and deformability is significantly influenced by the structure (fabric and bonding) and by the destructuration processes. A better understanding of fracture development behavior is gained through a combination of acoustic emission and photographic monitoring on non-homogeneous samples with natural pre-existing heterogeneities due to cementation or to density. The results show that the destructurati…