L'assistance météorologique dans la lutte contre les incendies de forêts (forêts méditerranéennes)

International audienc

A ply scale non local fibre criterion for CFRP women ply laminates structures

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An orthotropic specific damage model with inclusion consideration

International audienc

3D finite element investigation on the plastic flows of rolling contacts—correlation with railhead microstructural observations

International audienceIn this work, a three-dimensional elasto-plastic finite element model is used to simulate the rail mechanical response to the action of a rolling wheel. Plastic flows in the near-surface layer are computed as a function of the traction coefficient. The depth and the distortion of the plastically deformed layer are analysed versus this traction coefficient and correlated qualitatively to the microstructural observations of plastic flows in real railheads and existing theoretical studies. The deviations of the numerical results with reality are discussed in terms of the presence of a solid third body layer, neglected in the simulations

Hot-crack test for aluminium alloys welds using TIG process

Hot cracking is a critical defect frequently observed during welding of aluminium alloys. In order to better understand the interaction between cracking phenomenon, process parameters, mechanical factors and microstructures resulting from solidification after welding, an original hot-cracking test during welding is developed. According to in-situ observations and post mortem analyses, hot cracking mechanisms are investigated, taking into account the interaction between microstructural parameters, depending on the thermal cycles, and mechanical parameters, depending on geometry and clamping conditions of the samples and on the thermal field on the sample. Finally, a process map indicating the limit between cracking and non-cracking zones according to welding parameters is presented

Dynamic behavior of the weld pool in stationary GMAW

Because hump formation limits welding productivity, better understanding of the humping phenomena during the welding process is needed to access to process modifications that decrease the tendency for hump formation and then allow higher productivity welding. From a physical point of view, the mechanism identified is the Rayleigh instability initiated by strong surface tension gradient which induces a variation of kinetic flow. But the causes of the appearance of this instability are not yet well explained. Because of the phenomena complex and multi-physics, we chose in first step to conduct an analysis of the characteristic times involved in weld pool in pulsed stationary GMAW. The goal is to study the dynamic behavior of the weld pool, using our experimental multi physics approach. The experimental tool and methodology developed to understand these fast phenomena are presented first: frames acquisition with high speed digital camera and specific optical devices, numerical library. The analysis of geometric parameters of the weld pool during welding operation are presented in the last part: we observe the variations of wetting angles (or contact lines angles), the base and the height of the weld pool (macro-drop) versus weld time

Behaviour of spreading molten metal drops deposited by fusion

International audienceAn experimental approach is presented in order to study the evolution of the spreading of a macro-drop of liquid metal. The objective of this work is to supply qualitative and quantitative information during the deposit of liquid metal in static pulsed Gas Metal Arc Welding (P-GMAW). The experimental results are analyzed in the light of dimensionless numbers in order to identify the involved physical mecanisms and appreciate the heat and mass e ects on the behavior of such a macro-drop

Thermo mechanical simulation of overlaid layers made with wire arc additive manufacturing and GMAW cold metal transfer

A thermo mechanical simulation of the wire arc additive manufacturing WAAM process is presented in this work. The simulation consists in the deposition of 5 successive layers of 316 L stainless steel on a 316 L base plate. The thermo mechanical analysis is solved in two dimensions under plane stress assumption. Nonetheless, the metal addition is taking into account in this numerical analysis. An increment of material is added at each time step. This numerical approach allows reducing the computational time. The temperature and residual stress fields are computed at each time step. Two patterns of deposition strategy are also investigated. It is shown that the longitudinal stress varies mainly along the vertical axis. A sample with 5 overlaid layers has been scanned with neutron diffraction technique in order to measure the final residual stresses. Both numerical and measured residual stresses are in good agreement. The Aster finite element software is employed for the numerical analysi