Micromechanical Modeling of Effective Orthotropic Elastic and Viscoelastic Properties of Parallel Strand Lumber Using the Morphological Approach

International audienceStrand-based wood and bamboo composites are a class of structural materials which are increasingly being used in the construction industry. These bio-based composites consist of orthotropic wood or bamboo strands bonded together with small amount of resin (glue). In order to estimate the effective properties of such composites, a specific micromechanical approach from the literature, called the “morphological approach” (MA), is employed. The accuracy of the MA in estimating the effective elastic and viscoelastic properties of an idealized unit cell of a special strand-based wood composite product, a parallel strand lumber (PSL) beam, is investigated using numerical reference solutions obtained by full-field finite-element (FE) simulations. The MA is also compared to analytical micromechanics equations previously proposed by the authors for predicting the effective properties of strand-based composites. MA results are shown to be closer to the numerical reference solutions than previous analytical estimates. Thus, the MA can be used as a valuable alternative for computing the effective properties of strand-based composites with rectangular shaped orthotropic strands. More generally, it could be used in efficient multiscale analysis of large structural composites made from various wood and bamboo strands using less restrictive unit cells. From a fundamental viewpoint, this paper shows a novel application of the MA to orthotropic reinforcements in a Prony series–based viscoelastic matrix

Mean stress effect under Multi-Axial High Cycle Fatigue loading for cast A356-T6 alloy

Mechanical engineers are submitted to the antagonistic criteria when designing security components, such as, used in aeronautic, automotive and industrial components. They have to look for solutions leading to have as less as possible the weight, cost and in the same time as more as possible the security under complex and severe conditions of use. They consider fatigue to be the most common mechanism which causes components fail. In this context, cast A356-T6, which presents a good casting properties and mechanical strength resistance, will be studied in this paper. This work presents an experimental investigation to characterise the effect of mean stress on the Multiaxial High Cycle Fatigue (HCF) of cast A356-T6 alloy containing natural and artificial defects with various Secondary Dendrite Arming Spacing (SDAS). Traction, torsion and combined traction-torsion fatigue tests have been carried for two loading ratio Rσ = 0 and Rσ = −1. The fractured surfaces are analyzed through fractographic Scanning Electron Microscope (SEM) in order to determine the defect causing failure. To study the effect of the mean stress, the results are reported in kitagawa diagrams and Goodman diagrams for all the studied cases. In order to characterise qualitatively the effects of the defect size and SDAS, surface response method has been used. Interesting relationships and correlations have been obtained and introduced to improve the defect stress gradient (DSG) criterion for such defective material. The obtained results show clearly that: (i) the mean stress has detrimental, it is more significant in tension, lesser in tension-torsion case and slightly in torsion tests. (ii) The improved DSG criterion describes very well the trend of the fatigue limit as a function of defect size and SDAS

Design and development of Ionization Profile Monitor for the Cryogenic sections of the ESS Linac

International audienceSaclay CEA/IRFU is working for the delivery of five Non-Invasive Profile Monitors in the frame of the in-kind contribution agreement signed with the European Spallation Source. Neutrons will be produced by spallation reactions of 2 GeV proton beam impinging on a Tungsten target. To accelerate protons a powerful linear accelerator of 5MW is under construction. Diagnostic devices are mandatory tools for the tuning and protection of the machine. The non-invasive profile monitors provide a measurement of the beam profile in transverse directions to the beam propagation. This project raises several physical and technical challenges including low signal detection of ions or electrons, profile distortions induced by the beam Space Charge effect and non-uniformities of electric field. Simulation and model of the critical aspects of the detector have been performed in order to prove the performance and the feasibility of the detector. A series of prototypes has been built with different readout types, and tested in real conditions at the 3MeV proton accelerator IPHI. All of them show some advantages and drawbacks revealed by the tests in real beam conditions. In this paper we present the results of the tests for the various configuration readout systems to agree with the model and simulation of the detector. In concluding remarks, we will discuss the performance of the prototypes and point out the camerabased one to be the more suitable for the final design.Key words: Beam diagnostic / Linear proton accelerators / MCP / Strip detector / Particle beam measurement