Determination of brazed joint constitutive law by inverse method

An important parameter often neglected for the calculation of residual stresses in brazed ceramic/metal assemblies is the joint constitutive law. In situ camber measurements on a model system (axisymmetric TZM/InCuSil ABA/316L samples) performed using a special vertical dilatometer during the whole brazing thermal cycle are compared with results of FEM calculations based on published filler metal constitutive laws. A strong disagreement is observed. Actual constitutive law of the joint is determined from these measurements using a numerical inverse method. Calculated displacements are fully consistent with experimental ones. True solidification temperature of the joint is determined. The identified constitutive law of the joint exhibits a low flow stress from solidification temperature to 320°C

Automatic statistical volume element modeling based on the unified topology model

Needs for new particle based heterogeneous materials as led to the development of many Statistical Volume Element (SVE) modeling schemes tailored to specific shapes of particles or meshing procedures. To generalize the numerical analysis of particle filled SVEs, a modeling methodology based on the Unified Topology Model (UTM) is proposed. Using the concept of Boundary Representation (BRep) and a modified Random Sequential Adsorption (RSA) algorithm, the geometry of a Statistical Volume Element (SVE) can be generated automatically with any shape of particles. Using an integration of Computer-Aided Design (CAD) and mesh tools, a mesh size map is constructed with the objective of minimizing the number of mesh elements while preserving quality of the discretization. The SVE is meshed using proven CAD model meshing algorithms for a robust and reliable result. Simulation and post processing are carried out automatically, without any user interaction. To illustrate the potential of this new method, a short glass fiber / epoxy matrix composite is modeled with spherical and elongated cylindrical particles

EXPERIMENTAL AND NUMERICAL ANALYSIS OF THE HOT TEARING SUSCEPTIBILITY OF A CuCrZr ALLOY

ABSTRACT The precipitation hardened CuCrZr alloy is used in fusion machines for the heat sink of intensely cooled plasma facing components (PFC) due to its good thermal and mechanical properties. Albeit, the feedback from its application in Tore Supra (French tokamak) showed that this alloy is very sensitive to hot tearing during electron beam welding. Hot tears also known as solidification cracks occur in solidifying parts undergoing tensile stresses that are transmitted to the mushy zone by the coherent solid underneath. In order to characterize the hot tearing susceptibility of the CuCrZr alloy, welding tests based on the investigations of the Joining and Welding Research Institute (JWRI) have been performed. Electron beam fusion lines are performed on a thin rectangular plate equipped with thermocouples and firmly clamped at its extremity in the vacuum chamber. As the width of the plate decreases, conditions leading to the formation of hot tears appear in the run-in, thus defining a critical width hot tearing wise. The JWRI welding tests are then analysed by means of numerical modelling and available hot tearing criteria. To do so, missing thermophysical and thermomechanical properties are determined by associating laboratory tests and numerical analysis. The viscoplastic strain and viscoplastic strain rate undergone by the solidifying alloy are considered as hot tearing (HT) indicators. Critical values at the onset of hot tearing are determined for this particular alloy. In addition, HT initiation conditions are compared with propagation conditions using a simple numerical approach. I INTRODUCTION The precipitation hardened CuCrZr alloy is a potential candidate for use as a heat sink of the first wall components for the future thermonuclear fusion reactor ITER [1] owing to its good mechanical and thermal properties. The feedback from its use in Tore Supr

Une approche simplifiée pour schématiser l'effet de surface sur le comportement mécanique d'un polycristal

Si l'intérêt des modèles polycristallins pour décrire le comportement mécanique des matériaux métalliques n'est plus à démontrer, le traitement rigoureux du passage micro-macro, en présence d'une surface libre reste encore un problème ouvert, notamment si le matériau exhibe des non linéarités. On présente dans ce papier une démarche approchée basée sur la résolution d'un problème inverse pour traiter le changement d'échelle en recalant les paramètres d'une règle de localisation, dont la forme est postulée a priori. Ce recalage est effectué sur les résultats d'analyses par éléments finis de motifs représentatifs du milieu hétérogène. On traite, à titre d'application, la description du comportement d'un alliage de structure cubique à faces centrées par un modèle polycristallin élastoviscoplastique. On analyse plus particulièrement, en fonction de la distance à la surface, la réponse mécanique au niveau des grains du polycristal