Modeling creep behaviour of boiler grade steels - Application to grade 92 steel

International audiencePower generation is now striving to improve the global efficiency of boiler plants, targeting 50% or higher. To accommodate the necessary increase in steam temperature, new materials may be developed and/or existing materials must be employed to their best. This is mandatory for the design of boiler components. One contribution by V&M in that direction is the setting up of numerical models for major boiler grades regarding their creep resistance. In coordination with Mines ParisTech, the first application has been made to Grade 92.The methodology is presented together with the first simulations. Typically, creep is modelled using two deformation mechanisms which correspond respectively to a low stress regime and a high stress regime. Damage is also taken into account. Calculations were carried out using ABAQUS ®. Numerical results are compared with a series of creep tests performed at Vallourec Research Aulnoye (VRA). Further development and applications of the model are finally discussed

How to efficiently apply soft thin coating to existing Finite Element contact model

International audienceIn case of very thin surface coatings, the coating layer is often ignored in a large-scale Finite Element Analysis. This is mainly due to extensive numerical cost required to capture the correct mechanical behaviour of the layer, especially if the coating is significantly softer than the substrate.To overcome the excessive computational cost, due to the full discretization of the thin layer, in large-scale structural contact simulations one can consider a polynomial approximation of the solution field inside the layer. This formulation allows for a reduced representation of the surface layer and proves to be suitable for incorporation within existing finite element codes. Inclusion of the method scales down to an additional stiffness to the system of equations. Furthermore, it can be used in a classical finite element contact solver without strong additional modifications.Significant computational cost reduction is obtained for proposed 2D test-cases in comparison to fully discretized layer approach. It is especially apparent with soft layers on harder substrates. Hence, it is a promising method to be used in large scale structural simulations for studying the mechanical behaviour of systems with thin soft coating