FE2 multiscale approach for modelling the elastoviscoplastic behaviour of long fibre SiC/Ti composite materials

Multiscale FE2 elastoviscoplastic analysis of composite structures

Evaluation of cyclic plasticity models in ratcheting simulation of straight pipes under cyclic bending and steady internal pressure

Coarsening and dissolution of γ′ precipitates during solution treatment of AD730™ Ni-based superalloy: Mechanisms and kinetics models

A microstructure-sensitive constitutive modeling of the inelastic behavior of single crystal nickel-based superalloys at very high temperature

The prediction of the viscoplastic behavior of Ni-based single crystal superalloy is still a challenging issue due to the non-isothermal loadings which can be encountered by aeronautical engines components such as high pressure turbine blades. Under particular in-service conditions, these materials may experience temperature cycles which promote the dissolution of the strengthening γ′ phase of the material on (over)heating, and subsequent precipitation on cooling, leading to a transient viscoplastic behavior. New internal variables representing the microstructural changes under those specific thermal loadings have been introduced in the framework of crystal plasticity using a macroscopic approach (no representation of the γ/γ′ microstructure of the alloy) to account for the transient creep behavior induced by microstructure changes. This modeling approach captures first order effects on the creep behavior due to (a) γ′ precipitates volume fraction evolution of each kind of particles of a bimodal distribution of precipitates (which evolves according to thermal history), (b) recovery of the dislocation density and, (c) material orientation. In addition, a damage law keeping in memory all the thermal history and recovery processes has been introduced to account for the unconventional post-overheating creep life. This model is calibrated on non-isothermal creep experiments on [0 0 1] oriented single crystals made of MC2 alloy. It is able to predict creep strain (primary, secondary, tertiary), whatever the temperature history of the material. In addition, it can be used to quantify the effect of slight variation of the as-received γ′ volume fraction on the creep behavior.

https://www.ovgu.de/ifme/zeitschrift_tm/2010_Heft1_3/05_Cormier_Cailletaud.pdf

Constitutive modeling of the creep behavior of single crystal superalloys under non-isothermal conditions inducing phase transformations

In this work, numerical simulations for predicting uni- and multi-axial ratchetting behaviors are carried out, using a polycrystal plasticity model. In this multi-scale modeling, the single crystal behavior is based on crystallographic slip (intragranular scale), whereas the polycrystal behavior is obtained from an explicit transition rule to calculate the local stresses and strains (intergranular scale). A systematic study is performed to show the effect of intergranular and intragranular hardening on the ratchetting behavior. For illustrative purposes, two examples are presented: the model is applied to simulate the experimental results from the literature for a 316 austenitic stainless steel and for a 1026 carbon steel. It was demonstrated that the polycrystalline model was successful in describing the inelastic behavior of the two considered materials adequately.

A polycrystalline model for the description of ratchetting : effect of intergranular and intragranular hardening

A new polycrystalline plasticity model to improve ratchetting strain prediction

Generalization of the polycrystalline β-model: Finite element assessment and application to softening material behavior

The prediction of the creep behaviour and life of components of aeronautic engines like high pressure turbine blades is still a challenging issue due to non-isothermal loadings. Indeed, certification procedures of turboshaft engines for helicopters consist of complex thermomechanical histories, sometimes including short and very high temperature excursions close to the γ'-solvus (T~1200°C) of the blade alloy. A better design of those components could be gained using a model that takes into account non-isothermal loadings inducing microstructural changes. Most of the commonly used models consider only a nearly constant (or slowly evolving) microstructure, i.e. far from the rapid microstructure evolutions encountered during close γ'-solvus overheatings where a rapid dissolution/precipitation of the γ'-phase and fast recovery mechanisms were observed by Cormier et al. (2007b). A new constitutive modelling approach was hence recently proposed in a crystal viscoplasticity framework to capture the transient effects of such rapid microstructure evolutions on the creep behaviour and life (Cormierand Cailletaud (2010a)). In this article, an updated version of this model is detailed. Special attention will be paid to (i) the effect of the accumulated plastic strain on the microstructure evolution, (ii) the introduction of an additional damage formulation, and (iii) the creep strain at failure. The performances of the model are illustrated on the basis of isothermal or complex non-isothermal creep experiments performed on nearly [001] oriented samples.

https://hal-mines-paristech.archives-ouvertes.fr/hal-00722620/document

Georges Cailletaud

Papers

Constitutive modeling of the creep behavior of single crystal superalloys under non-isothermal conditions inducing phase transformations

A polycrystalline model for the description of ratchetting : effect of intergranular and intragranular hardening

A new polycrystalline plasticity model to improve ratchetting strain prediction

Generalization of the polycrystalline β-model: Finite element assessment and application to softening material behavior

A Microstructure Sensitive Approach for the Prediction of the Creep Behaviour and Life under Complex Loading Paths