Coupled thermo-mechanical simulations of shot impacts: Effects of the temperature on the residual stress field due to shot-peening

International audienceShot-peening is an industrial surface treatment used to improve fatigue life of mechanical components. This process generates a compressive residual stress field on the part's surface and offers a protection against crack initiation and propagation, corrosion, etc. Although the consequences of the process on fatigue life are well known, the physical influence of the relevant parameters is not fully understood. Few of the existing shot-peening models are thus able to reproduce the correct residual stress field obtained via the actual process. This paper presents a finite element simulation of an impact including thermo-mechanical effects to investigate the influence of temperature on the residual stress field obtained through shot-peening. The influence of parameters of the process such as velocity, radius and hardness of the shot has also been studied in relation with thermal effects. It is observed that the temperature can reach 200 °C in the material. Further, the temperature significantly affects the residual stress field for high shot velocities. It can be concluded that shot-peening is a complex combination of physical processes, including thermal effects, which should be taken into account to better master this manufacturing process

Cyclic calculations and life estimation in thermomechanical fatigue

International audienceThe present paper describes a new numerical procedure devoted to the calculation of aeronautic engines and to the fatigue life assessment evaluation. The original aspects consists (1) in a new method used to determine the mechanical steady state of a structure under thermomechanical loading, (2) in a short review of an advanced fatigue model which can reproduce the Woehler curve, including the influence of the mean stress

A low cycle fatigue model for low carbon manganese steel including the effect of dynamic strain aging

International audienceCarbon manganese steel A48 (French standards) is used in steam generator pipes of the nuclear power plant where it is subjected to the cyclic thermal load. The Dynamic Strain Aging (DSA) influences the mechanical behavior of the steel in low cycle fatigue (LCF) at favourable temperature and strain rate. The peak stress of A48 steel experiences hardening–softening–hardening (HSH) evolution at 200°C and 0.4% s-1 strain rate in fatigue loading. In this study, isotropic and kinematic hardening rules with DSA effect have been modified. The HSH evolution of cyclic stress associated with cumulative plastic deformation has also been estimated

Cyclic Viscoplastic Constitutive Equations, Part I: A Thermodynamically Consistent Formulation

International audienceCyclic viscoplastic constitutive equations are increasingly used for the inelastic analysis of structures under severe thermomechanical conditions. The purpose of the paper is to show how the classical models can be modified in order to follow the general principles of thermodynamics with internal variables. Using the restrictive framework of standard generalized materials, the state variables associated to various kinds of kinematic and isotropic hardening are selected. The evolution equations for these internal variables are then formulated in a slightly less restrictive form. For each hardening process, the separation of the total plastic work into energy dissipated as heat and energy stored in the material is discussed in detail

Modélisation de la propagation de fissure dans les aubes de turbines monocristallines

PARIS-MINES ParisTech (751062310) / SudocEVRY-MINES ParisTech (912282301) / SudocSudocFranceF

Modélisation multiéchelle du comportement thermo-mécanique des CMO et prise en compte des effets du vieillissement thermique

L'utilisation des Composites à Matrice Organique sur de longues durées, nécessite de prendre en compte les effets du vieillissement qui peuvent considérablement modifier les propriétés mécaniques au cours du temps et réduire la durée de vie. L'objectif de ce travail est de développer un modèle macroscopique utilisable dans le contexte du calcul de structures par Eléments Finis, couplant les différents aspects : viscoélasticité, endommagement et vieillissement thermique. Nous proposons une démarche multiéchelle s'appuyant sur les différentes échelles du composite. Le comportement du pli est obtenu à partir du comportement de ses constituants (fibre et matrice) par la méthode appelée Transformation Fied Analysis. Afin d'analyser les effets du vieillissement thermique, une importante campagne expérimentale a été menée comprenant une caractérisation de type mécanique et physico-chimique. Les effets du vieillissement sont intégrés dans le modèle par l'intermédiaires de variables internesThe use of organic matrix composites for long-term applications leads to take into account the effects of thermal ageing which can considerably modify the mechanical properties and reduce the composite lifetime. The aim of this study is to develop a macroscopic model for structural computation using the finite Element method and to couple different aspects such as : viscoelasticity, damage and thermal ageing. We suggest a multiscale approach laying on the different scales of a composite. The ply behaviour is deduced from the behaviour of the constituents (fibre and matrix) by using Transformation Field Analysis method. In order to analyse the effects of thermal ageing, an important experimental part has been carried out, including mechanical and chemical measurements. Ageing effects are introduced in the model using internal parametersTROYES-SCD-UTT (103872102) / SudocSudocFranceF

Etude de l'endommagement d'un superalliage monocristallin en fatigue thermo-mécanique multiaxiale

PARIS-MINES ParisTech (751062310) / SudocSudocFranceF