Continuum models of ductile fracture : A review

International audienceThe past 20 years have seen substantial work on the modeling of ductile damage and fracture. Several factors explain this interest. (i) There is a growing demand to provide tools which allow to increase the efficiency of structures (reduce weight, increase service temperature or load, etc.) while keeping or increasing safety. This goal is indeed first achieved by using better materials but also by improving design tools. Better tools have been provided which consist (ii) of material constitutive equations integrating a physically-based description of damage processes and (iii) of better numerical tools which allow to use the improved constitutive equations in structural computations which become more and more realistic. This article reviews the material constitutive equations and computational tools, which have been recently developed to simulate ductile rupture

Ductile tearing of 2024 aluminum alloy panels

International audienceTwo 2024 aluminum alloys are studied. Their second phase volume fraction differ as well as their mean inter-particle ....

Characterization and modeling of ductile rupture with relationship to microstructures in 2198 Al-Li alloy for aeronautic application

International audienceDamage and fracture mechanisms of two 2198 Al-Li thin sheet alloys having different thicknesses (2 and 6 mm) are investigated. Two heat treatments are studied: T3 and T8. Mechanical tests are carried out on flat specimens including smooth tensile samples and U-notched specimens (with various notch radii). Test data are used to identify the parameters of constitutive equations describing plastic anisotropy. Crack initiation and stable propagation is studied using Kahn tear tests. The microscopic fracture surface of the different specimens is observed using SEM (Scanning Electron Microscopy). Smooth and notched samples exhibit a slant fracture surface. With increasing notch severity, the fracture mode changes significantly. Failure initiates at the notch root in a small triangular region, outside this zone, slant fracture is observed. Observations show two different failure mechanisms with respect to triangular and slant zones

A combined phenomenological model for the representation of anisotropic hardening behavior in high strength steel line pipes

International audienceLine pipes have anisotropic mechanical properties, such as tensile strength, ductility and toughness. These properties depend on both prestrain during the cold forming process and on the anisotropy of the mother plates. In this study, a phenomenological model combining isotropic and kinematic hardening is developed to represent anisotropic hardening behavior of high strength steel line pipes. The model is adjusted on experiments carried out on smooth and notched axisymmetric bars and plane strain specimens. The model is used to simulate bending tests carried out on large pipes containing a geometric imperfection.Numerical results suggest that prestraining in pipe forming process significantly affects the bending capacity of pipes

Recent advances in modelling ductile rupture

International audienceA brief account of recent advances in modelling ductile rupture is given. The importance of the inhomogeneity in the distribution of cavity nucleation sites is firstly emphasized. Then some recent extensions of the Gurson model to account for non spherical void shape are presented. Finally recent progress in modelling cavity coalescence is highlighted

Nonlocal computational methods applied to composites structures

International audienceA nonlocal finite element method is used to solve numerical problems appearing when a standard finite element method, coupled with a Newton-Raphson algorithm, is used to model the degradation of organic or ceramic matrix composites structures (OMC or CMC) even under simple solicitations (traction, flexion, ...). The main problem is related to instabilities and localisation, which lead to the divergence of the solver. In order to overcome these difficulties, a new method is developed. It consists in the use of nonlocal description of the material combined with an arc length algorithm. This ensures a good numerical conditioning which allows the parallelization (using a FETI method) of the calculations and therefore high performance computations.This set of tools allows to run 3D simulations in order to follow the initiation and the propagation of fracture in cases representative of industrial problems which require very fine meshes

Comment on "Effect of carbide distribution on the fracture toughness in the transition temperature region of an SA 508 steel"

International audienceCritical cleavage stress values and carbide sizes obtained in a recent work by Lee et al. [Acta Mater. 50 (2002) 4755] are recalculated using 2D and 3D finite element simulations and new constitutive law, instead of small scale yielding assumption and likely improper choice for the behavior of SA 508 steel. A new model based on the weakest link concept with the determined carbide size distribution (CSD) is succesfully applied to predict KJc measurements obtained on SA 508 steel and on a similar material (22NiMoCr3-7)