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Title: Two Prediction Methods For Ductile Sheet Metal Failure

Abstract

Two analytical approaches are detailed for the determination of Forming Limit Diagrams (F.L.D.) and compared with experimental results. The first one is the 'Enhanced Modified Maximum Force Criterion EMMFC' and the second one is the 'Through-Thickness Shear Instability Criterion TTSIC'. The criteria are both written in an intrinsic analytical form and are applicable to linear and non-linear given strain paths as it occurs in any FEM codes for sheet-metal forming simulation. Finally, the two methods are complementary depending on the nature of failure and the predicted curves are in reasonable agreement with the trend of experimental results for a wide range of materials.

Authors:
 [1];  [2]
  1. INSA de Lyon, LaMCoS, 20 avenue Einstein, 69621 Villeurbanne (France)
  2. MECANIUM, 66 boulevard Niels Bohr, 69603 Villeurbanne (France)
Publication Date:
OSTI Identifier:
21057024
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 907; Journal Issue: 1; Conference: 10. ESAFORM conference on material forming, Zaragoza (Spain), 18-20 Apr 2007; Other Information: DOI: 10.1063/1.2729528; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ALLOYS; COMPUTERIZED SIMULATION; FAILURES; FINITE ELEMENT METHOD; INSTABILITY; MATERIALS WORKING; METALS; NONLINEAR PROBLEMS; SHEAR; SHEETS; STRAINS; THICKNESS

Citation Formats

Brunet, Michel, and Clerc, Patrice. Two Prediction Methods For Ductile Sheet Metal Failure. United States: N. p., 2007. Web. doi:10.1063/1.2729528.
Brunet, Michel, & Clerc, Patrice. Two Prediction Methods For Ductile Sheet Metal Failure. United States. doi:10.1063/1.2729528.
Brunet, Michel, and Clerc, Patrice. Sat . "Two Prediction Methods For Ductile Sheet Metal Failure". United States. doi:10.1063/1.2729528.
@article{osti_21057024,
title = {Two Prediction Methods For Ductile Sheet Metal Failure},
author = {Brunet, Michel and Clerc, Patrice},
abstractNote = {Two analytical approaches are detailed for the determination of Forming Limit Diagrams (F.L.D.) and compared with experimental results. The first one is the 'Enhanced Modified Maximum Force Criterion EMMFC' and the second one is the 'Through-Thickness Shear Instability Criterion TTSIC'. The criteria are both written in an intrinsic analytical form and are applicable to linear and non-linear given strain paths as it occurs in any FEM codes for sheet-metal forming simulation. Finally, the two methods are complementary depending on the nature of failure and the predicted curves are in reasonable agreement with the trend of experimental results for a wide range of materials.},
doi = {10.1063/1.2729528},
journal = {AIP Conference Proceedings},
number = 1,
volume = 907,
place = {United States},
year = {Sat Apr 07 00:00:00 EDT 2007},
month = {Sat Apr 07 00:00:00 EDT 2007}
}
  • A correct prediction of a possible sheet metal failure is essential to sheet metal forming simulations. The use of the conventional forming limit curve (FLC) is the standard approach on industrial level for this problem. The FLC concept is limited to the case of linear strain paths, however. The initial FLC is no longer valid in the case of nonlinear strain paths. The algorithm Crach allows for a transient prediction of the forming limit for localized necking in the case of arbitrary strain paths. For high strength steels and aluminium sheets there is also a risk of fracture without priormore » localized necking. This paper presents a fracture model that accounts for ductile fracture (caused by void nucleation, void growth and void coalescence) and shear fracture (caused by shear band localization). For both types of fracture, stress state parameters are introduced which can be applied for the plane stress state and for the general 3D stress state. The fracture limits are defined by the equivalent plastic strain at fracture as a function of the stress state parameter based on different experiments with nearly constant stress state parameter. These fracture limit curves are a basis for an integral damage accumulation in the sheet metal forming simulation for arbitrary nonlinear strain paths. The model Crach for the prediction of localized necking and the two fracture models for ductile and shear fracture are combined in the comprehensive failure model CrachFEM. CrachFEM can be linked via a user material model MF GenYld to different explicit FEM codes.« less
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  • Full three dimensional numerical cell model analyses are carried out for a metal reinforced by short fibers, to study the development of ductile matrix failure. A porous ductile material model is used to describe the effect of the nucleation and growth of voids to coalescence. In each case studied the computations are continued through the mechanically unstable regime, where an open crack forms near the ends of the fibers by the coalescence of voids in the matrix. Comparison of predictions for an isotropic hardening model and a kinematic hardening model are used to evaluate the effect of a metal thatmore » forms a rounded vertex on the yield surface. The full three dimensional model is used to study effects of deviations from equal transverse tension in directions perpendicular to the fibers.« less
  • In this work an improved material model is proposed that shows good agreement with experimental data for both hardening curves and plastic strain ratios in uniaxial and equibiaxial proportional loading paths for steel metal until the final fracture. This model is based on non associative and non normal flow rule using two different orthotropic equivalent stresses in both yield criterion and plastic potential functions. For the plastic potential the classical Hill 1948 quadratic equivalent stress is considered while for the yield criterion the Karafillis and Boyce 1993 non quadratic equivalent stress is used taking into account the non linear mixedmore » (kinematic and isotropic) hardening. Applications are made to hydro bulging tests using both circular and elliptical dies. The results obtained with different particular cases of the model such as the normal quadratic and the non normal non quadratic cases are compared and discussed with respect to the experimental results.« less
  • A failure model for cross-rolled beryllium SR-200 sheets is developed for material loaded in a complex state of stress. Coefficients of the Tsai-Wu criterion are determined from a series of special laboratory experiments. Tests include circular plates loaded by a concentric ring, as well as in-plane compression and off-axis plate specimens. Complex states of stress lead to brittle failure of the anisotropic material. Failure surfaces obtained from the criterion form a family of ellipses when plotted in standard Cartesian coordinates. The criterion is incorporated into a general purpose finite element analysis code. Numerical simulation incrementally applies loads to a structuralmore » component that i being designed and checks each nodal point in the model for exceedance of the failure criterion. To demonstrate applicability of the predictive capability of the criterion, a 2.54-mm thick beryllium plate is placed under clamped edge conditions and loaded to failure by a central transverse point load. A numerical model of the structure predicts the failure load to within 3%.« less