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Title: Modelling of Local Necking and Fracture in Aluminium Alloys

Abstract

Non-linear Finite Element simulations are extensively used in forming and crashworthiness studies of automotive components and structures in which fracture need to be controlled. For thin-walled ductile materials, the fracture-related phenomena that must be properly represented are thinning instability, ductile fracture and through-thickness shear instability. Proper representation of the fracture process relies on the accuracy of constitutive and fracture models and their parameters that need to be calibrated through well defined experiments. The present study focuses on local necking and fracture which is of high industrial importance, and uses a phenomenological criterion for modelling fracture in aluminium alloys. As an accurate description of plastic anisotropy is important, advanced phenomenological constitutive equations based on the yield criterion YLD2000/YLD2003 are used. Uniaxial tensile tests and disc compression tests are performed for identification of the constitutive model parameters. Ductile fracture is described by the Cockcroft-Latham fracture criterion and an in-plane shear tests is performed to identify the fracture parameter. The reason is that in a well designed in-plane shear test no thinning instability should occur and it thus gives more direct information about the phenomenon of ductile fracture. Numerical simulations have been performed using a user-defined material model implemented in the general-purpose non-linearmore » FE code LS-DYNA. The applicability of the model is demonstrated by correlating the predicted and experimental response in the in-plane shear tests and additional plane strain tension tests.« less

Authors:
 [1];  [2];  [3];  [2];  [4]
  1. Structural Design, Offshore Construction Engineering, SUBSEA7, NO-4056 Tananger (Norway)
  2. SINTEF Materials and chemistry, Applied mechanics and corrosion, NO-7465 Trondheim (Norway)
  3. SIMLab, Department of Structural Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)
  4. (Norway)
Publication Date:
OSTI Identifier:
21057338
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 908; Journal Issue: 1; Conference: NUMIFORM '07: 9. international conference on numerical methods in industrial forming processes, Porto (Portugal), 17-21 Jun 2007; Other Information: DOI: 10.1063/1.2740797; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM ALLOYS; ANISOTROPY; COMPRESSION; COMPUTERIZED SIMULATION; DUCTILITY; FINITE ELEMENT METHOD; FRACTURES; L CODES; NONLINEAR PROBLEMS; SHEAR; STRAINS; STRESSES; TESTING

Citation Formats

Achani, D., Eriksson, M., Hopperstad, O. S., Lademo, O.-G., and SIMLab, Department of Structural Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim. Modelling of Local Necking and Fracture in Aluminium Alloys. United States: N. p., 2007. Web. doi:10.1063/1.2740797.
Achani, D., Eriksson, M., Hopperstad, O. S., Lademo, O.-G., & SIMLab, Department of Structural Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim. Modelling of Local Necking and Fracture in Aluminium Alloys. United States. doi:10.1063/1.2740797.
Achani, D., Eriksson, M., Hopperstad, O. S., Lademo, O.-G., and SIMLab, Department of Structural Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim. Thu . "Modelling of Local Necking and Fracture in Aluminium Alloys". United States. doi:10.1063/1.2740797.
@article{osti_21057338,
title = {Modelling of Local Necking and Fracture in Aluminium Alloys},
author = {Achani, D. and Eriksson, M. and Hopperstad, O. S. and Lademo, O.-G. and SIMLab, Department of Structural Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim},
abstractNote = {Non-linear Finite Element simulations are extensively used in forming and crashworthiness studies of automotive components and structures in which fracture need to be controlled. For thin-walled ductile materials, the fracture-related phenomena that must be properly represented are thinning instability, ductile fracture and through-thickness shear instability. Proper representation of the fracture process relies on the accuracy of constitutive and fracture models and their parameters that need to be calibrated through well defined experiments. The present study focuses on local necking and fracture which is of high industrial importance, and uses a phenomenological criterion for modelling fracture in aluminium alloys. As an accurate description of plastic anisotropy is important, advanced phenomenological constitutive equations based on the yield criterion YLD2000/YLD2003 are used. Uniaxial tensile tests and disc compression tests are performed for identification of the constitutive model parameters. Ductile fracture is described by the Cockcroft-Latham fracture criterion and an in-plane shear tests is performed to identify the fracture parameter. The reason is that in a well designed in-plane shear test no thinning instability should occur and it thus gives more direct information about the phenomenon of ductile fracture. Numerical simulations have been performed using a user-defined material model implemented in the general-purpose non-linear FE code LS-DYNA. The applicability of the model is demonstrated by correlating the predicted and experimental response in the in-plane shear tests and additional plane strain tension tests.},
doi = {10.1063/1.2740797},
journal = {AIP Conference Proceedings},
number = 1,
volume = 908,
place = {United States},
year = {Thu May 17 00:00:00 EDT 2007},
month = {Thu May 17 00:00:00 EDT 2007}
}
  • The earlier combined model [Faulkner and Jiang, Mater. Sci. Technol. 9, 665 (1993)] is improved by means of modifying the kinetics of segregation and taking into account the nucleation of grain boundary precipitates, the precipitate growth and coarsening. The newly developed model predicts the influence of the heat treatment on the widths of precipitate-free zones, the growth rate and the dispersion of the precipitates on the grain boundaries during the growth of precipitates. It also predicts the critical time when coarsening begins, the size and dispersion of precipitates on the grain boundaries during coarsening. The application of the model inmore » predicting the size and inter-particle spacing of MgZn{sub 2} grain boundary precipitate and the widths of precipitate-free zones in 7150 aluminium alloy as a function of heat treatment is discussed in Part 1 of this paper, and the comparison of the predicted and experimental results will be addressed in Part 2.« less
  • The amount and type of alloying elements in aluminium affect the as-cast microstructure through the dependence of solidified fraction on undercooling. This can be quantified by the growth-restriction parameter Q. Phase-diagram calculations using the CALPHAD method show the effects of thermodynamic parameters on Q. In binary systems, the deviation from linear dependence of Q on solute concentration is assessed. In ternary alloys, model systems elucidate the role of solute interaction in the liquid and solid, and can be used to interpret the behaviour in actual systems. Growth restriction is discussed in relation to solidification modelling and the attainment of amore » fine, equiaxed microstructure in wrought and shape-casting alloys.« less
  • Ductile fracture is a local phenomenon, and it is well established that fracture strain levels depend on both stress triaxiality and the resolution (grid size) of strain measurements. Two-dimensional plane strain post-necking models with different representative volume element (RVE) sizes are used to predict the size-dependent fracture strain of a commercial dual-phase steel, DP980. The models are generated from the actual microstructures, and the individual phase flow properties and literature-based individual phase damage parameters for the Johnson-Cook model are used for ferrite and martensite. A monotonic relationship is predicted: the smaller the model size, the higher the fracture strain. Thus,more » a general framework is developed to quantify the size-dependent fracture strains for multiphase materials. In addition to the RVE sizes, the influences of intrinsic microstructure features, i.e., the flow curve and fracture strains of the two constituent phases, on the predicted fracture strains also are examined. Application of the derived fracture strain versus RVE size relationship is demonstrated with large clearance trimming simulations with different element sizes.« less
  • The forming limits of austenitic stainless steel sheets were studied in this work. It was found that the observed limit of straining in stretch forming, when both of the principal stresses are positive, is not set by localized necking, but instead by inclined shearing fracture in the through thickness direction. It appears that the forming limits of austenitic stainless steels may be predicted fairly well by using the classical localized and diffuse necking criteria developed by Hill. The strain path-dependence may be accounted for by integrating the effective strain along the strain path. The fracture criteria of Rice and Traceymore » and Cockcroft, Latham and Oh were also studied. The results were in qualitative agreement with the experimental observations. Recent experiments with high-velocity electrohydraulic forming of austenitic stainless steels revealed localized necks in stretch formed parts, which are not commonly observed in conventionally formed sheet metal parts.« less