A mechanism-based approach to modeling ductile fracture.

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Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used ... continued below

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82 p.

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Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III & McFadden, Sam X. January 1, 2004.

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Description

Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential to provide more detailed information about the near tip deformation fields.

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82 p.

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  • Report No.: SAND2003-8804
  • Grant Number: AC04-94AL85000
  • DOI: 10.2172/918221 | External Link
  • Office of Scientific & Technical Information Report Number: 918221
  • Archival Resource Key: ark:/67531/metadc889586

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  • January 1, 2004

Added to The UNT Digital Library

  • Sept. 22, 2016, 2:13 a.m.

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  • Dec. 7, 2016, 5:37 p.m.

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Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III & McFadden, Sam X. A mechanism-based approach to modeling ductile fracture., report, January 1, 2004; United States. (digital.library.unt.edu/ark:/67531/metadc889586/: accessed December 15, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.