Ductile fracture of an aluminum sheet under proportional loading

Jinjin Ha, Madhav Baral, Yannis P. Korkolis

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


The ductile fracture of an AA6111 aluminum sheet after a thermal cycle typical of auto-body paint-baking is investigated with the hybrid experimental-numerical method. The plastic flow of the material is examined by uniaxial tension, plane-strain tension, disk-compression and notched-tension experiments, that are used to calibrate the Yld2004-18p anisotropic yield criterion and the combined Swift-Voce hardening model. Then, the fracture behavior under equibiaxial and plane-strain tension, as well as uniaxial tension and shear, is characterized using a specially-developed cruciform specimen, along with center-hole and shear specimens, respectively. The cruciform fracture specimen proposed here contains two shallow hemispherical depressions (dimples) in the test-section, to initiate fracture. For the fracture characterization, special emphasis is put on specimen design, so that the stress states developed at the neighborhood of the fracture initiation point remain proportional throughout the loading history. In all experiments, the surface strain fields are measured by a stereo-type digital image correlation system. This information is used to validate finite element simulations of the fracture experiments. It is found that the Yld2004-18p model provides a better agreement with experiments than von Mises does, which underscores the sensitivity of the hybrid method to the plasticity models adopted. Once validated, these simulations are used to obtain the fracture loci in terms of two stress-state metrics, i.e., the stress triaxiality and Lode angle parameter.

Original languageEnglish
Article number103685
JournalJournal of the Mechanics and Physics of Solids
StatePublished - Nov 2019

Bibliographical note

Funding Information:
This work was supported by an industrial sponsor, and the authors acknowledge this with special thanks. We thank Profs. F. Barlat and J.H. Kim of POSTECH, Korea, for giving us access to an in-plane biaxial testing machine and helping us perform some of the cruciform experiments reported here. We also wish to acknowledge Scott Campbell for his assistance with the specimen preparation, and Jacqueline McNally in expertly machining the dimples in the cruciform specimens.

Publisher Copyright:
© 2019 Elsevier Ltd


  • Aluminum sheet
  • Anisotropy
  • Ductile fracture
  • Lode angle
  • Paint-baking cycle
  • Plasticity
  • Stress triaxiality

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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