Reduction of measured toughness due to out-of-plane constraint in ductile fracture of aluminium alloy specimens

M. Mostafavi, D. J. Smith, M. J. Pavier

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Abstract

It is generally believed that a lower bound on the fracture toughness of a material is obtained from a standard test, particularly in metals where yielding occurs prior to fracture. The understanding is that in such a test the material around the crack tip is highly constrained hence reducing the extent of yielding. In this paper, we report the results of fracture tests where a tensile load is applied to a biaxial aluminium alloy specimen in the direction parallel to the crack front in addition to the fracturing load normal to the crack surface. We show that in this case a lower fracture toughness is measured than that obtained from a standard test. Indeed, for the highest value of tensile load used in our tests the J-integral at fracture was half the value measured in a standard test. It is also shown that the volume of the plastic region can be used to measure the effect of constraint, irrespective of the manner in which the constraint arises. This approach suggests an even lower fracture toughness may be obtained than that measured here in certain loading conditions.

Original languageEnglish
Pages (from-to)724-739
Number of pages16
JournalFatigue and Fracture of Engineering Materials and Structures
Volume33
Issue number11
DOIs
Publication statusPublished - Nov 2010
Externally publishedYes

Keywords

  • Biaxial test
  • Constraint
  • Fracture
  • J-integral
  • Plasticity

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