Ductile fracture criteria would be a very useful engineering tool in predicting failure of metals in practical deformation processes.
In the present study, a ductile fracture criterion for a cracked plate of n-th power strain hardening material has been investigated theoretically and experimentally under plastic uniaxial tension.
The relation between the critical strain far from a crack at fracture and a crack length was derived theoretically based on the energy conservation law and by analytical estimation of the strain energy for a cracked plate. The experiment on 0.80%C steel was conducted to compare with theory. Also, the strain and stress distributions near a crack tip were discussed.
The following conclusions were obtained:
(1) The total strain energy
I for a cracked plate is expressed as the sum of
I∞ without a crack and
Ic due to a crack, where
Ic is represented by the product of
I∞, square of a crack length
C2 and constant α, that is,
Ic=α·
C2·
I∞.
(2) The relation between the critical strain ε
∞ and a crack length is given by ε
∞·
C1/1+n=const.
(3) The experimental results are in good agreement with theory.
(4) The strain distribution ε near a crack tip is predicted as follows,
ε
∝ε
∞(C/r)
1/1+n(ε
∞: strain far from a crack,
r: radial coordinate)
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