Numerical Analysis of the Effects of Void Growth and Crack Tip Opening on Ductile Fracture
Hom, Craig Lee
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https://hdl.handle.net/2142/71696
Description
Title
Numerical Analysis of the Effects of Void Growth and Crack Tip Opening on Ductile Fracture
Author(s)
Hom, Craig Lee
Issue Date
1988
Doctoral Committee Chair(s)
McMeeking, Robert M.,
Department of Study
Theoretical and Applied Mechanics
Discipline
Theoretical and Applied Mechanics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Abstract
The ductile rupture of metal alloys depends on the presence of small second phase particles which nucleate microscopic voids. Plastic flow in the metal allows the voids to grow and link up to create larger flaws such as cracks. In previous research, the basic mechanics of ductile fracture has been examined using two-dimensional models. However, some problems in ductile fracture are inherently three-dimensional. In this work three such problems are solved using large deformation finite element computations.
First, the finite element technique was used to study the growth of initially spherical voids in a cubic array under remote uniform loads of uniaxial tension, pure shear and high triaxial stress. The results show that shape change has a strong effect on the material's behavior. Indeed for low triaxial stress states, the effect of voids on the material response is stronger than expected due to void elongation. For higher triaxiality, the voids interact strongly to cause rapid drops in the material's load carrying capacity.
The second problem examines the effects of tip blunting and differential thinning on a crack in a thin elastic-plastic sheet. The finite element results show that two shear bands at 45 degrees to the plane of the sheet develop. Also, the results indicate the stresses are significantly higher in the near tip region at the midplane of the sheet than predicted by plane stress theory.
Finally, the growth and interaction of an array of initially spherical voids ahead of a blunting plane strain crack tip were studied. The finite element results show that spherical voids grow towards the crack tip and coalesce with the crack before they coalesce with each other. Increases in plastic strain were observed in the near tip region due to the presence of the voids. The results are used to discuss ductile crack growth in engineering alloys.
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