Mechanism of subcritical crack growth in the alumina reinforced aluminum-copper composite: Effects of interface and matrix microstructure
Liu, Gang
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/23639
Description
Title
Mechanism of subcritical crack growth in the alumina reinforced aluminum-copper composite: Effects of interface and matrix microstructure
Author(s)
Liu, Gang
Issue Date
1995
Doctoral Committee Chair(s)
Shang, Jian Ku
Department of Study
Engineering, Materials Science
Discipline
Engineering, Materials Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
Micromechanisms of fracture and fatigue crack growth were examined in an $\rm Al\sb2O\sb3/Al$-Cu composite and its matrix alloy, with particular emphases on effects of matrix and interfacial microstructure. The matrix and interfacial microstructures were controlled by aging the composite to underaging (UA), peak-aging (PA), slight overaging (OA-1) and extensive overaging (OA-150) conditions. The interface between the matrix and $\rm Al\sb2O\sb3$ was free of interfacial precipitates in the UA condition, but covered with small and coarse precipitates in the PA and OA conditions, respectively. Slight overaging was chosen to produce a yield strength similar to that of the UA condition so that the effects of the matrix microstructure and the interface microstructure on the fracture and fatigue crack growth behavior could be separated. Fracture studies indicated that failure mechanisms changed from particle cracking in UA composite to a near-interface fracture in PA and interface failure in OA composites. The fracture toughness in the composite was found to be proportional to shear strength of the $\rm Al\sb2O\sb3/Al$-Cu interface. Fatigue cracks in the composite propagated primarily in the matrix by avoiding particles. In the near-threshold regime, crack growth rate of the composite was controlled by matrix properties and was insensitive to interfacial microstructure. High threshold in the PA composite is related to high yield strength, high crack closure level, and small crack-tip opening displacement of the composite. At high stress intensities, crack growth was strongly dependent on interface microstructure. Fast crack growth in the OA composite resulted from the low fracture toughness and interfacial decohesion. At elevated temperatures, fatigue crack growth was accelerated by cyclic-deformation induced crack-tip overaging at 150$\sp\circ$C and by softening of the composite at 300$\sp\circ$C.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
