Global constraint-insensitive fracture in SiC particulate-reinforced AA 2009
- Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering
Experimental results prove this hypothesis: the effective plastic fracture strain ([var epsilon][sup [minus]p][sub [line integral]]) for a discontinuously reinforced metal matrix composite (MMC) is insensitive to globally imposed triaxial tensile stress, because the elastic reinforcement independently produces high local matrix constraint during plastic deformation. The value [var epsilon][sup [minus]p][sub [line integral]] is measured for SiC particulate-reinforced AA 2009-T6, with cylindrical circumferentially notched (global constraint ratio, [sigma][sub m]/[bar [sigma]], of 1.0) and smooth tensile specimens ([sigma][sub m]/[bar [sigma]] of 0.3), as a function of temperature. The MMC fractures by microvoid-based processes associated with the SiC at all temperatures. The ratio (r) of smooth to notched specimen [var epsilon][sup [minus]p][sub [line integral]] equals unity from 25 C to 200 C and is less than values of 2 or higher typical of monolithic Al alloys at similar global constraint. This result establishes that global constraint does not degrade MMC fracture resistance because of the unique effect of local matrix constraint. The ratio r for the MMC increases from near 1 at 200 C to a maximum of 3.3 at 250 C, indicating a loss of local matrix constraint, possibly due to reduced matrix-particle load transfer or microvoid nucleation at low strains. Uncertainties hinder precise definition of [var epsilon][sup [minus]p][sub [line integral]] vs global [sigma][sub m]/[bar [sigma]]. Global constraint-insensitive fracture for the MMC suggests that plane strain fracture toughness differences between the composite and unreinforced matrix are not well defined by smooth specimen ductilities. Further, MMC fracture toughness should be insensitive to global constraint and associated cracked specimen dimensions.
- OSTI ID:
- 7028290
- Journal Information:
- Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Vol. 25:7; ISSN 0360-2133
- Country of Publication:
- United States
- Language:
- English
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