Global constraint-insensitive fracture in SiC particulate-reinforced AA 2009

Journal Article · Fri Jul 01 04:00:00 EDT 1994 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02665479· OSTI ID:7028290

Somerday, B P; Gangloff, R P ^[1]

---

1. 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), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 25:7; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ALLOYS
ALUMINIUM ALLOYS
CARBIDES
CARBON COMPOUNDS
COMPOSITE MATERIALS
FRACTURE PROPERTIES
MATERIALS
MECHANICAL PROPERTIES
SILICON CARBIDES
SILICON COMPOUNDS
TENSILE PROPERTIES