Bridge toughening enhancement in double-notched MoSi{sub 2}/Nb model composites

Journal Article · Mon Apr 01 04:00:00 EST 1996 · Metallurgical Transactions, A

OSTI ID:250719

Pickard, S M; Ghosh, A K ^[1]

---

1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering

Single-ply composites containing both laminate and continuous Nb fiber reinforcement coated with Al{sub 2}O{sub 3} debond coatings in an MoSi{sub 2} matrix are used as model systems for investigating bridge toughening concepts for various precrack configurations., When cracks are introduced symmetrically on either side of the ductile phase with zero crack offset spacing (S = 0), a minimum amount of energy is expended in plastic deformation and the local rupture process in the metal, as measured by the area of the force displacement curve in tension. For asymmetric precracks introduced on either side of the ductile reinforcement, as the offset spacing, S, was varied from 1 to 20 R (R being the ductile phase half-thickness), the overall extension continuously increased within the bridging ligament. The effective ligament gage length was nearly equal to the crack spacing in the limiting case of a weak interface. However, the ductile Nb phase developed a Nb{sub 5}Si{sub 3} reaction layer on its surface which was strongly bonded to the Nb and was found to undergo periodic cracking, leading to numerous shear bands within the ductile phase. This unique and previously unreported mode of metal deformation in shear loading has been analyzed using a simple geometric model. The results indicate that the profusion of shear bands is the primary source of toughening enhancement in the case of asymmetric crack geometry, which was not recognized in prior work of this type.

• OSTI ID: 250719
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 4 Vol. 27; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
BONDING
BRITTLENESS
CHEMICAL REACTIONS
COMPOSITE MATERIALS
CRACKS
DEFORMATION
DUCTILITY
FIBERS
FRACTURE PROPERTIES
INTERMETALLIC COMPOUNDS
LAMELLAE
MATHEMATICAL MODELS
MOLYBDENUM SILICIDES
NIOBIUM
STRESSES