Crack Paths 2006

C O N C L U S I O N S

x Short cracks up to 400 microns in length grow under the fatigue limit of the metal

matrix composite in a shear dominated modewith drastically varied growth rate and

with bowing and branching mechanisms due to the local particle dependency.

x With an increase in the applied stress range and/or increased length, the

microstructure sensitivity of short crack growth decreases. This appears to be a

consequence of the transition from a single slip band at the crack tip to a multiple

slip-plastic zone.

x A commoncharacteristic of the particulate reinforced metal matrix composites is that

the long crack growth rate in the intermediate range of K ' , is independent of the

reinforced particle. This is in contrast to the near threshold

t h K ' values where there

is a strong influence of the particles.

x A crack phase diagram for particle reinforced metal matrix composites was

presented. It indicated the range of the applied stress and crack length for different

crack growth mechanisms in these materials.

x A series of finite element models were constructed to study the effect of particle size,

particle spacing (volume fraction), particle fracture and debonding on the crack tip

stress, strain and opening displacement (CTOD)of a nearby short crack. The analysis

provided an understanding of the mechanism of short crack trapping/untrapping in

the particle reinforced metal matrix composites.

A C K N O W L E D G E M E N T

The author wishes to acknowledge his research collaborators: Drs. C.S. Li, Z. Xia, and

G. Meijer whocontributed at various stages of the results presented here. The research

was supported, in part, by the Natural Sciences and Engineering Research Council of

Canada (NSERC).

R E F E R E N C E S

1. Lloyd, D.J. (1994). In: Intrinsic and Extrinsic Fracture Mechanisms in Inorganic

Composite Systems, pp. 39-47, Lewandowski, J.J. and Hunt, Jr., W.H. (Eds.) T M S

Publ.

2. Davidson, D.L.(1991). Metall. Trans. A, 18A, 2115-2138.

3. Ellyin, F., Xia, Z., Li, C.-S.(2005). In: Fracture and DamageofComposites, pp. 73

103, Guagliano, M. and Aliabadi, M.H. (Eds.), W I TPress, USA.

4. Christman, T., Suresh, S. (1988). Acta Metall. Mater. 36, 1691-1704.