characteristic strength is higher compared to the previous case, i.e. the damage parameter remains lower. This results underlines how the choice of the Weibull parameters, usually determined experimentally, affects the global response. CONCLUSIONS The focus of the paper was to analyze the effect of randomness of microstructure of FGM on the fracturedamage behavior. To this aim, a micro-mechanics model able to consider the stochasticity of placement of second phase particles is adopted: OOF, a finite element code able to operate directly on microstructural images and to create finite element meshes that take into account microstructural features, is used in conjunction with a statistical approach for brittle fracture. The numerical analyses for the stochastically graded microstructure can be compared with those obtained for a continuous (homogeneously graded) model which does not take into account the microstructural randomness and discreteness. The results demonstrate the need to consider microstructural details for accurately modeling FGM as regards their fracture and damage accumulation behavior. In fact, the heterogeneous microstructure can affect the initiation of cracks. This work is currently in progress. In particular, the study aims to quantitatively assess the effect of the characteristic Weibull parameter on damage accumulation. Moreover the model could be extended to account for other factors not considered in this case, such as the adhesion (strong or weak) at the interface between the two phases. REFERENCES 1. Giannakopoulos A.E. and Suresh S. (1997) Int. J. Solids Struct. 34, 2357. 2. Jitcharoen J., Padture N.P., Giannakopoulos A.E. and Suresh S. (1998) J. Am. Ceram. Soc. 81, 2301. 3. Carter W.C., Langer S.A. and Fuller E.R. The OOF manual: version 1.0, 1998. NIST Internal Report, NISTIR 6256, http://www.ctcms.nist.gov/oof/ 4. Petterman H.E. (2000) Mater. Sci. Engng. A 276, 277. 5. Weissenbek E., Petterman H.E. and Suresh S. (1997) Acta Mater. 45, 3401. 6. Dao M., Gu P., Maewal A. and Asaro R.J. (1997) Acta Mater. 45, 3265. 7. Cannillo V., Carter W.C., to appear 8. Weibull W. (1951) J. Appl. Mech., 18, 293. 9. Khalili A., Kromp K. J.Mater Sci. Lett. (1991) 26, 6741.
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