Deformation and fracture of a particle-reinforced aluminum alloy composite: Part II. Modeling
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I. INTRODUCTION
IN Part I of this article, the results of tensile and fracturetoughness tests were provided for a 7093/SiC15p composite, where the designation implies that a 7093 aluminum alloy is reinforced with 15 vol pct of SiC particles. The discontinuously reinforced aluminum (DRA) was heat treated to obtain different microstructures, to determine the influence of matrix mechanical properties on the composite response. As indicated in that article, the matrix properties had a significant effect on the composite properties. The important data included the elastic modulus, stress-strain behavior, strain to failure, and fracture toughness of the composite and the monolithic matrix. Briefly, the results indicated that the yield strength of the composite was the highest in the peak-aged (PA) and the lowest in the highly overaged (OA3) condition. The strain to failure and the fracture toughness followed an opposite trend, exhibiting the lowest value for the PA condition due to severe plastic flow localization. The dominant damage mode was particle cracking for yield strengths above approximately 400 MPa. The density of particle cracks increased with the imposed strain. Below a strength of 400 MPa, the damage was mostly in the form of near-interface matrix failure and some interface failure. B.S. MAJUMDAR, Associate Professor, is with the Department of Materials and Metallurgy, New Mexico Tech, Socorro, NM 87801. A.B. PANDEY, Senior Scientist, is with UES, Inc., Dayton, OH 45432. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A
In this article, the deformation and failure behavior are modeled. Existing models are integrated into the current analysis to the extent possible. The rationale for the modeling was two-fold: (1) to predict the deformation and failure response, and (2) to understand the sequence of events leading to fracture. The results of the modeling should enable the development of composites with a superior blend of mechanical properties, such as a higher elongation with the same or an increased yield strength. In what follows, the models for elastic modulus, elastic-plastic stress-strain behavior, elongation to fracture, particle-fracture statistics, and fracture toughness are illustrated. Most of the predictions refer to a 15 vol pct 7093/SiCp DRA that was discussed in Part I of this article. However, elongation predictions are also compared to data from other systems reported in the literature. The constituent matrix data in the different aging conditions were obtained from tension tests on a 7091 aluminum alloy, which has a very similar composition to the 7093 alloy. II. MODELING A. Elastic Modulus The self-consistent scheme of Budiansky[1] for spherical particles provided a ratio of composite modulus to matrix modulus (Ec /Em) of 1.26, for a volume f
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