Fracture Toughness of DMMCby Richard J. Arsenault, Univ of Maryland, College Park, United States,
Abstract: The fracture toughness of discontinuous metal matrix composites (DMMC) is always less than the fracture toughness of the matrix, in the same heat treatment or annealed condition. If a specific case is considered, a 20 V% SiCp/6061 composite aged to the T-6 condition has a fracture toughness (KIC) of approximately 10 MPa.m 1/2 , where as 0 V% 6061 may have a KIC of > 40 MPa.m 1/2 . There maybe obvious reasons why the KIC of the composite is less than that of matrix alloy, but there still numerous questions associated with the fracture characteristics of DMMC. In an investigation the following observations were made: The crack appears to go around intact SiC particles leaving a distinct outer coating on the SiC particles. The observance of cracking of the SiC particles in front of the crack tip due to the advance of the crack tip is a rare event. If there are preexisting fractured SiC particles, the crack proceeds through the precracked SiC particles. An important factor where considering the fracture toughness of SiC/Al composites is that matrix has a high dislocation density and a small subgrain size, even where the composite is in the annealed condition. Therefore the matrix of the composite can be equated to a cold worked condition. Cold working always reduce the fracture toughness.
Subject Headings: Cracking | Toughness | Composite materials | Matrix (mathematics) | Particles | Metals (chemical) | Professional societies | Heat treatment
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