The effect of particulate fracture in determining fracture toughness of metal matrix composites

Conference · Mon Dec 31 04:00:00 EST 1990

OSTI ID:10119387

Lucas, J P ^[1]; Liaw, P K ^[2]; Stephens, J J ^[3]; Nunes, J ^[4]

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1. Sandia National Labs., Livermore, CA (United States)
2. Westinghouse Electric Corp., Pittsburgh, PA (United States). Science and Technology Center
3. Sandia National Labs., Albuquerque, NM (United States)
4. Army Materials Research Agency, Watertown, MA (United States). Materials Technology Lab.

Although the fracture toughness of discontinuous reinforced metal matrix composites (DR MMCs) is reduced significantly in comparison to its matrix alloy, the fracture mode remains ductile for all Al- based materials studied. Failure of DR MMCs occurs ultimately by void growth and coalescence in the matrix phase, similar to unreinforced material. Brittle fracture of the particulates also contributes to the microfracture process and thus to fracture toughness. Fracture surface, metallographic, and acoustic emission results indicate that particulates contained in the process zone fracture either by single-faceted or multi-faceted cracking ahead of the main crack. Moreover, fracture of primary void initiating particulates depends on the reinforcement type, size, and the particulate/matrix interface microstructure. These factors influence the stress level at which void nucleation occurs at particulates. Fractographic evidence indicates that void nucleation and growth begin at a low nominal level of stress in particular for large particulates exhibiting extensive interfacial precipitation. Fracture of reinforcing particulates encompassed in the crack tip process zone has a strong effect on the fracture toughness of MMCs. Emphasis is placed on the role of particulate cracking and the mechanism of interparticulate ligament failure in determining the fracture toughness. In addition, fracture toughness results obtained by short bar and conventional compact tension methods were found to be in remarkable agreement. Using a stress-modified strain criterion continuum model for ductile fracture, the fracture toughness of particulate reinforced metal matrix composites is described reasonably well.

• Research Organization: Sandia National Labs., Livermore, CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-76DR00789
• OSTI ID: 10119387
• Report Number(s): SAND--90-8490; CONF-901008--13; ON: DE92006866
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602
360603
ALUMINIUM BASE ALLOYS
COMPOSITE MATERIALS
COPPER ALLOYS
CRACK PROPAGATION
FRACTURE PROPERTIES
HEAT TREATMENTS
MECHANICAL PROPERTIES
MICROSTRUCTURE
MORPHOLOGY
PARTICLE SIZE
REINFORCED MATERIALS
SILICON ALLOYS
SILICON CARBIDES
STRUCTURE AND PHASE STUDIES
TENSILE PROPERTIES
WHISKERS