Composite strengthening. Annual report
It was demonstrated that a strong interfacial bond is required to produce the observed strengthening in discontinuous SiC/Al composites. Dislocation generation (which is the strengthening mechanism) is dependent upon a good bond existing between the silicon carbide (SiC) and the aluminum (AL) matrix. Although it has been shown that the stresses developed in the matrix as a result of the differences in the coefficients of thermal expansion between SiC and Al are greatly reduced by the motion and generation of dislocations, an elastic residual stress can still remain. An investigation was undertaken, and it was determined that with the discontinuous SiC/Al composites a tensile-elastic-residual stress remains in the matrix. This determination is based on results from a theoretical model, tensile and compression testing, and x-ray measurements. The results from all the tests and the model are in agreement. The magnitude of the residual stress is small, e.g., with 20 V% whisker in an annealed 6061 aluminum alloy matrix, the residual stress in 70 MPa. If the matrix is annealed 1100 Al, then residual stress is still smaller; 43 MPa. The tensile residual stress produces a Bauschinger Effect (BE) which is highly dependent upon the initial direction of loading. If the initial direction of loading is in tension, the BE is small, if the initial direction of loading is in compression, the BE is very large. It has been observed that as the strength of the matrix increases, e.g., due to alloying or age hardening, the percentage increase in yield or ultimate tensile strength decreases for a given volume per cent SiC/Al composite.
- Research Organization:
- Maryland Univ., College Park (USA). Engineering Materials Group
- OSTI ID:
- 5601636
- Report Number(s):
- AD-A-164838/5/XAB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360303* -- Composite Materials-- Mechanical Properties-- (-1987)
AGE HARDENING
ALLOYS
ALUMINIUM ALLOYS
BONDING
CARBIDES
CARBON COMPOUNDS
COMPOSITE MATERIALS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISLOCATIONS
EXPANSION
FABRICATION
HARDENING
INTERFACES
JOINING
LINE DEFECTS
MATERIALS
MATRIX MATERIALS
MOTION
SILICON CARBIDES
SILICON COMPOUNDS
STRESSES
THERMAL EXPANSION