The 3-dimensional strengthening of metal matrix composites reinforced with short fibers. Ph.D. Thesis
The behavior of metal matrix composites reinforced with discontinuous cylindrical inclusions is investigated analytically using the finite element method. Issues of reinforcement volume fraction, shape, arrangement, and orientation, interfacial properties, and the presence of residual thermal stresses are addressed. In addition a new model for the estimation of Young`s modulus for these composites is presented. Aligned fiber shaped inclusions provide greater strengthening than aligned disk shaped inclusions. The reinforcement providing the least strengthening in this study is a slightly oblate shape. Debonding at the inclusion ends is more damaging to the composite strength than interfacial sliding. Staggering of reinforcements reduces the composite strength relative to the aligned case when the interface is strong. However, when debonding occurs, staggering can improve the strength of the composite if the inclusion aspect ratio is large enough. The orientation of half the fibers transverse to the loading direction results in a reduction in composite strength when the fiber aspect ratio is low. With an aspect ratio of 10 the model results in a high level of constraint, which in turn leads to a high composite strength. High aspect ratios also lead to compressive stresses at the ends of the fibers aligned with the load. Thermal residual stresses have less of an effect on the brittle matrix model than the metal matrix model and less of an effect for cylindrical inclusions than for spherical inclusions. A metal matrix model better reflects the stress strain response of WC/Co composites observed in experiments than does a brittle matrix model. A new model for estimating Young`s modulus for discontinuous reinforced composites is developed. Comparison with experimental data shows this model to better predict Young`s modulus in Al/SiC and WC/Co composites than models previously used.
- Research Organization:
- California Univ., Santa Barbara, CA (United States)
- OSTI ID:
- 264013
- Report Number(s):
- N-96-23607; NIPS-96-07655; TRN: 9623607
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1993
- Country of Publication:
- United States
- Language:
- English
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