Size and shape effects in metal matrix composites
- Washington State Univ., Pullman, WA (United States)
The plastic deformation in metal matrix composites reinforced with elastic particulates is investigated. The main issue is to develop a model which explains the influence of particle size, shape and volume fraction on the overall strength of the composite. Two approaches will be presented. One approach is based on the continuum theory of plasticity, and the other is based of the gradient-dependent theory of plasticity. In the continuum theory approach we use a finite unit cell composed of a rigid inclusion surrounded by a matrix metal, e.g. Al/SiC system. For uniformly distributed particles, the overall homogeneous response of the composite is determined by employing an upper bound theory, yielding a relationship that predicts the effect of the particle`s shape and its volume fraction on the flow stress of the composite. It is shown, for example, that prolate particles under axisymmetric loading provide higher strength than oblate ones with the same volume fraction. The results the analytical model compare very well with experimental data found in the literature and with finite element calculations, for relatively large particle spacings. For small spacings, however, the interaction between particles becomes significant due to the highly heterogeneous strain field, significantly affecting the flow stress of the composite. This effect is modelled by considering a local inhomogeneous strain perturbation resulting from the strain incompatibility between the matrix and particles. This leads to the development of a gradient-dependent flow stress which measures the influence of high strain gradients, leading to constitutive equations that include the effect of particle spacing and shape effects. The resulting model describes very well the experimental observations for various MMC systems. It is also compared with mechanistic models that are based on dislocation-particle interaction.
- OSTI ID:
- 175324
- Report Number(s):
- CONF-950686--
- Country of Publication:
- United States
- Language:
- English
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