Mechanical Behavior Simulation Of Particle-compounded Materials

With the increasing applications of particulate reinforced metal matrix composites in engineering, it is necessary to conduct intensive investigation on their mechanical behavior and strengthening mechanism. Therefore, analytical and numerical modeling are interested to provide necessary theoretical fundament for the design of micro-structure and properties of the composites, and to explore possible new ways to develop new materials and to improve performance.Based on the approach of mean disturbance strain of matrix, the normalized relationship between the disturbance strain and eigen strain of multiple kinds of reinforcing particles was studied. An Eshelby particle-compound mechanical model was established, and the valid expression of stress in particles was deduced in detail. A full expression for compliance tensor of multi-particle reinforcing compound was formulated eventually. The secant modulus and equivalent Poisson's ratio of matrix and the compound were introduced to simulate nonlinear stage of the stress-strain curve. Employing the elastic compliance tensor of the compound, the calculation of yield strength and the prediction of stress-strain relation near the yielding point of the compound were obtained by the model. The Eshelby model was also used to study the stress-strain curve, the stress in each component and the effect of geometrical factors of the particles on mechanical behavior of SiCp/Al-2618 composite. The simulated results were compared with experimental data to investigate validity of the model and strengthening mechanisms.An axisymmetric unit-cell model and multi-particle plane strain model by finite element method were also built up based on the software ANSYS. Simulation of stress-strain curve was carried out by adopting the approach of solving average stress of composite through application of displacement load. Additionally, the influence of geometrical factors of particles on mechanical properties of the composite was examined by the FE analysis.Two types of 15v%SiCp/Al-2618 composites, which were produced by a spray-forming-deposition process, were used as experimental comparison with soft matrix and hard matrix respectively by different aging treatment. The mechanical properties, microstructure and stress-strain curve of the composites were measured to provide referencebasis for the verification and revision of the modeling work.The Eshelby particle-compounded mechanical model combing tangent modulus method should be adopted to model hard matrix composite; while for composite with soft matrix the secant modulus method should be adopted. As for the FEM unit-cell model, it is feasible to be used for predicting stress-strain curve of the composite with hard matrix but unsuitable to predict that of the composite with soft matrix.The observation of dislocation density in SiCp/Al-2618 composite by TEM indicates that micro-strengthening mechanism due to dislocation density has a little effect on-the composite. The contribution of dispersion strengthening and grain refining to the strength of the composite are only 0.38 MPa and 7 MPa respectively. Therefore, the effect of micro-strengthening mechanisms on the matrix is not obvious. The microstructure observation of the composite in which many SiC particles have been broken indicates that the particles, may take much load during straining. Meanwhile, the modeling proves that loadin the particles is much higher than in matrix during straining. Consequently, load transfer mechanism is suggested the main strengthening mechanism of these particle-reinforced composites.Through the modeling work of the composite by FEM axisymmetry model and plane strain model, it is shown that particle shape has significant influence on yield strength of the composite. Among the particles of basic shapes, cylindrical particle possesses the best strengthening effect; particles of sharp shape like triangle and rectangle have better strengthening effect than spherical particles. Among the polygonal particles, the sides of the: polygon have little effect on yield stress of the composite when they are greater than 5. Additionally, the stress in particles, young's modulus and yield stress of the composite gradually increase with the. increase of particle aspect ratio. Compared with the Eshelby model, the FEM model is more sensitive to the variation of particle aspect ratio, which indicates.that particle shape contributes more to the strength by means, of strain constraint effect than of the mismatch strain effect.The simulation results show that the reinforcing particle with higher young's modulus has better reinforcing effect. With the increase of volume fraction of particles, the effect becomes more, obvious. The yield stress, of the composite gradually increases with the increase of volume fraction of particle. Compared with the FEM model, the Eshelby model is more sensitive to the variation of volume fraction, which indicates that volume fraction contributes more to the effect of mismatch strain than to the strain constraint. With the increase of volume fraction, the stress in the particles gradually increases predicted by FEM model but decreases by Eshelby model due to the different principles of the two models and it seems that the Eshelby model is more reasonableIt can be concluded that geometrical factors of reinforcing particles have significant effect on mechanical properties of the particle-reinforced composites, and the effect is sensitively relied on the stress-strain curve of the matrix alloy and the matching of elastoplastic properties between reinforcing particles and matrix. There is no simple analytic expression of the effect, and it can only be represented by specific modeling data. Therefore, it is necessary and feasible to carry out microstructure design of the particle-reinforced composites by modeling.