Effects Of Reinforcement Network Distribution On Mechanical Properties Of SiCp/Al Composites Via Finite Element Method

The distribution of reinforcement is an important factor that influences the mechanical and physical properties of metal-matrix composites(MMCs).In this thesis,the deformation,fracture behaviors and mechanical properties of Si Cp/Al composites with network architecture were predicted by finite element method(FEM)simulation technology.A novel modeling method was applied to establish geometrical model of network composites.Based on the novel models,microstructure design and optimization strategies were studied.A new approach,i.e.FEM simulation optimizing network microstructure,was successfully explored.In homogeneous composite with the same fraction of particles,the work hardening rate and the yield strength increased with Si C particle size decreasing.During composite deformation,the finer particles promoted the matrix to generate more disloactions.Thus,the matrix carried more stress,that led to higher strength of composite.However,defects density increased with particle size increasing,leading to fracture strength of the composite decreasing.Therefore,crack initiated by particle fracture in coase particle reinforced composite.The reinforcement aspect ratio significantly affacts the composite mechanical properties.The elastic modulus and yield strength of Si Cw/Al composite with aspect 20:1 were 90.9 GPa and 324 MPa,which were much higher than that of Si Cp/Al composite(85.9 GPa and 299 MPa).It is noted that the composite mechanical properties were sensitive to reinforcement aspect ranging from 5:1 to 10:1.It was found that reinforcement continuity is the key factor of network composite properties.The high local volume fraction of particles means high reinforcement continuity.And thus,the particles can carry more loads,leading to higher modulus and strength of composites.However,when the local volume fraction of Si C particle was over 0.38,the network composite may experience brittle fracture.The source of particle shape effects on the properties of network composites was ascribled to the stress concentration.The hexahedron particle led higher stress concentration,thus higher stress was generated in network layers,which was beneficial to composite properties.However,higher stress led particle fracture earlier.And thus,the elongation of composite decreased.The effect of aspect ratio on network composite properties showed a competition relation between aspect ratio and structural design.On the one hand,increasing aspect ratio decreased reinforcement continuity,leading to reinforcement carrying lower load.On the other hand,aspect ratio was beneficial to load bearing capability of reinforcement.In addition,with the aspect ratio increasing from 1:1 to 10:1,the material elongation increased from 4.7% to 6.5%.It implied that increasing aspect ratio was a feasible method to further enhance the network composite elongation.The complexity of network architecture showed a great influence on the fracture behavior of materials.The original network architecture provided a main crack propagation path.Thus,the elongation of network composite was low.It was proved that the elongation can be improved by modifying the structure or creating architecture with more cells.A network composite was prepared with thick network layers.However,the size of reinforcement-lean phase in prepared network composite was lower than the structural design,giving rise to easier reinforcement-lean phase brittle fracture and crack deflection.A part of reinforcement-lean phases showed plastic deformation characterize.This phenomenon indicated that the deformation of reinforcement-lean phase was not uniform.It implied that the deformation between network cells was mutually coordinated and restrictedThe simulation predictions agreed experimental results well: the elastic modulus and strength were enhanced by network architecture design,however the elongation decreased;the microcrack were preferentially generated in the network layer parallel to load direction(Pa W).The microcrack of Pe W tended to converge.The reinforcement of Pa W could carry more load than that of the network layer perpendicular to load direction(Pe W);the reinforcement-lean phase blunted microcrack of Pa W;the model-I crack dominated the failure behavior of the network composite;the main crack propagated from Pe W to Si C/Al-Al "interface".Thess phenonmena showed that the simulation technique was reliable.