Micromechanics Of Particulate Reinforced Composites

The thesis is to interpret the particle size effect on the equivalent stiffness and plasticbehaviors of composites from different point of views. Based on the inherentmicrostructures of composites, some innovative methods are developed. The basicresearch contents are as follows.(1) Numerical studies on the effective shear modulus of particle reinforced composites withan inhomogeneous interphase are systematically performed. The influences ofinterphase thickness, variation laws of interphase properties, boundary conditions andparticle volume fraction on the equivalent shear modulus are carefully investigated, andthe accuracy of the existing models is verified.(2) A micro-mechanics model is developed to study the effective elastic properties ofcomposites reinforced by regularly distributed particles. Particle interaction anddistribution are simultaneously taken into account by using strain Green’s function,which is determined by utilizing the conditions of geometric symmetry. TheDouble-Inclusion configuration is introduced to describe the role of the interphase.The overall elastic properties are described by three independent elastic constantsexpressed in the explicit form.(3) Particle size effect is attributed to the synergism mechanism between particles andthe host matrix. A molecular-chain-network based micromechanics model waspresented for exploring particle size effect on the effective modulus. In the presentmodel, particles are regarded as junctions among molecular chains, which areequivalent to the cross-links pre-existing in the polymer. At a certain particleconcentration, the smaller the particle size, the higher is the cross-link density in thecomposites, and the higher is the effective stiffness of the resulting composites.Therefore, particle size effect would be clearly demonstrated from a new point ofview, which is different from all the existing explanations.(4) A micromechanics–based model is proposed for the finite strain deformation offilled elastomers based on generalized Eshelby’s tensor and Mori Tanaka’s method.The present formulation leads to a clear explanation of the constraint effect ofrubber–like matrix on the inclusions. Comparisons with experiments and other micromechanics models are conducted. It is observed that an improvement inpredictive capability for the composite with randomly dispersed particles wasachieved by the present method. Based on the latest experiment of single molecularchain, a compact network model is fatherly developed to reflect the microstructureeffect on the stress–strain relations of rubbery polymer and the resultingcomposites.(5) An incremental damage model of PRC has been extended to three-phase compositesfor interpreting particle size effect. The interphase was perfectly incorporated as athird phase with the help of double-inclusion model. Progressive damage wascontrolled by a critical energy criterion. Based on the developed model, particle sizeeffect on the mechanical behaviors of composites was clearly interpreted from therole of the interphase, which is different from all the existing researches.(6) A new micromechanics model of particulate reinforced composites was proposedto describe the evolution of debonding damage, matrix plasticity and particle sizeeffect on the deformation. A ductile interphase was involved to analyze thedependence of elastic plastic damage behavior on particle size. The equivalentstresses of the two constituents were determined by field fluctuation method.Furthermore, a unit cell (UC) based FEM was used to understand their evolutionand demonstrate the role of the interphase.